Harnessing energy from domestic, municipal and industrial refuse

Problems and options for those organisations contemplating changes in their refuse-disposal policies and processes are reviewed. Controlled incineration is potentially the safest method of destroying the more toxic industrial wastes such as PCBs, which are especially persistent. The use of the resulting hot gases to produce superheated steam to drive a turbine and thereby generate electricity can be a bonus. Factors influencing the incineration of either raw municipal waste or refuse-derived fuels are discussed and two quite different types of incinerator design are described and their characteristics compared. The first type, which employs a reciprocating grate, is simple, effective and capable of burning untreated refuse, albeit with rather low combustion efficiencies. The second type, which uses a fluidised-bed incinerator, is also thought capable of burning untreated refuse, although the pelletised combustible components would be preferred. In addition, the fluidised bed requires more complicated control of the combustion reactions, with the result that higher combustion temperatures and efficiencies can thus be achieved. In essence, effective incineration of refuse requires highly sophisticated machinery, expensive pollution-control equipment and high standards of management. The incomplete incineration of wastes at temperatures below 1100°C can lead to the formation of dangerous end-products, for example, partially-burned PCBs can give rise to dioxins and di-benzofurans, which are also highly toxic substances.