The present invention relates to converting a fuel to combustible gas.
European patent application No. 80300003.3, publication No. 0013590, describes and claims a method of converting a fuel (which may be a liquid fuel or a solid fuel or a mixture of liquid and solid fuels) to a substantially inerts-free combustible reducing and/or synthesis gas product, the method comprising passing the fuel into a fuel conversion zone comprising a conversion bed of solid particles which are maintained at an elevated fuel conversion temperature and fluidized by a fluidizing gas which is passed into the bottom of the conversion bed and rises upwardly therethrough, the conversion bed comprising particles containing reactive calcium sulfate (CaSO.sub.4) which constitutes substantially the sole source of oxygen used in the conversion of the fuel, and the fluidizing gas passed into the bottom of the conversion bed comprising at least one gas phase and/or vapour phase substance which serves to promote and/or mediate the transfer of oxygen to the fuel and/or partially converted derivatives thereof from the CaSO.sub.4 (which is thereby reduced to calcium sulfide, CaS), the fluidizing gas being substantially free of (a) molecular oxygen, and (b) unreactive and/or inert materials which would dilute the combustible gas product.
In preferred embodiments, particles from the conversion zone are fluidized by molecular oxygen-containing gas in an oxidation zone separate from the fuel conversion zone so as to oxidize calcium sulfide in said particles to CaSO.sub.4, and particles which have been fluidized in the oxidation zone are returned to the fuel conversion bed for use in converting further quantities of fuel, the molecular oxygen-containing gas being in excess to substantially suppress the empirical reaction: EQU 2CaS+30.sub.2 .fwdarw.2CaO+2SO.sub.2 ( 1)
In preferred embodiments, the conversion bed contains particles comprising calcium oxide (CaO) to react with and fix sulfur from the fuel as CaS so that the combustible gas product has a low sulfur content, and particles from the conversion zone are preferably fluidized by a gas containing molecular oxygen in a regeneration zone so as to convert CaS to CaO with the liberation of sulfur as sulfur oxide (principally SO.sub.2) and/or elemental sulfur, and particles containing CaO are returned to the conversion bed directly and/or indirectly for use in reacting with and fixing sulfur from further amounts of fuel undergoing conversion.
Many multi-step processes, such as the fuel-conversion process as hereinabove referred to, employ a discrete vessel for each step. A drawback of this almost universal practice is that the flow of particles from one vessel to another is through pipes or conduits which for practical reasons must be so positioned that the flow pattern of particles within each vessel departs appreciably from the ideal.