Low pollution method of burning fuels

Abstract

A low pollution method of burning a fuel comprises gasifying the fuel in a gasifier bed containing particles which are fluidized by a fluidizing gas containing substantially no inert components. The resulting combustible gas is burned with air diluted with nitrogen to reduce NO.sub.x formation. In addition, NO.sub.x production from the nitrogen content of the fuel is reduced as a result of the gasification of the fuel to combustible gas before combustion with air. Preferably the gasifier bed contains CaO to fix sulfur from the fuel as CaS. In one embodiment, the gasifier bed (51) contains CaSO.sub.4 and the fluidizing gas contains H.sub.2, inter alia, which mediates the transfer to the fuel of chemically-bound oxygen from the CaSO.sub.4 (which is thereby reduced to CaS). Particles containing CaS are passed to an oxidizer bed (72) wherein they are fluidized by air. The CaS is exothermically oxidized to CaSO.sub.4 by extracting oxygen from the air which is thereby heated and substantially exhausted of oxygen. The hot CaSO.sub.4 is transferred from the oxidizer bed (72) to the gasifier bed (51) for gasifying further amounts of fuel, and the hot oxygen-depleted air is cooled by heat exchange (in 80) with boiler feed water, and then added to combustion air (in 69) to reduce the peak flame temperature when the combustible gas is burned at the burner (56) thereby mitigating NO.sub.x production from reactions in the flame between oxygen and nitrogen from the atmosphere. Because the fuel is gasified in the absence of diluents, the gasifier bed (51), combustible gas conduit (55), the burner (56) and gas circulation fans are of reduced sizes. The low pollution combustion of the fuel necessitates no modification of the furnace or boiler (84) and results in no increase in its operating costs or reduction in efficiency.