Construction of iterative algorithm and economic optimization analysis of co-combustion of sewage sludge with coal

Abstract

ABSTRACT To govern the sewage sludge, which restricts the development of urbanization, the co-combustion of sewage sludge in coal-fired power plants is considered one of the most appropriate methods. Two methods, flue gas dehydration and electric heating dehydration, are used to dry sewage sludge to the target moisture content. And the economic impact of the two methods was evaluated on coal-fired power plants. The boiler efficiency and fuel consumption are obtained by the thermal balance calculation. When the anhydrous sludge ratio was 2% and the water content was 30%, the fuel consumption was 81.11 kg/s and the boiler efficiency was 91.32%. As the water content and the anhydrous sludge ratio increase, the fuel consumption gradually increases, while the boiler efficiency gradually decreases. And the net present value is used to evaluate the economic impact of the co-combustion of sewage sludge in coal-fired power plants. Among them, the maximum NPV value of the flue gas dehydration scheme with a sludge mass ratio of 3% and a moisture content of 40% reached 1163.34 million. Furthermore, the sensitive factors that affect the net present value are obtained as the anhydrous sludge ratio and government subsidies through sensitivity analysis. Combined with the combustion characteristics in the boiler, the recommended range for the moisture content of the sludge is 30%~40%, and the recommended range of anhydrous sludge ratio is 3–5%.