A Novel Coal-Based Hydrogen Production System With Low $CO2$ Emissions

In this paper, we have proposed a novel coal-based hydrogen production system with low $CO2$ emission. In this novel system, a pressure swing adsorption $H2$ production process and a $CO2$ cryogenic capture process are well integrated to gain comprehensive performance. In particular, through sequential connection between the pressure swing absorption (PSA) $H2$ production process and the $CO2$ capture unit, the $CO2$ concentration of PSA purge gas that enters the $CO2$ capture unit can reach as high as 70%, which results in as much as 90% of $CO2$ to be separated from mixed gas as liquid at a temperature of $−55°C$⁠. This will reduce the quantity and quality of cold energy required for cryogenic separation method, and the solidification of $CO2$ is avoided. The adoption of cryogenic energy to capture $CO2$ enables direct production of liquid $CO2$ at low pressure and thereby saves a lot of compression energy. Besides, partial recycle of the tail gas from $CO2$ recovery unit to PSA inlet can help enhance the amount of hydrogen product and lower the energy consumption for $H2$ production. As a result, the energy consumption for the new system’s hydrogen production is only $196.8GJ/tH2$ with 94% of $CO2$ captured, which is 9.2% lower than that of the coal-based hydrogen production system with Selexol $CO2$ removal process and is only 2.6% more than that of the coal-based hydrogen production system without $CO2$ recovery. More so, the energy consumption of $CO2$ recovery is expected to be reduced by 20–60% compared with that of traditional $CO2$ separation processes. Further analysis on the novel system indicates that synergetic integration of the $H2$ production process and cryogenic $CO2$ recovery unit, along with the synthetic utilization of energy, plays a significant role in lowering energy penalty for $CO2$ separation and liquefaction. The promising results obtained here provide a new approach for $CO2$ removal with low energy penalty.