Cement Energy and Environment

hours) impelled adoption of waste heat recovery (WHR) based power generation. The plants opted to live with higher PH and cooler vent gas volume and temperature to derive the benefit of higher capacity power generation. The grid power cost in South Korea is much lower (equivalent of Rs. 1.85 per kWh/h). Coal being imported , Korean plants opted for waste derived fuels (WDF), such as pet coke and reject tyres to the possible extent. Plants 3 and 4 have both 4- and 5-stage preheaters with conventional precalciners and modern coolers. The fuel energy consumption of these plants varies from 720 to 780 kcal/kg (average 730). Plants 5 and 6 have a mix of both 4- and 5- stage preheaters, the latter with SLC. The grid power cost is similarly low in Thailand (equivalent of Rs. 1.80 per kWh/ h). Lignite and pet coke are used as substitute fuels, even up to 50 per cent (in plant 6). The fuel energy consumption in these two plants ranges from 720 to 740 kcaljkg clinker for modern kilns and 780 to 850 kcal/kg clinker for older generation kilns. It appears from the overall review of fuel consumption by all the 9 p lants that the Indian plants are more fuel efAcient (706 to 750 kcaljkg clinker). This despite using either domestic coal (calorific value ,.,4000 kcaljkg) or imported coal of lower calorific value (6000 to 6500 kcal/kg) than in Southeast Asian countries. Plants 7,8 and 9 use expert ki ln control systems (Fuzzy logic, Linkman , etc.), on-line quality control of raw meal and fuel, etc. vi . Coal g rinding - A ll the plants show a marked tendency to switch over from the conventional ball mill to VRM. Plants 2,3,5,7 and 9 have only VRM for coal grinding. As the power consumption for coal mill is clubbed with that of the ki ln and cooler, a relative assessment was not possible. It appears to be lower than 4 kWh per tonne of cement. For plants using both ball mill and VRM (plants 1 ,4 and 8) the power consumption in coal grinding exceeds 4 kWh/tonne of cement and even reaches up to 5 to 6.5 kWh/tonne of cement. vii. Cement grinding - A bizzare situation of hybrid technology use is revealed in cement g rinding - the area of the highest power consumption. There are different combinations of al l th e three 8 technologies - ball mill, ball mill + roll press and VRM from plant to plant. Each plant opted for different levels of modernisation of cement grinding depending upon its specific techno– economic considerations. All the old plants retained some of their old ball mills and enhanced output capacity by addition of roll presses or VRMs. The operational data lead to the following inferences : Ball mills with separator consume 35 to 40 kWh/tonne (plants I , 2, 3, 4, 5 and 6), 31 kWh/ tonne (plant 7) and around 34 kWh/ tonne (plants 8 and 9). VRM consumes 31 kWh for plant 4 and 29 kWh in plant 3 against 37 kWh by ball mill with separator in the same plant (plant 3). The ball mill + roll press combination shows lower power consumption - 27.3 kWh in compared to 40 kWh by ball mill in plant 6, 26 kWh in plant 7 and 24.7 kWh in plant 9. Working experience with both VRM and roll press + ball mill by plants in Korea and Thailand revealed (in discussions) that the latter are more energy economic and also involve lesser breakdown repair and maintenance. Before concluding, it should be noted that, besides the technology level and operational parameters , surveillance and control management practices are also equally important for energy conservation. All the plants studied have ISO 9000 accreditation, and some have ISO 14000 accreditation also. It can therefore be presumed that control and supervision in all the plants are of world standard. Conclusion In conclusion , there may be a tendency to assess the performance of the plants from a comparison of their fuel and power efficiencies, based on the available data. This will however be a hasty and simplistic approach for any serious analysis, in so far as each plant has its own advantages or limitations and constraints - of vintage, location and of both internal and external factors controlling the options for modernisation. It w ill hence be more prudent to cite the plant-wise energy consumption data and the technology and operational parameters contributing to them. This approach has been followed in this study. The techno– economic scenario and outlook of the country have a . major impact upon the energy conservation status. We, therefore , cite here the best average fuel and f '