Proposal and evaluation of a hydrogen and electricity cogeneration system based on thermochemical complementary utilization of coal and solar energy

In this study, an efficient and clean hydrogen and electricity cogeneration system based on thermochemical complementary utilization of coal and solar energy is proposed, and the feature is that steam-to-methane ratio in the high-temperature syngas generated by supercritical water coal gasification is more than 3:1. Thus, without injecting new steam into syngas and only further increasing the temperature will provide very suitable reaction conditions for hydrogen production by steam methane self-reforming in syngas, which has lower energy consumption relative to a conventional reforming process. Through thermochemical complementary utilization, the solid fuel coal and solar energy are first converted into methane-rich syngas by supercritical water coal gasification, then methane-rich syngas and solar energy are converted into hydrogen-rich syngas by steam methane self-reforming, realizing the cascade utilization of chemical energy. Hydrogen is separated from the hydrogenrich syngas by pressure swing adsorption, and the purge gas is introduced into the gas turbine to generate electricity. The results show that the total energy and exergy efficiencies of the integrated system are 49.37% and 49.84%, respectively, which increased by 4.91 and 4.97 percentage points relative to the reference system. In the integrated system, the hydrogen output is 452.40 MW (13582 kg/h, 28 bar), the electricity output is 209.47 MW, and the chemical energy of the syngas is 978.49 MW, which is approximately 49.14% higher than that of 656.09 MW in the reference system. Energy utilization diagram revealed that the key to the improved performance in the integrated system lies in the reduction of exergy destruction during the fuel conversion and heat exchange, which decreased by 3.76 and 6.68 percentage points relative to the reference system, respectively. This work provides a competitive option for large-scale hydrogen and electricity cogeneration systems.

Automated summary

In this study, an efficient and clean hydrogen and electricity cogeneration system is proposed, which utilizes coal and solar energy through thermochemical complementary utilization. The system achieves high-temperature syngas generation through supercritical water coal gasification, allowing for hydrogen production with lower energy consumption by steam methane self-reforming. The integrated system shows improved energy and exergy efficiency, higher hydrogen and electricity output, and enhanced utilization of chemical energy compared to the reference system. The reduction of exergy destruction during fuel conversion and heat exchange is identified as the key to the improved performance.