Proposal and evaluation of a hydrogen-power-heat cogeneration system using solar-driven supercritical water co-gasification of sludge and coal

Supercritical water gasification is a clean sludge treatment technology. However, the high moisture content of sludge results in this technology achieving only harmless treatment of sludge, without realizing its resource utilization. To address this limitation, this work proposes a hydrogen-power-heat cogeneration system using solar-driven supercritical water co-gasification of sludge and coal. The system is characterized by adding high heating value coal to low heating value sludge, enhancing the heating value of the gasification feedstock and establishing a supercritical water sludge-coal co-gasification technology, thereby achieving synergistic resource utilization of sludge and coal. Concurrently, concentrated solar energy is employed to provide the reaction heat for the co-gasification process through thermochemical complementation, thereby synergistically converting the gasification feedstock and solar energy into hydrogen-rich syngas, and enabling hydrogen separation and storage as well as efficient utilization of purge gas. The baseline system integrates a photovoltaic system with a conventional sludge-coal co-gasification process supplied by syngas oxy-combustion heat. The results indicate that, with identical energy input, the hydrogen chemical energy output of the cogeneration system reaches 64.67 MW, while the solid oxide fuel cell power output is 19.36 MW accounting for 8.84 % of the total energy input. System energy efficiency is 61.14% and exergy efficiency 47.22%, exceeding the baseline by 12.66 and 19.00 percentage points. The key improvement stems from lowered exergy destruction in heat exchange and energy conversion processes, with reductions of 4.73 and 3.19 percentage points, respectively. This work presents an innovative approach for synergistic solar energy and sludge-coal utilization.