Cement Energy and Environment

ropeway, depending upon the distance of haulage. From the energy consumption data for transportation , it can be inferred that longer ropeway or belt ( 15 km and more) increases the relative energy consumption in mining and transport (plants 2 and 5) up to 8-10 kv\lh/tonne of material in comparison to shorter distances (4 to 6 km) with energy consumption range of 2 to 5 kVvh/tonne of material (plants 3 to 6) . Such higher energy consumption is however partially compensated through higher transportation capadty,the material being size-reduced. iii) Crushing - In-pit crushing by mostly impactors and double rotor swing hammers is found to be the common practice and most energy-economic. Plant I adopted semi-mobile roll crusher to compensate for higher energy consumption arising from longer haulage (9 km). iv) Raw meal grinding– A composite picture of energy consumption emerges because of varied , mostly hybrid technology adopted by most plants. adopting Plants solely plants studied, except plants 8 and 9 with high Bond index of limestone (8.5 to 9.5), all others use softer limestone (Bond index ranging from 6.5 to 7.5). The fineness of ground raw material is within 2 to 3.5% retained on 212 urn sieve. v. Kiln system and cooler - The kiln-preheater– precaldner-cooler systems in the 9 plants studied provide a complex picture with vcuying degrees of modernisation. Obviously plants with 6-stage preheaters (PH), low pressure - drop (LP) twinstring cyclones, and, separate line calciners (SLC) or pyrorapid calciners (plant 1 [kiln3], 8[kiln2], 9[kiln2], plant 7) show the lowest fuel consumption - 690 to 710 kcal/l<g dinker. These plants are also fitted with the latest generation pyrostep coolers of different reputed brands, providing more than 68 per cent recuperating efficiency. The process and operational efficiency of the plants are manifest in the exit gas temperature of PH and cooler vent. It is around 300°c and VRM for raw meal grinding (plants 7 Panoromic view ot Jechon Cement Plant, South Korea 250° - 280°( respectively, and 9) show lower energy consumption (15 to 20 kwh/tonne of material). Plants adopting a mix of both VRM andball mill, or a roll press - ball mill combination(plants 1,2,3 and 6) show a much higher range of energy consumtion - 20 to 26 kVvh/tonne of material. A notable exception is plant 4 having both ball mill and VRM, but consuming only 15 kWh/tonne. With subdued production, the plant operated only the VRM. Plants having only ball mills (plants 5 and 8) show much higher energy consumption - 25 to 30 kVvh/ tonne of material . No doubt, grindability of the material and fineness of grinding have significant impact on the energy consumption. Among the 7 for plants 7,8 and 9, while the values are much higher, 3oo>C and 35(YlC, respectively, for plants I and 2. Plants 3 and 4 show similar PH exit gas temperature but much lower cooler vent exit gas temperature - 19QlC to 22rPC, because of effident modern cooling system. Plants 5 and 6 show similar PH exit gas temperature, while the cooler vent gas temperature varies from 2oo>C (plant 6) to 3500C (plant 5). The former has conventional cooler while the latter has pendulum cooler. All the plants (except plant 8) use imported high calorific value (6500 to 6800 kcal/kg)-low– ash coal from Australia, China, Indonesia and South Africa. In Taiwan, the relatively high grid-power cost (equivalent of Rs. 3.86 per kVvh/h during peak