Dispersion and ultra-fast reaction of calcium-based sorbent powders for SO 2 and air toxics removal in coal combustion

Abstract

This paper addresses the various fundamental issues related to the reaction and dispersion of sorbents, and the impact of developments in the sorbent science and technology on the design and operation of CFB combustors. The central role of sorbents in fluidized-bed combustors, the current state of the art in sorbents for SO 2 capture, and their influence on NO x and other pollutant removal are highlighted. The existing CFB designs and the current sorbent technology are capable of achieving up to 90% sulfur capture. Sulfur removals of greater than 93%, expected to be mandated in the near future, require considerable increase in Ca/S ratios and lead to increased NO x , reduced combustion efficiency, and other operating problems. The current CFB combustor design and operating parameters such as temperature, sorbent particle size etc., can be optimized for best possible sulfur and NO x control using limestone sorbent. There is a need, and a definite scope for improving the sorbents to augment sulfur capture without increasing sorbent consumption. This paper also elaborates the development of high reactivity limestone sorbents and their exceptionally high sulfur capture rate and capacity. The kinetics of sulfur capture dictates smaller particle sizes for higher rate of reaction. Thus, the analyses of sorbents of size less than 50 μm with consideration of their application towards sulfur capture during coal combustion is attempted. A viable option for operating CFBs with smaller sorbent particles at higher temperatures is examined. Current challenges such as improved sorbents development for advanced combustion/gasification systems, capture of trace air toxics and other metallic species, and improved particle separation systems for CFB operation, are also discussed.