Operating Experience of the Upgradation of Raw and Coal mill at MCL Alathiyur
M. Srinivasan : Sr. VP (Mfg.)S. Shanmugam : VP (Mfg.)
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Contents
Introduction
Raw Mill LM 38.3Upgradation with LSKS 57 Classifier and Vortex Rectifier
Coal Mill LM 20.2DUpgradation with LSKS 36ZD Classifier for Pet coke grinding
Conclusion
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Madras Cement Ltd. (MCL) is a flagship company of RAMCO Group.
MCL is having five Cement manufacturing units, three cement grinding units and two packing units with the total annual capacity of 13 Million tones.
Introduction
ISO 9001:2008ISO 14001:2004 IS 18001:2007
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Introduction
MCL Alathiyur plant with two clinkerisation units, is located at Alathiyur in Tamil Nadu, India.
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MCL Alathiyur Cement Plant, Tamil Nadu
Introduction
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The cement plant at Alathiyur was setup in two phases.
Line-I was installed with a capacity of 2350 tones/day in 1997 and presently operational at 3500 tones/day.
Line-II was installed with a capacity of 3000 tones/day in 2001 and presently operational at 3500 tones/day.
Line-II was repeat of Line-I with upgraded capacity.
Loesche VRM LM 56.2+2C was considered for clinker grinding in Line-II in place of OK mill 33.4 of Line-I
The products manufactured are Ordinary Portland Cement as per BIS & Sri Lanka Standards (SLS), Portland Pozzolana Cement and Sulfate Resistant Portland Cement (SRPC).
Introduction
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Line 1 Line 2
Commissioned (year) 1997 2001
Kiln FLS – 3500 t/d FLS - 3500 t/d
Raw Mill Loesche LM38.3 Loesche LM38.3
Coal Mill Loesche LM20.2D Loesche LM20.2D
Clinker Mill O.K 33.4 Loesche LM 56.2+2 C
Two coal based captive thermal power plants each 18MW ensure uninterrupted power supply
Alathiyur Plant Details
Introduction
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Contents: Raw Mill LM38.3
Introduction: Raw Mill LM 38.3
Technical Details of Raw Mill
Operating data before modifications
Constraints in plant operation
Driving force for the upgradation
Modifications carried out
Classifier Details
Vortex Rectifier
Comparative Opertaing Data
Benifits achieved after upgradation
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Raw Mill-1 was commissioned with rated capacity of 180t/h @17%R90 µm to cater the kiln of 2350t/d in 1997.
Raw Mill-II was commissioned with rated capacity of 215 t/h @ 17%R90 µm to cater the kiln of 3000t/d in 2001.
By the time of ordering Line-II, MCL decided to upgrade Line-I to have same capacities.
Raw Mill-I was successfully upgraded by replacing classifier from LJKS65 to LSKS52 and bigger tires in 2000/2001.
Both raw mills were in smooth & stable operation at output of 215-220 t/h @17% R90µm
Introduction : Raw Mill LM 38.3
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Technical Details of Raw Mill
Type of mill LM38.3
Rated Capacity (t/h) 215 @ 17% R 90μm
Feed Moisture (%) Normal: 5 Maximum:10
Table diameter (mm) 3800
Grinding rollers 3 Nos.
Main Gear Box Flender KMP 450
Main Gear box rating (kW) 1320
Classifier Size LSKS52
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The Raw mill was designed for a feed moisture of 5% normal & 10% maximum.
Over a period of time, the normal feed moisture increased to more than 10% causing the reduced raw mill output to 205-210 t/h from 215-220 t/h.
During monsoon, Mill output was further reducing to 190 t/h. Hot Gas Generator (HGG) had to be operated to get the output of 210 t/h to meet the clinker production.
Since more heat was required for drying, the gas volume was to be increased in mill and thereby causing higher product residue.
Raw Mill motor was overloaded frequently with periodic power kicks.
Constraints in plant operation
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Constraints in plant operation
Kiln feed had to be reduced as the Raw mill was unable to support the raw meal requirement.
At high residue of raw meal on 212 µm, problems related to clinker burning resulted in high free lime of >2.5%.
HGG had to be turned on, consuming about 2 t/h of fine coal.
Raw mill with HGG met the raw meal requirement but residue was still high.
The raw mill fan was a bottleneck to handle higher gas flow.
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Operating data of Raw Mills before modifications
Description Raw Mill 1 Raw Mill 2
Feed Moisture (%) >=10% >=10%
Mill Output dry (t/h) 207 210
Product Residue % 212 µm 2.5-3.0 2.5-3.0
Product Residue % 90 µm 19-20 19-20
Mill Motor Power (kW) 1150 1170
Fan Power (kW) 1310 1530
Specific Power: Mill (kWh/t) 5.56 5.57
Specific Power: Fan (kWh/t) 6.32 7.29
Total Specific Power (kWh/t) 11.89 12.86
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MCL decided to further enhance the kiln capacity to 3500 t/d
Accordingly the revised capacity requirement from raw mill was>= 230 t/h to support the upgraded kiln.
Product residue @212 µm was required to be less than 2%
Driving Force for the Upgradation
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Modifications Carried out
Replacing the existing classifier from LSKS 52 by a larger size LSKS 57 with inbuilt Vortex Rectifier. This was the first Vortex rectifier in India.
Modified louver and armor ring to maintain uniform gas flow/velocity profile inside the mill.
Increase the capacity of the raw mill fan by replacement/ retrofitting
Increase the size of the following ducts due to higher gas flow:
Mill inlet ductMill Outlet ductDuct from Cyclone to mill fan inlet
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Comparison between LSKS52 and LSKS57
Description LSKS52 LSKS57
Rotor diameter (mm) 3080 3400
Rotor Height (mm) 2000 2200
Area of rotor (m2) 19.35 23.50
Classifier Details
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Classifier Details
Vortex Rectifier
LSKS With Vortex RectifierLSKS
Rotor
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Vortex RectifierVortex Rectifier reduces the turbulences at the mill outlet
Vortex kinetic energy recuperation
Homogenous velocity distribution at mill outlet
Uniform/ laminar flow pattern at mill outlet
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Vortex Rectifier
With vortex RectifierUniform and Laminar Flow
Without Vortex Rectifier
Hard twisted gas flow created by high speed rotation of classifier rotor
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Classifier without vortex rectifier
Classifier with vortex rectifier
Laminar Flow
Turbulent Flow
Results of CFD
Flow Characteristics
Vortex Rectifier
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Vortex Rectifier
Actual Photographs during installation at site.
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Comparative operating data of Raw Mill 1
Description Before Modification After Modification
Classifier Size LSKS 52 LSKS 57
Feed Moisture (%) >=10 >=10
Mill Output (t/h) dry 207 231
Product Residue 212 µm (%) 2.5-3.0 1.5-2.0
Product Residue 90 µm (%) 19-20 16-17
Specific Power: Mill (kWh/t) 5.56 4.55
Specific Power : Fan (kWh/t) 6.33 6.28
Total Specific Power (kWh/t) 11.89 10.83
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Comparative operating data of Raw Mill 2
Description Before Modification After Modification
Classifier Size LSKS 52 LSKS 57
Feed Moisture (%) >=10 >=10
Mill Output (t/h) dry 210 233
Product Residue 212 µm (%) 2.5-3.0 1.5-2.0
Product Residue 90 µm (%) 19-20 15-16
Specific Power : Mill (kWh/t) 5.57 4.42
Specific Power : Fan (kWh/t) 7.29 6.52
Total Specific Power (kWh/t) 12.86 10.94
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Improvement Raw Mill 1 Raw Mill 2Output (%) 11.59 10.95
Product Residue % on 90 µm 3 (Absolute) 4 (Absolute)
Product Residue % on 212µm 1 (Absolute) 1 (Absolute)
Specific Power : Mill Motor (kWh/t)
1.01 1.15
Specific Power : Fan (kWh/t) 0.05 0.77
Total Specific Power (kWh/t) 1.06 1.92
Performance Improvement
Comparative operating data
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At feed moisture >=10% average output increased to >230 t/h at improved residue.
Product Residue on 212 µm, which is crucial for burning came down to 1.5-2%.
Product Residue on 90 µm came down to 15-16%.
The mill can be operated at 240t/h-245t/h with increased Hot Gas from HGG.
Saving of about 1-2 kWh/t in specific power drawn by mill and fan.
Achieved the lowest specific power consumption (mill + fan) RM-1 : 10.82 kWh/t
RM-2 : 10.94 kWh/t
Benefits achieved from upgradation
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With improved particle size distribution of mill product, free lime in clinker reduced to <2%
Quality of clinker improved : C3S >=55%
Kiln is being operated to its full capacity due to increased raw meal of better quality
Stable Kiln Operation established
Benefits achieved from Upgradation
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Contents : Coal Mill LM 20.2D
Introduction: Coal Mill LM 20.2D
Technical Details of coal mill
Difficulties in Pet coke grinding
Solutions for Pet coke Grinding
Modifications carried out
Classifiers
Comparative Operating Data in Pet coke Grinding
Comparative Operating Data in Coal Grinding
Benefits achieved from Upgradation
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Introduction : Coal Mill LM 20.2D
MCL Alathiyur has two Coal mills of LM 20.2D size.
The coal mills were designed for lignite grinding with central feed.
The coal mills were operating smooth & stable, meeting all performance guarantees.
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Mill Size LM 20.2 D
Fuel Type Lignite / Coal
Feed Moisture (%) 15
Product Rate (t/h) 23 ( wet basis )
Product residue % @90μm 15
Table diameter (mm) 2000
Grinding rollers 2 Nos.
Main Gear Box Flender KMS 595
Main Gear box rating (kW) 330
Classifier Size LKS 40ZD
Technical details of Coal Mill
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Difficulties in Pet coke grinding
MCL started using imported Pet coke & coal due to techno-economicreasons.
In Pet coke grinding, the mill operation was very unstable due to non-uniform bed formation
Due to spheroid and uniform shape of Pet coke, the nipping under rollers is extremely difficult.
Due to the low volatile matter in Pet coke, it has to be ground to a fineness of <2% Residue on 90µm for complete combustion.
The existing LKS Classifier was not able to provide efficient separation for the very fine grinding of Pet coke. The fines along with grits returning on the table leads to over grinding and unstable bed formation.
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Solutions for Pet coke Grinding
The stability of mill could be achieved/improved by:
An efficient and state of art classifier, designed suitably for very fine grinding, minimizes the fines in return grits.
Due to reduced fines in return grits, the over grinding is avoided and stable/uniform bed formation is ensured.
Additionally the bed stability can be influenced by:
Increasing dam ring height
Water sprinkling on table
Reducing table speed (varying mill motor speed)
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Modifications Carried out
Replacing the existing classifier from LKS 40ZD by LSKS 36ZD
Modified louver and armor ring to maintain uniform gas flow/velocity profile inside the mill.
Modified dam ring suitable for Pet coke grinding
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Classifiers: LKS...ZD and LSKS...ZD Type
LKS Classifier New LSKS Classifier
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Description Before Modification After Modification
Classifier Size LKS 40 ZD LSKS 36 ZD
Output (dry basis) (t/h) 13 17
Product Residue @ 90 µm (%) 4 1.5 -2
Mill Motor Power (kW) 250 190
Fan Power in GRR Mode (kW) 420 450
Specific Power: Mill (kWh/t) 19.23 11.18
Specific power: Fan (kWh/t) 32.30 26.47
Total Specific Power (kWh/t) 51.53 37.65
Comparative Operating Data in Pet coke Grinding
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Description Before Modification After Modification
Classifier Size LKS 40 ZD LSKS 36 ZD
Output (dry basis) (t/h) 23 28
Product Residue @ 90 µm (%) 18 <16
Mill Motor Power (kW) 280 230
Fan Power in GRR Mode (kW) 440 475
Specific Power: Mill (kWh/t) 12.17 8.21
Specific Power: Fan (kWh/t) 19.13 16.96
Total Specific Power (kWh/t) 31.30 25.17
Comparative Operating Data in Coal Grinding
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Benefits achieved from Upgradation
Improvement Coal Pet coke
Mill Output dry basis (%) 21.73 30.76
Product Residue % 90µm 2 (Absolute) 2 (Absolute)
Specific Power (kWh/t) Mill + Fan
6.13 13.88
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Pet Coke usage increased up to 85%
Improved mill stability ; especially in Pet Coke grinding
Mill Vibration reduced to <2mm/sec
Improved burning efficiency in kiln due to homogenous quality of pulverized fuel
Abnormal coatings in Kiln eliminated
Kiln is being operated to its full upgraded capacity
Reduced running hours of coal mill and it’s increased availability for maintenance etc.
Benefits achieved from upgradation
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Conclusion
The performance of upgraded raw mill and coal mill met the expectation of MCL to cater the enhanced kiln capacity at improved clinker quality.
With significant saving in specific power of grinding sections, MCL achieved specific power consumption of 63-64 kWh/t in PPC for complete plant, which is the benchmark in the industry.
The series of national awards for the highest energy efficient plant bears a testimony of innovative commitment by MCL.
MCL would like to put on record the appreciation for continuous support given by OEM such as Loesche to meet the target.
MCL firmly believes in continual improvement and is working together with Loesche to further reduce specific power ; especially in clinker grinding with similar Upgradation philosophy.
THANK YOU