Performance of Low-Rank Coal in Atmospheric Fluidized Bed Combustion. Technology Transfer Report

摘要

This report presents test data generated at GFETC and discusses the implications of this data in regard to the technical and economic feasibility of using low-rank coals in the AFBC. Atmospheric fluidized bed combustion offers a number of potential advantages over conventional pulverized coal combustion due to the intense turbulence in the fluidized bed and long residence times of solids in the bed without a long linear flow path. Advantages of the AFBC include flexibility to handle varying fuels, sulfur capture by limestone, high combustion efficiency, compact combustor size, lower NO/sub x/ emissions, and reduced slagging and fouling problems. Low-rank coals with high alkali-to-sulfur ratios offer a significant additional advantage: the ability to absorb significant sulfur on the alkaline ash. Results verify that AFBC is particularly well suited for the direct combustion of low-rank coals. With combustion temperatures above 1450 exp 0 F at 20% excess air or higher, the combustion efficiencies while burning low-rank coal were found to be above 98%, with efficiencies above 99% for most tests. The CO emissions were very low, typically below 0.05 lb/MMBtu or 50 ppMv. Overall heat transfer coefficients to water-cooled tubes while burning low-rank coals were comparable to those obtained with other fuels in AFBC, or 20 to 60 Btu/h-ft exp 2 - exp 0 F. These are considerably higher than those obtained in conventional coal-fired systems which are typically 5 to 15 Btu/h-ft exp 2 - exp 0 F. Factors influencing heat transfer included mass velocity, bed particle size, bed temperature, and ash recycle. (ERA citation 11:006936)