Economic analysis on sewage sludge drying and its co-combustion in municipal solid waste power plant

Abstract

Co-treatment in municipal solid waste power plant has been deemed to one of the most suitable ways to handle sewage sludge. Economy of the co-treatment process is very concerned in the waste incineration plant. Thermal calculation of sewage sludge co-combustion was done. Four common sludge drying schemes was compared: flue gas drying, steam drying, electric heating drying in the waste incineration plant and in situ electric heating drying in the sewage treatment plant. Sensitivity analysis was also performed. When the water content was 30–40% and the absolute-dry sludge ratio was 2–3%, the boiler efficiency was reduced by 0.56–1.12% compared with the case without mixing sludge, and the power generation decreased by 0.2568–0.3767 MW in steam drying scheme and by 0.0037–0.0094 MW in other schemes. Net present value (NPV) of flue gas drying was the highest among the four sludge drying schemes, which was more than 20 ¥ million, while the scheme of electric heating drying in the waste incineration plant had the lowest NPV, which can't recoup the initial investment. Sensitivity coefficient of flue gas drying was smallest among different schemes, showing that the risk of this program was the smallest. Absolute-dry sludge ratio and unit subsidy for sludge treatment were sensitive factors for NPV in flue gas scheme, which had a sensitivity coefficient of 1.123–1.171 and 1.232, respectively. Operating parameters optimization of co-combustion of sludge was done and ways to improve economic efficiency was discussed.