Incineration of wastes in novel high-efficiency tumbling and rotating, fluidized bed incinerator

At the present time, the sewage treatment plants in the United Kingdom produce about 25,000,000 t of sewage sludge each year at a concentration of 4% solids. New regulations in the United Kingdom forbid sea dumping, and in the near future new incinerators will be required to dispose of about 5,000,000 t per year. The research program at the Sheffield University consisted of design and construction of a small-scale cylindrical rotating fluidized bed incinerator with an inside diameter of 200 mm and an axial length of up to 200 mm. The fluidizing medium was silica sand (0.6-0.7 mm) and the bed depth 30-50 mm. The rotational speed of the bed varied between 100 and 1,000 rpm (which produced 1-100 g loading). Coal, oil, sewage sludge, and chicken manure (biomass) were burnt in the bed at temperatures between 700 degrees and 900 degrees C. Measurements of heat transfer rate, bed temperature, and exhaust gas composition were carried out over a range of operating conditions. The influence of rotational forces on basic fluidization characteristics (pressure drop, minimum fluidization, and particle mixing) were also investigated on a perspex model. The results obtained from the research work demonstrated that the rotating fluidized bed incinerator can produce considerably higher combustion intensities (i.e., process intensification), has a wide turn-down range (i.e., versatile), has low toxic emissions (i.e., clean technology), and has a more easy and rapid start-up than conventional stationary fluidized bed incinerators. Other advantages of the system include: good mixing, simpler fuel injection, low thermal inertia, and good heat transfer rates. Other potential applications for this system include boilers, open cycle gas turbines, and combined gas/steam cycles.