Waste Heat Recovery in Cement Plants by Fluidized Beds
Publication Date: 2012-Jul-17
The IP.com Prior Art Database
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WASTE ~AT RECOVERY IN CEMENT PLANTS BY FLUIDIZED BEDS by C. B. Thunem,1 Fraley,2 and
The cement production process produces several high temperature waste gas streams. Traditional approaches to recovery of this waste heat utilize waste heat recovery boilers oject description along with ~h~ economic
analysis is presented.~
¯ The authors describe the integration of a fluid Bed cooler and a cir- culating fluidized bed comhustor (CFBC) into a cement process. Heat re- covered along with supplemental coal firing supplies all electrical power for the plant. The fluid bed cooler recovers heat from the alkali bypass of a flash calciner. The circulating fluidized bed combustor uses waste cooling air fro~ the clinker cooler as preheated combustion air for the CFBC.
The economic model includes capital cost, operating cost, and con- struction schedule. Results include net cash gain and internal rate of return along with a sensitivity analysis.
Stanley Consultants, Inc., Muscatine, lowa.
M. W. Kellogg, R&D Center, Houston, Texas. i149
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Not too many years ago energy costs and efficiencles were virtually ignored by corporate decision makers. The prevailing attitude was "my business is manufacturing and my capital is best spent improving and ex- panding my manufacturing capacity." With energy now contributing a sig- nlflcant fraction of the overall product cost in many industries, there is general recognition that control of fuel and electric costs is just as important to remaining competitive as is improving manufacturing methods.
This is particularly true in the cement industry.
Cement manufacture consists of mining and grinding rocks, melting them to form clinkers, then grinding those clinkers to a powder. Through re-~ covery of waste heat and inclusion of technology such as flash calciners, the industry has reduced the fuel requirement per ton of cement from about 7 ~illion Btu per ton in old plants to less than 3 =illion Btu per ton in the most modern plants.
While these efficiency improvements have dramatically reduced the fuel required for cement manufacture, electricity cost, as a percentage of prod- uct cost has continued to rise. Most attempts at controlling cost of elec- tricity have focused on load management through computerized monitoring and control of electric usage.
Ironically, a large number of cement plants used to produce their own electricity. The electricity was usually generated through recovery of waste heat. However, they abandoned this capability in the late 60s and early 70s. The on-slte generation of electricity was eliminated for a variety of reasons. One of the main reasons was the reluctance of electric
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utilities to allow tie-ins between the industrial electric generator and the utility grid. This occasionally required operation of the cement plant simply to produce electricity. These problems, along with a relatively low power cost, encouraged managers to leave ele...