Cement, Energy and Environment

industry. Considering these components means unlocking both environmental and social benefits and cost-effective measures. A few potential interventions which describe these opportunities are discussed in this section. Re-use of waste heat Cement clinker production operates at very high temperature, thus generating of a lot of heat. Typically, the excess heat is captured and re-used in either used for drying of raw materials like limestone, clay or alternative fuels, or in the production of power. Dry process cement plants offer nearly 40% of heat energy to be tapped from flue gases of the pre-heater and cooler. In other words, this quantity of heat ranges from 180-250 kcal/kg clinker at a temperature of 300-400 C. Moreover, heat of 80-130 kcal/kg clinker is also available at a temperature range of 200- 300 C from the exhaust air of grate cooler (National Productivity Council, 2017). Reusing such high quantities of waste heat can effectively produce up to 25% of power consumption of a cement plant without changes in kiln operations (National Productivity Council, 2017). Reuse of waste heat potential in Indian cement industry is estimated at around 500 MW, while the installed capacity till date is only about 275 MW (National Productivity Council, 2017). Such a gap provides huge opportunity for adopting relevant technology and contributing to the overall cost reductions. Use of alternative raw materials Additive raw materials such as fly ash and slag can be used to replace clinker in cement manufacture. Such substitution not only manages power plant ash and conserves limited natural resources like limestone and coal, but also reduces greenhouse gas emissions. While fly ash in the manufacturing process improves both durability and workability of cement. ground blast furnace slag improves its chemical resistance and provides higher long-term strength. However, logistics barriers between cement plants and other plants often dissuade cement manufacturers to adopt such substitution. Studies estimate that CO emission reduction of 2 approximately 2.2-6 kg/tonne of cement for every 1% increase in blended cement production is possible, keeping all other parameters constant (National Productivity Council, 2017). While Bureau of Indian Standards currently allows a maximum addition of 35% of fly ash in Portland Pozzolana Cement (PPC) considering other requirements such as setting time are met, actual addition of fly ash in PPC ranges from 15% to 32% with an average of 28%, thereby showing room for possible increment in use of additive raw materials (National Productivity Council, 2017). Decarbonated alternative calcium containing raw material can be considered as a potential solution to substitute limestone and reduce CO emission. Such 2 substitution offers a dual advantage as not only the emissions linked to decarbonation of raw materials, but those linked to the fuel consumed for such decarbonation can also be eliminated. Few examples for such decarbonated alternative raw materials include blast furnace slag, limited ash, coal ash, concreter crusher sand, aerated concrete meal and lime residues from sugar industry. But there are a few factors that primarily determine the use of these alternatives: § composition of the conventional raw materials at the considered plant; § local availability and cost of decarbonated raw materials; § their composition and particularly their silica, alumina, magnesia, sulphur, VOC or trace 10