Audit Of Ball Mill Circuits.pdf

Viviers Center

D. JUNIQUE

PROCEDURE FOR THE AUDIT OF BALL MILL CIRCUITS

OCTOBER 1996

TABLE OF CONTENTS I-

Introduction

p1

II-

Finishing mill follow-up

p2

III-

Operating problems and their analyses

p3

IV- Internal mill inspection

p4

1- Internal inspection objectives

p4

2- Material analysis methods 1- Material levels 2- Material sampling

p5 p5 p5

3- Equipment analysis methods 1- Typical compartment dimensions 2- Compartment liners 3- Diaphragms and inlet and outlet heads 4- Grinding charges

p7 p7 p7 p8 p 12

4- Interpretations of results 1- Material levels 2- Particle-size evolution within the mill 3- Liners 4- Diaphragms 5- Grinding charges 6- Retention time

p 15 p 15 p 16 p 19 p 21 p 25 p 27

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V-

Separation balance

p 29

1- Objectives

p 29

2- Method of analysis - Distribution curve

p 29

3- Distribution curve calculation

p 29

4- Rosin-Rammler slope

p 35

5- Separator Inspection 1- Static separator 2- 1st or 2nd generation separator or both 3- 3rd generation separator

p 36 p 36 p 37 p 40

6- Interpretations of results 1- Mesh selection 2- Sampling locations for the distribution curve 3- Average values of the distribution curve 4- 3rd generation separator

p 41 p 41 p 41 p 45 p 45

VI- Material balance

p 46

1- Objectives

p 46

2- Calculation principle

p 46

3- Junction calculation method 1- From the distribution curve 2- From Blaine, temperature 3- Other methods

p 47 p 47 p 47 p 48

4- Selection of sampling locations

p 49

5- Numerical example

p 50

6- Interpretations of results 1- Static separator 2- Sample representativity

p 52 p 52 p 52

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VII- Air flow balance

p 54

1- Objectives

p 54

2- Selection of measuring locations

p 54

3- Air flow measurements 1- Anemometric measurements 2- Pitot tube, Strauscheib measurements 3- Gas analysis

p 55 p 55 p 56 p 59

4- Interpretations of results 1- Anemometric measurements 2- Pitot tube, Strauscheib measurements 3- Gas analysis 4- Calculation of air inleakage from gas analysis 5- Mill ventilation ratios

p 60 p 60 p 60 p 63 p 64 p 66

VIII- Drying / Heat balance

p 67

1- Objectives

p 67

2- Drying and heat balances 1- Drying balance 2- Heat balance

p 67 p 68 p 68

3- Interpretations of results 1- Drying balance 2- Heat balance

p 70 p 70 p 71

IX- Energy balance

X-

p 72

1- Objectives

p 72

2- Energy balance

p 72

3- Interpretations of results 1- Energy balance 2- BB10 Test

p 74 p 74 p 74

Conclusions

List of computer analysis programs

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p 75 p 77

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1 I - INTRODUCTION This document is intended for the diagnosis and analysis of problems with ball mill circuits, in order to bring about the required modifications for a suitable operation. Various types of grinding will be covered: clinker grinding raw mix grinding fuel grinding All grinding mills are designed to reduce the size of the material at the lowest possible cost and for the last 2 types of mills, to dry the material. For a given mill with 1, 2 or 3 compartments or birotator, the types of analysis are similar. A typical finishing mill generally consists of:

grinding mill static separator (in certain installations) dynamic separator(s) filter(s)

A roller press or crusher may be installed ahead of the grinding mill. In that case they perform somewhat like a grinding mill fist compartment (they would be treated as such). The following balances will be fully covered:

sampling and internal mill observations separation (dynamic separator distribution curve) material air flow energy drying (raw mix and fuel)

The calculation formulae will be developed as well as the computer programs for the calculations. Important: All the analyses must be conducted on stable operation. Measuring devices and various collectors (power, material and air flows, temperature) must be reliable and calibrated.

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2 II - FINISHING MILL FOLLOW-UP A file should be completed for each finishing mill, updated after each modification and containing the following process parameters:

☞

A diagram of the finishing mill - material and gas circuits

☞

Equipment characteristics (type, make, power, dimensions, typical outputs, etc.)

☞

Grinding charges (charge classification, reloading sequences and dates)

☞

Background of process modifications (liner replacements, separator modifications)

☞

Accounts of installation problems (output, power, etc.)

☞

Process balances even if sketchy (air flow, material, internal mill investigation, etc.)

☞

Operating data for each product (equipment adjustments, various power draws, air flows, pressures, composition, fineness, etc.)

☞

Source and type of drying gases (essentially raw or fuel mills), type and volume of fuel (in the case of an auxiliary furnace)

This list is not complete and any parameter modifications that could improve the understanding of the finishing mill operation can and should be recorded. This follow-up gives an idea of the evolution of the finishing mill performances. The audit, involving the techniques presented in this document, consists of a series of prompt measures that provides a more precise insight of the grinding mill operation at a given time.

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3 III - OPERATING PROBLEMS AND THEIR ANALYSES The Table hereunder reviews the principal causes of a finishing mill operation problems, the effects produced and the analyses that should be undertaken to highlight and quantify the problems. Causes Grinding charges poorly adapted or worn out (ball diameter, filling rate)

Poor internal conditions (liner and diaphragm wear)

Poorly set separator

Main effects produced

Analyses to be given priority

Drop in output

•

Internal sampling

Increase in kWh/t

•

Material balance

Grains

•

Energy balance

•

BB10 grindability

•

Retention time

Drop in output

•

Internal inspection

Grains found at the outlet

•

Internal sampling

Increase in kWh/t

•

Energy balance

•

BB10 grindability

Variations of the circulating charge (elevator power draw, volume of rejects)

•

Distribution curve

•

Material balance

Drop in output

•

(Air flow and separator inspection)

Ball or liner coating or both

•

Air flow balance

Drop in output

•

Internal inspection

High residual moisture on the finished product

•

Air flow balance

•

Drying / heat balance

Change in the particle size distribution of the finished product Poor ventilation Poor ventilation (drying mill)

Drop in output No matter the type of operating problem, it generally produces a drop in output causing an increase in energy consumption per tonne of finished product. The drop in output is not necessarily outstanding, often it is a timedependent drift. Hence it is important to keep an operating record for each product in the finishing mill. Certain particular signs will sometimes allow quick spotting of the source of the problem (see 2nd column in the above Table). In this case, the analyses indicated in the column should be undertaken as a priority. When the cause of the operating problem is not clear, a complete audit should be done. Note:

If time and means are not available, the two priority actions to take are : -

Internal inspection and material sampling Distribution curve of the dynamic separator

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4 IV - INTERNAL GRINDING MILL INSPECTION The grinding mill is the machine that reduces the size of the materials. The role of the separator is to classify the grains according to their size. The grinding mill plays therefore a key function in the finishing mill.

IV - 1 - Internal Inspection Objectives The internal mill inspection is an important step in the audit. It should provide a qualitative evaluation of the mill operation. The reduction of the particle size of the material which is dependent upon the conditions of the mill parts must be qualified. This can be done through: -

observations and material sampling

-

observations of the parts: liners, grinding charge, ventilation ring, etc.

The results can be recorded in a typical form (see appendix). An internal inspection must be made during a crash stop of an installation (all equipment, ventilation and material feeds having completely stopped) so as to reflect the condition of the mill in operation. Safety instructions must be kept in mind before making any move. It is strongly recommended to take pictures of the overall compartment and also detailed pictures of all the essential items covered by the internal audit (liners, diaphragms, charge, etc.). For each mill, “typical shots” can be systematically taken at the same locations each year. For example:

-

General view of each compartment in both directions

-

Liner details

-

Global view of the diaphragm

-

Details of the grates and their openings

-

Ventilation ring detail

-

...

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5 IV - 2 - Material Analysis Methods IV - 2 - 1 - Material Levels

☞

Evaluate the material level of each compartment

-

Compartment 1, generally short and equipped with lifting liners, the material level with respect to the balls is homogeneous and therefore a simple average value is sufficient for characterization

-

Compartment 2, generally long and equipped with classifying liners, three evaluations must be made (inlet, center and outlet)

Suitable material level Part of the balls must emerge from the material

☞

Check if there is an accumulation of unground grains at the outlet grate of the compartment and try to

quantify it (no grains, a few grains, large accumulation).

IV - 2 - 2 - Material Sampling

☞

Sample material in order to characterize the evolution of the particle-size distribution over the length of

each compartment. -

Determination of the sampling locations (see diagram hereafter)

Sampling shall be made near the beginning and end of the compartment (a few cm from the diaphragms) The other locations should be at equal distance one another with about a 50 cm spacing in compartment 1 and 0.75 to 1 m maximum in compartment 2 (modulation as a function of the compartment length to obtain a minimum of 4 to 5 locations per compartment, up to 7 or 8, even more, for a good-size compartment 2). Practical guide for the audit of grinding mills - 96/10

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6 Compartment no 1

Compartment no 2

Samples

Charge

Direction of rotation C1 1

2

3

4

5

6

1

2

C2 3

4

5

- Sampling procedure At each sampling location, dig, using a sampling scoop, a 10 to 15 cm deep transverse trench, over a half diameter of the lifting side of the mill, in order to take material from the ball charge (the surface layer might become polluted by the material deposit following the crash stop). Take, over the entire length of the trench, between 0.5 and 1 L of material adapted to the material fineness. The coarser the material the larger the sample (sample representativity). In compartment 2 where ball size is smaller, it is recommended to use a sieve (10 to 15 mm mesh) to facilitate the material / ball classification. Caution: grains, eventually too coarse, retained on the sieve, must be added to the material and not discarded with the balls. Following the grading analysis of each sample, a curve should be plotted for each compartment showing the percentage of retained particles as a function of the compartment length. This analysis makes it possible to see the evolution of the particle-size distribution of the material in each compartment and adjust the size of the balls. The sieve sizes depend on what is available. As a basis:

Compartment 1

Compartment 2

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10 mm 5 mm 2.5 mm (important) 1 mm 500 µm 5 mm 2.5 mm (important) 1 mm 500 µm 200 µm 100 µm 63 µm 40 µm

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7 IV - 3 - Equipment analysis methods IV - 3 - 1 - Typical dimensions for each compartment

☞

Measure the useful diameter and length.

The useful length means beyond inlet or outlet heads. The useful diameter takes into account 1 out of 2 steps.

☞

Measure the rotating speed of the mill

When the mill is rotating, take as a reference point a door for example, record the time required for the shell to make a given number of rotations. Calculate the rotating speed (V).

☞

Check the V/Vc ratio

Vc is obtained using the formula :

42.3

Vc (rpm) =

useful Ø (m)

With the measured rotating speed (V in revolutions / minute) the percentage of the critical speed can be determined (required value for the calculations of the mill power). This is the V/Vc ratio or % Vc. Usually mills rotate at between 70 and 75% of the critical speed.

IV - 3 - 2 - Liners for each compartment

☞ Survey the types of liners (lifting, classifying, etc.) length and number of rows. For classifying liners, note the number of plates in a given row (see picture p 8). ☞

Measure the steps (difference in height between 2 consecutive plates in a given row). Make several measurements, identify the maximum and minimum step and estimate an average value.

Step

Lifting liners

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Combined lifting and classifying liners

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8

Step

Classifying liners: 1 inclined plate

☞

Classifying liners: 1 flat plate + 1 inclined plate

Take note of broken, tilted plates

A tilted plate is a plate that is no more in the same plan as the others be it on the vertical or horizontal axis, even both. As a result the step liner is modified (vertical axis) as well as the slope (horizontal axis). When there are too many tilted plates the charge efficiency may be reduced.

☞ ☞

Note the wear on the plates particularly scratches (specially in compartment 1)

Note the possible presence of material coatings on the liners (hard material should be distinguished from dust that might have settled during the crash stop).

IV - 3 - 3 - Diaphragms and outlet or inlet heads - a - Inlet head

☞

Measure the diameter (beginning and end) of the mill shell inlet and its length.

☞

Note the possible presence of turns and their length, promoting the feed of material. Turn height

Mill shell length Mill shell diameter

Mill shell inlet turns

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9

☞

Note how the material is fed (Toboggan, ladder)

Toboggan at the feed end

☞

Ladder at the feed end

Take note of broken or tilted plates or both and wear conditions

Inlet head showing severe wear (pronounced scratches and waving)

Intermediate diaphragm showing severe wear (pronounced waving and irregular slots)

- b - Outlet head

☞

Take note of broken or tilted plates or both and wear conditions

☞

Measure the diameter of the ventilation ring and estimate its permeability

Permeability =

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% of free surface Total ring surface

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10

Ventilation ring diameter

Measurement of the ventilation ring diameter

- c - Diaphragms

☞

Type of diaphragm (simple, double, double adjustable) and supplier (Slegten, Pfeiffer, Polysius, FLS...)

☞

Measure the diameter and assess the permeability of the ventilation ring.

☞

Note the number of sectors and possible staggering.

Staggered sectors generate a more or less large spacing that can be assimilated to a slot. If that spacing is large, coarse grains are likely to enter compartment 2.

☞

Slot position (radial, tangential, circumferential).

Radial slots

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11

Tangential slots

Circumferential slots

☞

Measure the slots (several measurements including estimated maximum, and average values).

Scrap

Slot width

Slot measurement (slots not peened but presence of scrap) Practical guide for the audit of grinding mills - 96/10

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12

☞

Estimate the slot permeability and wear conditions (possible peening) Slot permeability = % of opening remaining unclogged (estimate visually). Peening is characterized by a partial closing of the slots and with the edges appearing notched. Scrap and peening restrict the entrance of the material and the slots must be cleaned.

☞

Note the presence of scrap, check if it is hard (loss in permeability) or not. It is normal to see material in the slots (crash stop) but in that case it loosens up.

peened slots - notched edges

peened slots - opening variation

IV - 3 - 4 - Grinding charges

☞

Measure the length of the free space in 2 or 3 locations along the length of the compartment.

The height is measured on the mill diameter between the center of a step or liner plate and the ball charge. Length measurements should be averaged in order to determine the filling rate. It is estimated that the material increases the actual ball filling rate by about 2% in a compartment having a suitable material rate.

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13

Measure from 1/2 a step or plate transversal center

Vertical measurement

Middle axis

Measurement of the free space height (filling rate)

☞

To complete the free space measurement, measure the distance between the charge and the lower

part of the ventilation ring.

Distance between the charges and the lower part of the ventilation ring.

☞

Estimate, for compartments equipped with classifying liners, the charge classification (very good, right,

poor, reverse) given that the large balls should be at the beginning of the compartment and then, in a regular decreasing order, the small ones at the end of the compartment.

☞

Measure the diameter of the largest and smallest visible ball (gives an idea of the charge wear

compared to its original conditions). Practical guide for the audit of grinding mills - 96/10

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14

☞

Note the possible presence of ball coatings. Ball coatings or liner coatings or both may be the cause

of charge declassification.

☞

Note the possible presence of foreign matters as well as their nature in the ball charge. These foreign

matters hinder the charge action and may get stuck in the slots (scrap).

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15 IV - 4 - Interpretations of results IV - 4 - 1 - Material levels - Compartment 1 • The material should be essentially at the same level as the balls. This level can be controlled to a constant output by means of adjustable scoops (on a double diaphragm only, opening varying according to the inclination of the scoop) and by adjusting the grading of the grinding charge. In operation the material level is controlled by means of an electronic listening device placed at about 1/3 of the compartment length and 15˚ below the horizontal axis (where balls drop). A charge that is too coarse, hence permeable, will let the material flow too rapidly and the compartment will become relatively empty of material. This will create inter ball and ball / liner shocks without grinding results and cause the deterioration of the equipment. A charge that is too fine will increase the material rate and when the balls fall back on a bed of material that is too thick, they loose their grinding efficiency.

Scoop

Increased position

Scoops (intermediate diaphragm) Compartment 2 The material level should be located : 3 to 4 cm above the charge at the beginning of the compartment at the same level as the charge in the middle of the compartment 3 to 4 cm below the charge at the end of the compartment The material rate, at constant flow, can be adjusted only by the grading of the charge. Note: The grinding charge grading should be mainly determined according to the desired fineness of the finished product and following the analysis of the curves showing the evolution of the particle-size distribution of the material in each compartment.

Practical guide for the audit of grinding mills - 96/10

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16 IV - 4 - 2 - Evolution of the particle-size distribution of the material in the mill Curves based on samples of material in the mill (for each compartment) should show a decreasing pattern over the entire length of the compartment.

FINENESS EVOLUTION IN THE MILL % Cumulative Rejects 100 90 80 70 60 50 40 30 20 10 0 1

2

3

4

5

6 Samples

7

8

9

10

11

12

40 µm

63 µm

100 µm

200 µm

500 µm

1 mm

2.5 mm

5 mm

Diaphragm

Diaphragm

Case 1 - Proper evolution of the particle-size distribution of the material

FINENESS EVOLUTION IN THE MILL % Cumulative Rejects 100 90 80 70 60 50 40 30 20 10 0 1

2

3

4

5

6 Samples

7

8

9

10

11

12

40 µm

63 µm

100 µm

200 µm

500 µm

1 mm

2.5 mm

5 mm

Diaphragm

Diaphragm

Case 2 - Compartment 1: There is no more evolution between sample 4 and 5 at the end of the compartment. Compartment 2: same, no evolution on the last 2 samples The grinding charges in the 2 compartments should be reviewed

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17

FINENESS EVOLUTION IN THE MILL % Cumulative Rejects 100 90 80 70 60 50 40 30 20 10 0 1

2

3

4

5

6 Samples

7

8

9

10

11

12

40 µm

63 µm

100 µm

200 µm

500 µm

1 mm

2.5 mm

5 mm

Diaphragm

Diaphragm

Case 3 - Compartment 1: Curves are ascending at the end of the compartment, this is typical of an accumulation of grains in the intermediate diaphragm. If the slots are clean and of proper size, the solution is to raise the grinding power by increasing the charge grading. Compartment 2: OK The grinding charge of compartment 1 should be reviewed.

A good working criterion for compartment 1 charge is to have less than 5% retained on the 2.5 mm mesh at the beginning of compartment 2 for a cement mill. Caution: A mill is often used for several products and before changing a charge, the compatibility of the charge with all the manufactured products (internal samplings and observations) should be insured. Unfortunately, as seen before, the particle-size evolution curves are distorted by the circulating charge. The greater the circulating charge, the shorter the material flow time and the flatter the curves. To do away with the circulating charge, a mathematical treatment procedure is used (based on internal samples) to plot a RFCS curve (Reduced Fineness Curve Slope). The index is calculated only for compartment 2 (grinding). The RFCS index characterizes a mill for its ability to reduce the size of the material. The RFCS calculation is explained in the grinding stage section. In practice, the corresponding calculation sheet is filled (see appendix) with the particle-size distribution analyses of the samples taken in the mill.

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18 A straight line is obtained that looks like this:

LOG RFCS(x) vs LOG x 3.0 2.5 2.0 1.5 1.0 0.5 0.0 -1.4

-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

LOG x Regression Line a = 1.158 b = 2.866 R2 = 0.997

RFCS 10

( )

x Log RFCS (x) = a • log 1000

+b

3.5

RFCS 100 51.0

RFCS for a CEM Type 1 cement at a 45 µm mesh reference, has usual values at Lafarge Ciments ranging between 11 and 83 with an average standing at 35. The higher the RFCS the more efficient the grinding charge.

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19 IV - 4 - 3 - Liners - Compartment 1 Compartment 1 does the crushing, hence the need to lift the grinding charge with the lifting liners. From a process standpoint, the step should not be worn out by more than 60% to maintain a lifting function. In practice the original step usually measures 70 mm. When it wears down to less than 30 mm, assurance should be given that this will not affect the performance of the mill.

Border line step Suitable step

Case 1 - Lifting liners with a suitable step on the front plates and a border line step on the back liners

Case 2 - Lifting liners with completely worn out and heavily scratched steps On this open-circuit mill, the mere replacement of the C1 liners resulted in a flow rate increase from 20% to 25%. Practical guide for the audit of grinding mills - 96/10

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20 - Compartment 2 Compartment 2 works by attrition (grinding produced by the rubbing of balls against the material), liners being usually of the classifying type. They may consist of 1 to 3 plates depending on the mill diameter (see pictures p 8). -

1 plate (25 cm): small diameter mill, short compartment

-

2 plates (50 cm): usual situation

-

3 plates: recommended for large diameter mills exceeding 4 m in diameter

The last plate of each group of 2 or 3 is inclined (which produces the classifying effect), the preceding ones can be flat or inclined. The original step measures about 12 cm, and given the small size of the balls (60 mm max.) in compartment 2, the evolution is slow. Wear usually takes place in the form of scratches perpendicular to the compartment axis.

☞

Pay attention to coating.

Wear - Heavy scratches and coating starting.

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21 IV - 4 - 4 - Diaphragm Note the type of intermediate diaphragm. - a - Simple diaphragm It won’t allow the adjustment of the material level in compartment 1. Possible adjustments involve the permeability of the grinding charge and eventually the partial clogging of the slots. This type of diaphragm is not recommended.

- b - Double diaphragm A front face provided with slots, a rear face provided with blind plates and between the two, lifters which control the material flow. Drawback: The lifts are fixed and non adjustable.

- c - Adjustable double diaphragm - Picture page 15 A diaphragm similar to a double diaphragm with a system that regulates the amount of material transferred from C1 to C2. The lifting liners are replaced with scoops allowing, depending on the adjustment, more or less material to be picked up.

☞

Note the “opening” range of the diaphragm in this case. -

Slegten: The number of scoops and their positions (opened at x%, closed, not used)

-

Polysius: Lifting liner recess

-

Pfeiffer:

Slide opening

The adjustment can be performed only during a mill stop, which explains that in practice the scoop adjustment is very seldom modified during product switching. For a Slegten diaphragm, the optimum scoop adjustment can be determined for each product only through a series of adjustments of the number of opened scoops and their opening positions (in general, there are 6 to 8 scoop positions). After each adjustment, the material rate in compartment 1 should be measured. It is a time-consuming and tedious job but which is important when switching from a straight product to a blended product for example. The material rate of compartment 1 is one of the indicators of performance. For the other types of diaphragms, the procedure is similar. manufacturer should be used.

Practical guide for the audit of grinding mills - 96/10

The adjustment control designed by the

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22 - d - Slots - Pictures page _____ Slots have an opening width depending on the type of products: -

6 to 7 mm for a cement mill (intermediate diaphragm)

-

10 to 12 mm even up to 16 mm for a raw mill (intermediate diaphragm)

The following should be adhered to: Slot opening width of the outlet diaphragm = opening width of the intermediate diaphragm slots + 2 mm. The adherence to this rule allows the grains having reached the intermediate diaphragm, but too coarse to be ground in compartment 2, to move out of the mill without interfering with the operation of compartment 2.

☞

Check the slot wear

Slots have a double inverted clearance. The first one must insure that the grains do not get stuck, the second one facilitate the release of the material either towards compartment 2 or mill discharge. Manufacturers provide dimensions of the total slot surface with ratios in the range of: 10 to 20 cm2 per tonne/h of material passing through the diaphragm (= flow of fresh material + rejects)

Side 1 Clearance

Slot Width

Side 2 Clearance

Slot Diagram

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23 wear zone

peening

C1 slide clearance becomes non-existant

Width of original slot

Width of worn out slot

C2 side clearance

peening

Worn out slot diagram

After excessive diaphragm wear, the slot width increases and the C1 side clearance disappears which will cause the plugging of the slots with grains or scrap. While waiting for the diaphragms to the replaced, frequent cleaning of the slots are required.

☞

Insure that the slots don’t get peened picture page 12

Peening is caused by the impact of the balls on the diaphragm resulting in the closing of the head slots of side 1 clearance; peening is characterized by slots of variable width and notched edges. Peening may induce in the long term total plugging of the slots. It is then necessary to clear the slots to allow a suitable flow of material through.

Practical guide for the audit of grinding mills - 96/10

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24 - e - Ventilation Ring It must be as large (compatibility with the filling rate of the balls + material) and as permeable as possible to promote mill ventilation. However the grate must remain sufficiently rigid to prevent balls from moving from one compartment to another.

Case 1 - Good permeability

Case 2 - Average permeability

Case 1 - Grate offering a good permeability if the bar spacing is right (25 to 30 mm) This is certainly one of the best types of ventilation ring combining permeability and sturdiness. Caution: In case of cramming of compartment 1 there is a risk that coarse grains might enter into compartment 2. To prevent this a grate can be installed on compartment 2 side.

Case 2 - Sturdy grate but less permeable than case 1. It is still acceptable to the extent that the holes with a diameter larger than 25 mm are sufficiently numerous.

Case 3 - Low permeability

Case 4 - Zero permeability

Case 3 - Sturdy grate but with lower permeability because of a lack of holes. Not recommended in closed-circuit but acceptable in open-circuit where mill ventilation is lower. Case 4 - Grate with an almost nil permeability. Very few holes of small diameter which will get plugged up with material. The result is practically no mill ventilation left. Ventilation rings of this type are stiff found in closed-circuit mills. This belongs more like to the handy-man world (a few holes drilled on a blind plate) than to process technology. This type of grate should be banned and replaced with bars with a spacing adapted to the grading of the grinding charge of compartment 2 (mainly open-circuit where balls can be reduced to a 17 even 15 mm diameter and liners not necessarily of the classifying type). Practical guide for the audit of grinding mills - 96/10 Department of Studies - Viviers

25

IV - 4 - 5 - Grinding charge - a - Compartment 1 Filling rate of 30 to 35% which corresponds to a good compromise between flow rate and specify consumption. The grinding charge is made up of large-diameter balls to crush the material. In clinker mills, 4 sizes of balls: 90, 80, 70 and 60 mm are typically used: 90 mm 80 mm 70 mm 60 mm

20.0% by mass 38.4% by mass 25.6% by mass 16.0% by mass

Apparent density: about 4.5 t/m3. An average value for a typical charge as described above. This value may vary ± 0.1 t/m3 depending on the installed charge. The apparent density will be lower if the charge is coarser. In raw mills the same mass proportions with an almost identical range of balls can be found The raw mix is easier to grind (decrease in ball range), but the grading at the inlet is coarser (increase in ball range). The ball sizes and proportions constitute a theoretical base that should be adjusted after an internal inspection and on the basis of the fineness curves plotted from material sampling data. If the charge does very little work at the end of the compartment and the 2.5 mm mesh reject < 5%, the charge will have to be improved.

Case 2 page 24.

If on the contrary an accumulation of grains is found in the

intermediate diaphragms with 2.5 mm mesh rejects > 5%, the charge will have to be made coarser. To maintain a good crushing performance an average mass of approximately 1.8 kg per ball should be maintained.

- b - Compartment 2 Filling rate of 28 to 32% Compartment 2 or finishing compartment must produce the fineness and the ball diameters are relatively small (in a closed circuit) or very small (in an open-circuit since the material must have the required fineness at the mill discharge). The theoretical charge is divided into 2 zones: the first of transition (between compartment 1 and compartment 2) and the second of finishing. Practical guide for the audit of grinding mills - 96/10

Department of Studies - Viviers

26 Transition zone consisting of 50 and 40 mm balls in numbers equal to that of the 60 mm balls of compartment 1. Number 60 mm = Number 50 mm = Number 40 mm. Finishing zone made up of balls < 40 mm and with a distribution following slegten equations. Ø = 3.3 e-0.1x Where:

Ø x

= ball diameter = abscissa in compartment 2 (in meters) with origin at the diaphragm

Knowing for a given diameter the section length and on the basis of the filling rate and apparent density, the ball mass of the section can be calculated (see the corresponding working sheet in the appendix). Apparent density: roughly 4.7 t/m3. Average value for a typical charge as described above. This value may vary ±0.12/m3 depending on the installed charge. The apparent density will be higher if the charge is finer. Here too reference is made to a theoretical base that will require adjustment based on the internal samples but also the type of mill and the desired fineness. It is clear that in open-circuit the charge has to be improved to obtain the desired fineness at the mill discharge; the same applies for a very fine product. The finer the charge, the finer the product, the greater the risk of coating that will have to be minimized with better ventilation, failing that with a grinding aid. A problem often encountered is the multiplicity of products for a given mill. In that case a grinding charge for both compartments needs to be determined to reach a compromise between optimum charges for each product. The finer the grinding charge the longer the material will be retained in the mill. To give an idea of the differences the charge makes between an open and closed circuit, the retention time is: 3 to 5 min in closed circuit 15 to 20 min. in open circuit

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Department of Studies - Viviers

27 IV - 4 - 6 - Retention time Fluorescein introduction Compartment 1

Compartment 2

Sampling location

The retention time is measured when the mill is in stable operation The procedure consists of introducing a tracer and to take samples at regular intervals at the mill discharge (fluorescein, impregnated on the product either with alcohol for clinker or water for raw mix, is used). The suggested dosage is 2 g / t of feed. The introduction of fluorescein and the sampling must take place as close as possible to the mill inlet and outlet. In plotting a fluorescein concentration curve with time, the retention time at the maximum concentration peak is obtained (graph hereafter). From the retention time, the mass of material in the mill can be calculated and a C/M ratio that should be between 8 and 12 can be determined. The C/M ratio only puts a number on the average material level through the entire mill. The material level should be determined visually during the internal inspection of each compartment. C M

= =

Ball mass Mass of material in the mill

In practice this gives reliable results for a compound mill but this is rarely the case for a birotator mill. This phenomenon can be explained by the fact that the retention time is determined by the maximum intensity peak, whereas it would be preferable perhaps to calculate it by surface integration.

Practical guide for the audit of grinding mills - 96/10

Department of Studies - Viviers

28 The procedure doubles up the internal inspection, and given its mediocre precision, is almost never used to-day. It can still be used relatively speaking to compare an operation with another (tests on circulating charges for example) because it offers the advantage of not requiring the stoppage and opening of the mill gates.

Fluorescein intentisy (%) 100 90 80 70 Max. 4 min. 60 50 40 30 20 10 0 0

1

2

3

Practical guide for the audit of grinding mills - 96/10

4 Time (min.)

5

6

7

8

Department of Studies - Viviers

29 V -SEPARATION BALANCE V - 1 - Separation balance objectives The separation balance is done on the separator and allows deduction to be made of its performance coordinates as much from the standpoint of the characteristic values as for the various material flows. It is produced from data obtained from material samples taken at both the separator inlet and outlet. The sampling procedure is explained in the material balance section.

V - 2 -Analysis procedure - Distribution curve From the particle size distribution analysis of the separator inflow and outflow, a distribution curve is plotted (abscissa in logarithmic coordinates, ordinate in normal distribution coordinates). From the curve the following characteristics are determined: - acuity limit -

bypass

-

imperfection

-

fines cumulative yield

To allow the determination of the separator efficiency. From at least one given flow, the separator inflows and outflows (taken from the average R/A calculation) are calculated as well as the circulating charge.

V - 3 - Distribution curve calculation Reminder: Additional details of this calculation can be found in the section “Finishing mill operation”. Feed

Separator

Rejects Fines

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30 Note:

The distribution curve should be calculated over the entire inflows and outflows. If the separator

is ventilated, the dust carried by the gases must be included. It can be written:

1)

A = R + F on a flow basis

2)

A • ax = R • rx + F • fx for each size fraction

Where: -

A, R, F = feed, rejects and fines flows (t/h) “X” = index characterizing a size fraction ax, rx, fx = feed proportion (rejects and fines respectively) in the size fraction X A • ax is the material flow (t/h) in size fraction X at the feed end R A

From these 2 equations : R A

(x)

is the

R A

(x)

=

fx - ax fx - rx

is obtained

ratio predicted by the particle size distribution of size fraction x

For the overall particle-size distribution, the average R/A ratio is the integration of all the size fractions and can be summarized after simplification by the formula: ∑ (fx - ax) • (fx - rx)

Average R/A =

∑ (fx - rx)2

On the other hand the probability (Px) for an inflow grain of size x to end up with the rejects can be expressed: Rrx

Px =

Aax This equation can be transformed with equations 1) and 2) into:

Average

Px = Average

R A

rx

R rx + (1 - Average A

R ) fx A

The average sieve size of each size fraction can be calculated by the formula: dx =

For example between 2 and 4 µm

dx =

(2 • 4)

(d1 • d2)

= 2.83

The separator distribution curve is drawn by plotting on the graph the function : px = f(dx)

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Department of Studies - Viviers

31 2 straight lines are obtained, the first, slightly inclined (zone where the separator does not recognize the size of the particles, if not globally) and the second, more inclined, called acuity line (zone where the separator recognizes the size of the particles). All the calculations are made in a spread sheet (see appendix). Example of a calculation of the beginning of the distribution curve found in the appendix.

Laser gross result

% Cumulative passing

Mesh (µm)

Fines

Feed

Rejects

(1) 88.91

97.81

74.57

60.78

(2) 76.32

95.72

67.36

50.64

(3) 65.51

92.71

59.89

41.04

(4) 56.23

88.68

52.74

32.21

(5) 48.27

83.60

46.03

24.49

etc.

Mesh

dx

fx

ax

rx

dx

R/A mesh

(1) - (2)

(88.91 • 76.32) ^ 0.5 = 82.4

97.81 - 95.72 = 2.09

74.54 - 67.36 = 7.18

60.78 - 50.64 = 10.14

89.9

0.636

(2) - (3)

(76.32 • 65.51) ^ 0.5 = 70.7

95.72 - 92.71 = 3.01

67.36 - 59.89 = 7.47

50.64 - 41.04 = 9.60

85.4

0.677

(3) - (4)

(65.51 • 56.23) ^ 0.5 = 60.7

92.71 - 88.68 = 4.03

59.89 - 52.74 = 7.15

41.04 - 32.21 = 8.83

80.1

0.650

(4) - (5)

56.23 • 48.27) ^ 0.5 = 52.1

88.68 - 83.60 = 5.08

52.74 - 46.03 = 6.71

32.21 - 24.49 = 7.72

73.6

0.617

Average R/A

0.647

etc.

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Department of Studies - Viviers

32 It is from the distribution curve that the separator operating parameters are determined. 99.9 99.8 99.5 99 98 95 90

Fines cumulated yield curve

80 70 60 50 40 30 20

Line slope = imperfection

10

Bypass reading

Intersection point of the 2 lines

2 1 0.5 0.2 0.1 1

10

Fines cumulated yield 83.4 %

Circulating charge Bypass Acuity limit Corr. bypass Normalized imperf.

141% 6.2% 16 µm 10.6% 0.37

100

Acuity limit reading

Imperfection d 25 (µm) d 50 (µm) d 75 (µm)

Normalized 0.38 28 µm 40 µm 58 µm

Gross 0.40 26 µm 38 µm 56 µm

- a - Lafarge circulating charge The Lafarge circulating charge is the ratio of the rejects flow over the fines flow, expressed as a percentage may be expressed in the form of

Lafarge CC = R / F

CC =

R/A 1-R/A

Quite often suppliers use the ratio of the feed flow over the fines flow as a definition of the circulating charge or call it the circulation rate. Supplier CC

= =

A/F 1 + Lafarge CC

Practical guide for the audit of grinding mills - 96/10

Department of Studies - Viviers

33 - b - Flow calculation The distribution curve has allowed the calculation of the average R/A, i.e. the rejects flow with respect to the feed flow. Assuming any given flow and with the equation: A = R + F, it is easy to recalculate the other 2 flows.

- c - Acuity limit It is the minimum particle size that can be recognized by the separator. It is expressed in micrometers and is the abscissa of the intersection point of the 2 lines. The lower the acuity limit, the best the separation. It varies with the type of separator.

- d - Bypass It is the minimum probability for a particle to end up in the rejects. It is expressed as a percentage and is the ordinate of the intersection point of the 2 lines. The bypass should be as low as possible but is influenced by the circulating charge (the type of separator aside). This is why a “corrected bypass” free of the circulating charge is calculated using the formula: Corrected bypass =

Bypass • (1 + circulating charge) circulating charge

The Lafarge circulating charge being defined by the ratio:

Practical guide for the audit of grinding mills - 96/10

rejects flow fines flow

Department of Studies - Viviers

34 - e - Imperfection Slope of the acuity line using the formula: d 75 - d 25

I =

2 • d 50 This is the “gross imperfection”. d 25, d 50 and d 75 (µm) being the abscissa of the corresponding coordinates Px at 25, 50 and 75%. The lower the imperfection (hence the steeper the slope) the better the separation. The imperfection is also a function of the bypass. Therefore a “normalized imperfection” is calculated from the Tromp curve, with no bypass, using the formula: 100 (Px - Actual bypass)

P’x =

100 - Actual bypass The “normalized imperfection” is then calculated by the same formula as that of the gross imperfection. A parameter which is the stripping dimension is also used. It is the sieve size for which a particle has as much chance to end up in the rejects as in the fines.

- f - Fines cumulative yield For each sieve size it is the ratio: (1 - average R/A) = Fx / Ax A curve showing the cumulative percentage of the feed particles going into the fines is obtained, the maximum percentage being called fines cumulative yield. This yield gives a better prediction of the separator efficiency than the bypass.

Practical guide for the audit of grinding mills - 96/10

Department of Studies - Viviers

35 V - 4 - Rosin-Rammler Slope It defines the range of the particle-size distribution of the separator fines and is calculated from the laser analysis. Draw on a graph (abscissae in logarithmic coordinates, ordinates in decimal coordonates) the relationship: Ln Ln (proportion of cumulative rejects) = f (Ln sieve size). Rosin-Rammler adjustment 98.9 93.4 80.8 63.2

% passing

45.5 30.8 20.0 12.7 7.9 4.9 3.0 1.8 1

10 Sieve size (µm)

100

Rosin - Rammler line Rosin-Rammler Slope =

0.81

Equation of the Ln Ln (100/R) line =

0.8130 Ln (x) + -2.9371

Correlation coefficient = 0.9972

In this example the Rosin-Rammler slope (n RR) is 0.81. The more efficient the separator the higher the n RR. The Rosin-Rammler slope can be calculated 3 ways: -

total slope: from 2 µm to x µm (x µm is the maximum sieve size that produces a very good correlation coefficient)

-

from 2 to 30 µm for a fine product

-

from 2 to 20 µm for a very fine product

Practical guide for the audit of grinding mills - 96/10

Department of Studies - Viviers

36 V - 5 - Separator inspection The inspection report sheet shown in the appendix should be used.

V - 5 - 1 - Static separators Static separators are connected to the mill ventilation and can be adjusted only one way: by tilting the blades. The blades are tilted in such a way that be fineness of the filter dust is compatible with that of the finished product. The more tangential the blades (the static is closed) the higher the fineness of the fines. Fines Adjustable blades

Fresh air bleed valve

Thimble Inner cone Outer cone

Rejects Feed (mill sweep) Static separator

☞

Check the internal mechanical condition: wear, material clogging.

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Department of Studies - Viviers

37 V - 5 - 2 - 1st or 2nd generation separator or both

☞

Check the condition of the diaphragm.

☞

Check the condition of the ventilation blades. Record their quantity and dimensions.

☞

Check the condition of the distribution plate.

☞

Check the condition of the rejects and fines cone.

☞

Check the condition of the liners.

☞

Check the operation of the valves under the separator.

☞

Selector blades:

Number of blades Measure length and width Tilt Measure the distance to the casing (interior liners) and the diaphragm

diaphragm d h L

☞

casing d

Check the cleanliness of the return air vanes. Material clogging.

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38

Motor shaft

Selector blades

Ventilating blades

Diaphragm control

Casing

Return air vanes Air flow

Rejects cone

Fines cone

Rejects

1st Generation Internal-Ventilation Separator (Sturtevant)

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39

Fresh air

Feed Exhaust

Cyclone Table

Recycling ventilator Fines Return air vanes

Rejects

2nd Generation External-Ventilation Separator

The ventilation and the fines recovery with external cyclone on the 2nd generation separators produce a better fines recovery than the 1st generation separators. Ventilation being important as it reduces the temperature of the finished product, these separators also produce better raw mill drying results.

Practical guide for the audit of grinding mills - 96/10

Department of Studies - Viviers

40 V - 5 - 3 - 3rd generation separator

☞

Check the condition of the cage bars.

☞

Check the condition of the fixed blades (O’SEPA) sometimes adjustable with other makes (SEPOL).

☞

Check the condition of the liners.

☞

Check the operation of the valves under the separator.

☞

Measure the dimensions of the cage. Fines

Feed

Secondary air

Cage

Primary air Fixed blades

Rejects rd

3 Generation Separator (O’SEPA)

It is the type of separator which right now produces the best separation performances. It is easy to adjust for the desired fineness. The strong ventilation allows the temperature of the product to be lowered. On the other hand if the type of separator does not take as much space, i.e. requires a larger filter since all the production goes through it, contrary to the 1st and 2nd generation separators where the filter only handles the dust.

Practical guide for the audit of grinding mills - 96/10

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41 V - 6 - Interpretation of the distribution curve results V - 6 - 1 - Sieve size selection It is always interesting to use as many sieve sizes as possible, however the smallest mesh should be less than 2 µm for the sake of analysis accuracy. The largest selected sieve size should be that which corresponds, for the fines, to the percentage immediately lower than the 100% passing.

V - 6 - 2 - Sampling locations for the calculation of the separator distribution curve Instantaneously, a separator is not perfectly stable this is why it is better to smooth out these fluctuations by taking samples of material several times. At each location, take 4 to 6 samples of equal mass over a period of about 2 hours and place in a box These samples after homogenization will be analyzed by laser. It is also possible, with one person available at each sampling location, to take 4 to 5 samples over a period of 5 to 10 min. This procedure is used when controlling the operation of the separator during regular tests. The distribution curve calculation should be done from material samples taken from all the separator inlets and outlets (simple case p 29). More complex cases are illustrated in the following diagrams. Feed (A)

Dust (P)

Separator

Dust collector

Rejects (R) Finished Product (F)

Fines (Fs)

In this case A = R + Fs + P The distribution curve must be plotted considering: F = Fs + P

Practical guide for the audit of grinding mills - 96/10

Department of Studies - Viviers

42

☞

All that is required is to take samples of material at locations: A, R and F for the calculation of the

distribution curve. This is a case particularly encountered with 2nd generation separators.

Dust (P) (QPb) Dust grinding mill (B)

(QB)

Separator

(QBb) (QBa)

Dust collector grinding mill Finished Product (PF)

Feed (A)

(QPa) Dust collector separator + grinding mill

(Ba)

Dust collector separator

(Bb + Pb)

(Pa) Fines (Fs)

Rejects (R)

This is certainly the most complex case encountered in finishing mills where a filter handles at the same time grinding mill dust and separator dust. To plot the distribution curve, determine the separator outlet dust and fines flows, then recalculate a particle-size distribution of these 2 flows in proportion to the outputs. In practice this requires the elaboration of the material balance and part of the finishing mill air flow balance. Sample:

☞

Separator feed (A)

☞

Separator fines (Fs)

☞

Separator rejects (R)

☞

Fines from the grinding mill dust collector (Ba)

☞

Fines from the grinding mill + separator dust collector (Bb + Pb)

☞

Fines from the separator dust collector (Pa)

☞

Finished product (PF)

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43 Measure:

☞

Grinding mill outlet air flow (QB)

☞

Grinding mill outlet air flow towards mill filter (Qba)

☞

Grinding mill outlet air flow towards mill + separator (Qbb)

☞

Separator outlet air flow towards separator filter (Qpa)

☞

Separator outlet air flow towards mill + separator filter (Qpb)

☞

Additionally a first hypothesis must be made on the dust concentration at the mill outlet

As a general rule, it is estimated based on the gas velocity in the conduit. It ranges between 200 and 600 g / m3. (Average values since concentrations in excess of 1000 g/m3 have been encountered under high ventilation in a small diameter duct.

☞

The 2nd hypothesis consists of considering, in terms of particle-size distribution and BSS, that: P = Pa +

Pb and B = Ba = Bb.

Practical guide for the audit of grinding mills - 96/10

Department of Studies - Viviers

44 Calculation method Based on the estimated dust concentration and grinding mill outlet air flow, the mill outlet total dust tonnage is calculated. The distribution between mill filter and mill + separator filter branches is done in proportion to the air flows of each branch. The equation is written: BSS (Pa) • x + BSS (Ba) • y = BSS (Bb + Pb) • (x + y) Where:

x

=

separator dust flow to separator + mill filter

y

=

mill dust flow to separator + mill filter

x+y

=

total separator + mill filter flow

This equation is resolved given that y is known (hypothesis of the mill outlet dust concentration in proportion to the air flows) as well as the BSS. At this stage of the calculation the following is therefore known: -

mill filter flow separator + mill filter flow separator dust flow towards separator + mill filter mill dust flow towards separator + mill filter finished product flow (= feed flow)

The dust flow to the separator filter is calculated in proportion to the air flows of the branches coming out the separator and the calculated separator dust flow to the separator + mill filter. The material flow of the 3 filters being therefore known, the separator fines flow (Fs) remains to be deduced. For the calculation of the distribution curve, calculate a reconstituted particle-size distribution (size by size) of the total fines (F) based on the grading of the fines (Fs) and dust (P) in proportion to their respective flows.

☞

Verify the assumed hypotheses, insuring that:

The separator feed flow (A), calculated from the distribution curve, corresponds to that calculated by the elevator power (knowledge of the elevator characteristics required). The measured Blaine fineness of the finished product with that obtained by the addition of the Blaine fineness of the 3 filters + separator fines (Fs) in proportion to their respective flows.

Practical guide for the audit of grinding mills - 96/10

Department of Studies - Viviers

45 V - 6 - 3 - Average values of the separator distribution curve The values of the distribution curve parameters depend highly on the circulating charge. Here is what is usually obtained with properly controlled finishing mills. 1st generation 200 to 350% > 20 µm 20 to 50% > 0.45 0.75 to 0.85

Parameters Circulating charge Acuity limit Bypass Gross imperfection Rosin-Rammler n

2nd generation 100 to 250% 15 to 25 µm 10 to 35% 0.30 to 0.35 0.85 to 1

3rd generation 100 to 250% < 15 µm 5 to 10 % < 0.30 to 0.35 >1

- a - The acuity limit testifies of the ability of a separator to strip a finished product. - b - The bypass corresponds to the minimum probability of a particle to end up with the rejects. The higher it is, greater is the amount of fine product returning to the mill, which is inefficient. - c - The imperfection gives an idea of the separation difficulty. The higher it is, the less sharp is the stripping and the higher the amount of coarse particles in the finished product.

V - 6 - 4 - 3rd generation separators For the 3rd generation separators, a ventilation criterion characterized by the following ratios is determined: - Qf / Qa, kg / m3 - Qp / Qa, kg / m3 Where:

Qf

=

material flow at the separator feed end

Qa =

flow of air entering the separator (it is the actual volume (m3) and not n/m3)

Qp =

flow of material fines leaving the separator In general the following should occur:

Qf/Qa = 2 kg/m3 Qp/Qa < 0.8 kg/m3

Notes:

In Qf, f means feed In Qa, a means air, not to be confused with the separator feed (alimentation) material flow In Qp, p means product

Practical guide for the audit of grinding mills - 96/10

Department of Studies - Viviers

46 VI - MATERIAL BALANCE VI - 1 - Material balance objectives The material balance gives the flow of material in each circuit branch. The most important point lies, without a doubt, with the separator and its circulating charge which was discussed in the previous section. It also quantifies the filter fines flow. A filter overloaded with material will give a poor performance and create air flow problems. For electrostatic filters, manufacturers use a dimension ratio of: 10 to 50 m2 / 1000 m3 / h to obtain stack dust in the order of 30 to 40 mg 1 m3. (Surface area of collecting electrodes with respect to the gas flow through the filter). If the volume of the filter inlet dust is too large, it is more than likely that the concentration of the filter outlet dust will increase. For bag-house filters, the dimension ratio varies between 60 and 140 m3 / h / m2 (filtration velocity or working rate) which corresponds to velocities ranging from 1 to 2.3 m / min. It defines, based on the gas flow, the surface area of the filtering medias. With this kind of filters, if there is sequential unclogging, a material overload will translate into an increase of filter loss of charge causing air flow problems. If there is unclogging by a loss of charge, an increase in the energy required for the cleaning of the bags will become apparent.

VI - 2 - Calculation principle The flow of the finished product in a dry state is equal to the feed flow. This is known. On certain installations provided with mass measurements of rejects, this flow is also known. It is used as a basis of calculation but more currently used for checking the dynamic separator distribution curve and the different computations resulting from the junction calculation method. The calculation of the flow traveling in the elevator (under its own power) is also more of a checking mean than a basis of calculation.

Practical guide for the audit of grinding mills - 96/10

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47 It is very difficult to know the power efficiency of the motor and in practice the verification consists of confirming the suitable efficiency of the motor (about 0.9). Using an installation diagram as shown in section VI-4, the calculation principle can be described as follows:

☞

Starting from the finished product flow, the separator feed and rejects flows are determined from the

separator distribution curve. The separator feed flow that will be used as a basis for the evaluation of the elevator is now known.

☞

For the elevator, the filter and mill outlet flows are determined using the junction calculation method.

Verification of the separator feed flow based on the elevator power.

☞

On this simple installation, 2 distribution curves were sufficient to establish the material balance.

☞

If additional junctions are encountered, the same method is applied as often as necessary.

VI - 3 - Junction calculation method VI - 3 - 1 - Using the distribution curve The distribution curve calculation has been discussed previously. The same procedure is used to determine the material flow in the installation. This is what is called the junction calculation method. The principle is that of a distribution curve but only the average R/A ratio is retained. Given one flow the other 2 can be calculated knowing that: A = R + F.

VI - 3 - 2 - Using Blaine and temperature The distribution curve works very well with a separator. As a matter of fact, in separators there is particle sorting and the particle-size distribution of the various flows are very different. The junction calculation method derived from the distribution curve is more random precisely because the particle-size distribution of the different material flows are too close.

Practical guide for the audit of grinding mills - 96/10

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48 This could translate into an average R/A > 1, which is impossible since to meet: A = R + F, F would have to be negative. In this instance, except when weighing trucks, an attempt can be made to calculate the different flows using the global fineness (BSS). Q(A) • BSS(A) = Q(R) • BSS(R) + Q(F) • BSS (F) By the same principle, a reduced simplified heat balance of the 3 points can be established. In this perspective, at least one temperature reading at each material sampling location should be made during the sampling process. Actually this temperature procedure is used more to confirm the Blaine method than to determine the various material flows. Wall losses cannot be taken into account. Moreover, the thermocouple reaction time allows time for the material to cool down slightly. (The thinnest possible thermocouple, although mechanically weak, should be selected to obtain a better reaction time). Another alternative for a filter is to assume a dust concentration of the gas flows entering the filter and calculate the material flow with respect to the gas flows. (Case of the mill + separator filter pp 41 & 42).

VI - 3 - 3 - Other methods Certain installations are now equipped with separator rejects scale providing a way to verify part of the material balance. Another verification is possible by calculating the elevator flow based on its power (and its characteristics).

Q=

Where:

Q Pc Pv

ρ h g

= = = = = =

(Pc - Pv) • ρ • 3600 h•g

Flow (t/h) Power draw of elevator when loaded (kW) Power draw of elevator when running empty (kW) Elevator motor electrical output Elevator height (m) 9.81

Practical guide for the audit of grinding mills - 96/10

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49 VI - 4 - Selection of sampling locations

☞

Take material samples on the 3 branches each time 2 material flows intersect to form a third one, or

when a flow splits in two. 3

Separator

Separator Filter 5 Finished Product

4 Feed

Mill

E L E V A T O R

Mill Separator

2

1

Case of a finishing mill equipped with a 3rd generation separator. The mill filter dust is returned to the separator by the elevator.

☞

In the above case, take samples at locations 3, 4 and 5 needed for the distribution curve.

☞

The separator feed being made up of mill outlet + mill filter material flows, samples should be taken at

locations 3 (already done for the distribution curve), 1 and 2. The number of samples and sampling frequencies are the same as for those used for the determination of the distribution curve. Samples taken around the separator form an integral part of the material balance. After homogenization of each sample, the particle-size distribution should be determined (laser) as well as fineness (BSS). For drying mills, it is preferable to express the material balance on a dry basis.

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50 VI - 5 - Numerical example The following data will be considered: -

Feed = 100 t / h The separator distribution curve is that given on p 32 Mill discharge BSS = 1800 cm2 / g Mill filter BSS = 3400 cm2 / g Separator feed BSS = 2000 cm2 / g Elevator power draw when running empty = 5 kW power draw when loaded = 23 kW height = 25 m The junction calculation method applied to the elevator gives R/A = 0.85 (R = mill discharge, A = separator feed)

- a - Separator flow Feed flow = finished product flow (location 5) = 100 t/h (dry basis) The distribution curve gives a circulating charge of 141% (R/F) A= R= F= F=

Location 3 Location 4 Location 5 100 t/h

Given R/F and F, it is easy to calculate R R= A= A=

1.41 • 100 = 141 t/h R+F 141 + 100 = 241 t/h

- b - Elevator flow The elevator flows (locations 1, 2 and 3) must now be calculated.

☞

Choose:

A = Elevator discharge = mill feed (location 3) R = Mill discharge (location 1) F = Mill filter dust (location 2) The choice of R and F may be reversed, all that is needed is to know what they represent. But A must always be chosen as being the resultant of the 2 other flows. Mill Filter (location 2)

Mill Discharge (location 1)

Separator Feed (location 3)

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51 The only known flow is the separator feed. Using the junction calculation method (simplified distribution curve) the mill discharge (location 1) and mill filter dust (location 2) flows are then calculated. The junction calculation method gives an average R/A = 0.85 A = 241 t/h R = 0.85 • 241 = 204.85 t/h (mill discharge) A= R+F F= A-R F = 241 - 204.85 = 36.15 t/h (mill filter) The material balance has therefore been established for the installation. However it is necessary to check the calculated flows mainly around the elevator. - Verification by fineness On the basis of the flows and the fineness of the materials entering the elevator, the elevator discharge fineness should be close to 20000 cm2/g. (204.85 • 1800) + (36.15 • 3400)

=

2040 cm2/g

241 Given the precision of the Blaine test, a 100 to 200 points variation is deemed acceptable. In the present case, the Blaine 40 points variation confirms the validity of the flows calculated by the junction calculation method. - Verification by the elevator power draw Efficiency =

Flow • Height • 9.81 (Ploaded - Pempty) • 3600

Efficiency =

241 • 25 • 9.81 (23 - 5) • 3600

= 0.91

An efficiency of 0.91 is a suitable value confirming also the flow entering the elevator. The material balance is therefore validated. The flows can also be verified by the material temperature using the same principle as for fineness. This method is however less accurate since abstraction is made of wall losses. It is used when the 3 flow finesses are almost identical.

Mass measurements offer the best verification or starting base. Weighing of rejects. It is increasingly more common to have a scale installed to weight the separator rejects and to serve as a mill operation parameter. -

Weighing of trucks. Difficult to put in practice but more reliable.

Practical guide for the audit of grinding mills - 96/10

Department of Studies - Viviers

52 VI - 6 - Interpretations of results Notwithstanding the difficulty in reconstituting the particle-size distribution of the total fines (see distribution curve section), there is generally no or very few problems with the distribution curve of dry dynamic separators. On the other hand, difficulties are encountered when establishing the static separator inflows and outflows. The other problems stem mainly from the calculations by the junction calculation method and are of 2 types: -

sample representativity

-

too close a particle-size distribution of the materials making up the flows.

VI - 6 - 1 - Static separator Right now nobody seems to know how to take samples of gas-suspended materials. This is why materials are sampled strictly where only materials circulate (airslides, chutes, belt conveyors, ...). It is practically impossible, for this reason, to produce a distribution curve with a static separator (no sampling of materials at the static separator inlet). Consequently, if the fines flow can be calculated, the static separator rejects and feed flows cannot. The only solution is to estimate a rejects flow. Another solution would be truck weighing which could be useful for filter dust for instance. This is rarely done for practical reason and also because too risky for the quality of the finished product. For a filter with a small flow, weighing would have to be done over one or several hours to be suitable but then what would happen to the fineness of the finished product without filter dust?

VI - 6 - 2 - Sample representativity With bag-house filters in particular, fineness is not always uniform in relation to unclogging cycles and the material flow is sequential. Quite often filters unload in airslides which do not have blending capability. Material sampling resulting from the sum of a filter + separator fines for example, in an airslide, will become hampered. At times only separator fines will be sampled, at other times, a filter blend having a higher flow compared to the average will be sampled. Practical guide for the audit of grinding mills - 96/10

Department of Studies - Viviers

53 Hence the need to increase the number of samples to smooth out this phenomenon. A second source of error is due to the existing depression (caused by dusting). It is a depression which, when the scoop is withdrawn from the duct, will lose a portion of the surface layer of the material and as a result may distort the particle-size distribution. The best way to counteract this phenomenon is to use a scoop that can be closed before being pulled out of the duct in order to eliminate the depression inside the sampler.

Simple samplers

Closed position before pulling out of the duct

Open position in the duct “Anti-depression” samplers

Practical guide for the audit of grinding mills - 96/10

Department of Studies - Viviers

54 VII - AIR FLOW BALANCE VII - 1 - Air flow balance objectives The balance determines the ventilation of each equipment, chiefly the mill and dynamic separator. Initial air inleakage can also be located and quantified by a drop in output and energy increase of the draft ventilator. For drying mills, this also serves as a basis for the drying balance.

VII - 2 - Selection of measurement locations An air flow measurement must be made at the inlet and outlet of each equipment (repeat the measurements to make sure of the result).

In ducts, the gas streams must be as stable as possible, and not subjected to

turbulences. Turbulences are generated by elbows, guide vanes, a change in section - - - -. The measurement should preferably be made over 3/4 of a long and straight portion (8 to 10 times the diameter of the duct). Unfortunately it is not always possible and to minimize the error, testing is done on 2 diameters at 90˚. 5 Ø and 3 Ø adhered to

5 Ø and 3 Ø not adhered to 3Ø

5Ø

2 Measurement Axis

Gas Direction 2 Ø exploration at 90°

Measurement Axis

Practical guide for the audit of grinding mills - 96/10

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55 VII - 3 - Air flow measurements VII - 3 - 1 - Anemometer measurements

Propellor Propellor

Reader

Length dial Timer

Maxant Type Anenometer

Electronic Anemometer

They are made on so-called “open” sections such as ventilator horn, mill fresh air inlet... An integrating anemometer is used that cumulates length with time during the measurements. Sweep the entire open surface with a motion as regular as possible. The “maxant” anemometer is equipped with 2 dials. The first one gives length (m), the second, time (s). By dividing length by time, velocity (m/s) is obtained. Nowadays electronic anemometers give directly the velocity measurement. By multiplying the acceleration by the cross section, the flow in m3/s is obtained. To obtain flow at 0° C (normal: Nm3) a temperature correction must be made: NM3 =

m3 • 273 273 + Ø

Where Ø: temperature, °C. To take a flow measurement using an anemometer it is necessary to:

☞ ☞ ☞

measure the cross-section measure the temperature at the measuring location measure the velocity (anemometer)

Note: Rectangular ducts:

It is considered that in corners there is none or very little flow. Hence a 0.96 coefficient is

used in the calculation of the cross-section: S + L • 1 • 0.96 This cross-section is called air flow cross-section.

Practical guide for the audit of grinding mills - 96/10

Department of Studies - Viviers

56 VII - 3 - 2 - Pitot, Strauscheib, Type R pitot tube measurements They are made on so-called “closed” sections such as ducts. Either a pitot tube (clean gas flows), or a type R pitot tube, or a Strauscheib tube (dust-laden gas flows) is used.

Strauscheib

Pitot Dynamic pressure

Static pressure Total pressure

Pressure meter

The formula used is drawn for Bernoulli’s law and applies to clean gases.

V=

2•g•h

ρ Where

V g h p

= = = =

Velocity ( m/s) 9.81 Measured dynamic pressure average (mmCE) Gas unit mass (kg/m3)

By multiplying the velocity by the cross-section the flow is obtained. But it is necessary beforehand to calculate the unit mass of the gases taking into account first their composition and then apply a temperature and pressure correction.

ρ = ρ0 • Where:

P = Pst = Ø =

273 273 + Ø

•

10336 + Pst 10336

Standard unit mass (kg/m3) Static pressure (mmCE) Temperature (°C)

Practical guide for the audit of grinding mills - 96/10

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57 In general for clinker mills, the unit mass of the dry air gases (P0 = 1.293 kg/m3) is used if the additions are in small quantity and the moisture is low. If not, it must be recalculated based on the gas analysis. A flow in m3 is obtained that will require a temperature and pressure correction to obtain a flow in NM3/h. Q (Nm3 / h) = Q (m3 / h) • Where:

Ø

273

•

10336 + Pst

273 + Ø =

Pst =

10336

Temperature (°C) Static pressure (mmCE)

To measure the flow using a Pitot or Strauscheib tube, it is necessary to:

☞

measure the cross section

☞

measure the temperature at the measuring location

☞

measure the static pressure at the measuring location

☞

measure the dynamic pressures on the testing duct axis

The dynamic pressure is read directly on the meter by connecting the total and static pressures. Dynamic pressure = total pressure = static pressure. Notes:

Rectangular ducts: it is considered that in corners there is none or little flow. Hence a 0.96 coefficient

is applied for the calculation of the cross-section: S = L • 1 • 0.96. - Strauscheib or Pitot type R tube: The static pressure is measured opposite the total pressure (Pitot tube at 90°) and therefore a correction coefficient (k) must be determined in the laboratory (or supplied by the manufacturer) and applied directly to the calculated velocity. For a Pitot tube k = 1. Additionally, the Strauscheib tube is used in dust-laden atmospheres. Nonetheless the Bernoulli formula is applied (no other means are known today) by correcting the unit mass of the gases from the dust concentration. Calculate the unit mass of the gases with the temperature and static pressure correction, then add to it the dust concentration (kg/m3).

ρ total (kg / m3) = (ρ0 gas • temperature correction • pressure correction) + dust The dust concentration is determined after doing the material balance (the hourly amount of material moving in the duct is then known).

Practical guide for the audit of grinding mills - 96/10

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58 3

Proceed by iteration until the gas flow (m /n) • dust concentration equals the material flow transported in the duct. Strauscheib tube measurements are subject to criticism and this should be remembered when completing the air flow balance. The general formula is:

V=k•

Where:

2•g•h ρ + dust

V

=

gas acceleration, m/s

g

=

9.81

h

=

dynamic pressure average, mmCE

Q m3 / s = V • cross section

Numerical example In the configuration of the finishing mill (p 49), the material balance gives a mill filter material flow of 36.15 t / h. An air flow measurement was done with the Strauscheib tube in the mill discharge duct leading to the mill filter. A first analysis, omitting the dust, reveals a flow of 108 000 m3 / h with a ρ for gases of 0.928. The dust concentration is calculated to be 36.15 • 106 / 108 000 = 335 g / m3 of dust. Now proceed by iteration, since by including the ρ dust corrections, the flow will change. The new ρ will then become 0.928 + 0.335 = 1.263. This will give a flow of 92 700 m3 / h. The dust flow will then become 335 • 106 • 92,700 = 31 t/h instead of 36.15 as desired. The new dust concentration is 36.15 x 106 / 92,000 = 390 g / m3. Repeat the calculations by iteration until the obtention of : dust concentration • flow = 36.15 t/h. A concentration of 400 g / m3 for a flow of 92,400 m3 / h will be found. On the Pitot calculation sheet, use the target value function which will immediately give the correct dust concentration value. Caution:

Dust concentrations are expressed in g / m3.

Practical guide for the audit of grinding mills - 96/10

Department of Studies - Viviers

59 VII-3-3 - Gas analyses They are used to recalculate the gas unit mass but will also serve when doing the drying balance (moisture). They must be done at the same locations as the air flow measurements if the composition of the gases varies (air inleakage, material drying). The O2 and CO2 analyses are done by pumping the gases out of the duct and the test gases are dried before going through the various analyzers. The actual analysis should be recalculated taking moisture in the duct into account. In a cement plant, the essential analyses involve O2, CO2, N2 and H2O. O2 and CO2 are determined dry, H2O as is. N2 = 100% - (% actual O2 + actual CO2 + % H2O) • % actual gas = % dry gas • (1 - proportion of H2O) H2O is analyzed either by pumping, or by measuring the dry and humid temperatures.

O2 Analyser

Test gas

CO/CO2 analyser Gas analyzers

Practical guide for the audit of grinding mills - 96/10

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60 VII - 4 - Interpretations of results VII - 4 - 1 - Anemometric Measurements Except when using the technique consisting of sweeping the surface with a regular motion, there are no particular problems with small and large dimensions. On the other hand, with big horns (> 1 m) at times the sweeping may not give good results (case of the separator fresh air intake - Martres BK4 where the separator air flow closure was not good). A point by point measurement on 2 axis at 90° has allowed the closure of the separator air flow balance and meeting the plant annubars.

VII - 4 - 2 - Pitot, Strauscheib, Type R Pitot Tubes - a - Exploration Most of the time, a regular depth exploration is used instead of taking an equivalent surface ring measurement which requires a depth recording for each duct. In the case of regular depths, instead of calculating the arithmetical mean of the dynamic pressures, the root mean is determined. This method gives good results provided the gas flows are not too irregular. If the gas flows are too irregular, the equivalent surface ring exploration should be done. In this case the mean of the dynamic pressures is determined arithmetically.

Practical guide for the audit of grinding mills - 96/10

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61 The diagram and table below provide the depths based on the number of measurement points for a 1 m diameter duct. Positioning of the measurement points of the equivalent surface rings D 1m

Table for D = 1 m

d1 d2

Number of points

Point designation

d3

6

a1 a2 a3 a4 a5 a6 a1 a2 a3 a4 a5 a6 a7 a8 a1 a2 a3 a4 a5 a6 a7 a8 a9 a 10 a1 a2 a3 a4 a5 a6 a7 a8 a9 a 10 a 11 a 12

B

A

8

6

5

4

3

2

1 10

a1

a3 a4

A

a2 B

a5 a6

The indicated values in the Table apply only for D = 1 m

For D = x, multiply the values by x

12

Distance from the edge 0.044 0.146 0.296 0.704 0.854 0.956 0.032 0.105 0.194 0.323 0.677 0.806 0.895 0.968 0.026 0.082 0.146 0.226 0.342 0.685 0.774 0.854 0.918 0.974 0.021 0.067 0.118 0.177 0.250 0.356 0.644 0.750 0.823 0.882 0.933 0.979

- b- Dust-Laden Atmospheres In case of dust-laden atmospheres, the standard Pitot tube gets plugged up too rapidly and the flow cannot be measured. Hence, either a Straucheib or Type P Pitot tube is used. Their main feature is that they are provided with a total pressure - taking opening that is bigger than that of the standard Pitot Tube. It will get plugged up also but less rapidly allowing a measurement to be made.

☞

Pull out and clean the tube after each measurement.

Practical guide for the audit of grinding mills - 96/10

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62 The rapidity with which plugging takes place is not in itself an indication of the dust concentration in the duct. Other phenomena such as the nature and fineness of the dust come into play. Contrary to what may be thought, when plugging occurs, the observed dynamic pressure suddenly increases. Note the difference in the diameter of the openings Total Pressure

Static Pressure

Left : Strauscheib — Right : Pitot - c - Dirty Conduits It occurs sometime that a conduit in an almost level position and carrying dust, becomes dirty. This can be the case of a conduit where dust-laden gases circulate between the tower and a drying mill. Also, tower gases are moist and humidity promotes sticking at the base of the conduit (during stoppage, this phenomenon is amplified by condensation) The gas circulation cross section becomes artificially reduced and the effective cross-section must be calculated.

h initial Ø

accumulated material

The easiest way in that case to calculate the effective cross-section for gas circulation of is to use the mill filling rate procedure.

☞ ☞

calculate the initial cross-section from the initial diameter measure h (comparable to the free height of a mill)

Practical guide for the audit of grinding mills - 96/10

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63

☞

calculate the “filling rate” Effective Cross-section = initial cross-section • (1 - “filling rate”)

VII - 4 - 3 - Gas analyses O2 and CO2 analyses are done by pumping over a very short time (1 to 2 min.) and should be confirmed once or twice. The moisture analysis by pumping takes much longer (30 min. to 2 hours depending on the moisture level) and can be checked in case of doubt, being understood that testing must be conducted during stable mill operation. The moisture analysis under dry humid temperatures is spotty and should be checked one or twice. How to choose between the two types of moisture analysis? -

by pumping: it covers everything (particularly dust-laden gases) and integrate with time. Its main drawback is the set-up (electrical pump, meter, silicagel, sampling lance).

☞

Make sure you place a glasswool pad at the end of the lance to filter the dust.

☞

Make sure you limit condensation between the lance outlet and the silicagel (the shortest possible

distance). Incline the lance towards the silicagel to capture any possible condensation. Moisture calculation: % moisture by volume = 100 •

volume of absorbed water volume of absorbed water + volume of pumped gas (at 0° C)

The volume of absorbed water is in fact a mass of water to be translated into volume. Volume of water (Nm3) =

mass of water (kg) • 22.4 18

22.4 l = volume occupied by a mole of gas. The correspondence of the units gives Nm3. 18 g = molar mass of water. The correspondence of the units gives kg. - by dry humid temperatures: spot measurements must be limited specially to the exhaust gases. Drawbacks: there can be no dust (it will stick to the damp cotton and distort the measurement). The dry temperature should not exceed 110 to 120 ° C otherwise the cotton dries very rapidly and the measurement becomes impossible.

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64 Use very thin thermocouples to get a quick answer. Watch the humid temperature because it will progressively increase to a certain level; read it and switch over to the dry temperature; read it immediately. Humidity readings are done using humid air Tables.

VII - 4 - 4 - Air inleakage calculation by gas analyses In drying mill circuits, air inleakage can be calculated with the O2 or CO2 elements or both which are influential elements. But it is necessary for reasonable accuracy to have different analyses of the ambient air. This is why these calculations cannot be made unless the hot drying gases originate from a tower or a grate. Air inleakage calculated with O2: % air inleakage / intake = 100 •

outlet O2 - intake O2 20.94 - outlet O2

20.94 = O2 of ambient air Air inleakage calculated with CO2: % air inleakage / intake = 100 •

intake CO2 - outlet CO2 intake CO2

Caution: The analyses being run on a dry basis, the air inleakage percentage is expressed on a dry basis. Example: Intake O2 = 8% (as measured) CO2 = 25% (as measured) H2O = 8% (as measured) 10,000 Nm3/h (as measured)

Outlet O2 = 11.5 % (as measured) CO2 = 15.5 % (as measured) H2O = 18.2 % (as measured) 15,000 Nm3/h (as measured MILL

Vaporisation : 2,000 Nm3 / h

With O2: % air inleakage / intake = 100 •

With CO2: (11.5 - 8) (20.94 - 11.5)

= 37%

Practical guide for the audit of grinding mills - 96/10

% air inleakage / intake = 100 •

(25 - 15.5) 25

= 38%

Department of Studies - Viviers

65 The moist measured intake flow is 10,000 Nm3 / h at 8% H2O = 9,200 Nm3 / h dry and 800 Nm3 / h water. The calculated air inleakage averages 37.5%. The dry flow at the outlet will be 9,200 • (1 + 0.375) = 12,650 Nm3 / h representing an air inleakage of 3,450 Nm3 /h. Let’s assume that the ambient air contains 2% moisture. The water carried by the air inleakage will be : 12,650 + 800 + 2,00 + 70 = 15,520 Nm3 (to be compared with the measurement taken). 800 = volume of water contained in the intake gases. 2,000 = volume of the material evaporable water in the mill (drying). 79 = volume of water carried by the air linkeage. The outlet moisture will be : (800 + 2,000 + 90) / 15,520 = 18.5% (to be compared with the measurement taken). Gas outlet

Gas intake “Moist” silicagel “Dry” silicagel

Thermometer Sampling lance

Reservoir

Pump

Meter

Gas moisture by pumping

Dry / humid switch Readers

Dry thermocouple

Humid thermocouple Thermocouples - Standard above - Dry / humid below Practical guide for the audit of grinding mills - 96/10

Department of Studies - Viviers

66 VII - 4 - 5 - Mill ventilation ratios An important aspect of the air flow balance is the determination of the mill ventilation. It is expressed as a fictitious gas velocity in the mill in empty tube equivalent. All that is needed is to divide the actual gas volume by the internal cross-section of the mill. As a general rule, the actual volume is calculated at 100° C which is an average temperature in a mill It is very difficult to measure the volume of gas crossing the mill, although 2 possibilities exist. 1st by measuring the tube outlet flow but in this case it is distorted (by excess) by the air inleakage, namely at the trommel outlet. This is what can be qualified as an optimistic hypothesis. 2nd by measuring the tube inlet flow, but in this case it is distorted (by default) by the impossibility of measuring the air entering with the material. This is what can be qualified as a pessimistic hypothesis. The actual value stands between these 2 hypotheses. The ventilation ratio for a mill is:

in open circuit, from 0.6 to 0.8 m/s in closed circuit, from 1 to 1.5 m/s

If the finishing mill is equipped with a static separator, the ventilation can be increased up to 2 m/s provided the static fines are compatible with the finished product. Also: - gas velocity at 100° C over the charge (varies according to filling rate) in open circuit from 0.8 to 1.2 m/s in closed circuit from 1.4 to 2.1 m/s - specific ventilation in Nm3 / kg of finished product (varies according to mill output, and gives an evaluation of the cooling / drying potential. The ratio ranges from 0.3 to 1 Nm3 / h of finished product depending on the installation. Currently, in finishing mills equipped with 3rd generation high-efficiency dynamic separator, it is preferable to return the dust-collected fines at the base of the elevator. This allows a strong ventilation of the tube and furthermore it is an assurance of quality of the finished product.

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67 VIII - DRYING / HEAT BALANCE VIII - Drying / Heat Balance Objectives The balance allows material drying optimization and the quantification of the drying energy required. The recirculation of the exhaust gases can be also adjusted. Therefore it is possible to give priority to the optimization of the energy supplied by the heat source especially if the latter is generated by a furnace (saving on the purchase of fuel). This type of balance can be done on raw or fuel mill circuits. It is sometimes possible to give consideration to a drying balance on a clinker mill when a cementitious addition is very damp and used in large proportion. In this case the question is to find out if it is useful to add hot gases to the mill or if the heat produced by the mill is sufficient.

VII - 2 - Drying and Heat Balances The drying balance is in fact combined with a heat balance because besides knowing where the water in the material is eliminated and in what amount, 2 ratios are determined that are related to the energies involved. The first ratio is the theoretical drying efficiency which is the total energy provided at the inlet per kg of evaporation water. Total energy means the energy supplied by the heat source but also by the sensible heat from the inlet gases and materials (the reference used is 0° C). This ratio may also be expressed as a percentage of the theoretical vaporization (596 kcal / kg of water) to the total supplied energy. The second ratio is the useful drying efficiency which is the pure energy provided at the inlet per kg of evaporation water. The pure energy is strictly coming from the heat source(s).

☞

Measure (flow, temperature) and analyze(H2O) the gas flows coming in and out of the installation and for

each equipment if it is desired to find out more precisely when water evaporation takes place.

☞

Sample (flow, temperature) and analyze (H2O) the materials coming in and out of the installation and for

each equipment if it is desired to find out more precisely when water evaporation takes place.

☞

In the case of a furnace the fuel analysis and flow (pure energy) should be obtained but also all the

amount of air entering the furnace (primary and diluted). It is essential for the calculation of the volume of the combustion smokes and their analysis. It is frequently difficult to measure the gas flow at the mill inlet (very short duct).

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68 VIII - 2 - 1 - Drying Balance The drying balance may be expressed in kg of water / h or in Nm3 / h of vapor. However it is preferable to use kg/h on account of the ratios. Determination of the water flow in and out of the circuit or for each equipment or both.

- Material Volume of water (Nm3/h) = material flow (kg/h) • H2O proportion • 22.4 / 18 Mass of water (kg/h) = actual gas flow (Nm3/h) • H2O proportion - Gas Volume of water (Nm3/h) = actual gas flow (Nm3/h) • H2O proportion Mass of water (kg/h) = actual gas flow (Nm3/h) • H2O proportion • 18 / 22.4 - Air inleakage Don’t forget that ambient air carries water The loss of water in the material in an equipment is called vaporization and is often expressed in Nm3/h)

VIII - 2 - 2 - Heat Balance It is expressed in kcal / h (or kJ / h) and covers, except in special cases, the entire circuit. It is expressed by reference to 0° C. - Material Sensible heat (kcal / h) = material flow (kg/h) • temperature • average specific heat at the temperature (kcal / kg). - Gas Sensible heat (kcal / h) = material flow (Nm3/h) • temperature • average specific heat at the temperature (kcal / Nm3/h). - Fuel Sensible heat (kcal / h) = fuel flow (kg/h) • temperature • average specific heat at the temperature (kcal / kg). Combustion energy (kcal / h) = fuel flow (kg / h) • inferior heat capacity (kcal / kg). - Mill Part of the mill energy is transformed into heat and is included in the heat balance. Heat supplied (kcal / h) = mill power (kW) • 1 h • proportion of transformed energy • 860. 860 : 1 kWh = 860 kcal.

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69 In general

- 90% of the electrical energy is transformed into mechanical energy - 95% of the mechanical energy is transformed into heat - overall, 85% of the electrical energy is transformed into heat

Note: I HP = 0.735 kW

1 kW = 1.36 HP

1 J = 0.239 cal

1 cal = 4.186 J

1W=1J/s

1 kW = 1 kJ / s

1 kWh = 3,600 kJ = 860 kcal

1 thermie = 1000 kcal

- wall losses They are not measured but estimated A percentage of the sum of the intakes is used (kcal / h)

- vaporization Do not forget, in the outlets, that the vaporization of water at 0° C uses 596 kcal / kg of evaporated water. A vaporization value at 0° C is taken since the balance is expressed by reference to 0° C.

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70 VIII -3 - Interpretations of Results VIII - 3 - 1 - Drying Balance For economical reasons, the contribution of hot gases should be minimized (specially if there is a furnace), but at the same time a certain outlet temperature must be maintained to avoid water condensation in the filter (risk of bag plugging and possible corrosion). It is considered that an outlet temperature in excess of 25 to 30° C above the dew point should be maintained. In general, on standard installations, the heat source is controlled so as to maintain a mill outlet temperature at around 80 to 85° C which is sufficient to prevent condensation in the filter. The ambient air humidity varies with the climate, so the easiest way is to contact the local weather bureau.

For information: Temperature (° C)

Relative humidity (%)

Humidity (% by volume)

25 20 15 10 5 25 20 15 10 5 25 20 15 10 5

100 100 100 100 100 80 80 80 80 80 60 60 60 60 60

3.1 2.3 1.7 1.2 0.9 2.5 1.8 1.4 1.0 0.7 1.9 1.4 1.0 0.7 0.5

It can be seen that as a first attempt, only a very small error can be make on the drying balance by considering the ambient air humidity to be between 1 and 3% based on the temperature.

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71 VII - 3 - 2 - Heat Balance The lower the theoretical and useful drying efficiencies the better the drying optimization. On very efficient installations the theoretical efficiency ranges from 1,100 to 1,200 kcal / kg of evaporation water. An efficient installation requires:

high inlet gas temperature (400° C). low outlet gas temperature, between 80 and 90° C (this minimizes heat losses). recirculation of a portion of the exhaust gases (heat recovery) large amount of evaporation water (material H2O >5%)

It is usual to see theoretical efficiencies between 1,400 and 1,500 kcal / kg of evaporated water, in particular, even when the material moisture is low when the installation operates under favorable conditions.

- mill The electric power of motors is recorded and do not forget the electric motor performance when calculating the actual power transmitted to the mill. It is estimated that 80 to 90% of the electrical energy of a ball mill is transformed into heat.

- wall losses They are not measured because they represent only a small fraction of the heat balance. The analysis and site measurement of wall losses are very time concerning. It is estimated that wall losses range between 5 and 10% of the total energy input.

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72 IX - ENERGY BALANCE IX - 1 - Energy balance objectives This balance, contrary to others, does not allow the detection of a precise area of operation problem. This is above all a global indicator of the operation of an installation that is expressed in kWh / t of finished product. It is possible however to quantify the energy required for each equipment and the total energy required to produce one tonne of finished product. By regularly following up this ratio for each product, any possible drifting along the way can be detected. Any such drifting will be an incentive for finding what causes it by reviewing the other balances. An increase in kWh / t is often the result of a drop in production (same energy consumption but a lower divider).

IX - 2 - Energy balance

☞

Record the electric power of each piece of “process” equipment -

mill motor elevator dynamic separator motor(s) exhaust ventilator(s) dynamic separator fresh air ventilator

The other pieces of equipment such as auxiliary dust collectors, air slides, pneumex, are not included in the “process” energy balance. They are normally integrated in the overall circuit total.

☞

Record the finished product output.

☞

Sample on the conveyor belts (once is enough) all the ingredients entering the mill.

☞

Have a BB10 grindability test done.

The BB10 mill is a calibrated laboratory mill which gives the theoretical “process” energy required to grind a material at a desired fineness. The test is conducted on the reconstituted finished product (ingredients sampled from the conveyor belts). A curve is plotted with the kWh / t in ordinate and the corresponding finenesses in abscissa. For cement the fineness is expressed in BSS. For raw mixes, the fineness is expressed in amount retained on the 100 µm mesh. The kWh / t of the circuit corresponds to the fineness of the finished product.

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73 If the mill operates under good conditions, the same fineness should correspond fairly well to the same BB10 kWh/t. Production energy (kWh / t)

70

BB10 Cement grindability

60

50

40

30

20

BSS fineness (cm2/g) 10 1000

1500

2000

2500

3000

3500

4000

4500

Production energy (kWh / t)

18

BB10 raw mix grindability

16 14 12 10 8 6 4 2

% retained on 100 µm mesh 0 0

5

10

15

20

25

30

35

40

Typical examples of grindability results Practical guide for the audit of grinding mills - 96/10

Department of Studies - Viviers

74 IX - 3 - Interpretations of results IX-3-1 - Energy balance Very often an average is made of the different equipment powers taken from the record of the installation operating data. Assurance must be given that the computer data are right. Hence it is good to have an electrician make a control measurement of the electric power of the motor of each equipment. The energy balance is calculated from the actual power consumptions (without taking into account the electrical efficiency of the equipments). A “process” consumption (kWh/t) is determined as well as a consumption of the mill itself which by far is the equipment that utilizes the largest amount of energy in a finishing mill (80 to 95% in general).

IX - 3 -2 BB10 Test The BB10 mill is a closed-circuit mill without ventilation. The BB10 test was designed for clinker. The practical correlation giving the energy consumption vs the number of revolutions has been done with finishing mills producing Portland cement or straight products (slag, ...). It is estimated that for Type CEM I cement, the BB10 test is reliable within about 5%. For Type CEM II cement and when the addition is limestone, there is a different behaviour of the addition fines between production (ventilation sweeps the fines) and the test (no ventilation). The same type of problem is encountered on pure products when high finenesses are obtained (BSS fineness > 4,000 cm2 / kg). The phenomenon is the same with blended cement, i.e. an overgrinding of the fines that forms coating & thereby reduced grinding efficiency. In these 2 foregoing cases the curve is normal in the lower part but distorted in the high fineness range. It becomes very steep. When during production a grinding aid is used, it is difficult to maintain the same dosage in the BB10 because of the small amount of material (1 kg). The result is an offset on the overall grindability curve. For all these reasons, the grindability test error is about 10% with blended cement (with or without admixture) and also for BSS finenesses below 3,000 - 3,500 cm2/g. Beyond that the interpretation is very uncertain. With blended cement it is a good practice to run a BB10 test on the pure clinker. By comparing with previous tests, it is possible to find out if the increase of the finishing mill kWh/t is due to a change in clinker grindability (major ingredient).

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75 X - CONCLUSION The mill follow-up is very important because it helps in spotting a progressive drifting of the installation in terms of flow or total electrical power. The progressive drifting should be an incentive to try and determine the cause of a problem by means of airflow, drying balances, etc. The evolution of the grinding charges and the internal conditions of the equipment as well as any eventual modifications should be analyzed. In that perspective the follow-up becomes very important from an historical standpoint and help in determining the causes of operation problems. Grinding aids promote the disposal of the fines from the mill by preventing agglomeration. Also, they have a beneficial effect on the material flow and in general will slightly increase the Blaine fineness for equal strength.

☞

It is recommended, for each product, to look for the optimum dynamic separator recirculation

rate. (This should be done when the grinding charge is suitable after sorting out the charge for example) This consists of varying either the rejects and feed or elevator power requirements and identifying the requirement at which maximum feed is obtained. Plot a curve of feed flow vs requirements. Caution:

The rejects are the dynamic separator rejects. The feed is the fresh feed from the finishing mill and not the separator feed.

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76 For satisfactory mill operations, follow-up and targeted actions are required without having to produce exhaustive balances (refer to mill follow-up manual).

☞

Do a charge sorting out every 8000 h for compartment 1, 10000 h for compartments 2 and 3.

☞

Do a regular internal inspection of the mill (observations and if possible sampling of material to check

the evolution of the fineness). The grinding medium filling rate should be readjusted by adding balls.

☞

“Chase air inleakage” to insure a good mill ventilation (critical with drying mills).

☞

Check the operation of the dynamic separator (distribution curve).

☞

Check the operation of the valves.

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77 LIST OF ANALYSIS COMPUTER PROGRAMS - Pitot - Distribution - Rosin - Rammler - RFCS (PCFR in French) - Moisture (silicagel cartridges) - Moisture (dry / humid) - Elevator flow - Drying / heat balance - Charge characteristics - Compartment 1 charge calculation - Compartment 2 charge calculation - Filling rate - Smoke calculation - Gas characteristics

Available under excel 4 or 5 in Macintosh or Window version

- Pitot : Airflow calculation. - Distribution curve : Calculation and plotting of the distribution curve (can be used also for the junction calculation method). - Rosin - Rammler: Calculation and plotting of the Rosin - Rammler curve. - RFCS: Calculation and plotting of the RFCS curve. - Moisture (silicagel cartridges): Calculation of gas moisture by pumping. - Moisture (dry / humid): Calculation of gas moisture by dry and humid temperature measurements. - Elevator flow: Calculation of the material flow from the elevator power draw and its characteristics. - Drying / heat balance: Calculation of the drying and heat balances (several possible configurations. Maximum: 2 heat sources + furnace + 1 recirculation + 1 water spray). - Charge characteristics: Calculation of the charge characteristics for each compartment with graphs and power drawn by each compartment.. - Compartment 1 charge calculation: Calculation of compartment 1 charge plus large ball selected on the basis of the material and mill characteristics. - Compartment 2 charge calculation: Calculation of compartment 2 charge. - Filling rate: Calculation of the compartment filling rate based on the measured height of the free space. - Smoke calculation: Calculation of the combustion smokes and their analysis based on the solid fuel elementary analysis. - Gas characteristics: Calculations of the combustion smokes and their analysis based on the gas fuel elementary analysis. An outline, for all these calculation sheets, is given in the appendix. A list (not complete) of equipment suppliers with price estimate is also given in the appendix together with the characteristics of the balls and cylpebs vs their sizes.

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78

LIST OF APPENDICES

Separator inspection report Mill (2 compartments) inspection report Mill (3 compartments) inspection report Ball and cylpeb characteristics Testing equipment suppliers

Calculation sheets

Pitot Distribution curve Rosin - Rammler RFCS Moisture (silicagel cartridges) Moisture (dry / humid) Elevator flow Drying and heat balances Charge characteristics Compartment 1 charge calculation Compartment 2 charge calculation Filling rate Smoke calculation Gas characteristics

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79 MILL FOLLOW-UP

SEPARATOR INSPECTION REPORT

Type of separator :

STURTEVANT

Plant :

Mill :

Date :

Type of cement : MEASUREMENTS, RECORDS, OBSERVATIONS

COMMENTS

Good

Average

Poor

Good

Average

Poor

Good

Average

Poor

Diaphragm condition Ventilation blades condition

Distribution plate condition Selector blades (1) 1st and

Number Length Width Inclination Distance from casing

mm mm ° mm

Number Length Width Inclination Distance from casing

mm mm ° mm

2nd Selector blades (2) G E N E R A T I O N

Good

Average

Poor

Yes

No

Good

Average

Poor

Good

Average

Poor

Good

Average

Poor

Rejects cone condition

Plugged return air vanes Liner wear condition Rejects valve

in order out of order

Fines valve

in order out of order

3rd G E N E R A T I O N

Cage bars condition Fixed blades condition Liner wear condition

Rejects valve

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in order out of order

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80

LIST OF APPENDICES

Separator inspection report Mill (2 compartments) inspection report Mill (3 compartments) inspection report Ball and cylpeb characteristics Testing equipment suppliers

Calculation sheets

Pitot Distribution curve Rosin - Rammler RFCS Moisture (silicagel cartridges) Moisture (dry / humid) Elevator flow Drying and heat balances Charge characteristics Compartment 1 charge calculation Compartment 2 charge calculation Filling rate Smoke calculation Gas characteristics

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81 MILL FOLLOW-UP MILL (2 COMPARTMENTS) INSPECTION REPORT Plant :

Mill :

Date :

Type of cement : MEASUREMENTS

Material level

C1

Above* Under* Above* Under*

Material C2

mm mm

C1

Useful length Useful diameter

M M

C2

Useful length Useful diameter

M M

Height of free space

C1 C2

M M

Filling rate

C1 C2

% %

Largest ball mm mm

Smallest ball mm mm

Dimensions

C1 C2 Grinding Charge

COMMENTS

Pollution from

to be calculated to be calculated

Liners External elements

Ball classification

Good

Null

Inverse

C1 C2 Liners

Type

Step

C1 C2

mm mm

Mill shell inlet

Ø

M

Intermediate diaphragm

Slot width % plugging Ventilation ring Ø Permeability

mm % M %

Outlet diaphragm

Slot width % plugging Ventilation ring Ø Permeability

mm % M %

Equipment Parts

Coating

Coating C1 C2

Balls yes / no * yes / no *

Liners yes / no * yes / no *

* Strike out the non applicable mention

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82

LIST OF APPENDICES

Separator inspection report Mill (2 compartments) inspection report Mill (3 compartments) inspection report Ball and cylpeb characteristics Testing equipment suppliers

Calculation sheets

Pitot Distribution curve Rosin - Rammler RFCS Moisture (silicagel cartridges) Moisture (dry / humid) Elevator flow Drying and heat balances Charge characteristics Compartment 1 charge calculation Compartment 2 charge calculation Filling rate Smoke calculation Gas characteristics

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83 MILL FOLLOW-UP MILL (3 COMPARTMENTS) INSPECTION REPORT Plant :

Mill :

Date :

Type of cement : MEASUREMENTS Material level

C1

Material C2 C3

mm mm mm

C1

Useful length Useful diameter

M M

C2

Useful length Useful diameter

M M

C3

Useful length Useful diameter

M M

Height of free space

C1 C2 C3

M M M

Filling rate

C1 C2 C3

% % %

Largest ball mm mm mm

Smallest ball mm mm mm

Dimensions

C1 C2 C3 Grinding Charge

COMMENTS

Above* Under* Above* Under* Above* Under*

Pollution from

to be calculated to be calculated to be calculated

Liners External elements

Ball classification

Good

Null

Inverse

C1 C2 C3 Liners

Type

Step

C1 C2 C3

mm mm mm

Mill shell inlet Intermediate diaphragm 1 & 2 Equipment Parts Intermediate diaphragm 2 & 3

Outlet diaphragm

Coating

Coating

Ø

M

Slot width

mm

% plugging Ventilation ring Ø Permeability

% M %

Slot width

mm

% plugging Ventilation ring Ø Permeability

% M %

Slot width % plugging Ventilation ring Ø Permeability

mm % M %

Balls

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Liners

Department of Studies - Viviers

84 C1 C2 C3

yes / no * yes / no * yes / no *

yes / no * yes / no * yes / no *

* Strike out the non applicable mention

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85

LIST OF APPENDICES

Separator inspection report Mill (2 compartments) inspection report Mill (3 compartments) inspection report Ball and cylpeb characteristics Testing equipment suppliers

Calculation sheets

Pitot Distribution curve Rosin - Rammler RFCS Moisture (silicagel cartridges) Moisture (dry / humid) Elevator flow Drying and heat balances Charge characteristics Compartment 1 charge calculation Compartment 2 charge calculation Filling rate Smoke calculation Gas characteristics

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86

Ø (mm) 90 85 80 75 70 65 60 59 58 57 56 55 54 53 52 51 50 49 48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10

BALL & CYLPEB CHARACTERISTICS BALLS CYLPEBS Unit mass Developed surface Ø L Unit mass (g) (m2/t) (mm) (mm) (g) 2977 8.55 25 50 191 2508 9.05 25 32 123 2091 9.62 22 28 83 1723 10.26 19 24 53 1401 10.99 16 22 35 1122 11.83 12 15 13 882 12.82 839 13.04 25 25 96 797 13.26 22 22 65 756 13.50 19 19 42 717 13.74 16 16 25 679 13.99 12 12 11 643 14.25 608 14.51 574 14.79 542 15.08 511 15.38 480 15.70 452 16.03 424 16.37 398 16.72 372 17.09 348 17.48 325 17.89 303 18.32 281 18.76 261 19.23 242 19.72 224 20.24 207 20.79 191 21.37 175 21.98 161 22.62 147 23.31 134 24.04 122 24.81 110 25.64 100 26.53 90 27.47 80 28.49 72 29.59 64 30.77 56 32.05 Balls 50 33.44 43 34.97 P = V • 7.8 38 36.63 V = 4/3 • PI • R ^ 3 33 38.46 S = 4 • PI • R ^2 28 40.49 SD = S/P = 3 • 1000 / (R • 7.8) 24 42.74 20 45.25 17 48.08 Cylpebs 14 51.28 11 54.95 P = V • 7.8 9 59.17 V = PI • D ^ 2/4 • L 7 64.10 S = PI • D ^ 2/2 + D • L 5 69.93 SD = S/P 4 76.92

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Developed surface (m2/t) 25.64 28.53 32.47 37.67 43.71 59.83 30.77 34.97 40.49 48.08 64.10

Legend P = V = PI = S = SD =

mass volume 3.1416 surface developed surface

Department of Studies - Viviers

87

LIST OF APPENDICES

Separator inspection report Mill (2 compartments) inspection report Mill (3 compartments) inspection report Ball and cylpeb characteristics Testing equipment suppliers

Calculation sheets

Pitot Distribution curve Rosin - Rammler RFCS Moisture (silicagel cartridges) Moisture (dry / humid) Elevator flow Drying and heat balances Charge characteristics Compartment 1 charge calculation Compartment 2 charge calculation Filling rate Smoke calculation Gas characteristics

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88

TESTING EQUIPMENT FOR MILL BALANCES TESTING EQUIPMENT ANEMOMETER

PRESSURE GAUGE

TYPE Mini Air 2 Macro SCHILTKNECHT Macro probe 80 mm Ø Ref. 648 / 24 PDM 208 Neotronics Solomat EDM

PRESSURE GAUGE Ref: Zephir - SM Air - Neotronics Limited PITOT TUBE

Type S Air Flow Developments

PITOT TUBE

Strauscheib Tube

GAS PUMP

GAS METER

MEASURING RANGE 0.1 - 40 m/s

±1999 mm CE ± 400 cm CE Pressures 0.00 to 99.99 mm H2O 100 to 999.9 mm H2O 1000 to 1224 mm H2O Velocity 1.5 to 141 m/s For clean gases us to 800° C Length 0.48 m Length 1.00 m Length 1.52 m Length 2.74 m For gas with high dust concentration

N 010 KN 18

12 l/mm

Galus 2000

Q max. : 6 m3 / h P max. : 0.5 b for dry and clean gases

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SUPPLIER

(1996) PRICE (T.E.)

Mesureur 72-76 rue du Château des Rentiers 75013 PARIS Tel (1) 45 83 66 41

Probe : 8 000 F

Neotronics Solomat

4 000 F

Neotronics Solomat 16 rue Jacques TATI - B.P. 187 91006 Evry Cedex Tel.: (1) 60 77 89 90 Fax: (1) 60 77 93 73

12 000 F

Casing 5 000 F

Neotronics Solomat

1 990 F 2 350 F 3 200 F 4 990 F

S.F. 2 l. Zone artizanale - Ile du Moulin 07400 Le Teil Tel. : 75.52.18.75 Fax : 75 52.25.25 Kurt Neuberger - 4 Bd d’Alsace 68300 Village Neuf Tel. : 89.70.35.00 Fax : 89.69.92.52 Schlumberger ZAC Val de Murigny BP 227 51061 Reims Tel. : 26.05.65.72

Length : (2 • 1.5 m) = 2 910 F Fabrication: CLV design

1 440 F

700 F

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89

TESTING EQUIPMENT FOR MILL BALANCES TESTING EQUIPMENT

TYPE

MEASURING RANGE

THERMOCOUPLE

For Type K Thermocouple Long Standard probe SI 1300 Short Standard probe SI 1300

Range 1 = -200° C to +200° C Range 2 = 200° C to 1370° C

GAS BAG (gold beater’s skin)

Volume : 10 Litres

SILICAGEL O2 ANALYZER

O2 - CO - CO2 ANALYZER

CO - CO2 ANALYZER

Herrmann - Moritz Oxymeter HM 100 Paramagnetic Herrman - Moritz Trigaz 123 PX O2 Paramagnetic CO Electrochemical Cell CO2 Infrared Detector SIEMENS Ultramat 22 Infrared transmitter

For drying test gases Digital display 0 to 100% Outlet 0-1V or 0-10V Elec. outlet 4 - 20 mA Digital display O2: 0 to 100% CO: 0 - 2000 or 0 - 10000 ppm CO2: 0 - 20 or 0 - 30 or 0 100% Digital display CO 0 - 5000 ppm (recommended) CO2 0-5%

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SUPPLIER

(1996) PRICE (T.E.)

A.I.S. Le Divin 69620 Bagnols Tel.: 74.71.70.61 Fax: 74.71.77.05 PROLABO - BP 369 75526 Paris Cedex 11 Tel.: (1) 49.23.15.00

Casing: 1700 F L SI 1300 : 810 F C SI 1300 : 550 F 200 F

Prolabo Pekly - 5 rue du Théâtre 91884 Massy Tel: (1) 69.53.73.00 Fax: (1) 69.53.73.01 PEKLY

25 300 F

51 200 F CO Cell Ref. AL75 = 1750 F

Siemens S.A. Dept. instrumentation industrielle 39 - 47 Bd Ornano 93527 Saint Denis Cedex 2 Tel.: (1) 49.22.38.51 Fax.: (1) 49.22.30.62

47 910 F

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90

LIST OF APPENDICES

Separator inspection report Mill (2 compartments) inspection report Mill (3 compartments) inspection report Ball and cylpeb characteristics Testing equipment suppliers

Calculation sheets

Pitot Distribution curve Rosin - Rammler RFCS Moisture (silicagel cartridges) Moisture (dry / humid) Elevator flow Drying and heat balances Charge characteristics Compartment 1 charge calculation Compartment 2 charge calculation Filling rate Smoke calculation Gas characteristics

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91 PITOT ANALYSIS PLANT: PRODUCT: MEASUREMENT POINT: CONDUIT DIAMETER LENGTH WIDTH

Input Results

MILL: DATE:

1.00

m m m

TEMPERATURE STATIC PRESSURE

100 -150

°C mm CE

PITOT COEFF.

0.84

DUST

300

GAS COMPOSITION if dry air is not involved %H2O % dry CO % dry CO2 % dry O2

15.00 0.00 15.00 8.00

DYNAMIC PRESSURES 25.00 22.00 23.00 25.00 25.00 20.00

3

g/m

Number of values:

0.79 23.29 0.928 1.228

m2 mm CE kg/m3 kg/m3

VELOCITY FLOW

16.21 12.73 9.18 45824 33052

m/s m3/s Nm3/s M3/H Nm3/H

DUST (t/h)

13.75

CONDUIT CROSS-SECTION AVERAGE DYN. PRESS. RHO without dust RHO with dust

6

The gas composition analysis is done on the H2O %. If H2O > 0 → takes the analysis into account. If H2O = 0 → gas = dry air.

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92

LIST OF APPENDICES

Separator inspection report Mill (2 compartments) inspection report Mill (3 compartments) inspection report Ball and cylpeb characteristics Testing equipment suppliers

Calculation sheets

Pitot Distribution curve Rosin - Rammler RFCS Moisture (silicagel cartridges) Moisture (dry / humid) Elevator flow Drying and heat balances Charge characteristics Compartment 1 charge calculation Compartment 2 charge calculation Filling rate Smoke calculation Gas characteristics

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93 DISTRIBUTION CURVE The sieve sizes shall be classified in decreasing order PLANT: MILL: SEPARATOR:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29

Mesh (µm) 88.91 76.32 65.51 56.23 48.27 41.43 35.56 30.53 26.20 22.49 19.31 16.57 14.22 12.21 10.48 9.00 7.72 6.63 5.69 4.88 4.19 3.60 3.09 2.65 2.28 1.95

PLN CLINKER SEPOL

Page 1 Input

DATE: 95 / 5 / 16 PRODUCT TYPE: CPA 52.5 CP2 LASER TYPE : MALVERN VIVIERS

% cumulative passing Fines Feed Rejects 99.82 76.93 61.80 98.64 70.97 52.73 96.45 64.32 43.23 93.02 57.65 33.89 88.26 51.14 25.54 82.30 45.01 18.77 75.47 39.48 13.81 68.25 34.68 10.46 61.11 30.62 8.33 54.60 27.23 7.06 48.72 24.39 6.31 43.46 21.98 5.91 38.78 19.88 5.69 34.59 17.98 5.51 30.80 16.21 5.32 27.34 14.55 5.07 24.15 12.97 4.77 21.21 11.48 4.42 18.52 10.12 4.06 16.09 8.87 3.72 13.96 7.78 3.40 12.14 6.84 3.12 10.63 6.05 2.87 9.39 5.38 2.65 8.36 4.81 2.43 7.48 4.30 2.22

dx

P (x) %

82.4 µm 70.7 µm 60.7 µm 52.1 µm 44.7 µm 38.4 µm 32.9 µm 28.3 µm 24.3 µm 20.8 µm 17.9 µm 15.4 µm 13.2 µm 11.3 µm 9.7 µm 8.3 µm 7.2 µm 6.1 µm 5.3 µm 4.5 µm 3.9 µm 3.3 µm 2.9 µm 2.5 µm 2.1 µm

91.5 85.9 79.3 71.2 61.5 50.5 39.5 29.6 21.6 15.1 9.8 6.1 5.6 6.5 9.15 11.92 14.23 15.72 16.71 17.31 17.65 18.74 20.54 22.93 24.95

% cumulative passing

AVERAGE R/A = 100.00 90.00 80.00 70.00 60.00 50.00 40.00 30.00 20.00 10.00 0.00 1.00

R/A fraction 0.606 0.610 0.549 0.485 0.217 0.695 0.625 0.614 0.597 0.592 0.587 0.578 0.570 0.563 0.559 0.557 0.561 0.568 0.569 0.571 0.573 0.565 0.566 0.569 0.554

0.584

Fines Feed Rejects

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10.00 Mesh (µm)

100.00

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94

DISTRIBUTION CURVE PLANT: MILL: SEPARATOR:

PLN CLINKER SEPOL

Page 2

DATE: PRODUCT TYPE: LASER TYPE:

FINES CUMULATIVE

CIRCUL. CHARGE

141%

YIELD 83.3%

BY PASS ACUITY LIMIT CORRECTED BY PASS NORM. IMPERFECTION

6.2% 16 µm 10.6% 0.38

IMPERFECTION

d 25 (µm) d 50 (µm) d 75 (µm)

95 / 5 / 16 CPA 52.5 CP2 MALVERN VIVIERS

NORMALIZE D 0.38 28 µm 40 µm 58 µm

RAW 0.40 26 µm 38 µm 56 µm

99.9 99.8 99.5 95 90 80 70 60 50 40 30 20

10 5

2 1 0.5 0.2 0.1 1

10

100

1000

Number of points on the left side of the curve (optional):

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95

LIST OF APPENDICES

Separator inspection report Mill (2 compartments) inspection report Mill (3 compartments) inspection report Ball and cylpeb characteristics Testing equipment suppliers

Calculation sheets

Pitot Distribution curve Rosin - Rammler RFCS Moisture (silicagel cartridges) Moisture (dry / humid) Elevator flow Drying and heat balances Charge characteristics Compartment 1 charge calculation Compartment 2 charge calculation Filling rate Smoke calculation Gas characteristics

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96

ROSIN - RAMMLER CURVE PARTICLE-SIZE DISTRIBUTION

Rosin - Rammler Adjustment % cumulative passing 8.87 10.34 11.95 13.74 15.75 18.01 20.55 23.40 26.56 30.06 33.91 38.11 42.66 47.59 52.82 58.32 64.03 69.92 75.66 81.05 85.90 90.06 93.44 96.03 97.87 99.06 99.72

Number of usable points

% cumulative retained 91.13 89.66 88.05 86.26 84.25 81.99 79.45 76.60 73.44 69.94 66.09 61.89 57.32 52.41 47.18 41.68 35.97 30.08 24.34 18.95 14.10 9.94 6.56 3.97 2.13 0.94 0.28

98.9 93.4 80.8 63.2 % passing

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

mesh µm 1.95 2.28 2.65 3.09 3.60 4.19 4.88 5.69 6.63 7.72 9.00 10.48 12.21 14.22 16.57 19.31 22.49 26.20 30.53 35.56 41.43 48.27 56.23 65.61 76.32 88.91 103.58

45.5 30.8 20 12.7 7.9 4.9 3 1.8 1.00

ROSIN - RAMMLER SLOPE LINE EQUATION

100.00

27

ROSIN - RAMMLER STRAIGHT LINE

Calculated between points

10.00 mesh (µm)

1 2.0 µm 8.9 % pass

STANDARD MESH RECALCULATION

and

27 103.6 µm 99.7 % pass

1.02 LnLn (100/R) = 1.0173 Ln(x) + -3.0933

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Using regression line mesh % cumulative passing 2 8.8 4 17.0 8 31.3 12 43.3 16 53.3 24 32 45

68.3 78.6 88.7

(D90 - D10) / D50 Dimension for x % passing D 10 actual 2.2 µm D10 recalculated 2.3 µm D50 actual 15.3 µm D 50 recalculated 14.6 µm D 90 actual 48.2 µm D 90 47.5 µm recalculated

Designation

Department of Studies - Viviers

97 64 Correlation coefficient

0.9987

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95.6

Designation Designation Designation

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98

LIST OF APPENDICES

Separator inspection report Mill (2 compartments) inspection report Mill (3 compartments) inspection report Ball and cylpeb characteristics Testing equipment suppliers

Calculation sheets

Pitot Distribution curve Rosin - Rammler RFCS Moisture (silicagel cartridges) Moisture (dry / humid) Elevator flow Drying and heat balances Charge characteristics Compartment 1 charge calculation Compartment 2 charge calculation Filling rate Smoke calculation Gas characteristics

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Department of Studies - Viviers

99 RFCS CALCULATION Plant: Mill:

Product: Date:

Sampling data Sieves used (mm)

Input Sampling at (m)

0.043 0.061 0.087 0.103 0.160 0.400

Mill flow: C2 power: C2 length:

0.00 0.50 1.46 2.42 3.38 4.34 5.30 6.26 7.67

Compartment power Metric power

36.6 T/h 421 kW 7.67 m

11.50 kWh/t 1.50 kWh/t.m

Fineness curves results

Sampling 0.00 m 0.50 m 1.46 m 2.42 m 3.38 m 4.34 m 5.30 m 6.26 m 7.67 m

0.043 74.02 73.01 71.66 67.90 62.80 59.95 56.57 55.82 52.53

0.061 56.47 54.85 53.43 49.25 43.48 40.73 37.24 35.20 32.11

0.087 37.69 35.46 34.00 29.20 24.11 21.38 18.22 14.90 12.80

RFCS

14.0

22.7

42.8

% cumulative retained on mesh 0.103 0.160 0.400 30.63 22.17 7.20 28.37 20.43 5.71 26.97 19.79 4.12 21.97 15.42 1.99 17.30 10.85 0.75 14.57 8.67 0.41 11.59 5.92 0.18 8.31 3.61 0.08 6.66 2.48 0.06 60.1

86.0

199.8

RFCS Curve

LOG RFCS (x)

LOG RFCS(x) vs LOG x

3 2.5 2 1.5 1 0.5 0 -1.4

-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

-0.0

LOG x Regression line a= b= R2 =

1.190 2.845 0.967

LOG RFCS = a • Log

Practical guide for the audit of grinding mills - 96/10

( ) x 1000

+b

RFCS 10 RFCS 45 RFCS 100

2.9 17.5 45.3

Department of Studies - Viviers

100

LIST OF APPENDICES

Separator inspection report Mill (2 compartments) inspection report Mill (3 compartments) inspection report Ball and cylpeb characteristics Testing equipment suppliers

Calculation sheets

Pitot Distribution curve Rosin - Rammler RFCS Moisture (silicagel cartridges) Moisture (dry / humid) Elevator flow Drying and heat balances Charge characteristics Compartment 1 charge calculation Compartment 2 charge calculation Filling rate Smoke calculation Gas characteristics

Practical guide for the audit of grinding mills - 96/10

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101

MOISTURE MEASUREMENT (PUMPING) PLANT : MILL CIRCUIT: MEASUREMENT POINT: DATE : TIME :

Input TARE (g)

FINAL MASS (g)

NO 1 CARTRIDGE

400.0

426.0

NO 2 CARTRIDGE

450.0

451.0

NO 3 CARTRIDGE FLOW (litres) INITIAL METER READING

5000

FINAL METER READING

5550

METER TEMPERATURE (°C)

20.0 H2O volume :

Practical guide for the audit of grinding mills - 96/10

6.15%

Department of Studies - Viviers

102

LIST OF APPENDICES

Separator inspection report Mill (2 compartments) inspection report Mill (3 compartments) inspection report Ball and cylpeb characteristics Testing equipment suppliers

Calculation sheets

Pitot Distribution curve Rosin - Rammler RFCS Moisture (silicagel cartridges) Moisture (dry / humid) Elevator flow Drying and heat balances Charge characteristics Compartment 1 charge calculation Compartment 2 charge calculation Filling rate Smoke calculation Gas characteristics

Practical guide for the audit of grinding mills - 96/10

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103

Program by MOISTURE CALCULATION PLANT: DATE : Hans Schrama June 92 MEASUREMENT POINT: MILL CIRCUIT Input Case #1: Given dry and humid temperatures Results: Relative humidity and dew point T Dry (°C) 70 H2O Properties T Humid (°C) 50 T Dry (°F) 158 617.67 deg R crit P, mmH 166818 T Humid (°F) 122 581.67 deg R crit T, R 1165.67 Press, mmHg 760 kg/kg mol PM 28.97 Dry air molecular weight Kd 3.22 Dimensionless parameter Kw 3.24 Dimensionless parameter Pd 233.54 mm Hg Dry temperature saturated vapor pressure Pw 92.47 mm Hg Humid temperature saturated vapor pressure Pm 9.32 mm Hg Portion of vapor pressure due to depression Pa 83.14 mm Hg Partial vapor pressure 35.6 % Relative humidity Humidity

0.0764 kg H2O / kg dry air 0.0710 kg H2O / kg humid air 10.94% H2O (humid volume) Dew Point 577.84 deg R 47.9 deg C Case #2: Given absolute dry and humid temperatures Results: Dew point T Dry (°C) 100 T Dry (°F) 212 617.67 deg R Humidity 0.0615 kg H2O/kg dry air Press, mmHg 745 PM 28.97 kg/kg mol Pa Dew Point

67.03 9.00% 570.26 43.7

mm Hg Partial vapor pressure H2O (humid volume) deg R deg C

Practical guide for the audit of grinding mills - 96/10

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104

LIST OF APPENDICES

Separator inspection report Mill (2 compartments) inspection report Mill (3 compartments) inspection report Ball and cylpeb characteristics Testing equipment suppliers

Calculation sheets

Pitot Distribution curve Rosin - Rammler RFCS Moisture (silicagel cartridges) Moisture (dry / humid) Elevator flow Drying and heat balances Charge characteristics Compartment 1 charge calculation Compartment 2 charge calculation Filling rate Smoke calculation Gas characteristics

Practical guide for the audit of grinding mills - 96/10

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105

ELEVATOR POWER CALCULATION

Input

PLANT: MILL: DATE:

Data

Calculated value t/h

FLOW POWER DRAW WHEN LOADED

24.50

kW

POWER DRAW WHEN RUNNING EMPTY

5.00

kW

HEIGHT BETWEEN AXIS

26.25

m

ELEVATOR EFFICIENCY

0.92

250.80

Insert in the “data” column the known values. The program calculates the sought value using the equation:

Ploaded - Pempty =

9.81 x Flow x Height

Practical guide for the audit of grinding mills - 96/10

3600 x Efficiency

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106

LIST OF APPENDICES

Separator inspection report Mill (2 compartments) inspection report Mill (3 compartments) inspection report Ball and cylpeb characteristics Testing equipment suppliers

Calculation sheets

Pitot Distribution curve Rosin - Rammler RFCS Moisture (silicagel cartridges) Moisture (dry / humid) Elevator flow Drying and heat balances Charge characteristics Compartment 1 charge calculation Compartment 2 charge calculation Filling rate Smoke calculation Gas characteristics

Practical guide for the audit of grinding mills - 96/10

Department of Studies - Viviers

107 HEAT AND DRYING BALANCES Make a calculation list but start the calculation only when all the data are in. Subject: La Malle, Coal Mill - 95/12/13 Input Grinding or drying mill (G/D) Raw mix cement or coal (R/C/CO) Furnace (Y/N) Heat source No 1 (Y/N) Heat source No 2 (Y/N) Recirculation (Y/N) Water spray (Y/N) Listing of data General Ambient air temperature Ambient air relative humidity % wall losses Mill outlet gas temperature % air inleakage in mill outlet gas flow

Input G CO Y N N Y N

Retained values Grinding mill Coal With furnace Without HTS No1 Without HTS No2 With recirc Without water spray

4 80 8 80 14.2

4 80 8 80 14.2

0 19 12 56 9.4 0 42.9 95

0 19 12 56 9.4 0 42.9 95 25

Coal % of trapped total dust Milloutlet dry flow Mill inlet temperature Mill outlet temperature % mill inlet water % mill outlet water Grindability (KWH/T) % grinding energy transformed in cal % volatile materials Move to line 37 You can enter the detailed composition or indicate the kind of heat source Air, fuel kiln gas (A/F/C/D) Coal kiln gas or detail O2 N2 H2O CO2 SO2 3 Flow (Nm /H) Temperature Source 1 dust - flow (kg / h dry) - temperature Move to line 53 You can enter the detailed composition or indicate the kind of heat source Air, fuel kiln gas (A/F/C/D) Coal kiln gas or detail O2 N2 H2O CO2 SO2 3 Flow (Nm /H) Temperature Source 2 dust - flow (kg / h dry) - temperature Furnace You can enter the detailed composition or simply indicate the kind of fuel Normal NO2 LSC, FOD, Detail or gas (N/L/F/D/G) IHC Specific heat Caution: % by mass H C S O N H2O Fuel flow Furnace inlet fuel temperature % furnace air excess Aeraulic ratio 3 Nm of gas per kg of dry material % gas flow for a 40% material flow

Practical guide for the audit of grinding mills - 96/10

99

99

G 11856 Cal/g 99 24.6 74.9 0.0 0.0 0.5 0.0 141.3 15 1013

Gas 11856 0.3 24.6 74.9

141 15 1013

2.82 70

2.82 70

0.5

Department of Studies - Viviers

108 HEAT BALANCE FOR A COAL MILL WITH FURNACE AND RECIRCULATION Page 1 (results) La Malle - Coal Mill - 95 / 12 / 13 General Ambient air relative humidity Ambient air moisture (for 1 Nm3) Ambient air O2 (for 1 Nm3) % wall losses % air inleakage in mill outlet gas flow Coal Inlet dry dust flow % mill inlet water Inlet flow Inlet water Vaporization water Inlet temperature Coal grindability Furnace Fuel : gas Fuel flow Fuel ihc Fuel consuming capacity COMPOSITION:

N2 CO2

COMPOSITION : smoke producing capacity N2 CO2 No 1 Heat Source Flow % O2 (dry) % O2 % CO2 (dry) % CO2 % H2O No 2 Heat Source Flow % O2 (dry) % O2 % CO2 (dry) % CO2 % H2O

Practical guide for the audit of grinding mills - 96/10

80% 0.00620 Nm3 0.208 Nm3 8% 14.242 % 0.00 t/h 9.4% 20.97 t/h 1.97 t/h 1.97 t/h 12° C 42.9 kwh/t 141 Kg/h 11,856 kcal/kg 13.30 Nm3/kg Neutral smokes 10.51 Nm3 1.40 Nm3 Total smokes 150.08 Nm3 116.88 Nm3 1.40 Nm3 # N/A Nm3/h % % % # N/A Nm3/h % % %

Ambient air temperature Ambient air N2 Mass of 1 Nm3 of humid air Basic aeraulic ratio Mill outlet gas temperature Trapped dry dust flow % mill outlet water Mill outlet dry flow Residual water Mill outlet humid flow Outlet temperature % of electrical energy transformed into heat

2,083 Nm3/h 21,206 Nm3/h (per kg of fuel)

Furnace inlet temperature Furnace excess air Combustion neutral smokes

4° C 0.786 Nm3 1.290 kg 2.8237 Nm3 / kg 80° C 0.00 t/h 0% 19.00 t/h 0.00 t/h 19.00 t/h 56° C 95% 15° C 1,013% 14.74 Nm3/kg

H2O SO2

2.84 Nm3 Nm3

O2 H2O SO2

28.12 Nm3 3.68 Nm3 Nm3

Temperature % N2 % SO2 Dew point

°C % % °C

Temperature % N2 % SO2 Dew point

°C % % °C

Department of Studies - Viviers

109 HEAT BALANCE FOR A COAL MILL WITH FURNACE AND RECIRCULATION Page 2 (results) La Malle - Coal Mill - 95 / 12 / 13 Mill Inlet Mill inlet temperature Mill Outlet Outlet total gas flow (humid) Circuit Outlet Outlet total gas flow (humid) Max. H2O concentration (w/o condensation) Condensation ratio % outlet N2 % outlet water % outlet dry gas O2 Items No 1 heat source (Nm3/h) Source 1 dust (Kg/h) No2 heat source (Nm3/h) Source 2 dust (Kg/h) Furnace (Kg/h) Air inleakage (NM3/h) Coal (kg/h) Coal moisture (t/h) Sprayed water Mill motor _______ Input total

165° C 53,650 Nm3/h

Recirculated gas flow (humid)

31,300 Nm3/h 0.37 kg/Nm3 20.75% 71.95% 9.65% 19.66%

Effective aeraulic ratio H2O effective concentration Dew point % outlet CO2 % outlet SO2 % outlet humid gas O2

Input flows 0 0 0 0 141 7641 19000 1.971 0 -

°C 0 0 0 0 4 12 12 4 -

Theoretical drying efficiency (total inlet calories / kg of evaporation water) useful drying efficiency (pure inlet calories / kg of evaporation water)

Practical guide for the audit of grinding mills - 96/10

Temperature before recirculation

kcal/h 0 0 0 0 1701922 8785 58956 23656 0 665937 2459323

Items Vaporization (Kg/h) Exhaust dust (Kg/h) Coal (Kg/h) Trapped dust Residual water Dry gases (kg/h) Water vapor (Nm3/h) Wall losses

256° C 22,350 Nm3/h 2.82 Nm3/kg 0.078 kf/Nm3 45.6° C 0.63% 0.70% dry 0.00% 17.77% 19.66% dry

Output flows 1971 0 19,000 0 0 28280 3020 -

Output total 1248 kcal/kg 863 kcal/kg

°C 0 56 0 56 80 80 -

kcal/h 1174896 0 291047 0 0 686744 86693 196746 2436125

∆ E - S/E = 0.94%

Department of Studies - Viviers

110 Heat balance of a coal mill with furnace and recirculation Page 3 (results) La Malle - Coal Mill - 95 / 12 / 13 58%

100%

Mill outlet gas Flow 53650 Nm3/h Flow 14.9 Nm3/s Flow 19.3 m3/s Temperature 80 °C Aeraulic ratio 2.82 Nm3/kg

Flow % H2O Dust

Coal 21.0 9.4 0.0

Circuit outlet Flow 31300 Flow 8.7 Flow 11.2 Temperature 80 % O2 (dry) 19.7 H2O amount 0.078 % H2O by volume 9.6 Cond. ratio 21 Dew point 46

Filter or cyclones or both

Circuit outlet coal Coal flow 19.0 t/h dry Dust flow 0.0 t/h dry Total flow 19.0 t/h dry Total flow 19.0 t/h humid Temperature 56° C % H2O 0%

t/h % t/h

Exhaust dust flow

Flow

42% Flow Flow Flow Temperature

l/h

Coal Mill

Mill Power draw % wall losses

815 8

kw %

Air inleakage Percentage 14 Percentage 18 Flow 7641 Relative humidity 80 Temperature 4

Ambient Air Furnace

Flow Flow Flow Temperature

Mill Inlet 43556 12.1 19.4 165

% outlets % inlets Nm3/h % °C

Origin of Exhaust Gas Water 38 kg/h → 417 kg/h →

Nm3/h Nm3/s m3/s °C Before Recirculation Flow 21206 Nm3/h Flow 5.9 Nm3/s Flow 11.4 m3/s Temperature 256 °C

47 519

Practical guide for the audit of grinding mills - 96/10

Nm3/h Nm3/s m3/s °C

No 1 Heat Source: none Flow 0 Nm3/h Flow Nm3/s Flow m3/s Temperature °C Dew point °C % O2 (dry) %

0.0 t/h dry

Water spray 0

Recirculation 22350 6.2 8.0 8.0

Nm3/h Nm3/s m3/s °C % kg/Nm3 % % °C

Comb. flow Air excess Gas flow Gas flow Gas flow Temperature

Furnace : Gas 141 1013 21206 5.9 11.4 256

Kg/h % Nm3/h Nm3/s m3/s °C

No 2 Heat Source: none Flow 0 Nm3/h Flow Nm3/s Flow m3/s Temperature °C Dew point °C % O2 (dry) %

Nm3/h Nm3/h

Department of Studies - Viviers

111 No 1 Heat Source No 2 Heat Source Material Spray Total

0 0 1971 0 2427

kg/h kg/h kg/h kg/h kg/h

→ → → → →

0 0 2453 0 3020

Practical guide for the audit of grinding mills - 96/10

Nm3/h Nm3/h Nm3/h Nm3/h Nm3/h

Department of Studies - Viviers

112

LIST OF APPENDICES

Separator inspection report Mill (2 compartments) inspection report Mill (3 compartments) inspection report Ball and cylpeb characteristics Testing equipment suppliers

Calculation sheets

Pitot Distribution curve Rosin - Rammler RFCS Moisture (silicagel cartridges) Moisture (dry / humid) Elevator flow Drying and heat balances Charge characteristics Compartment 1 charge calculation Compartment 2 charge calculation Filling rate Smoke calculation Gas characteristics

Practical guide for the audit of grinding mills - 96/10

Department of Studies - Viviers

113 GRINDING CHARGE

Compartment 1

Charge Rotating speed

1993 / 94 20.0 tr/min

Useful length Useful diameter

4.90 m 2.52 m

Apparent unit mass

Plant Mill Date Compartment 2

C1

4.5 t/m3

C2

4.7 t/m3

6.04 m 2.48 m

Useful length Useful diameter Usual value charge Usual value charge

for

a

typical

for

a

typical

Input C1 Charge

Ball Ø 90.0 mm 80.0 mm 70.0 mm 60.0 mm

% by mass 32.4 % 31.0 % 22.5 % 14.1 %

Tonnage 11.50 t 11.00 t 8.00 t 5.00 t 35.50 t Filling rate Average mass per ball Number of balls Developed surface

32.3 % 1.732 kg 20,502 10.03 m2/t

% by mass vs diameter 35.0 % 30.0 % 25.0 % 20.0 % 15.0 % 10.0 % 5.0 % 0.0 %

90.0 mm 80.0 mm 70.0 mm 60.0 mm

C2 Charge Ball Ø 50.0 mm 40.0 mm 30.0 mm 25.0 mm

% by mass 14.0 % 15.5 % 15.5 % 55.0 %

Tonnage 5.90 t 6.50 t 6.50 t 23.10 t 42.00 t

Filling rate Average mass per ball Number of balls Developed surface Developed surface at end of charge

30.6 % 92 g 457,363 26.03 m2/t 30.77 m2/t

% by mass vs diameter 60.0 % 50.0 % 40.0 % 30.0 % 20.0 % 10.0 % 0.0 %

50.0 mm 40.0 mm 30.0 mm 25.0 mm

Mill Power (Slegten) C1 C2 Total

381 kW 453 kW 834 kW

Efficiency

0.93 897 kW

axle mechanical power motor electrical power

Perfect classification distribution 50.0 % 40.0 % 30.0 % 20.0 % 10.0 % 0.0 %

1 2 3 4 5 Powers for each compartment are calculated on the basis of the characteristics and filling rate of the compartment and the rotating speed of the mill. Ref. formulae in grinding section.

Practical guide for the audit of grinding mills - 96/10

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114

LIST OF APPENDICES

Separator inspection report Mill (2 compartments) inspection report Mill (3 compartments) inspection report Ball and cylpeb characteristics Testing equipment suppliers

Calculation sheets

Pitot Distribution curve Rosin - Rammler RFCS Moisture (silicagel cartridges) Moisture (dry / humid) Elevator flow Drying and heat balances Charge characteristics Compartment 1 charge calculation Compartment 2 charge calculation Filling rate Smoke calculation Gas characteristics

Practical guide for the audit of grinding mills - 96/10

Department of Studies - Viviers

115

FIRST COMPARTMENT CHARGE CALCULATION Plant Mill Date

Input

Bond Formula 15,000 13.9 3.65 15.8 71.4 3.09

Feed grading, 20% retained Bond work index (W) Useful mill diameter Rotating speed % of critical speed Material unit mass Largest calculated ball Largest selected ball

18,000 10.6 3.65 15.8 71.4 2.67

µm kWh/t m tr/min % t/m3

20,000 11.4 3.65 15.8 71.4 1.63

µm kWh/t m tr/min % t/m3

µm kWh/t m tr/min % t/m3

89.8 90

mm mm

85.6 90

mm mm

78.4 80

mm mm

4.25 32 4.5

m % t/m3

4.25 31.5 4.5

m % t/m3

4.25 31.5 4.5

m % t/m3

Bond index

Standard values Clinker Raw Coal 13.49 10.57 11.37

Unit mass

Standard values Clinker Raw Coal 3.09 2.67 1.63

Bond Formula Useful length of first compartment Selected filling rate Charge apparent density (4.5)

63.04

Charge mass Mass percentage of the largest ball size

20

Number of corresponding balls

Charge distribution in 4 sizes

63.04

t

20

%

11,529

20

%

11,529

balls

63.04

t

18,052

balls

t % balls

Ø

t

%

Ø

t

%

Ø

t

%

90 80 70 60

12.61 24.11 16.15 10.17

20% 38% 26% 16%

90 80 70 60

12.61 24.11 16.15 10.17

20% 38% 26% 16%

80 70 60 50

12.61 25.29 15.92 9.22

20% 40% 25% 15%

Practical guide for the audit of grinding mills - 96/10

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116

LIST OF APPENDICES

Separator inspection report Mill (2 compartments) inspection report Mill (3 compartments) inspection report Ball and cylpeb characteristics Testing equipment suppliers

Calculation sheets

Pitot Distribution curve Rosin - Rammler RFCS Moisture (silicagel cartridges) Moisture (dry / humid) Elevator flow Drying and heat balances Charge characteristics Compartment 1 charge calculation Compartment 2 charge calculation Filling rate Smoke calculation Gas characteristics

Practical guide for the audit of grinding mills - 96/10

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117

SECOND COMPARTMENT CHARGE CALCULATION SLEGTEN DISTRIBUTION Plant Mill Date

Input

Density =

Val D’Azergues BK2 94/04/25 7.8 t/m3

C2 useful length C2 Useful diameter Filling rate Ball charge

7.75 3.60 33 125.0

Available sizes 50 mm 40 mm 30 mm 25 mm 20 mm

% 4.1 2.1 12.0 35.0 46.7

T 5.2 2.7 15.1 43.7 58.3

Number 10,157 10,157 136,519 685,401 1,785,055

100%

125.0

2,627,289

Average mass / ball

(g)

47.6

Developed surface

(m2/t)

32.86

Developed surface at end of compartment (Balls < 25 mm)

(m2/t)

35.17

Practical guide for the audit of grinding mills - 96/10

C1 charge (T) 60 mm balls (T) Number of 60 mm balls

56.0 9.0 10,157

Department of Studies - Viviers

118

LIST OF APPENDICES

Separator inspection report Mill (2 compartments) inspection report Mill (3 compartments) inspection report Ball and cylpeb characteristics Testing equipment suppliers

Calculation sheets

Pitot Distribution curve Rosin - Rammler RFCS Moisture (silicagel cartridges) Moisture (dry / humid) Elevator flow Drying and heat balances Charge characteristics Compartment 1 charge calculation Compartment 2 charge calculation Filling rate Smoke calculation Gas characteristics

Practical guide for the audit of grinding mills - 96/10

Department of Studies - Viviers

119

MILL FILLING RATE

PLANT: MILL: DATE: INPUT COMPARTMENT 1 Useful diameter Height of free space

(m) (m)

3.21 2.10

Filling rate

(%)

30.7

Useful diameter Height of free space

(m) (m)

3.21 2.10

Filling rate

(%)

33.7

Useful diameter Height of free space

(m) (m)

3.22 2.00

Filling rate

(%)

34.7

COMPARTMENT 2

COMPARTMENT 3

Practical guide for the audit of grinding mills - 96/10

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120

MILL FILLING RATE

0.90

0.85

H D

0.80

0.75 H/D 0.70

0.65

0.60

0.55

0.50 0

5

10

15

20

25

30

35

40

45

50

Filling rate (%)

Practical guide for the audit of grinding mills - 96/10

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121

LIST OF APPENDICES

Separator inspection report Mill (2 compartments) inspection report Mill (3 compartments) inspection report Ball and cylpeb characteristics Testing equipment suppliers

Calculation sheets

Pitot Distribution curve Rosin - Rammler RFCS Moisture (silicagel cartridges) Moisture (dry / humid) Elevator flow Drying and heat balances Charge characteristics Compartment 1 charge calculation Compartment 2 charge calculation Filling rate Smoke calculation Gas characteristics

Practical guide for the audit of grinding mills - 96/10

Department of Studies - Viviers

122 SMOKE CALCULATIONS Fuel No2 Carbon Hydrogen

Fuel 3 Neutral air

85.90 %

Dry neutral S.

10.50 %

Sulfur

3.00 %

Oxygen

0.36 %

Nitrogen

Fuel 2

Humid neutral S.

10.55546 9.97154 11.14827

Nm3/Kg of fuel Nm /Kg of fuel 3

Nm /Kg of fuel 3

Tot. dry neut. S.

4,986

Nm /h

Water

Excess air

134.23

%

Ashes

Total dry S.

11,678

Nm3/h

Analysis total

0.24 %

100 %

Fuel Q

0.50 T/H

% fuel

100.00 %

O2, Outlet

12.00 %

Total humid S.

0.00 %

12,423

Analysis of neutral smokes

3

3

Nm /h

of fuel alone %

Dry

Humid

CO2

16.09 %

14.39 %

SO2

0.21 %

0.19 %

N2

83.70 %

74.86 %

H2O

0.00 %

10.56 %

Total

100.00 %

100.00 %

0.00 %

Input Water, Outlet

6.00 %

Practical guide for the audit of grinding mills - 96/10

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123

LIST OF APPENDICES

Separator inspection report Mill (2 compartments) inspection report Mill (3 compartments) inspection report Ball and cylpeb characteristics Testing equipment suppliers

Calculation sheets

Pitot Distribution curve Rosin - Rammler RFCS Moisture (silicagel cartridges) Moisture (dry / humid) Elevator flow Drying and heat balances Charge characteristics Compartment 1 charge calculation Compartment 2 charge calculation Filling rate Smoke calculation Gas characteristics

Practical guide for the audit of grinding mills - 96/10

Department of Studies - Viviers

124 GAS CHARACTERISTICS Gas Source La Malle 95/12 - Type “H” gas Gas fuel composition Type of gas Hydrogen H2 Carbon oxide CO Methane CH4 Ethylene C2H4 Ethane C2H6 Propylene C3H6 Propane C3H8 Butylene C4H8 Butane C4H10 Pentane C5H12 Carbon dioxide CO2 Nitrogen N2 Oxygen O2

% 97.30 2.10 0.20 0.10 0.30 100.00

Content in

Fuel consuming capacity

m3/m3 A 0.000 0.000 0.973 0.000 0.021 0.000 0.002 0.000 0.001 0.000 0.000 0.003 0.000 1.000

Vair B 2.36 2.38 9.54 14.4 16.84 21.84 24.37 29.64 32.41 40.87 0 0 -4.77

m3/m3 A•B 0.000 0.000 9.282 0.000 0.354 0.000 0.049 0.000 0.032 0.000 0.000 0.000 0.000 9.717

7.677 0.003 1.025 8.70 2.022 10.73

m3/m3 m3/m3 m3/m3 m3/m3 m3/m3 m3/m3

11.78 88.22 9.56 71.59 18.85

% % % % %

Total carbonic gas VCO2 C 0 1 1 2 2 3 3 4 4 5 1 0 0

m3/m3 A•C 0.000 0.000 0.973 0.000 0.042 0.000 0.006 0.000 0.004 0.000 0.000 0.000 0.000 1.025

Total water vapor VH2O D 1 0 2 2 3 3 4 4 5 6 0 0 0

m3/m3 A•D 0.000 0.000 1.946 0.000 0.063 0.000 0.008 0.000 0.005 0.000 0.000 0.000 0.000 2.022

Density with respect to air E 0.0695 0.968 0.555 0.976 1.048 1.480 1.557 2.007 2.096 2.671 1.529 0.968 1.105

A E 0.000 0.000 0.540 0.000 0.022 0.000 0.003 0.000 0.002 0.000 0.000 0.003 0.000 0.570

Heat capacity superior inferior SHC in kWh/m3 IHC in kWh/m3 F 3.52 3.51 11.08 17.65 19.58 26.06 28.22 34.99 37.41 47.11 0 0 0

A•F 0.000 0.000 10.781 0.000 0.411 0.000 0.056 0.000 0.037 0.000 0.000 0.000 0.000 11.286

G 2.96 3.51 9.97 16.53 17.88 24.34 25.94 32.68 34.49 43.52 0 0 0

A•G 0.000 0.000 9.701 0.000 0.375 0.000 0.052 0.000 0.034 0.000 0.000 0.000 0.000 10.163

Input Smoke capacity Dry Humid Smoke analysis (% volume)

Dry Humid

0.79 Vair + gas nitrogen + VCO2 = V ds + VH2O = V hs CO2 N2 CO2 N2 H2O

Practical guide for the audit of grinding mills - 96/10

Calculated heat capacity SHC 9706 kcal/Nm3 IHC 8740 kcal/Nm3 IHC 11856 kcal/kg Proposed Heat capacity SHC kcal/m3 Equals kcal/Nm3 Elementary weighted analysis C H N 74.44 24.47 0.51

Vent mass 0.737 kg/Nm3 Density / Air 0.570 at 15°C

Note: m3/m3 is equivalent to Nm3/Nm3

O 0.00

Department of Studies - Viviers