Cement Energy and Environment

Jllateria/ Ba/auce C0 2 Em ission from a 111 iII ion tonne cement plant. The main reaction in the rotary ki ln is decarbonat ion, Stoichiometrically ( 40 + 12 + 48) 100 CaO + C0 2 - heat 56+44 56+ 44 Therefore from kiln reactions, we get 44 tonnes ofC0 2 for every I00 tonnes ofCaCOr We require 4500 tonnes of limestone to produce 3000 tonnes ofclinker per day. For I 00 tonnes of CaC0 3 , we get 44 tonnes of C0 2 • For 4500 tonnes of CaC0 3 , we get, 44 x 4500 = 1980 tlday 100 So the C0 2 emi ssion from decarbonation reaction is 1980tlday. From ful!l Coal is burnt in ki ln as the kilns reaction is endotherm ic, so C0 2 is also emitted by burning coal. The reaction and calculations are as follows: C+O 2 Stoicl1iometrically 12 + 32 44 So 12 tonncs of carbon gives rise to 44 tonnes of C0 2 . We consume 360 tonnes of coal per day. However, taki ng the carbon in fue l to be 60%, but that the vo lati les also contribute C0 2 • 75 X 44 X360 C0 2 evolved = = 990 t/day 100 X 12 Therefore total C0 2 from the kiln exhaust = 1980 + 990 = 2970 t/day Avai lable C0 2 per day is. say 3000 tonnes. 18 Urea reactions 34 tonnes of Nl-1 1 + 44 tonnes of C0~60 tonnes of urea 44 tonnes of COz is required to produce 60 tonnes of urea But 3000 tonnes ofC0 2 is available So, amount of urea that can be produced 60 X 3000 = 4090 t/day 44 Ammonia required for producing 3682 tonnes of urea. 4090 X 34 60 23 17 tonnes /day Merits and Economics The total cost of manufacture is expected to run into a few hundred crore rupees and the return on investment is yet to be worked out. This process will considerably bring down the C0 2 levels in atmosphere coming from current manufacture. ft s ma in advantages are mentioned below: • Reduced C0 2 release into the atmosphere from cement plants. • Economic utilisation of C0 2 for manufacture ofurea, a nitrogenous fertili ser. But the economic feasibility of hydrogen manufacture by electrolysis ofwater needs to be examined first. Also the commercial viabi Iity ofthe project as awhole remains to be proven. Conclusion The process outlined above is commended for detailed techno-economic feas ibility study by R&D personnel and entrepreneurs. If proved success ful. it wi II mark a synergy between cement and urea manufacture industri es for the larger benefit of the planet. • + II