Performance assessment of a multiple generation system integrating sludge hydrothermal treatment with a small modular nuclear reactor power plant

A proposed integrated multiple generation (MG) system incorporating hydrothermal carbonization (HTC) of sludge with a small modular nuclear reactor (SMR) mPower aims to address sewage sludge (SS) treatment and freshwater scarcity issues in eastern coastal China, while providing a stable and reliable power production. The core of the MG system design involves the combustion of hydrochar to enhance the steam parameters of the SMR. By superheating and reheating the steam from the SMR, the system increases the total output power and the temperature of the extracted steam to supply the necessary heat for both sludge HTC and seawater desalination. When the hydrochar combustion rate is 20 t/h, the sludge feed rate is 44.21 kg/s, yielding a net system output power of 188.81 MW, with hydrochar contributing 24.24 MW of net power and a freshwater production rate of 62.88 kg/s. The evaluation results of the MG system are as follows: total system efficiency is 34.34 %, effective electric efficiency is 30.04 %, net sludge-to-electricity (STE) efficiency is 16.82 %, and the global-warming potential (GWP) per unit of sludge-generated electricity is 1.31 kg/kWh. Additionally, the system requires only 6.44 years to recover the initial investment. The exergy efficiency of the HTC process is 37.08 %, leading to a net STE exergy efficiency of just 7.77 %. Moreover, sensitivity analysis results indicate that increasing the hydrochar combustion rate, while sacrificing some efficiency, is beneficial for the MG system.