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.