COMBUSTION CHARACTERISTICS OF SEWAGE SLUDGE USING A PRESSURIZED FLUIDIZED BED INCINERATOR WITH TURBOCHARGER

摘要

A new type of sewage sludge incinerator that combines a pressurized fluidized bed combustor and a turbocharger driven by flue gas was proposed. This plant has four main advantages. (1) The combustion rate can be improved since the oxygen partial pressure in the combustor is increased by the pressurization. The incinerator volume can be substantially smaller than that of an atmospheric incinerator with the same incineration capacity. Thus, the amount of supplementary fuel can be reduced because the heat loss from the incinerator can be decreased. (2) Because the maximum operating pressure is 0.3 MPa (absolute pressure), which matches the pressure required for the turbocharger, a pressure vessel is unnecessary. (3) An energy savings of more than 40% can be achieved compared with a conventional plant since the FDF and the IDF are unnecessary. (4) Because steam in the flue gas becomes the working fluid of the turbocharger, the turbocharger can generate surplus air in addition to the combustion air. The surplus air can be used in other processes, such as aeration, in sewage works. We constructed a demonstration plant (4.32 t/d scale) at a sewage works in Japan. The operation and combustion characteristics of the plant were clarified, and the design data of a commercial plant was obtained. As a result, the steady operation exceeded 600 hours in total. Consequently, about 40% of CO2 emissions originating from electric power consumption and supplementary fuel is expected to be reduced annually compared with emissions from a conventional plant at an incineration capacity of 100 tons/d. CO, NO_x and N2O emissions in the flue gas were less than half those of a conventional plant due to the effect of the pressurization. Therefore, this proposed incinerator can realize energy recovery and saving as well as a low environmental impact.