Combustion characteristics of sewage sludge in an incineration plant for energy recovery

A new type of sewage sludge incinerator that combines a pressurized fluidized bed combustor and a turbocharger driven by flue gas was proposed. In this study, the operation and combustion characteristics of a demonstration plant were clarified, and the design data for a commercial plant were obtained. The steady operation exceeded 600 h in total. CO, NO_x, and N₂O emissions in the flue gas were less than half those of a conventional plant. At an incineration capacity of 100 t/day, an energy savings of approximately 50% can be achieved compared with a conventional plant because the forced draft fan (FDF), the induced draft fan (IDF) and the feed water pump are unnecessary. Also, pressurization allowed reduction of the combustor volume, so about 25% of supplementary fuel can be reduced. Consequently, CO₂ emissions originating from electric power consumption and supplementary fuel is expected to be reduced by about 40% annually compared with emissions from a conventional plant; in addition, the cost of fuel and electricity can be reduced by 23 million yen. Therefore, this advanced incinerator for sewage sludge can realize energy recovery and savings as well as a low environmental impact.