Converting a fuel to combustible gas

Abstract

A sulfur-containing fuel is passed into a first fluidized bed (13) containing CaSO.sub.4 and CaO and an oxygen-transfer mediator (e.g. H.sub.2) whereby the fuel is converted to combustible gas (18), some CaSO.sub.4 being reduced to CaS and sulfur being fixed as CaS by reaction with CaO. Bed particles pass from the bottom layer of the first bed (13) into the bottom layer of the second bed (14) which is fluidized by air at conditions such that some, but not all of the CaS is selectively oxidized to CaSO.sub.4 with no liberation of sulfur moieties. Bed particles pass from the bottom layer of the second bed (14) to the bottom layer of a third bed (15) optionally after passage via a fourth bed (60, FIG. 2) between the second and third beds. In the third bed (15), particles are fluidized with air to convert CaS selectively to CaSO.sub.4 with no liberation of sulfur moiety whereby to raise the particles' temperature sufficiently above that of the first bed that particles passing from the bottom layer of the third bed into the bottom layer of the first bed provide sufficient sensible heat to maintain the fuel conversion temperature of the first bed (13). In the fourth bed (60, FIG. 2), particles are fluidized with air under such conditions that sulfur moiety is liberated, preferably at a rate which approximately equals the rate of sulfur-capture in the first bed (13) whereby to maintain approximately a constant amount of reactive CaO in the beds for sulfur-capture in the first bed (13).