FLUIDIZED-BED COMBUSTION OF ALTERNATIVE SOLID FUELS - STATUS, SUCCESSES AND PROBLEMS OF THE TECHNOLOGY

Fluidized bed combustion can be used for energy production or incineration for almost any material containing carbon, hydrogen and sulphur in a combustible form, whether it be in the form of a solid, liquid, slurry or gas. The technology's fuel flexibility arises from the fact that the fuel is present in the combustor at a low level and is burnt in the mass of a thermally inert bed material (typically this is limestone if sulphur capture is required, otherwise sand). However, fuel flexibility must either be built into the design of the combustor or alternatively the FBC system must be tailored for a specific fuel or combination of fuels. In addition, the designer must consider issues like heat release patterns, ash characteristics (particularly if the ash has any potential for agglomeration or fouling of heat transfer surfaces or blockage of the return valve in the case of a circulating FBC) and any special requirements of the fuel such as the need for sulphur or HCl capture. This paper surveys the literature on some of the more important alternative fuels and also makes specific recommendations about problems or major issues with those fuels. Particular attention is given to the use of FBC for petroleum coke, coal wastes, wood pulp sludges, and biomass residues. These fuels are emphasized because of their current economic importance, particularly in North America.