Thermodynamic and safety analysis for hydrogen production in a supercritical water gasification system of coal by multi-oxidizers distribution

Coal supercritical water gasification (SCWG) for hydrogen production technology is highly prospective due to the clean and efficient treatment process. A single oxidation reactor heating method is usually used in existing work limiting the efficient and stable operation of the system due to high component temperatures. This paper proposed the heat supply strategy of multi-oxidation reactor and heat exchanger layout to improve the system performance for the realization of reasonable matching of material flow and energy flow in each stage of the system. The improved system reduced the maximum temperature of the oxidation reactor from 1550 °C to 850 °C, and the system exergy efficiency and H2 yield reached 49.30 % and 101 kg/h (at the mass ratio of coal to water of 1:10), respectively. The exergy flow results showed that the improved system exergy loss was concentrated in the oxidation reactor (34.00 %) heat exchanger (28.86 %), cooler (19.07 %), and gasification reactor (9.70 %). Exergy efficiency increased as the mass ratio of coal to water increased to the maximum exergy efficiency of 53.50 %. As the temperature increased from 600 °C to 675 °C, the exergy efficiency decreased from 53.10 % to 48.70 %. System adjustability analysis showed that the system can be stabilized over a 40 %–100 % range of feed fluctuations. This work may provide an optimization strategy for efficient operation and dynamic safety regulation of H2 production by SCWG technology.