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The Evaluation of Midwestern Coal and Limestone in Coal-liquid Fuels for Fluidized Bed Combustors.

Brown-RC; Buttermore-WH; Foley-JE
Proc 12th Int'l Conf Slurry Technology 1987 :49-56
Fluidized-bed combustion (fbc) of coal in limestone beds effectively reduces so2 emissions from high-sulfur coal, but the relative inconvenience and high capital cost and maintenance cost of burning solid fuel rather than oil or gas limit its potential industrial and commercial adoption. Combustion of coal-water mixtures (cwm) in fluidized beds may overcome these obstacles. Solid fuel handling costs are replaced by those for a fluid, and the limestone additive can be combined with the coal in the fluid mixture, further reducing handling costs. The fundamental character of cwm combustion may also be an advantage. Attempts to burn cwm in conventional oil burners have been frustrated by the tendency of the coal particles to agglomerate and burn as a single large particle. This tendency may be an advantage in fbc units, because the larger particles help avoid fuel losses by elutriation of fuel from the bed. Use of dry fuels in fbc results in coal fines being lost with the fly ash. Agglomeration of fines in cwm may promote more efficient carbon burnup. Preliminary tests using the product from a hammermill pulverizer, without the use of additives, gave a reasonably stable and pumpable cwm. Carbon conversion was 85 to 99 pct without fly ash reinjection. Sulfur capture exceeded 80 pct at a ca/s ratio of 1.3, Using coarsely ground limestone as a component in the cwm. Attempts to use a lime sludge waste product from a water treatment plant showed that the sludge was not a suitable sorbent.
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MIR 7-90
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Proc. 12th Int'l Conf. Slurry Technology, 1987, PP. 49-56