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Energy and Environment, 1995

ISBN:
1-56700-052-5 (Print)

FLUIDIZED BED COMBUSTION OF WASTE CARBON FROM THE ANODE PRODUCTION. TECHNICAL AND ENVIRONMENTAL FEASIBILITY OF ENERGY PRODUCTION

M. Valk
Twente University of Technology, Department of Mechanical Engineering, P.O. Box 217, 7500 AE, Enschede, The Netherlands

E.A. Bramer
Dept. of Thermal Engineering, University of Twente, The Netherlands

Abstract

The combustion process in a bubbling fluidized bed of a waste material from the production of anodes for the aluminium industry is investigated and optimized. The waste gases from its bake furnaces are cleaned by a dry sorption system operating with a mixture of dust made from the remainder of used anodes (butts) and lime. The amount of this dust is about 20,000 metric tons per year, it consists mainly of carbon, contains few volatiles and has a low reactivity. Besides this the dust contains sulphur, chloride and fluor. As the calorific value is high a. study is made, including experimental research, to burn this dust for the generation of electrical power and steam A research program is executed in a 1MW-AFBC test facility with the objective to burn this dust in a fluidized bed with a sufficiently high combustion efficiency and low emission levels: SO2<200, NOx<200 and F<5 mg/Nm3. A stable in-bed combustion with combustion efficiencies up to 88 % is obtained by pelletization of the dust mixed with 8 % calcium hydroxide. This calcium hydroxide in the pellets provides, at bed temperatures below 1150 K, the required sulphur and fluor retention. The required NOx emission level is reached by staged combustion together with injection of urea in the freeboard.