Axial Flow Fans For Underground Mines

AXIAL FLOW FANS FOR UNDERGROUND MINES A SEMINAR REPORT SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF BACHELOR OF ENGINEERING IN MINING ENGINEERING BY SHIVRAJ SUMAN -15BMI70037

DEPARTMENT OF MINING ENGINEERING FACULTY OF ENGINEERING AND ARCHITECTURE JODHPUR-342001 2016

A SEMINAR ON AXIAL FLOW FANS FOR UNDERGROUND MINES

BY

SHIVRAJ SUMAN

UNDER THE GUIDENCE OF Dr. D.M. SURANA FORMER PROF. & H.O.D

DEPARTMENT OF MINING ENGINEERING FACULTY OF ENGINEERING AND ARCHITECTURE JODHPUR-342001 January 2016

ii

ABSTRACT Developed The practice of ventilation is continually evolving with new technological advances in the mining industry. In recent years the advances in diesel engine technologies, ventilation modeling software, and ventilation management capacities have redefined the historical methods used to evaluate systems. The advances re-evaluate previous methods used to calculate the airflow requirements for the dilution of diesel exhaust fumes. Modeling software has become an integral part of planning and developing ventilation systems in partnership

with

graphical

mine

design

software

packages

to

generaterealistic

representations of the mine. Significant advances in ventilation control strategies through remote sensors and monitoring capabilities have been developed to results in cost savings. Though there has been much advancement in mine ventilation technology, the practices and basic ventilation principals enacted through the ventilation engineer cannot be placated with technological advances only.

The design for the pre-ventilation system of the Okaba Coal deposit required 145 m3/s of air with a main fan pressure of 2.73 kPa, with four booster fans of air volume, 110 m3/s, 125 m3/s, 95 m3/s, 105 m3/s with fan pressure of 0.63 kPa, 0.87 kPa, 0.47 kPa, 0.50 kPa and with exhaust fan of 70 m3/s at fan pressure of 0.38 kPa respectively, all required to ventilate the mine. The design is basically on longwall mine as it met the geological condition, engineering properties of the deposit and the design parameters to ensure better safety of miners and offers a great coal recovery.

iii

ACKNOWLEDGEMENT The most pleasant point of presenting a report is the opportunity to thank those who have contributed to it. Unfortunately, the list of expressions of thankfulness, no matter how extensive, is always incomplete and inadequate. Indeed this page of acknowledge shall never be able to touch the horizon of generosity of those who tendered their help to me. First and foremost, I would like to express my deep and sincere gratitude to my guide, Prof. D.M. Surana, for his guidance and persistent help, this report would not have been possible. I am thankful to Prof. A.S. Sheoran Head, Mining Engineering Department MBM Engg. College Jodhpur, for giving me an opportunity to prepare this seminar report. An assemblage of this nature could never have been attempted without reference to and inspiration from the works of others. I acknowledge my indebtedness to all of them.

Date:

SHIVRAJ SUMAN ROLL NO.:15BMI70037 B.E.IV YEAR

iv

CERTIFICATE This is to certify that Mr. SHIVRAJ SUMAN, student of Final Year B.E. (Mining Engineering) has submitted the seminar report entitled “AXIAL FLOW FANS IN UNDERGROUND MINES” Which is record of his own work carried out under my guidance.

Dated Dr. D.M SURANA FORMER PROF. & HEAD Department of Mining Engineering M.B.M Engineering College, JODHPUR

v

CONTENTS

ABSTRACT………………………………………………………………………………… ii ACKNOWLEDGEMENT………………………………………………………………….. iii CERTIFICATE……………………………………………………………………………... iv CONTENTS ………………………………………………………………………………..v LIST OF FIGURES …………………………………………………………………………vi LIST OF TABLES………………………………………………………………………… vii 1.0 2.0

INTRODUCTION……………………………………………………………………1 PROCEDURE FOR FAN SALECTION OF MODERN …………………………...2 AXIAL FLOW FAN 2.1 Laws of fan……………………………………………………………………….2 2.1.1- fan vol. vs fan pressure graph………………………………………………3 2.1.2- mine char. for low,medium& high resistance……………………………...4 2.2 Fan selection using fan total pressure to save energy……………………………4 2.2.1- why fan total pressure………………………………………………………4 2.2.2-fan and pressure …………………………………………………………….4 2.2.3- using fan static pressure for fan selection………………………………….5

3.0 FEATURE OF FAN……………………………………………………………………...8 3.1 Technical features……………………………………………………………………9 3.1.1 blade profile …………………………………………………………………..9 3.1.2 multi stage A.A.F over centrifugnal fan …………………………………….11 3.1.3 dimension……………………………………………………………………13 3.1.4 energy consumption………………………………………………………….14 4.0 EXAMPLE OF SOME LARGE MINES………………………………………………15 5.0 SAFETY ASPECTS……………………………………………………………………15 6.0 CONCLUSION………………………………………………………………………...16 7.0 REFRANCES…………………………………………………………………………..17

vi

LIST OF FIGURES FIGURE

PAGE NO.

1: Air flow in underground mine(Akande and Moshood,2013)

1

2 :pressure profile in the inlet and outlet of a fan(Cenmark,2011)

5

3: fan selection made by matching the pressure drop across the system with fan static pressure(Cenmark,2011)

6

4: : fan selection made by matching the pressure drop across the system with fan total pressure(Cenmark,2011)

7

5: : The schematic of axial flow fan( Vutukuri &Lama ,1986)

9

6: Forces acting on a typical aerofoil section of axial flow fan

10

(Panigrahi and Mishra,2014) 7:structure and air flow mechanism of axial flow fan (www.orientamotar.com,2014)

13

8: Line diagram of various feature of axial flow fan

15

(www.marathonelectric.in,2015)

LIST OF TABLES & GRAPH TABLE & GRAPH

PAGE NO.

1 Graph : relation between fan volume vs fan static pressure (Hartman and wang,2011) 2 Graph : relation between fan volume vs fan pressure(Misra,1986)

3 4

1 Table : : fan specification- impellers (Axial flow fan general information, Fantech,2008)

13

vii

1. INTRODUCTION An axial flow fan moves air or gas parallel to the axis of rotation. By comparison, acentrifugal or radial flow fan moves air perpendicular to the axis of rotation. Axial flow fans are better suited for low-resistance ,high-flow applications, whereas centrifugal flow fans apply to high-pressure resistance ,low-flow conditions. Typically, the types of fans discussed in this manual can handle “resistances” up to approximately 1 in. of water. Axial fans can have widely varied operating characteristics depending on blade width and shape, number of blades and tip speed .The most common type of fan for air-cooled heat exchanger (ACHE) is less than 4.2m.diameter and has four blades. The most common type for wet cooling towers is 8.4m. diameter and has eight blades. A typical ACHE fan is shown in Fig1(Krog and Grau,2012).

Figure1:Airflow in an underground mine(Akande and Moshood,2013)

1

2.0PROCEDURE FOR SELECTION OF MODERN AXIAL FLOW FAN 2.1-Laws of Fan The fan laws are a set of proportionalities relating each of the following parameters of airflow with fan speed (n), air density (ρ) and impeller diameter (d). 

Air pressure (p)



Airflow quantity (Q)



Power developed (PPOW)

Through extensive experimentation and derivation the following direct proportionalities have been arrived. (a) For varying speed but with constant air density and impeller diameter: - Quantity varies directly as the speed . - Pressure varies as the square of the speed . - Power varies as the cube of the speed . - Efficiency is constant (b) For varying density but with constant speed and impeller diameter: - Quantity remains constant - Pressure varies directly as the density - Power varies directly as the density - Efficiency is constant (c) For varying impeller diameter but with constant speed and air density: - Quantity varies as the cube of the impeller diameter - Pressure varies as the square of the impeller diameter - Power varies as the fifth power of the impeller diameter - Efficiency is constant

2

2.1.1- Fan volume vs fan static pressure graph:-

Graph 1:relation between fan volume vs fan static pressure(Hartman and wang,2011)

Now, let us draw new curves for this same fan when it is run at a speed of 798 RPM and handling air at a density of 1.04 kg/m3. At the original speed of 600 RPM and air density of .2 kg/m3, the fan at its design point will deliver 115 m3/s at 1370 Pa using 225 KW of input power and giving an efficiency of 70.20 %. (Banerjee,2003).

3

2.1.2- Mine characteristic for low ,medium and high resistance:-

Graph 2: relation between fan volume vs fan pressure(Misra,1986)

When we install a fan in a mine, its performance will be determined by the point at which the mine characteristic cuts the fan characteristic. The mine or system characteristic is a curve which shows how the pressure drop across the mine varies as the quantity of air varies. The mine characteristic curve can be drawn using the relation P = RQ2 which was discussed earlier.

If we know the value of mine resistance (R), we can tabulate the values of ‘P’ for different values of ‘Q’. These values can then be plotted and we get mine characteristic curves. The mine characteristic for low, medium and high resistance is shown in Fig.(Hartman ,Mutmansky and Wang,2012). 2.2 Fan Selection Using Fan Total Pressure Energy 2.2.1Fan and Pressure:-A fan is a device designed to primarily deliver flow, usually of air, at relatively low pressure. The fan has an inlet opening for air to enter the fan and an outlet opening for air to leave the fan. The flow through these openings is the same and creates a velocity in each of these openings. The mo- tor, usually an electromotor, delivers energy to 4

the fan impeller and the impeller transforms the energy into the energy in the air handled by the fan. If we define control surfaces at the inlet and outlet openings, the energy in the air delivered by the fan is the difference between the energy of the air in the outlet opening minus the energy in the air in the inlet opening of the fan. This energy has two components, static and dynamic. Since the flow is equal for both inlet and outlet, we may define the energy addition by the change in pressure between the two openings. The fan total pressure is then defined as the difference of the total pressures in the fan outlet and inlet openings. The relations among these pressures are depicted in Figure (Cenmark,2011).

Figure 2:pressure profile in the inlet and outlet of a fan(Cenmark,2011)

5

2.2.2-Using Fan Static Pressure For Fan Selection:-First, we must stress that the fan performance is usually presented in terms of FTP vs. flow or FSP vs. flow. In Figures and 3 both presentations are used simultaneously for a typical utility centrifugal fan size 24 in. (0.6 m). The requested operating point of the system is 13,000 cfm (6135 L/s) at 1.5 in. w.g. (374 Pa) pressure at standard air density. In Figure 3 the system pressure drop has been matched with FSP, and it was found that the fan speed would be 1,035 rpm, and the fan would need a power of 6.22 bhp (4.64 kW). But, in reality, the fan at that speed would operate at a flow of 13,625 cfm (6430 L/s) at a system pressure drop of 1.65 in. w.g. (411 Pa) The flow in the sys-tem is about 5% higher, and the power need is 6.05 bhp (4.51 kW). In Figure the system pressure drop has been matched with FTP, and it was found that the fan speed is 989 rpm, and the fan would need a power of 5.29 bhp (3.95 kW). The flow now matches the requirement, the fan speed is down by almost 5%, and the power is down by 12.5%.

Figure 3:fan selection made by matching the pressure drop across the system with fan static pressure(Cenmark,2011)

6

The benefits of the correct match are lower fan speed, lower sound and significantly lower power. We can see that the selection of fans must be done by matching the fan performance (total pressure vs. flow) with the system requirement. Many fan manufacturers present performance data in the form of multi-rating tables, which include values of flow, static pressure, speed and power. Conversion of these data to total pressure is simple (the velocity pressure is calculated from the flow and outlet area), but it is assumed that the connection of the fan to the system is such that the conver-sion of velocity pressure to static pressure at the outlet of the fan is identical to the conversion experienced in the test set-up from which the data were derived.

Figure 4: fan selection made by matching the pressure drop across the system with fan total pressure(Cenmark,2011)

7

The use of total pressure makes this assumption obvious, while the use of static pressure for selection, while matching the flow to the required value, does not call into question the validity of the selection.(Cenmak and Murphy,2011) 3.0- FEATURE OF FAN 3.1- Technical Feature 3.1.1- Blade Profile :-A fan is simply a machine which develops the pressure necessary to produce the required airflow rate and overcome flow resistance of the system by means of a rotating impeller using centrifugal or propeller action, or both. The axial flow fans are commonly used in mine ventilation in lieu of centri-fugal fans due to high efficiency, compactness, non-overlo-ading characteristics, development of adequate pressure, etc. (Herdeen and Sullivian,2003). The axial flow fan in its simplest form as diagrammatically shown in Figure 1 incorporates a rotor, which consists of a hub fitted with aerofoil section blades in a radial direction. The blades or vanes which constitute the main component of axial flow fan are the surfaces that work by means of dynamic reaction on the air and develop positive air pressure during their rotation due to the development of lift force. The forces acting on a typical aerofoil section of an axial flow fan blade are shown in Figure . The lifting force acts at right angles to the air stream and the dragging force acts in the same direction of the air stream and is responsible for losses due to skin friction. (Panigrahi and Mishra,2014)

8

Figure 5: The schematic of axial flow fan( Vutukuri and Lama ,1986) The efficiency of axial flow fans is greatly dependent on the profile of the blade, and the aerodynamic characteristics of the fan blades are strongly affected by the shape of the blade cross section. The cross section of fan blades is of a streamlined asymmetrical shape, called the blade’s aerodynamic profile and is decisive when it comes to blade performance. Even minor alterations in the shape of the profile can greatly alter the power curve and noise level. Therefore, it is essential to choose an appropriate shape with great care, in order to obtain maximum aerodynamic efficiency. An aero-dynamic profile with optimum twist, taper and higher lift-drag ratio can provide total efficiency as high as 85–92%. The axial flow fan blades are of aerofoil sections and the idea behind using aerofoil blades is to maintain the proper stream-lining of air to reduce losses caused due to form drag as well as from strength considerations (Panigrahi et. Al,2009).

9

Figure 6:Forces acting on a typical aerofoil section of axial flow fan(Panigrahi and Mishra,2014)

10

3.1.2- Multi Stage A.F.F. Over CentifugalFan :(a) Axial Flow Fan:

(b)Centrifugal Fan: (1) Forward curved impellers:  Blades curve towards the direction of rotation.  Fans have low space requirements and low tip speeds.  Used against low to moderate static pressures.  Not recommended for dust or particulate that would adhere to blades. (2) Radial impellers:  Blades are in a radial direction from the hub.  Fan have medium tip speeds.  Radial blade shape resist material build up.  Can handle either clean or dirty air. (3)Backward inclined/curved impellers:  Blades are inclined opposite to the direction of fan rotation.  High fan efficiency and relatively low noise levels.  Blade shape is conducive to material buildup. (Deshmukh vol. 2,2005)

11

Figure7:structure and air flow mechanism of axial flow fan (www.orientamotar.com,2014) 3.2-Dimensions (a) Blades:-The blades have been designed for optimal performance, for both aerodynamic needs as well as noise characteristics. They are available in a range of materials as shown below:(b) Impeller Ranges:Diameters Blades Hub Dia.(mm) 315 to 900 5 or 10 150 560 to 1000 7 or 14 250 800 to 1250 3 or 6 255 800 to 1400 3, 6, 9 350 1000 to 1800 3, 6 or 9 400 1250 to 2000 3, 6, 9 or 12 550

Materials GRP , Nylon, Alum. or Anti-static GRP GRP, Nylon, Alum. or Anti- static GRP GRP, Nylon, Alum. or Anti-static GRP GRP, Nylon, Alum.or Anti-or 12 static GRP GRP or Aluminium GRP or Aluminium

Table 1: fan specification- impellers(Axial flow fan general information, Fantech,2008)

The stress limits of the blades vary from one material to another and simplified criteria are incorporated on the curves. However, if selecting fans using our interactive product selection CD, you may find solutions with higher pitch angles are chosen; these selections are quite acceptable .It should be noted that, as we are constantly reviewing the materials we use, these limits may be extended. (c) Hubs:-All hubs use Fantech TECH-LOCK® taper bushes as standard with one exception. The bush ensures ease of fitting and removal of the impeller from the motor shaft 12

should adjustment of the pitch angle, cleaning or repair of the impeller prove necessary. The exception is for bores above 65mm and 85mm diameter for the 400mm and 550mmdiameter hubs respectively. In these cases we supply impellers with simple through-bores.

(d) Fixings:-All impellers are assembled using high-tensile, zinc-plated set screws and selflocking nuts.

(d) Handing:-Right and left-hand blades are available enabling the selection of contrarotating or multi-stage axial flow fans up to 1400mm diameter. If contra-rotating fans of a larger diameter are required please refer to our sales department.

(e) Standard Material:-GRP blades will be supplied for normal clean ventilation applications as standard except where otherwise specified, or where local regulations prohibit their use.

(f) Balance:-The balance of all impellers is carefully checked to ensure vibration-free running. (g) Fully-adjustable Blades:-All impeller pitch-angles are fully adjustable. For the Elta Range, up to size 1400, the required blade angles are set on jigs but for sizes up to 1000 may also be set utilizing the graduated scale at the root of each blade. For the Elta 2000 Range pitch angle setting is by protractor.( Axial flow fan general information, Fantech,2008).

13

Figure 8: Line diagram of various feature of axial flow fan(www.marathonelectric.in) 4.0-EXAMPLE OF SOME LARGE MINES WHERE AXIAL FLOW FANS USED 

The deepest mines in the world are the TAU TONA and SVUKA gold mine of South Africa. The TAU TONA Mine or western deep no. 3 shaft is a gold mine in south Africa. At 3.9 km deep it is currently home to he world’s deepest mining operations rivaled only

by

mponeng

gold

mine

with

which

it

competes

for

no.

1

ranking.(www.anglogold Ashanti.com,2015) 

ANGICO-EAGLE LARONDE mine of north America. The design of a major underground ventilation is a complex process in this largest mine, the estimate air volume required for the proper ventilation while taking into consideration ,the no. and size of equipment as well as for mineral production .Mineralized zones at santa nino are up to 800 m long by upto 700m deep for a distance of almost 5 km.(www.agapito.com,2015)

14



Uranium mine in Pribram, Czech Republic of Europe.



BERGWERK SAAR in Saarland Germany.



Mount Isa Queenland Australia.



Platinum Palladium mines of Merensky Reef South Africa.



HUTTI GOLD MINE karnatka India.

5.0- SAFETY ASPECTS 

Mine fan should be continuously operated, except as otherwise approved ventilation plan ,or when intentionally stopped for testing of automatic closing doors and automatic fan singal devices, maintenance or adjustment of the fan.



When a main mine fan is intentionally stopped and the ventilating quantity provided by the fan is not maintained by the back up fan system only persons necessary to evaluate the effect of the fan stoppage or restart.  Mechanished equipment shall be shut off before stopping the fan.  Electric power circuits entering underground areas of the mine shall be deenergized.



When a back up system is used that does not provide the ventilating quantity provide by main mine fan, persons may be permitted in the mine and electric power circuits may be energized as specified in the approved mine ventilation plan.

15



If the unusual variance in the mine ventilation pressure is observed,or if an electrical or mechanical deficiency of main mine fan is detected,mine for main or equivalent mine official or in the absence of the mine foreman notified immediately and appropriate action or repairs shall be instituted promptly.



While persons are underground a responsible person designated by operator shall always be at a surface location where each main mine fan singal can be seen or heard.



The area within 30m. of main mine fan and intake air opening shall be kept free of combustible materials ,unless alternative precautions necessary to provide protection from fire or other product of combustible are approved in the ventilation plan.



If multiple mine fans are used the mine ventilation system operated during fan stoppages shall be intrinsically safe.(www.fansafety.com)

6.0- CONCLUSIONS An air screw fan or axial flow fan pushes the air toward in the direction parallel to the axis i.e. axially without changing the direction of air current unlike in the centrifugnal fan.An air screw fan require less space in installation compared to the centrifugnal fan.

On the reversal of the axial flow fan water gauge developed and quantity are much less about to 50 % of the original. Quantity of air can be varied within wide limit in the case of air screw fan by the varying the pitch of the blades. An air screw fan is more suited for low water gauge and high volume but an axial flow fan however can be conventionally used for developing high water gauge by installation of statges .An air screw fan is convient as an underground booster fan due to ease of installation and the requirement of space.Understanding and recognizing warning sign of air axial flow fan will helpful in reduce the injury and accident in underground mines.(www.axialflowfaninfo.com)

16

REFERENCES: Akande,J.M. and Moshood,O. 2013, Modelling of okaba underground coal mine ventilation system. International journal of engineering & technology,pp 766-768.

Banerjee, S.P. 2003, Mine ventilation fan laws,Lovely prakashan, dhanbad India.pp 1-7.

Cenmark ,J. and Murphy, J. 2011, Select fans using fan total pressure to save energy. Ashrae journal,pp 45-47.

Fan specification- impellers,Axial flow fan general information, Fantech,2008

Feature of axial flow fan, www.marathoelectic.com, 2015.

Keith ,W.,Brian P.and Daniel S. 2014,The practice of mine ventilation engineering, International journal of mining science and technology,pp 168-170.

Krog, R.B. and Grau, R.H. 2012, Fan selection for large-opening mines: vane axial or propeller fans which to choose ,U.S. Bureau of mines,pp 2.1-2.3. Krog ,R.B., Grau, R.H.,Mucho, T.P. and Robertson ,S.B. 2004,Ventilation planning layout for large opening mines,SME preprint Littleton,co: society for mining,metallurgy,pp 1-9. Meyer, J. and Marx,W.1999, The minimizing of pressure losses in a fan drift-mine shaft intersection, using computational fluid dynamics,R&D journal vol. 9, No. 3,pp 1-3. Panigrahi, D.C. and Mishra, D.P. 2014, Cfd simulations for the selection of an appropriate blade profile for improving engrgy efficiency in axial flow mine ventilation fans. Journal of sustainable mining, pp 15-17.

Structure of axial flow fan,www.orientamotar.com,2014.

17

18