Circulating fluidized bed combustion reactor with fly ash recycle

Abstract

A circulating fluidized bed combustion reactor and a process for combusting a solid hydrocarbon fuel in the same wherein fly ash recycling is utilized to regulate heat transfer and to minimize erosion of reactor operating components. The process comprises introducing a solid hydrocarbon fuel and an oxygen-containing gas into a combustion zone which is surrounded by a plurality of adjoining cooling tubes containing a circulating fluid; combusting the fuel in the presence of the oxygen-containing gas within a predetermined temperature range thereby forming hot exhaust gases containing solid particles; discharging the hot exhaust gases containing the solid particles from the combustion zone and cooling the exhaust gases by indirect heat exchange against the cooling tubes; separating the resultant cooled solid particles into at least a first portion which is recycled into the combustion zone and a second portion having an average particle size smaller than the first portion; separating the second portion into a gas stream substantially free of particles and a concentrated stream of particles; recycling the concentrated stream of particles into the combustion zone at a rate sufficient to maintain the predetermined temperature range within the combustion zone and exhausting the gas stream which is substantially free of solid particles.