FLUIDIZED-BED INCINERATION OF WASTE MATERIALS

This review discusses the status and the development of fluidized-bed technology in relation to the disposal of the different types of wastes in an environmentally acceptable manner. Wastes comprising solids, liquids and gases, and their mixtures have been adequately handled in fluidized-bed incinerators in combustion and co-combustion modes. The available literature is mostly on bubbling bed but the recent trend has been also to employ the circulating-bed incinerators. The significant advantages of fluidized-bed incinerators over conventional incinerators include their compact furnace, simple design, effective burning of a wide variety of fuels, relatively uniform temperature, ability to reduce emission of nitrogen oxide and sulfur dioxide gases, high pyrolysis rate of the waste material, high rate of solid particle oxidation as the charred surface of the waste is continuously abraded by the inert material, good mixing of solids and gases, and the fact that the gases are continuously replenished on the burning solid surface which enhances the rate of gas-phase combustion reactions. A wide variety of wastes have been burned in the fluidized-bed incinerators including municipal solid waste, agricultural waste, coal mine wastes, waste oils and sludges, wood wastes, petroleum refinery wastes, petrochemical wastes, sulfite liquors, sewage sludges, contaminated solids, and various hazardous and lethally poisonous materials. In this review several of the commercial and pilot-plant fluidized-bed incinerators have been briefly described and their findings reported. One pilot-plant is discussed in detail to bring out the general difficulties of design and an effective appreciation of the technology. These results, while promising, point to the need for further investigations to be able to successfully commercialize this technology particularly for those materials whose thermal destruction give rise to toxic emissions and whose stringent control is mandatory to avoid serious environmental pollution problems. Procedures for computing carbon combustion efficiency are discussed as are the procedures that may be employed to establish the quality of bed fluidization from the history of temperature and pressure fluctuation records, and from the computed values of different statistical functions which result.