Two-zone fluid bed combustion or gasification process

Abstract

A method of operating a fluidized bed system in a single vessel, typically as a combustor system for power or steam generation burning high-sulfur coal or as a gasifier for high-sulfur coal, which comprises forming an entrained fluidized bed in a first space region containing a first solid bed particle component, such as sand or hematite ore containing over 90% Fe.sub.2 O.sub.3, forming in a limited space region partially within the first region a dense fluidized bed containing a second solid bed particle component, such as larger particles of the hematite, both first and second component particles essentially comprising a material having long-term physical and chemical stability in the fluidized bed system so as to be substantially nonagglomerating and not subject to substantial attrition therein, effecting division of the dense fluidized bed into upper and lower zones, providing a recirculation path such as through a cyclone separator and particle reservoir for the first particle component from the first space region through the upper zone of the dense fluidized bed in the more limited space region, operating the fluidized bed system at a velocity such that the second component particles are effectively retained in the dense fluidized bed in the more limited space region, whereas the first component particles recirculate and interpenetrate through the upper zone thereof commingling with the second component particles, and maintaining different temperatures in the upper and lower zones of the dense fluidized bed. Typically, the temperature of the upper zone of the dense fluidized bed is conducive to capture of sulfur gases by a sorbent while a high temperature in the lower zone of the dense fluidized bed is maintained to be conducive to combustion of fuel and calcination of sorbent (for combustors) or gasification of fuel (for gasifiers).