Abstract
A conceptual design of an energy recovering system from sewage sludge incineration is proposed. This system consists of a pressurized fluidized bed combustor, a turbo charger, and a heat exchanger for preheating of combustion air. Electricity consumption can be reduced by producing high pressure air which can be used as the aeration air in the sewage treatment process. In order to know the combustion characteristics of the sewage sludge under the elevated pressure condition, combustion tests of actual wet sewage sludge were carried out by using laboratory scale pressurized fluidized bed combustor. Combustibility of the sewage sludge was good enough and almost complete combustion was achieved in the combustion of the actual wet sludge. CO emission and NOx emission were marvelously low especially during the combustion of wet sewage sludge regardless of high volatile and nitrogen content of the sewage sludge. However, nitrous oxide (N_2O) emission was very high. Hence, almost all nitrogen oxides were emitted as the form of N_2O. From these combustion tests, we judged combustion of the sewage sludge with the pressurized fluidized bed combustor is suitable, and the conceptual design of the energy recovering system is available.
