MP Birla Group has two cement plants at Chanderia (Rajasthan) – Birla Cement Works (BCW) and Chanderia Cement Works (CCW). Here is a case study on the various initiatives taken to reduce thermal and electrical energy consumption at for both the lines of CCW.
Cement clinker is manufactured primarily from limestone, clay, sand and iron oxide-bearing as raw materials. These materials are blended and finely comminuted to form the raw meal. The process of manufacture of cement consists essentially of crushing and grinding of the raw materials, mixing them intimately at certain proportions and burning them, usually in a rotary kiln at a temperature of approximately 1450 degree Celsius. The material sinters and partially fuses to promote the formation of the clinker phases. The principal phases in the cement clinker are tri-calcium silicate, di-calcium silicate, tri-calcium aluminate and calcium alumino ferrite. The clinker is then cooled and ground to fine powder with the addition of a few percent of gypsum. The resulting product is so called commercial Portland cement.
During the heating up and burning process, decomposition reactions, phases transformations and formation of new phases occur. These phenomena influence each other. Regarding, the energy consumption in the kiln plant, the important aspects are the enthalpies of the reactions, which may be endothermic or exothermic.
The share of energy consumed in a cement kiln attains 70 to 78 per cent of the overall energy consumed in the process of cement production as a whole. The residual (22 to 30 per cent) is the share of electrical energy. On the other hand, for the burning of the clinker kiln plant, thermal energy represents 92 to 96 per cent of the required energy and the electrical energy accounts for only 4 to 8 per cent. Therefore, potentials for reducing specific heat consumption in the kiln plant deserve priority (6 to 10).
Issues observed:
Huge false air across preheater area/preheater fan
Raw mix quality variation due to point stacking
False air across and hot dust falling from tertiary air duct(TAD) for CCW-1
Different fuel combination for both the kiln
False air from inlet/outlet seal of CCW-1 kiln
Action taken:
False air arrested and major leakages arrested during kilns shutdown
Formation of lime stone piles instead of point stacking (quality variation reduced)
Same fuel mix started for both the kilns
Dedicated SGA teams formed for regular arresting of false air
Change both inlet and outlet seal for CCW-1
Reduce kiln feed residue from 18 to 19 per cent to 16 to 17 per cent at +90
Reduced kiln feed residue from 4.67 to 2.5 per cent at +212
Results:
Thermal Energy consumption (Kcal/kg Clinker)
Kiln Line2017-182018-19
CCW Line -1740720
CCW Line -2736713
Increase throughput of cement mills
Clinker grinding technology has been continuously improving with numerous innovations in view of improving productivity and to reduce specific power consumption. In order to reduce the manufacturing costs for cement, it is very important to optimise the existing mill installations as far as the grinding process is concerned and also to use high quality spare parts and consumables like grinding media, rollers for roller presses, etc.
Ball mills are predominantly used machines for grinding in the cement industry. Although ball mills have been used for more than one hundred years, the design is still being improved in order to reduce the grinding costs.
Many types of grinding systems presently being used for clinker grinding in cement plants are:
- Open and close circuit ball mills
- Roller press in combi circuit/finished mode
- Vertical roller mill (VRM)
- Tube mill with pre-grinder/crusher
- We at MP Birla Group at Chanderia having two cement ball mills with roller press in combi circuit havedone performance optimisation of the cement grinding circuits by doing process diagnostic studies.
We have taken various action and trial in steps and increased throughput by 25 to 30 per cent for both the mills. Output for both the mills was only 225/240(CM-1/2) TPH of 2017-18 in PPC, which has been increased to 300 to 310(CM-1/2) TPH as annual average in 2018-19 and reduced power consumption from 30.38 kWh/tcement of 2017-18 to 27.51 kWh/tcement in 2018-19.
Issues/action we were facing at CCW:
Grinding media pattern: Grinding is generally an inefficient process and there are many factors that can affect grinding performance. Among the ways of assessing mill performance are examining the load behavior, mill power and the rate of production of fines. Grinding performance, in terms of material breakage and power consumption, has been studied with a wide range of operating parameters such as mill speed, charge filling, ball size and lifter type etc.
We have taken a series of mills circuit sampling and crash stop samples to establish the grinding media pattern inside the mills.Grinding media charged in this mono chamber was ranging from 50 mm to 15 mm and corresponding specific surface area is 38.7 m2/tonne in NCCW cement mill-1 and 35.2 m2/tonne in NCCW cement mill-2.
This mill chamber is mainly for fine grinding as we already have roller press for coarse grinding. Therefore, using small balls is known to be more efficient as this increases the surface area of media and improves the grinding effect along with classifying liners.
Initial grinding media pattern was as per below table:
Replaced the larger grinding media of 50 and 40 mm in with lower sizes. Redistribute total weight of existing charge in lower size media to keep same total weight of media. Increased the specific surface area from 40 m2/MT and later on 42m2/MT.
Higher residue at +45 R:As we are having ball mill with roller press in combi circuit Sepol separator, which was having huge seal air gap which has been reduced to 15.0 mm from 35 to 40 mm by installing new seal plates and proper maintenance. Also checked separator vanes and corrected its uneven gap of vanes from 30 to 35 mm to 15 to 20 mm, which helps us in better separation of fines and coarse. A team has been formed by management for inspection and corrective action to improve separator performance consisting production, mechanical, and quality officers.
Separator guide vanes correction: Separator guide vanes has been checked and as observed many of the vanes found worn out which was affecting the PSD of product. Separator guide vanes has been replaced. Uneven gap has been corrected and checked sample results accordingly to get desired results.
Circuit sampling and crash stop:-Increased frequency of circuit sampling and weekly crash stop sampling done to establish the above pattern.
Process optimisation: Analysed complete circuit and done process optimization to obtain desired production by maintaining quality requirements.
Results
Output for both the mills was only 224/242 (CM-1/2) TPH of 2017-18 in PPC which has been increased to 290-300(CM-1/2) TPH as annual average in 2018-19 and reduced power consumption from 30.38 kWh/T Cement of 2017-18 to 27.51 kWh/T Cement in 2018-19.
Optimisation of raw gridning roller press
Lime stone grinding technology has been continuously improving with numerous innovations in view of improving productivity and to reduce specific power consumption. In order to reduce the manufacturing costs for cement, it is very important to optimize the existing mill installations as far as the grinding process is concerned and also to use high quality spare parts and consumables.
Many types of grinding systems presently being used for raw meal grinding in cement plants are:
- Open and close circuit Ball mills
- Roller press in combi circuit/finished mode
- Vertical roller mill (VRM)
- Tube mill with pre-grinder/crusher
We at MP Birla Group at Chanderia plant, in the raw grinding circuit having two KHD supplied roller. Presses RP-1 and RP-2 with single circuit of fan/separator which produce 360 TPH raw meal as annual average which consumes 16.5 kWh/T raw meal.
We have to run one standby Ball mill to makeup extra requirement of Raw meal which consumed 25.0 kWh/T raw meal which was a big loss.We have done many small in house modifications, logic changes and process optimization in step to improve its productivity and to reduce power consumption.
After all the steps/trials, mill is running > 410 TPH with 14.5 kWh/T Raw meal and major advantage for our plant that we have almost stopped Ball mill operation to make up extra raw meal requirements.
In the raw grinding circuit having two KHD supplied roller Presses RP-1 and RP-2 with single circuit of fan/separator which produce 360 TPH raw meal as annual average which consumes 16.5 kWh/T raw meal. We have to run one standby Ball mill to makeup extra requirement of Raw meal which consumed 25.0 kWh/T raw meal which was a big loss. By optimization and various small in house initiatives, we have increased throughput and reduced power consumption. Continuous running of Ball mill also stopped.
Action:
We have studied the circuit completely and following issues observed and taken actions:-
A.Feed regulating gate (351SG3, 351 SG4) in both RPs always in closed position (0%). Even during close position, no material stays in its pre bin so there is no choke feeding. Its position to be checked and necessary modifications to be done for chock feeding
During maintenance both feed gate checked and gap was uneven for both RPs which was varying from 120 to 180 gap. We have reduced it up to 120 mm by adjusting the plate, choke feeding started due to this.
B.Level sensor in overflow bin below SKS separator is always showing 1.98 MT(Full) due to this there is always having some risk of filling material in separator and fines eject from separator overflow bin air slide to both elevators. Level sensor checked , its position changed and now it is working perfectly
C.Huge material accumulation at SKS air entry spiral and SKS outlet duct
D.It was observed many times that When both RPs running in auto condition and RP-1 tripped due to any fault whole fines from SKS rushed towards RP-2 and bucket elevator tripped many times. Logic changed and now fines controlling is better.
D.Motorised actuator required for SKS reject air distribution gate for RP-1 for better fines control/ Correct size Actuator installed for better fines control.
Uneven Gap observed in separator guide vanes disturbing PSD of the product which has been corrected.
RP feed regulating gate: The gap between fixed roller & bottom plate of gate should be uniform throughout the width of roller. To maintain the same, feed regulating gate plate repaired.
Results
After all the steps/trials, mill is running > 410 TPH with 14.5 kWh/T Raw meal and major advantage for our plant that we have almost stopped Ball mill operation to make up extra raw meal requirements.
Mill Throughput Before optimisationAfter optimisation 360 TPH410 TPH
Mill Power Before optimisationAfter optimisation 16.5 kWh/T Raw Meal14.5 kWh/T Raw Meal
ABOUT THE AUTHORS: Dinesh Kumar, D. Banerjee, D C Jagetiya, Narpat Anjana of MP Birla Group (Chanderia Cement Works, Chanderia), Rajasthan.This is only first part of the paper that was presented at NCCBM International seminar held in December 2019. The remaining part will be presented in the next issue.