Vrm Operation And Optimization.ppt

Operation and Optimization

vertical mill used for  pre grinding of clinker (lumps to coarse powder)  finish grinding (lumps to powder ) of - coal/petcoke for kiln - raw material for kiln - cement, OPC or mixed - slag, pure or mixed

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vertical mills comprise 2-4 conical rollers which are hydraulically pressed onto a horizontal rotating grinding table the roller axis is inclined at 15o to the table and, as axes of rollers and table do not intersect in the plane of the table the relative motion involves both rolling and sliding which enhances comminution feed material is directed onto the centre of the table and is thrown outward by rotation under the roller and into a rising air current at the periphery which is directed by means of Louvre ring.

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the air sweep passes through an integral rotary classifier, fine pass out with the air current while coarse material falls back onto the feed table. material drying occurs in air suspension between table and classifier. circulating load is typically 800%. Roller mills are prone to vibration due to an unstable grinding bed A major cause of material instability is fine, dry mill feed which can usually, be mitigated by spraying water directly onto the bed.

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grinding force = roller weight + pressure(force)

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max particle size in feed : 5 to 8 % of roller diameter

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G. Pfeiffer Loesche FLS Atox Polysius

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static type conventional type cage rotor type

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Vane adjustment Speed control Rotor seal affects efficiency

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Feed Size product fineness moisture content Grind ability abrasiveness

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Ball mill maximum 5% + 25 mm VRM up to 150mm

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5 % to 25 % +90um 1 % to 2 % +212um

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normal moisture content 3% to 10% H2O Possible to dry >20% H2O in vertical mills Up to 6 to 7 % H2O with kiln gases Above 7% H2O supplementary heat from auxiliary furnace or cooler

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material granulometry roller pressure Dam ring Louvre ring external circulation reducing gas flow pressure lost over the mill

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production rate, tones per hour grinding pressure (bar) or (kN/m2) Mill Motor kW grinding bed thickness Vibration level (mm/s) pressure drop across the mill mill outlet temperature Fan flow Rejects (If external recirculation present) water flow

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operating hours involuntary downtime hours kWh/tonne (mill motor + fan + separator) product fineness on 90/212 microns for raw mill, coal mill and blaines for cement mill feed moisture, % product moisture, % feed size

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running with high velocity in the nozzle ring gives a high pressure loss, but also a low reject rate however lower pressure drop with e.g. 45m/s is to prefer and will both give considerable power savings on the fan and less wear in the mill body

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proven technology very suitable for grinding blended cement or slag compact grinding installation energy saving up to 30 to 40 % kWh/Mt suitable for grinding moist feed easy maintenance and optimum utilization of wearing rollers

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VCM vs. RPCM

Grinding system

VCM pre grinding

RP pre grinding

VCM

RP&CM combinatio n

VRM

Closed circuit ball mill (raw mill)

Mill kWh/Mt of clinker

24

21

34

39

19

29

Separator and fan kWh/Mt

5.5

3.5

7

5.5

9.5

7

Auxiliary (kWh/Mt)

2.5

7

5

9

3

7

Maximum output

55

60

34

63

80

63

Source-Birla White

N/R Velocity

Reject Rate

m/s 75-85 60-65 40-45

% fresh feed Trace 5-10 20-30

lower pressure drop less wear of mill body liners fan power savings of 15-30%

Relative Pressure drop % 100 84 60

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a correct air flow in the mill is important, because the air is transporting the material and important factor for efficient separation air flow is kept constant through the mill and cyclone/ filter by operating the mill fan with constant power consumption on the motor this is normally done by the help of an automatic loop between the mill fan damper position and the power consumption of the mill main motor. alternatively by the help of an automatic loop between the speed of the mill fan motor and power consumption of the mill main motor

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A correct feed rate in the mill is important. if the feed rate is too high and the mill filled up with material and trip on vibration, because the mill fan don’t have the capacity to transport material out of the mill if the feed rate is too low the mill emptied out and trips on vibration, due to low grinding bed. the feed rate depends on the applied grinding pressure and the grind ability of the material the mill differential pressure or the mill motor power consumption is an indication of how much material inside the mill. Normally the feed rate is controlled by the mill motor power consumption through an automatic loop

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a constant and acceptable level of vibrations is important if vibration are too high then the mill be stopped by the safety interlocking of the mill in order not to damage the machine the vibrations are minimized by injecting water. The injected amount according to experience

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changes in feed material properties Equipment problems deficiency of control elements control signal errors external effects

Type of problems

Action

Mill vibration too high

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Mill output too low

Mill product too coarse Mill product too fine

reduce feed supply if differential pressure is high increase feed supply if differential pressure is low check water injection reduce grinding pressure lift rollers at excessive vibration check grinding pressure check differential pressure product fineness very fine coarser raw material grindability of raw material changed raw material too wet table and roller segments are worn increase speed of separator rotor check seiving of samples decrease speed of separator rotor increase feed supply

Type of problems

Action

Mill outlet temperature too high

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hot air amount too high hot gas temperature higher than normal adjust hot gas damper decrease oil for heat generator open cold air damper increase water injection

Mill outlet temperature too low

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raw material moisture increased increase hot air amount adjust hot gas damper adjust mill fan damper increase oil for heat generator close cold air damper if open decrease water injection

Grinding pressure decreases

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check hydraulic system, piping is leaking oil pump fault oil level in tank for hydraulic minimum oil temperature in hydraulic minimum malfunction of valves

Sealing air pressure minimum

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filter blocked check electrical equipment

Type of problems

Action

Starting the without grinding layer

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fill mill with material before start use automatic program for mill filing the filling must be done manually by starting transport devices in correct sequence fill in 300 to 500 kg of material

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Calculation of the capacity of the mill

Generally speaking the production capacity refers to grinding capacity and drying capacity of grinding mill The material grind ability will affect the grinding capacity, the roller pressure and the type of grinding mill G = K1 * D2.5 where G is the capacity of the mill K1 is the coefficient which is relevant to the type of roller mill, the selected and used pressure, the performance of grinded material. Different specification of roller mill so the K1 is different. K1 of Loesche Mill series roller mill is 9.6 and for Atox Mill is 7 and for MPS Mills is 6.6 D is the table diameter Example for MPS 2800 mill with table dia 2.25m G = 6.6 * 2.252.5 = 50.11875 ~ 50 tph

List of components in simulated Hydraulic circuit Description

T.P NO. in Circuit

Description

T.P NO. in Circuit

Pump

2

Flow control (adjustable)

29.3

Check valves

6.1, 6.2, 27a.3

Flow control (fixed)

18a

Relief valves

9.1, 9.2 & 26.3

Pilot operated check valve (piloted to both close & open)

25.3

2 X 2 normally open solenoid valve

11.1, 11.2, 18 & 27.1

Rotary flow divider

20

2 X 2 normally closed solenoid valve

27.2 & 28.3

Manifold containing of check valves, relief valve & anti cavitational valves

20a

4 X 2 solenoid valve

17.1 & 17.2

N2 accumulator (bladder type)

24.5

Meter out flow control (adjustable)

19

20a

Pre Tension

24. 24. 5 6 EN W

320

W

P = 5.5 kw n = 1500 rpm pump flow = 10 Lpm

145 bar

)(

29.3 (26 Lpm) T

E

19

18

)(

17. 11.2 2

Y

18 a end oil 18 is on, so rod of cyl is blocked from draining to tank

20

M

2

9.2

6.1 245 T PPump offbar if set pt = 145 bar is reached

25.3

E1

)(

B3 28.3

27.a3

27.1

E2 E

D

120 Lpm

W

11. 1 9.1 T

20

A

)(

A

B B

W A Tbar

27. 2

C C

17.1 is on, so 25.3 pilot opens & cap end cyl oil is drained to tank

269 bar

B 3

B 2

26.3

B 1

95 ba r

(315 bar)

17.2 is on & 11.1 off, so oil from pump is connected to rod end of cyl

X

17. 1 6.2 N2 pr = 0.5 X Tension pr (P1) After 5 sec pump Re-starts for Roller lifting

320

20

27.1

W

269 bar Cyl rod end oil is

blocked from flowing to tank as 11.1 & 18 are on.

E1

)( 145 bar

B3 28.3

29.3 (26 Lpm) T

E

19

18

)(

Y

17. 11.2 2

20

M

2

6.1 245 P 17.2 offbar for Lift

18 a

X

17. 1 6.2

9.2 W

11. 1 9.1 T

E2 E

D

120 Lpm

)(

A

A

25.3

B B

bar

W A Tbar

27. 2

C C

24. 24. 5 6 EN W

)(

20a

Lift ph-1 60

26.3

B 3

B 2

27.a3

B 1

95 ba r

(315 bar)

17.2 off, 27.1 & 27.2 on. So pump oil flows to cyl cap end by-passing 20 (Rotary flow divider) 17.1 off. So 25.3 (check valve) is pilot closed to stop cap end oil from flowing to tank.

T

Pump off after lift pr (P3) reaches 60 bar

B B

27.1 )( 145 bar

29.3 (26 Lpm) T

E

19

18

)(

Y

18 a 11.1 & 18 on. so rod end

17. 11.2 2

oil is blocked from draining to tank

20

M

9.2

6.1 245 T P Pump bar off after 170 mm W

W

check valve25.3 is piloted to close to block cap end oil flow to tank

E1

)(

A

B3 28.3

E2 E

2

D

120 Lpm

27. 2

20

A

is lift

25.3

C C

24. 24. 5 6 EN W

26.3

320

W A Tbar

Lift ph-2 ph-1 (170bar) (60 160 60 mm) bar bar

)(

20a

11. 1 9.1 T 269 bar 17.1 is off. So

B 3

B 2

95 ba r

(315 bar)

17.2 off for Lift Equal amount of oil supplied to all 3 cylinder by rotary flow divider (20)

B 1

27.a3

27.1 & 27.2 are off. So pump oil flows to cap end cyl via 20 (rotary flow divider)

17. 1 6.2

X

W

Pressure @ cap end cyl remains intact by check valve (6.1)

27. 2

27.1

B3 28.3

E2 E

E1

)( 145 bar

29.3 (26 Lpm) T

E

19

18

)(

17. 11.2 2

Y

20

M

2

18 a

mm

X

17. 1 6.2

9.2

6.1 245 P Pump-2bar is Level diff < 20 off

D

120 Lpm

W

11. 1 9.1 T

20

A

)(

A

B B

25.3

C C

24. 24. 5 6 EN W

26.3

320

W A Tbar

Lift Cylinder ph-2 ph-1 Levellin (170 (60 160 60 g bar) mm) bar bar

)(

20a

11.1 & 18 are on preventing flow of oil from rod end cyl to tank

269 bar

B 3

B 2

27.a3

B 1

95 ba r

(315 bar)

Check valve 25.3 is piloted to close block ing cyl cap end oil from drain ing to tank.

T

If 28.3 is on momentarily cap end cyl oil is drained to tank via 29.1 & cyl lowers to level.

W

is a variable orifice to control lower ing speed of roller/ cylinder

27. 2

27.1

B3 28.3

E2 E

E1

)( 145 bar

29.3 (26 Lpm) T

E

19

18

)(

17. 11.2 2

Y

20

M

2

18 a

9.2

6.1 245 T P Pump-2 isbarCheck valve 25.3 is off

D

120 Lpm

W

11. 1 9.1 T

20

A

)(

A

B B

25.3

C C

24. 24. 5 6 EN W

pilot closed.

26.3

320

W A Tbar

Cylinder Lift ph-2 Lowerin ph-1 (170bar) g (60 160 40 60bar mm) bar bar

)(

20a

Cyl is lowered by draining oil @ cap end to tank via (20a), (20), (27.1), (19) flow control& (17.2).

269 bar Item (19)

B 3

B 2

27.a3

B 1

95 ba r

(315 bar)

when lowering cyl, cap end oil is not drained to tank via 25.3 as cyl lowering speed cannot be controlled.

X

17. 1 6.2 Next operation tension mode starts when cap end pr < 10 bar so that no counter pressure is there when grinding

320

B3 28.3

Y

18 aend oil 18 is on, so rod (17.1), Orifice (18A) flowingare to ON tank

P = 5.5 kw tension n = 1500 pr rpm= pump 10 set pt flow – 5 =bar Lpm

2

6.1 245 P bar

9.2

Pump off if set pt = 180 bar is reached

X

17. 1 6.2

of cyl is blocked from (17.2) regulates draining to oil tank& (18)

W

Pump bar Restarts if

M

29.3 (26 Lpm) T

18

W

Reduce 20 E2 E 27.1 Tensio n )( E1 E Pressur A 180 OFF 185 bar e bar 19 )( 11. 1 17. 9.1 11.2 T 2 269 20

D

120 Lpm

25.3

17.1 is on, so (11.1), 25.3 pilot (11.2), opens (27.1),& cap end cyl oil is (27.2), drained to (28.3) are tank

A

27. 2

B B

)(

C C

W A Tbar

24. 24. 5 6 EN W

)(

20a

MILL in Increasin Operatio g n Tension 8 Pr bar

26.3

B 3

B 2

27.a3

B 1

95 ba r

(315 bar)

17.2 Set is on & 11.1 = point Set off, so oil 180 bar point = from Pump off pump is 180 bar if tension connected pr = end to rod of cylbar 180

T

pr = 0.5Pr X= IfN2Tension Tension set pt +pr 5 = 185 (P1) bar, (18) is OFF Pump On as momentarily to counter Pr is less than 10 bar reduce pressure