A biomass power generation system combined with sewage sludge incineration

Sewage sludge is a biomass resource that should be used effectively. At present, approximately 70 % of the sewage sludge in Japan is incinerated, so the rate of energy recovery from sewage sludge could increase drastically if energy were recovered during sludge incineration. To improve the heat balance, a power generation system using sewage sludge incineration has been developed that uses advanced sludge dewatering and small-scale steam power generation systems. In this study, we constructed a demonstration plant that could treat 35 t of wet sludge (dewatered, so the water content was 70 %) each day at an actual sewage treatment plant. We adopted a step grate type stoker furnace and used waste heat from sewage sludge incineration to generate electricity. We collected data for the power generated and consumed, from which we were able to estimate the greenhouse gas emissions. Using this method, we were able to generate more than 100 kW of electricity in each of the four seasons. The results of a case study based on an input of 24 t ds/day show that, compared with the conventional system, the amount of energy required to generate electricity can be reduced by about 70 %. Further, the test system produced surplus power.