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Operating Experience of the Upgradation of Raw and Coal mill at MCL Alathiyur M. Srinivasan S. Shanmugam
: :
Sr. VP (Mfg.) VP (Mfg.)
Contents Introduction Raw Mill LM 38.3 Upgradation with LSKS 57 Classifier and Vortex Rectifier
Coal Mill LM 20.2D Upgradation with LSKS 36ZD Classifier for Pet coke grinding
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.
The products manufactured are Ordinary Portland Cement as per BIS & Sri Lanka Standards (SLS), Portland Pozzolana Cement and Sulfate Resistant Portland Cement (SRPC).
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.
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
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.
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.
Vortex Rectifier Vortex Rectifier reduces the turbulences at the mill outlet Vortex kinetic energy recuperation Homogenous velocity distribution at mill outlet
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 1.52%. 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.
Difficulties in Pet coke grinding MCL started using imported Pet coke & coal due to techno-economic reasons. 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.
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:
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.
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
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.
