Cement and Energy

- BURNING ALTERNATIVE FUELS IN ROTARY KILNS Introduction B urning residues as alternative fuels in rotary kilns presents numerous advantages : • Lower energy costs. • Improved incineration conditions, since combustion in rotary kilns takes place at a substantially higher temperature than when burning in a conventional incineration plant. This means that toxic compounds are destroyed more effectively. • No residuals unlike as in incineration industry, since slag and ash get absorbed in the clinker and do not affect cement quality provided their percentage is kept limited, whereas residuals from an incineration plant have to be landfilled. Combining knowledge and experience in incineration plants and conventional combustion equipment for rotary kilns, integrated solut~ons have been developed for alternative fuel firing in rotary kilns. Alternative fuels Various types of alternative fuels can be used in rotary kilns depending on local supply availability (Table 1), each one with its specific influence on the flame pattern. Low calorific value waste fuels must be limited to a part of the total heat release as they lower flame temperature. On the other hand, the NO, emission can be reduced. A compromise may be reached when firing high and low calorific value waste fuels simultaneously enabling control of both the calcining process and NO, emissions. Therefore very adaptable combustion equipment is needed to allow firing with any kind of residue combination, depending on the supply available, whilst still maintaining' kiln productivity, clinker quality and environmental standards. Table - 1 Alternative Fuels Gaseous Landfill gas Pyrolysis gas Liquid High viscosity oils or tars Pasty wastes Waste oil Engine, hydraulic, used oils Solvents Waste water including organic components Greases Solid Animal powder Bark Asphalt Shredded plastics Shredded paper/cardboard Fluff Sludges (wate( treatment, paper) Slurry Impregnated woodship Wood wastes (furniture, packing ind.) Sawdust Rice husks Biomass Car carpet pieces Tyres, rubber wastes Rotoflilm"' burner for t.r.aditional solid and liquid fuels. 7