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 PSA H₂ production process and the CO₂ capture unit, the CO₂ concentration of PSA purge gas that entering 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 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 to 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 196.8 GJ/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. What’s more, the energy consumption of CO₂ recovery is expected to be reduced by 20–60% compared to 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.