processoptimization-rawmillcoalmill-moduleday2-230314110558-e03314c6.pdf

Mill Process optimization

1. © Confederation of Indian Industry
Process Optimization
Raw Mill & Coal Mill

2. © Confederation of Indian Industry
Contents
Drying Air requirement
Velocity profiling
Nozzle ring velocity calculations
Pressure Profiling
Mill Inspection Methodology
False air calculations across mill
Energy saving opportunities
Case studies of raw mill

3. © Confederation of Indian Industry
Contents
Mill optimization in pet coke grinding
Benchmarking Numbers
Coal conveying pipeline velocity calculations
Dewatering Curve
Important Process Parameters
Safety aspects of mill operation
Important Thumb Rules
Case Studies of coal mill

4. © Confederation of Indian Industry
Grinding operation: An overview
Largest electrical energy consumer in cement
manufacturing
Grinding alone consumes 60-70 % of the total
electrical energyLS Crusher
2%
Raw Grinding
23%
Kiln
25%Coal Grinding
4%
Cement Grinding
41%
Packing Plant
1%
Miscellaneous
4%

5. © Confederation of Indian Industry
Grinding process & application
Different grinding systems:
•Ball mills
•Vertical mills
•HPRG
•Ball mills with pre-grinder
•HoroMill
VRM-Most commonly used grinding technology for
raw material grinding
For Cement grinding VRM or Ball mill with HPRG

6. © Confederation of Indian Industry
VRM Components

7. © Confederation of Indian Industry
Drying air requirement
Drying air requirement in VRM is mainly depends
upon separator loading
Feed Moisture
Separator loading is mainly defined amount of air is
required to handle the material for separation.
Unit:-gm/m
3
Good range in raw mill:-630 gm/m
3
(best)
Optimum value depends upon supplier & make
.

8. © Confederation of Indian Industry
Drying air requirement
Volume through mill depends
Drying
Separator loading
Nozzle velocity
Minimum amount of heat is required to remove the
moisture from raw meal for drying purpose

9. © Confederation of Indian Industry
Numerical No 1
N1:
Design the raw mill fan with capacity of 300 TPH(9%
moisture) and acceptable separator loading:-630 gm/m
3
and also calculate the minimum heat requirement for
removing the moisture and also find the flue gas
temperature that is coming from preheater?
Given
Height above sea Level = 300m
Specific heat of flue gases= 0.23 kcal/kg C
Density of Flue gases = 1.42 kg/Nm
3
Fan design conditions = 90 degree C
Corrected density at 90 degree= 0.90 kg/m
3

10. © Confederation of Indian Industry
Numerical No 1
Specific heat of raw meal = 0.213 kcal/kg C
Product moisture = 1%
Specific heat of water = 1 kcal/kg degree
Reference Temperature = 0 degree C
Latent heat of Vaporization = 540 kcal/kg degree C

11. © Confederation of Indian Industry
Numerical No 1
Solution = 300 x1000x1000
= 3,00,000,000 gm/hr
Dust loading = 630 gm/m
3
630 gm material is required= 1 m
3
of gases
1.58 m3 gases is required= for 1 kg material
= 1.58 x 3,00,000
= 4,74,000 m
3
/hr
How to calculate the heat requirement to remove the moisture
from material?
Present moisture = 0.08 X 300
= 24 TPH

12. © Confederation of Indian Industry
Numerical No 1
Requirement:
sensible heat of Product + Sensible heat of gas + Latent heat
Sensible heat of flue= 24 x1000 x1x90
= 2.160 Mkcal
Sensible heat of Pro.= (300-24-3) x (90-25)x0.213
= 3.82 Mkcal
Moisture in product = 3 x 1x(90-25)
= 1.95 x 10
-4
Mkcal
Latent heat = 540 x 24 x1000
= 12.96 Mkcal(million calorie)

13. © Confederation of Indian Industry
Numerical No 1
Total heat = 2.160+12.96+3.82
= 15.12 Mkcal
Amount of heat required = 789 kcal/kg water
Amount of gases required = 4,74,000 m
3
/hr.
Density of flue gases at STP= 1.42 kg/Nm
3
= 4,74,000 X 0.9/1.42
= 300422.53 Nm
3
/hrs.
Kg/hr = 300422.53 x1.42
= 4,26,600

14. © Confederation of Indian Industry
Numerical No 1
Amount of gases in kg/hr = 4,26,600
Apply Concept of energy balance
15.12 = 4,26,000 X CP flue gasesx temp
difference
CP = 0.23 Kcal/kg degree C
Temp differ= 15.12 X1,000,000
4,26,000 X0.23
Temp difference= 154.31
T-0 = 154.31
T = 154.31 degree C

15. © Confederation of Indian Industry
Key point-Drying Air requirement
Minimum temp of flue gases which comes from preheater
should be greater than or equal to 154.31 degree C for
removing the moisture from raw material at mill inlet
789kcal/kg water heat requirement is approximately but
it generally varies from 800-900 kcal/kg water
Depending upon feed moisture & conditions it will
change

16. © Confederation of Indian Industry
Process Audit Methodology
Important parameters
Velocity profiling
Pressure profiling
Mill inspection
False air profile

17. © Confederation of Indian Industry
Velocity profiling
After drying air requirement calculations ,the velocity
profile across the mill is to be designed in such a way that
it not creates the excessive pressure drop across the
system
Nozzle ring velocity:-
Minimum amount of velocity is required to lift the
material in such a way that reject should be come
minimum from the mill.
As nozzle velocity increases the pressure drop across
the nozzle also increases therefore its very important to
operate the mill with optimum nozzle ring velocity.

18. © Confederation of Indian Industry
Velocity profiling
Range:-40-60 m/s
Optimum Value:-45-55 m/s
Nozzle ring velocity in raw mill is less as compare to
coal mill due to recirculation.

19. © Confederation of Indian Industry
Impact Of Nozzle ring Velocity

20. © Confederation of Indian Industry
Nozzle Ring velocity Calculations

21. © Confederation of Indian Industry
Armor Ring
The main purpose of armor ring is to
guide the air flow smoothly ,less
turbulence of gas inside the mill body,
avoid the erosion of inside body shell
liner and improve its classifying
efficiency.
Armor ring inclination
5 to 15 deg w.r.t vertical wall. Armor
ring inclination varies from supplier to
supplier.

22. © Confederation of Indian Industry
Armor Ring function
The smooth velocity profile of gas inside the mill.
It is necessary to determine on what angle the velocity
profile will be smooth inside the mill body (zero turbulence)
.
This will reduce the pressure drop across the mill and
subsequently reduce the power consumption.

23. © Confederation of Indian Industry
Numerical No-2
N2:-
Raw mill
Fan flow:-700000 m
3
/hr.
Height above sea level-330 m
Mill outlet temp:-85 degree C
Static pressure at fan inlet:--1000 mmwg
Mill pressure at outlet: -900 mmwg
Oxygen at mill inlet:-7%
Oxygen at mill outlet:-9.2%

24. © Confederation of Indian Industry
Numerical No-2
Fan inlet:9.6%
Mill inlet temp:-200 degree C
Mill inlet pressure;--50 mmwg
Nozzle Area:-3.4 m
2
Density of flue gases:-1.38 kg/Nm
3
Calculate nozzle ring velocity of mill?

25. © Confederation of Indian Industry
Numerical No-2
Step 1
To Calculate False Air Across Mill
Oxygen level at mill inlet = 7.0%
Oxygen level at mill outlet= 9.20%
False Air Across Mill = Mill outlet(O
2%)-Mill inlet(O
2%) x100
21-Mill inlet(Oxygen%)
% False Air = 9.2-7.0 x 100
21-7.0
% = 15.7%

26. © Confederation of Indian Industry
Numerical No-2
False air = 15.71%
Similarly for mill outlet to Fan inlet
= 9.6-9.2 x 100
21-9.2
= 3.38%
Step 2:-
To calculate flow at mill outlet
Mass flow rate at Fan inlet= Flow x corrected
density
= 700000 x CD

27. © Confederation of Indian Industry
Numerical No-2
Now Calculate CD
Apply density Correction
Mass flow rate at Fan inlet= 7,00,000 x 0.90
= 6,30,000 kg/hr
Step 3
Calculate flow at mill outlet in kg/hr
= 6,30,000-(0.0338 x6,30,000)
= 6,08,706 kg/hr

28. © Confederation of Indian Industry
Numerical No 2
Step 4
Calculate flow at mill inlet in kg/hr
= 6,08,706-(0.1571x6,08,706)
= 6,08,706-95627
= 5,13,709 kg/hr
Step 5
Calculate flow at mill inlet in m
3
/hr= Mass flow
Corrected Density
Calculate corrected density
Apply density correction at 200 degree C
= 6,80,727 m
3
/hr

29. © Confederation of Indian Industry
Numerical No 2
Step 6
Nozzle Velocity=
Volumetric Flow at mill Inlet(m
3
/s)
Nozzle Area(m
2
)
= 189/3.4
= 55 m/s

30. © Confederation of Indian Industry
Velocity Profiling Across Mill
5

31. © Confederation of Indian Industry
Velocity Profiling Across Mill
1:-Nozzle Ring Velocity
2:-Velocity on mill body
3:-Velocity on separator body
4:-Rotor cage velocity
5:-Mill outlet duct velocity:-16-17 m/s

32. © Confederation of Indian Industry
Rotor cage velocity
D=Inner dia of rotor cage(m)
H=Effective opening height in rotor cage(m)
Area= 3.14 x D XH
Rotor Cage Velocity= Volumetric flow at mil outlet(m
3
/s)
3.14 X DXH
Recommended range:-5-5.5 m/s

33. © Confederation of Indian Industry
Circumferential velocity
Circumferential velocity inside the rotor cage
should be in the range of 10-25 m/s for raw meal
in VRM.
Calculated by below formula:-
CV=n*3.14*D/60 m/s
n=separator rpm
D=rotor dia of cage(m)

34. © Confederation of Indian Industry
Specific Rotor Load= separator output in terms of fines
3.14 X D XH
D = Outer dia of rotor cage(m)
H = Effective opening height in rotor cage(m)
Recommended Value = 10 t/h/m
2
Specific Rotor Load

35. © Confederation of Indian Industry
Important Norms

36. © Confederation of Indian Industry
Pressure Profiling-VRM –Case Study
b)

37. © Confederation of Indian Industry
Important Process Points
Important points and parameters for pressure
profiling across mill
Mill inlet pressure
Pressure above nozzle ring
Pressure on separator body
Mill outlet pressure
Pressure drop profile across cyclone
Fan inlet pressure
Fan outlet pressure

38. © Confederation of Indian Industry
Pressure profiling-VRM
Observations:-
Mill Feed:-420 TPH
Mill inlet pressure is on higher side
Mill inlet pressure is -131 mmwg which is on higher
side as compare to acceptable range of 40-50 mmwg
as a result the system resistance across mill has been
increased it may be due to material accumulation at
inlet or design problem from supplier.
Excess mill fan speed
High pressure drop from PH fan outlet to mill inlet
Low recirculation gas volume

39. © Confederation of Indian Industry
Pressure profiling-VRM
Pressure above nozzle ring
Pressure above nozzle is -751 mmwgwhich shows that
pressure drop across nozzle is around 620 mmwgthat
is on very higher side as compare to acceptable
range(500-550mmwg) which may be due to design
problem of nozzle ring
High nozzle ring velocity
Dust accumulation in scamper ring area
High reject rate

40. © Confederation of Indian Industry
Pressure profiling-VRM
Pressure on separator body
Pressure on separator body is -854 mmwgwhich
means that the pressure drop from above nozzle to
separator is 103 mmwgthat comes under acceptable
range(100 mmwg)

41. © Confederation of Indian Industry
Pressure profiling-VRM
Observations:-
Mill Feed:-420 TPH
Mill outlet pressure is -956 mmwg which indicates that
the pressure drop from separator body to mill outlet is
around 102 mmwg which is on very higher side as
compare to acceptable range(40-50mmwg) it may be due
to design problem of duct and also velocity was found to
be around 21 m/s inside the duct which is more than the
acceptable norms(16-17 m/s) that creates the excessive
pressure drop across the circuit.

42. © Confederation of Indian Industry
Pressure Profiling across cyclones-VRM
Cylone1 Cylone2 Cylone3 Cylone4
-1034 -1080 -1040 -1080
-1095 -1118 -1107 -1118
61 38 67 38
Pressure drop across cyclones was found to be OK and
it comes under acceptable range(50-60 mmwg)
Recommended range for pressure drop across cyclones
For smaller cyclones :-50-60 mmwg
For large cyclone:-80-90 mmwg

43. © Confederation of Indian Industry
Improvement through CFD Study
Recommendations
Conduct CFD study from recirculation duct to mill inlet
duct to find the reason of excessive pressure drop and
rectify it through study
Saving potential:-At least 40 mmwg
Similarly to conduct CFD study across nozzle ring for
excessive pressure drop
Saving potential:-at least 50 mmwg

44. © Confederation of Indian Industry
Numerical No 3
N3:-Through CFD study around 50 mmwg pressure drop is to be
reduced across nozzle ring in the raw mill circuit. Calculate energy
saving potential in raw mill fan ,TPH = 400
Given
Fan inlet pressure = -1040 mmwg
Fan outlet = -30 mmwg
Electrical Power of fan = 3300 kW
Total saving = 50 X 3300
(-30)-(-1040)
= 163.35 kW
Total Saving = 163.35
400
= 0.40 kWh/ton of material

45. © Confederation of Indian Industry
How to Calculate False air across VRM Circuit?
Raw
mill fan
cyclone
O
23.10 %
O
23.10 %
O
2=5.60 %
O
2=6.2 %
Recirculation
Raw
mill
Hot gas from PH

46. © Confederation of Indian Industry
False Air Calculations across VRM
Oxygen level at mill inlet= 3.10%
Oxygen level at mill outlet= 5.60%
False Air Across Mill = Mill outlet(O
2%)-Mill inlet(O
2%) x100
21-Mill inlet(Oxygen%)
% False Air = 5.6-3.10 x 100
21-3.10
% False air = 13.96%
Similarly for mill outlet to mill inlet
= 6.2-5.6 x 100
21-5.6
= 3.89%

47. © Confederation of Indian Industry
False air infiltration across VRM
Observations:
False air % (Across Raw Mill)
Across Mill: 13.96%
Across MILL O/L TO FAN I/L : 3.89%
Total:-17.85%
False air infiltration points:
Mill body
Mill outlet duct
Across Cyclones

48. © Confederation of Indian Industry
False air infiltration across VRM
Separator Body
Tie rods
Through gravel gate vanes gap
Expansion joints in duct
Rocker arm

49. © Confederation of Indian Industry
Action Points
Mill door sealing for reducing false air
Material accumulation in the inlet ducts / scraper ring
area
Wear rate in mill outlet duct
Grid cone mainly for coal mill and cement mill
condition / closing gap of material feed gate 3KS/ 6 KS/
Double flap / RAV

50. © Confederation of Indian Industry
False air infiltration across VRM
Recommendations:
Arrest false air in raw mill circuit
Target false air less than 14%
Lowest observed false air in Raw mill circuit in
best operating plants: 10-12%
At least 4% false air can be reduced
Saving potential : 28 kW

51. © Confederation of Indian Industry
Energy Saving Calculations
Raw mill
Fan power = 3300 kW
RABH Fan
Fan power = 700 kW
Important point :-
Energy savings calculation of false air of raw mill is to be calculated
on RABH Fan because RABH FAN is the final fan that handling all the
volume of gases.
= 0.04 x 700
= 28 kW
Running hr = 7000
Electrical cost = Rs 5.45

52. © Confederation of Indian Industry
False air infiltration across VRM
AnnualSaving - INR10.68Lakhs
Investment - Nil
Electrical cost = Rs 5.45
Energy saving = 28 x 7000
Annual Saving = 28 x 7000 x5.45
= Rs 10.68 lakhs per annum

53. © Confederation of Indian Industry
Mill Inspection Methodology(Process points)
Velocity and pressure profiling -Every 15 days
Oxygen profiling across circuit-every 10 days
Seal air gap in separator:-once in a month
Static vanes gap in separator:-once in a month
Dynamic vanes conditions inside the separator:-once in a
month
Dam ring height inside the mill:
Depending upon main drive load & mill vibration the dam
ring height decision is to be taken
Nozzle ring condition :-check physical condition once in a
month

54. © Confederation of Indian Industry
Mill Inspection Methodology
(Process points)
Nozzle ring area:-For uniform velocity profile across
mill its important to check every 45 days
Water spray pattern:-check nozzle condition and spray
pattern which plays an important role in grinding and
mill vibration
Mill door sealing for reducing false air
Material accumulation in the inlet ducts / scraper ring
area
Wear rate in mill outlet duct

55. © Confederation of Indian Industry
Mill Inspection Methodology
(Process points)
Grid cone mainly for coal mill and cement mill
condition / closing gap of material feed gate 3KS/ 6
KS/ Double flap / RAV

56. © Confederation of Indian Industry
Mill Inspection Methodology
(Process points)
Seal Air Gap:-
A seal in good condition is of
paramount importance to avoid
contamination of the separator fines
by coarse particle from the feed.
A good seal gap helps in achieving
the proper residue in VRM operation
Normally the seal gap both vertical
and horizontal should be 6-10 mm

57. © Confederation of Indian Industry
Mill Inspection Methodology
(Separator)
Static & Dynamic vanes
Static Vanes
The main function of static vanes is to
maintain uniform velocity across the
rotor cage .
It has uniform opening with making an
angle throughout the circumference.
The mill residue is mainly depends
upon the static vanes gap therefore it
should be uniform

58. © Confederation of Indian Industry
Mill Inspection Methodology
(Separator)
Generally varies from 52 degree to 60 degree and
changes as per residue requirement or as per OEM
Good residue:-Gap minimum (see supplier manuals) but
in that case output is affected
Optimum residue:-As per original drawings

59. © Confederation of Indian Industry
Mill Inspection Methodology
(Separator)
Dynamic vanes:-
Product fineness is being controlled by rotor speed .
Present day roller mills with separators having starter
& rotor produce narrow PSD, with a steep particle
distribution.
Good ratios [%] R 212 μ / [%] R 90 μ = 1:10
Velocity inside the separator is controlled by rotor
which has dynamic vanes therefore physical condition
of dynamic vanes is very important.

60. © Confederation of Indian Industry
The purpose of dam ring is to
control material bed thickness over
table and allow smooth discharge of
ground material to nozzle ring and
maintain stable bed.
Height of dam ring is mainly
depends upon table diameter
(2-4% of table dia) but in case of larger
diameter of table this thumb rule is not
applicable.
Mill Inspection Methodology
(Dam ring Height)

61. © Confederation of Indian Industry
Mill Inspection Methodology
(Dam ring Height)
Too low dam ring height will cause higher vibration and
too high dam ring height will cause high motor amps
and roller skidding causing high vibration & lower
recirculating loads.
Dam ring height optimization is important part of mill
operation
Types of Dam Ring:-Inner and outer
Inner-Constant; Outer:-Variable(segmented)

62. © Confederation of Indian Industry
Mill Inspection Methodology(Nozzle ring)
Nozzle ring is also called as louver ring
Based on the rollers arrangement and
table design, the material reaches in
uneven flows towards the louver ring.
Nozzle ring plays an important role for
uniform velocity across the mill.
Optimum nozzle ring velocity creates the
minimum pressure drop across mill

63. © Confederation of Indian Industry
Mill Inspection Methodology
(Nozzle ring)
Better to design number of nozzles in such a way that
the area of each nozzle should be exactly same
Nozzle ring blade could be either be vertical or at an
angle of 35 -45 deg .

64. © Confederation of Indian Industry
Mill Inspection Methodology
(Water Spray Pattern)

65. © Confederation of Indian Industry
ENERGY SAVINGS IN VRM’s
Optimization of air flow across VRM
Installation of mechanical recirculation
system
High efficiency classifier
Installation of vortex rectifier
High level control system

66. © Confederation of Indian Industry
Fan Power Consumption in VRM
High in comparison to Ball Mill
Major Reason
Higher pressure drop
400 –900 mm WG
Higher air flow rates

67. © Confederation of Indian Industry
Pressure drop in a VRM
Ranges from 400 -900 mm Wg
Pressure drop
75% -Mill louvre
25% -Housing & classifier

68. © Confederation of Indian Industry
Why High Pressure Drop ?
High louvre velocity : 55 –85 m/sec
Why high louvre velocity ?
Lift particles of higher sizes
Grinding table to separator
Reduction of louvre velocity
Reduction of mill -P
Higher quantity of rejects at mill bottom

69. © Confederation of Indian Industry
Mechanical Recirculation System
Rejects handled mechanically
Recirculated back to mill through BE
Tremendous reduction in pressure drop &
energy consumption

70. © Confederation of Indian Industry
Optimization of air flow across mill
Air flow to mill as per separator requirement
Reduction of nozzle ring velocity to reduce Mill DP
Maintaining the optimum nozzle ring velocity in the
range of 45-55 m/s
Modification in VRM mill body to improve air & material
trajectory

71. © Confederation of Indian Industry
Louvre velocity –How much reduction
possible ?
Air flow through mill depends on
Louvre velocity
Drying requirement
Separator requirement
Reduction of louvre velocity to lower levels
Large material handling equipment
Large mill housing
Leads to pre-separation
Less stability & Table vibration
Optimum louvre velocities with mechanical
recirculation : 45 –55 m/sec

72. © Confederation of Indian Industry
Separators for VRM’s
I stage -Static separator
II stage-Dynamic
conventional
separator
III stage-High efficiency
separator

73. © Confederation of Indian Industry
High Efficiency Separators
Air requirement lower
High eff. -0.6 –0.8 kg matl / kg of air
Conv. -0.4 –0.5 kg matl. / kg of air
Better separation efficiency
Lower “P” across mill
Higher output & lower specific energy
consumption

74. © Confederation of Indian Industry
High efficiency
Separator
Old
Separator

75. © Confederation of Indian Industry
Features of high efficiency Separator
Minimum pre-separation in mill
housing
Maximum separation in the separator
Coarse return drops exactly in the
center of the table

76. © Confederation of Indian Industry
Benefits
Increase in output –10 to 30%
Reduction in specific energy –
1.5 to 3.5 units/ton
Very attractive financially
Features of high efficiency Separator

77. © Confederation of Indian Industry
Replacement with High Efficiency
Separator (Raw Mill)
Before After
Capacity 250 TPH290 TPH
Residue (90 ) 11.5% 13.2%
Mill power (units / ton)4.7 4.1
Fan power (units / ton) 8.5 6.2
Total Power 13.3 10.3

78. © Confederation of Indian Industry
Effect of Operating Pressure
Ube LM 40.4
Grinding Pressure
kN/m
2
650 662 675687 700
Capacity 290 295 300305 310
Kwh/ts, Mill 9.0 9.0 9.09.0 9.0
Vibration 4-5 4-5 4-54-54-4.5
Delta P of Mill 54 53.55352.5 52

79. © Confederation of Indian Industry
Effect of Operating Pressure
10 % increase in Grinding pressure
Capacity increase by 7%
Mill drive SEC no change
Fan power 0.5 kWh / MT reduction

80. © Confederation of Indian Industry
Influence of Feed Size for an LM 40.4
Raw Mill
Max 90 mm Max 30 mm
Capacity 240 262
Kwh/ts, Mill 8.05 7.41
Delta P, Mill 76 73
Vibration 5 -7 4 -6

81. © Confederation of Indian Industry
Case Studies

82. © Confederation of Indian Industry
rotor
„Vortex Rectifier“
grit cone
Case Study1
Vortex rectifier for classifier in LM 38.3
Increase in RM
output from 220
TPH to 240 TPH
10 % increase in
Output
10 % Reduction in
SEC

83. © Confederation of Indian Industry
CASE STUDY: Vortex rectifier for
classifier

84. © Confederation of Indian Industry
conventional design
high velocity
differences
LDC (new design)
homogeneous velocity
distribution
Install Vortex rectifier for classifier

85. © Confederation of Indian Industry
Case Study2:-
Pneumatic barriers in Loesche mills

86. © Confederation of Indian Industry
Case Study 3
False air reduction across the mill circuit by rocker arm
sealing & applying false air arrester.
Scope:
InLoescheMillLM563+3c/sthere
thereishugeamountoffalseair
ingressthroughmasterroller.
Actiontaken :
1.SamediscussedwithVendorM/sAlta
Vista&developedrockerarmsealing
withexpansionjoint.
2.PlantteamtoprovideCVRMdoor&
flangestofalseairarrestertoreduce
falseairingresstothemill.

87. © Confederation of Indian Industry
False air reduction across the mill circuit by rocker arm
sealing & applying false air arrester.
Benefits :
Sp power on cement reduced by 0.3kWh/Ton
Annual Electrical Cost Saving Rs. 27.85
Lakh/Annum

88. © Confederation of Indian Industry
Case Study 4
Reduction in Raw mill fan power consumption by
installation of aerofoil design louver ring in VRM
Plant:-JK Sirohi
Observations:-
Pressure drop across mill 892 mmwg
Non uniform velocity across nozzle which
creates the excessive pressure drop
Action Taken :-
Through study and consultation with supplier
the nozzle ring replaced with LNV aerofoil
louvers

89. © Confederation of Indian Industry
Case Study 4
Reduction in raw mill fan consumption by
installation of aerofil design louver ring in VRM
Benefits:-
After modification, pressure drop across nozzle has been
reduced by 62 mmwg
Output increased by 3 TPH
Savings:-150 kWh
•Total units saved : 1089000 KWH/Year
•Total Savings : 5.44 Million/Annum (@5. Rs/Unit)
•Total Investment : 0.35 Million
•Payback Period : 1 Month

90. © Confederation of Indian Industry
Case study No 5
Modification in Separator
Plant:-Aditya Cement Works
Capacity : 640 TPH (Lime stone) Mill
Loesche 69.6 Classifier : LSKS 107
Modification done :
New Skirting arrangement
New Guide Vanes
Nozzle ring modification
Guaranteed Benefit : 1.5 kW/h ton
Achieved Benefit : 1.0 kWh/ton

91. © Confederation of Indian Industry
Case Study No 6
Reduction of pressure across nozzle in VRM
through Aerofil ring
Plant:-UTCL Sewagram
Challenges & Problems
Raw mill having high specific power consumption and high pressure
drop.
Pressure drop in the era of nozzle ring was the majorconcern.
Higher sp.power consumption due to high weight linersinstallation

92. © Confederation of Indian Industry
Reduction of pressure across nozzle in VRM
through Aerofil ring
Countermeasures
To reduce the pressure drop after cross functional teams detailed
analysis and OEM reference, it was decided to replace the nozzle ring
armor ring and separator blanketing to be done.
As the material leaves the table at different velocities depending on
the table diameter. This is compensated for the new nozzle ring by
having a different inclination of louvres for different diameter; try to
match the horizontal velocity of the material leaving the table with the
air velocity.

93. © Confederation of Indian Industry
Reduction of pressure across nozzle in VRM
through Aerofil ring
Benefits
LNVT nozzle is designed with different inserts in the different areas
of the nozzle ring locations, where the resistance through the nozzle
is different for the air entry, as well as louvres of different
inclinations, depending on table diameter.
Results :
Sp. power consumption reduced by 0.15 kWh/T Mat.

94. © Confederation of Indian Industry
Case Study 7
Installation of Raw mill rotary airlock bypassduct.
Plant:-JK Cement Muddapur
Objective
Raw Mill Reliability Enhancement
Hard Coating formed in to Raw Mill feed Rotary Air Lock due to wet
Limestone leads to inevitable breakdowns in Mill.
Action
Preparation of Layout considering site space constraints
In house Fabrication of diverting gate and By Pass Duct
Installation of By pass system and modification in DCS
programming

95. © Confederation of Indian Industry
Installation of Raw mill rotary airlock bypassduct
Bypa
ss
Pipe
Bypass
Divertin
g gate
Fee
d
RA
L
34
Bypass
Pipe
Bypass
Divertin
g gate
Feed
RAL
Installation of Raw mill rotary airlock
bypassduct.

96. © Confederation of Indian Industry
Installation of Raw mill rotary airlock bypassduct
Benefits
Cost savings due to Power - Rs 91.98 lacs/Annum
Cost savings due to Production - Rs16.59 lacs/Annum
Total Cost Savings - Rs 108.5lacs/Annum

97. © Confederation of Indian Industry
Reduction in Classifier annual Gap in
Cement Mill
Classifier inlet velocity increased from 5 to 8 m/sec by reduction of
annular Gap thereby mill internal recirculation load reduced and mill
DP also reduced by 20mmwg which was resulted that mill output was
increased by 15-20 TPH
After this modification, the mill output more than 400 TPH
Benefits:
Sp. Power reduced by 0.3 kW/MT
Investment –12 Lakhs
Cost Saving –38 Lakhs/annum

98. © Confederation of Indian Industry
Coal Mill Optimization in pet
coke grinding

99. © Confederation of Indian Industry
Process Parameters
Nozzle ring velocity
Circumferential velocity inside the rotor case
Dust loading(gm/m
3
)
Dam ring height
Seal air gap
Distance between the static vanes of separator
Water spray pattern

100. © Confederation of Indian Industry
Nozzle ring velocity
Recommended velocity should be in the range
of 45-60 m/s(coal mill)
For low wear and tear inside the mill ,velocity
should be kept as minimum as possible.
Velocity could be optimized by checking
reject with design output.

101. © Confederation of Indian Industry
Circumferential Velocity
Circumferential velocity inside the rotor cage
should be in the range of 27-30 m/s for pet coke
grinding .
Calculated by below formula:-
CV=n*3.14*D/60 m/s
n=separator rpm
D=rotor dia in case(m)

102. © Confederation of Indian Industry
Dust loading
For fine petcoke grinding and reduce the load on
separator the mill outlet dust concentration
should be in the range of 250-300 gm/m
3
.
Should be kept as maximum as possible

103. © Confederation of Indian Industry
Dam ring height
Dam Ring height is required for pet coke
grinding is around 5-6% of table diameter .
In case of large diameter the maximum height
should be 145 mm.

104. © Confederation of Indian Industry
Seal air gap
Seal air gap is the most important parameter
for any type of grinding weather its petcoke or
coal the seal air gap should be less then 10mm
or should be kept as minimum as possible.

105. © Confederation of Indian Industry
Distance between static vanes
The distance between the static vanes of
separator should be uniform for maintaining
the uniform velocity profile across the
separator as a result centripetal force which
acts on the particle is to be maintained
constant

106. © Confederation of Indian Industry
Case Study-Atox Mill 22.5
Parameters Before After
Nozzle ring velocity(m/s) 42 55
Dam ringheight(mm) 145 120
Sealair gap(mm) 5-6 5-6
Dust loading(gm/m
3
) 170 210
Circumferential velocity(m/s) 27 27
Distance between static vanesVaryingfrom 30-
40 mm
30 mm-asper drawing
Residueon 90 micron 8% 1.5-2%
Water spraypattern 2000mm Nozzlesdistance
should be kept as
minimum as possible
from dam ring
height(less than 500
mm)
Investment Nil

107. © Confederation of Indian Industry
IMPACT ON RESIDUE
By maintaining all the parameters which have
been discussed in previous slide the residue of
petcoke on 90 micron is reduced from 6-7% to 1-
1.5% on 90 micron without investing a single
rupee

108. © Confederation of Indian Industry
Benchmarking-Pet Coke Grinding
Parameters Benchmark Target Value
False air(%) 11.9 less than 17%
Residue on 90 micron 1% 1.5%
Output in pet coke(TPH) 65% of designed Above 55%
Seal air gap(mm) 6 mm Less than 10 mm
Specific power
(kWh/tonof mat)
35 Less than 36 kWh

109. © Confederation of Indian Industry
Comparison of coal mills in pet coke grinding
Parameters Atox Polysius
Pfeiffer(MPS
3550 BK)
Loesche
Design (TPH) in normal coal 38 38 90 55
Operating output(TPH) in
pet coke
18-21 16-19 544-58 23-25
NozzleVelocity(m/s) 55-60 45-60 50-55 50-55
Circumferential
velocity(m/s)
27-30 27-30 27-30 27-30
Dam ring height(mm)
5-6% of
table dia
4-5%of
table dia
4% of table
dia
4-5% of
table dia
or
maximum
140 mm
Dust loading(gm/m
3
) 220-250 220-250 220-250 220-250
Grinding pressure(bar) 145 130 85 90
Seal air gap(mm)
Less than 10
mm
Less than
10 mm
Less than 10
mm
Less than
10 mm
Specific power(kWh/ton of
mat)
39 36 41 50

110. © Confederation of Indian Industry
Estimation of coal conveying pipeline velocity
Kiln Blower:-
Calculate velocity with the help of pencil type anemometer.
Q = A X V
= 10
Coal Conveying Pipeline dia=
Conveying Velocity =
Recommended Norms:-
26 m/s-Petcoke
27-28 m/s –Normal Coal
Any velocity is above this only
Contribute in energy losses
Blower
filter
Surrounding
air
Calculate velocity at
this point

111. © Confederation of Indian Industry
Hard Grove Index
The grind ability of coal & pet coke is indicated by the
Hard grove index (HGI). The lower the value, the harder
is the material to grind
Coal-50-60;Petcoke:-30 to 50
Maximum output achieved in Atox mill 22.5 in petcoke
grinding is 55% of designed(38TPH) as per discussed in
Case Study
Normal Coal Petcoke

112. © Confederation of Indian Industry
De-Watering Curve
Coal Contains hygroscopic or inherent moisture along
with free moisture
Inherent moisture can be removed by heating the coal
from 30 degree C to 105 degree C
As per guidelines and recommendations to dry to 1-2%
of hygroscopic moisture
Dewatering curve shows residual water vs. temperature
Recommended temp as per curve

113. © Confederation of Indian Industry
De-Watering Curve
70-72 degree C temp. is enough to remove the moisture from
coal meal

114. © Confederation of Indian Industry
Coal mill fineness-Norms
Due to risks of fire and
explosions coal should
generally not be grind finer
more than half of the
percentage of volatile
Recommended residue
Petcoke:-2-3% on 90 micron
Normal coal:-15% on 90 micron

115. © Confederation of Indian Industry
Type of Coal mill Circuit
Inert Coal Grinding circuit
Inert coal grinding plant uses hot gas source with low
oxygen, typically 2-4% and at temperature 200-400
degree C.
In inert coal grinding plant the system oxygen level at
filter inlet will be < 10% on wet basis.
Typically hot gases from preheater outlet is used in coal
grinding as heat source for drying

116. © Confederation of Indian Industry
Type of Coal mill Circuit
Non Inert Coal Grinding circuit
The non-inert coal grinding plant uses hot gas source
with oxygen level typically 17-21% at a temperature of
200-400 degree C.
Source:-cooler gases or HAG

117. © Confederation of Indian Industry
How to select Coal mill Circuit?

118. © Confederation of Indian Industry
Important Process Parameters
The minimum gas velocity inside duct should be kept
20 m/s for dust laden gas as coal is explosive in nature
therefore more venting volume is required for
dedusting.
Clean air velocity :16-17 m/s(after baghouse)
Mill outlet temperature as per Dew point
Nozzle ring should be maintained in such a way to
allow minimum reject from mill because there is no
recirculation
Nozzle ring velocity:-45-60 m/s

119. © Confederation of Indian Industry
Important Process Parameters
Water spray:-6-8% of total feed
Plays an important role in petcoke grinding
Dam ring height optimization
Seal air and static vanes gap inside the separator

120. © Confederation of Indian Industry
Safety aspects of coal mill operation
Suitable fineness of the product
As per thumb rule product residue on 90 μ should not be
less than 50% of volatile component
Temperature drop across the bag filter should not be
more than 5
0
C
Avoid Ignition source nearby area
O
2level should be less than 12 –14 %
for inert coal mill
14% O
2for bituminous coal & 12% O
2for lignite coal
Maintain CO level below 500 ppm after bag house

121. © Confederation of Indian Industry
Safety aspects of coal mill operation
Inertisation system
Inertisation system used in coal dust hopper or filter for
injection of CO
2or N
2for fire control.
Explosion relief venting:
Self-reclosing explosion door
Conventional Explosion door

122. © Confederation of Indian Industry
Self-reclosing explosion door
The self-reclosing explosion door is designed to re-
close automatically in order to prevent the ingress of
atmospheric air into the mill circuit .
Explosion doors with a low mass, low inertia venting
element and the air cushion principle to stop and
reverse its movement.
Self-reclosing explosion door is more expensive but
also the best, as it do not need to be replaced after the
explosion.

123. © Confederation of Indian Industry
Conventional Explosion door
Conventional explosion door are still and solid with a
heavy hinged lid for venting gases .
Explosion door is most important equipment for coal
grinding circuit. These are equipped in mill exit gas duct,
fine coal bin, etc.
The necessary opening area for explosion venting, and
thereby the amount and size of the relief valves depends
on the type of coal to be ground.
This will be operated at a particular explosion pressure
to the outside to avoid the damage / fire

124. © Confederation of Indian Industry
Case Studies-Coal Mill

125. © Confederation of Indian Industry
Case Study No-1
Separator upgradation in coal mill for petcoke
Plant:-ICL Dalavoi
Basic Specification Size of Mill :
Thyssen krupp 25/12 Type of Separator :
Sepol RMK 315 Rated mill capacity :
Coal –35 tph, 15% R on 90 micron
Modification carried out by SRMES
New internal mill body
New Gear Box arrangement
New Guide Vane assembly
Recommendation on table speed
New Sealing arrangement
New bottom cone arrangement

126. © Confederation of Indian Industry
Results After Modification

127. © Confederation of Indian Industry
Case Study No-2
Separator upgradation in coal mill for petcoke
Plant:-ICL Chilamkur
Size of Mill : Thys Sen Krupp 25/12/32
Type of Separator : Sepol RMK 210 (Dynamic separator) Rated mill
capacity :
Coal –25 tph, 17% to 20% R on 90 micron
Modification carried out by SRMES
New internal mill body
✓New Rotor with Shaft assembly (Dia2100 x 1050 ht)
✓New Guide Vane assembly (Ht930 mm x 32 Nos)
✓Modified gear box speed
✓Recommendation on GRR table speed
✓New Sealing arrangement
✓New bottom cone arrangement

128. © Confederation of Indian Industry
Benefits
Before modification mill was not running in petcoke
After Modification on pet-coke performance
Present Capacity : 12 tph@ <3% on 90 micron
Mill power:-240 Kw
Expected Capacity:-10 tph@<2% on 90 micron

129. © Confederation of Indian Industry
Case Study No3
Modification in Atox Coal Mill
Plant –UTCL Gujarat Cement works
Capacity : 25 TPH (Pet coke) Mill
Atox27.5 Classifier : RAKM 32.5
Modification done :
New Skirting arrangement
Modification of Existing guide vanes
Nozzle ring modification
Guaranteed Benefit : 7.5 kW/h ton
Achieved Benefit : 15.1 kW/h ton

130. © Confederation of Indian Industry
Case Study No4
Modification in Loesche Coal Mill
Plant :-
Capacity : 50 TPH (Pet coke)
Mill : Loesche 43.4 D Classifier : LSKS 59
Modification done :
New Skirting arrangement
New Guide Vanes
Nozzle ring modification
Guaranteed Benefit : 4 kW/h ton
Achieved Benefit : 5.27 kW/h ton

131. © Confederation of Indian Industry
Case Study No5
Modification in Water Spray
•Plant:-Nuvoco
•Angle of Coal Mill water spray nozzle was modified to improve the
grinding over table.
•It benefitted in Stable Coal Mill Operation and on the other hand
variation in coal mill main drive load reduced.
Before After

132. © Confederation of Indian Industry
Case Study No 6
Modification in dry chamber to increase mill
outlet temperature
Plant:-My Home Cement
Challenges
Due to low mill outlet temperature and high moisture in rawcoal as a
consequent plant team is not able to increase the output above 15.5
TPH
Coal mill inlet temperature low due to WHR operation
Countermeasures
Increase the mill dry chamber outlet center cone area from 0.01m
2
to
0.02m
2
to improve the mill inlet volume and increase the mill outlet
temperature
Results
Mill Production increased by 0.5TPH
Mill Specific power reduced by 0.8 kWh/ton ofmaterial

133. © Confederation of Indian Industry
Case Study No 7
Coal mill optimization through Dam Ring height
Plant:-Dalmia Cement
Action Taken
Coal Mill Main drive speed increased from 75 to 85% by
optimizing of dam ring height which was minimized the main
drive current Mill output increased by 2-3TPH
Benefits
Sp. Power consumption reduced by
0.5 kWh/Mt
Cost Saving -13 Lakhs/Annum

134. © Confederation of Indian Industry
Case Study No 8
Reduction of Coal Mill Sp. Power consumption by
installation of Standby RAL
Standby RAL has been provided by in-house thereby mill tripping
totally avoided by RAL jam
Increased Coal Mill Reliability from 90 to 96%
Benefits
Investment -2.5 Lakhs
Cost Saving -4 Lakhs/annum
Payback -8 months
FY
RAL
Stoppage hours
RAL
Frequency
For Last 3 years
148.65 220
From Nov’20
onwards
0 0

135. © Confederation of Indian Industry
Case Study 9
Hot air Duct tapping from TPP to Coal mill-2
Plant:-Ramco Cement
Background
The line-1 was upgraded from 3500 TPD to 4600 TPD of
Clinker production. To cater this enhanced capacity of pyro
system, the fuel requirement is as below :-
Parameters TPD
KilnProductivity 4600
FuelRequirement
Petcoke 443
Coal 636
Petcoke &Coal (50:50) 534

136. © Confederation of Indian Industry
Hot air Duct tapping from TPP to Coal mill-2
As per the above table the Coal Mill-2 has to run additional of 3-4 hrs. per
day to cater the overall fuel requirement of Line-1.
Coal Mill-2 is required to run during Line-2 shutdown also to avoid the
production loss in Line-1.
During Line-2 shutdown, we have taken the trial of Coal Mill-2 running
without hot air. But, due to insufficient air and temperature the mill was not
able to run even with the reduced feed and reduced table speed.

137. © Confederation of Indian Industry
Hot air Duct tapping from TPP to Coal mill-2
Hence, to run the Mill during Line-2 shutdown, it is
proposed to tap the hot air from TPP to Coal Mill Hot
ESP Fan inlet.
The temperature at the TPP ID Fan outlet is
maintaining around 150°C and 85000 m3/hr. gas flow,
which can be utilized for the Coal grinding.
The Coal Mill-2 availability requirement will be as
follows during Line-2Shutdown.

138. © Confederation of Indian Industry
HotgasductfromTPP Hot gas duct joining coal mill-2 inlet duct
Hot air Duct tapping from TPP to Coal mill-2

139. © Confederation of Indian Industry
Coal Mill-2 requirement during Line-2 Shutdown
Parameters
Additional Fuel
required
Coal Mill-2
Productivity
Coal Mill to be
run for Line-1
MT TPH hrs
Petcoke 113 15 8
Coal 152 19 8
Petcoke & Coal (50:50) 127 17 7
13
9
The adequacy of existing Hot ESP Fan was checked and found that the fan can
run with the available hot air from TPP.
Action Taken:-
The new duct (of diameter 1.60 m) has been laid for connecting the TPP ID Fan
outlet to Coal Mill-2 Hot ESP Fan inlet.
Benefit :-Kiln-1 running with normal feed at 295 TPH.
Production loss Avoided –35 TPH of kiln feed (21 MT clinker / hour)
Hot air Duct tapping from TPP to Coal mill-2

140. © Confederation of Indian Industry
Important thumb rules
Rotary airlocks shall not be composed of more than 6
cells/pockets Cell/pocket filling degree shall not
exceed 33 %
External material re-circulation shall be designed for
around 50-90% of nominal production rate
The specific loading of the rotor of the internal
separator shall be <=10 t/hm
2
The separator cage shall be capable of achieving 25 m/s
circumferential velocity

141. © Confederation of Indian Industry
The pressure drop across the cyclones should not
exceed 80-100 mmwgin case of large cyclone for raw
mill
For smaller cylonesthe range is 50-60 mmwg
Air to cloth ratio for raw meal / filter dust :2 m
3
/ m
2
/min for airslidedesign
Venting air quantity (m3 /h) should be more than 10-
12 % of the fan inlet air quantity.
Maximum Intake velocity at venting hood should be
1.5 m/s for bag filters.

142. © Confederation of Indian Industry
Important thumb rules
Venting velocity norms for bag filter
9-12 m/s velocity with dust laden(before bag filter inlet)-
Raw meal
16-17 m/s velocity with clean air (after bag filter)-Raw
meal
Bucket elevator norms

143. © Confederation of Indian Industry
Important thumb rules
Venting velocity norms for bag filter coal
17-19 m/s velocity with dust laden(before bag filter inlet)-
Coal
Acceptable range of false air across coal mill is 15%
Gas outlet temperature should be greater than dew point
of gas by 20 degree C
Dew point range in coal mill from flue gases(50-52 degree
C)
Outlet temperature of coal mill should be maintained as
per dewatering curve

144. © Confederation of Indian Industry
Important thumb rules
Limestone or sand can be used as a scrubbing agent to
dilute CO formation inside the circuit
Sometimes due to breakdown in the plant the coal mill
circuit could not be emptied therefore on that time for
diluting CO the above practice can be used

145. © Confederation of Indian Industry
Summary
Heat consumption for drying mills(VRM) in the range of
800-900 kcal/kg water
Fan volume design mainly depends upon
Separator loading /
Nozzle Ring velocity /
Drying air
Velocity and pressure profiling play an important to
minimize the SEC of mill fans
Inspection of mill also contribute a critical role for
maintaining the desirable output
Loss due to False air which contributes in Raw mill is
mainly depends upon RABH electrical power

146. © Confederation of Indian Industry
Summary
Conversion from Normal coal to petcoke deteriorates
the mill output
Best figures achieved:65% of OUTPUT in normal coal
Latest case studies suggest that there is lot of
potential in house modification for achieving and
optimizing the coal mill in pet coke grinding
Safety aspects in coal mill also very important because
recently some incidents happened due to CO explosion
in baghouse

147. © Confederation of Indian Industry
Question Bank
N4

148. © Confederation of Indian Industry
Numerical -4

149. © Confederation of Indian Industry
Numerical -4
1)Calculate the heat and mass balance of input and output
components of the VRM (cement mill), considering
radiation and convection heat loss to be negligible and
also estimate the heat requirement (kcal/hr.)of VRM.
2)Determine the amount of hot air being drawn from the
clinkercooler.
3) The power generation potential in the cooler hot air,
which is presently used for VRM (cement mill) heating, at
28% overall efficiencyof WHRS.
4) Hourly coal requirementin HAG.
5) Hourly monetary saving of WHRS power generation
using HAG, for cementmillheating

150. © Confederation of Indian Industry
Numerical -4
Input Parameters
Step1:-
Calculate the sensible & latent heat from Input parameters
Sensible heat from dry feed = Qd
= m*Cp*T
= 200x1000x0.21x(52-30)
= 924000 kcal/hr
Sensible heat from feed moisture = Mw*cp*T
Do the water balance for calculating the value of moisture
X = Total mass input with
moisture(TPH)
0.97*X = 200
X = 206.1 TPH

151. © Confederation of Indian Industry
Numerical -4
Mw = 206.18-200
= 6.186 TPH……………………………………….Eq -1
Qm = 6186*1*(52-30)
= 136092 kcal/hr
Sensible heat from water spray on table:-
Qm1 = 3500*1*(30-30)
= 0 kcal/hr
Do the Air balance for calculating the value of false air & recirculation
air:-
False air=15% of process fan flow
= 0.15*487490
= 73123 kg/hr

152. © Confederation of Indian Industry
Numerical -4
Recirculation Flow = Total Process Fan flow-Stack Flow
= 487490-128124
= 359366 kg/hr
Calculate the sensible & latent heat from Input parameters
Sensible heat from recirculation air= Qr
= m*Cp*T
= 359366x1000x0.239x(90-30)
= 5153308 kcal/hr
Sensible heat from false air = Mw*cp*T
= 73123*0.238*(30-30)
= 0 kcal/hr

153. © Confederation of Indian Industry
Numerical -4
Sensible heat of hot air Qha = m*Cp*T-Unknown
Step 2
Calculate heat input from electrical energy:-
P x 860 x motor eff. = 4000 x 860 x 0.95
= 3268000 kcal//hr
Total Heat input =924000+136092+5153308+3268000+Qha
Step 3
Calculate the sensible & latent heat from Output parameters
Sensible heat from product = mpx Cpx ΔT
= 200000 x 0.21 x (90-52)
= 1596000…………..Eq1

154. © Confederation of Indian Industry
Numerical -4
Sensible heat from mill exit gases
= 487490x 0.239x (90-30)……Eq2
= 6990606
Heat of evaporation ofmoisture in feed (HEvep)
= latent heat +sensible heat
= 6186 x [540+(90-52)]
= 3575508 kcal/hr………Eq3
Heat of evaporation ofWater (mill spray)
= 3500x1x[540+(90-30)]
= 2100000kcal/hr……….Eq4
Total heat output = Eq1+Eq2+Eq3+Eq4
= 14262114 kcal/hr

155. © Confederation of Indian Industry
Numerical -4
Step 4
Heat input = Heat output
Total Heat input = 924000+136092+5153308+3268000+Qha
= 14262114
Qha = 4780714 kcal/hr
= heat supplied from cooler
VRM Heat requirement= Heat Input
= 4780714+924000 kCal/hr
Amount of heat drawn from cooler
= M is asking
470714/(380-30)*0.246= 55525 kg/hr

156. © Confederation of Indian Industry
Numerical -4
Power generation = 0.28*4780714/860
= 1556.5 MW
HAG efficiency = 90%
NCV Of coal = 7000 kcal/kg coal
Hourly coal consumption
= 4780714/7000*0.90
= 758 kg/hr

157. © Confederation of Indian Industry
Annexures

158. © Confederation of Indian Industry
Annexures

159. © Confederation of Indian Industry
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