Performance assessment of a hydrothermal treatment-based sewage sludge-to-electricity system integrated with a coal-fired power plant

A system has been proposed that integrates the hydrothermal treatment of sewage sludge with coal-fired power generation to explore the commercial application of hydrothermal carbonization technology and enhance the efficiency of sludge-to-energy conversion. In the design scheme of the hybrid system, the sewage sludge needs to undergo three processes - hydrothermal carbonization, mechanical dewatering, and thermal drying - to transform into the hydrochar product with lower moisture content. This product is then transported through pipelines to the boiler system and co-combusted with coal, generating high-temperature steam to drive the turbine for power generation. When the hydrochar blending ratio reaches 10 %, the feed rate of sewage sludge is 51.19 kg/s, and the net output power of the system is 618.5 MW, with hydrochar contributing a net power of 54.13 MW. The evaluation results are as follows: the net sludge-to-electricity efficiency can reach 32.45 %, a reduction of 0.34 kg/s in CO2 emissions, and the system can recover the initial investment in only 7.72 years. Besides, the influence of hydrochar co-firing ratio on the system is also investigated. Taking into account factors such as boiler safety and system economy, the co-firing ratio should be controlled within the range of 7.5 % to 25 %.