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Incineration of industrial organic wastes in a circulating fluidized bed combustor Wong, Siu Ching Polly


The purpose of this study was to examine the feasibility of circulating fluidized bed incineration technology for solid organics wastes disposal. The study was divided into two parts: an applications study and a fundamental study. The applications study investigated the combustibility of selected industrial solid organic wastes and the effects of key operating parameters, i.e. temperature, excess air, primary-to-secondary air split ratio, suspension density and superficial gas velocity, on incineration performance of these wastes in a circulating fluidized bed incinerator. The fundamental study investigated the destruction of selected organics, i.e. chloroform and sulphur hexafluoride, as well as the hydrodynamic behaviour of gases and solids in the circulating fluidized bed incinerator. The incineration tests were carried out in the UBC pilot circulating fluidized bed combustor system. Results from the applications study showed that increases in incineration temperature and in excess air tend to improve the combustion efficiency of the pilot CFB system, but tend to increase NO[sub x] emissions. Increases in primary-to-secondary air split ratio, suspension density and superficial gas velocity tend to enhance the gas and solids mixing behaviour. As a result, combustion efficiency is improved while NO[sub x] emissions are increased. The chemical nature, i.e. volatile, sulphur and ash contents, and the physical nature, i.e. particle size, of the wastes have a direct impact on their combustion behaviour and emissions. In general, the UBC pilot circulating fluidized bed combustor achieved high combustion efficiencies, in excess of 99.9 %, for the solid wastes, although high CO emissions were observed. CO emissions may be reduced by addition of an insulated afterchamber system to the pilot system. Limestone addition was effective for in-situ sulphur capture. Incineration of the solid wastes in general led to a substantial reduction in solids residue. Results from the fundamental study showed that hydrodynamics within a circulating fluidized bed is very complex. Secondary air injection ports, baffles and reactor exit affect the hydrodynamic behaviour of solids and gases within the circulating fluidized bed. The UBC pilot circulating fluidized bed combustor system achieved destruction and removal efficiencies of essentially 100 % (at 870°C) and 97.05 % (at 915°C) for chloroform and sulphur hexafluoride respectively. The destruction of organics depends on both unimolecular and bimolecular reactions. Hence, the use of sulphur hexafluoride, a thermally stable compound, as a surrogate test burn compound results in a conservative prediction in the destruction efficiency of an incineration system. Thus, incineration temperature alone cannot ensure good combustion and destruction performance in an incinerator. The performance of an incineration system and its emissions are also affected by the nature of the wastes (chemical and physical) as well as by the operating conditions.

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