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 CO 2 emission. In this novel system, a pressure swing adsorption H 2 production process and a CO 2 cryogenic capture process are well integrated to gain comprehensive performance. In particular, through sequential connection between the pressure swing absorption (PSA) H 2 production process and the CO 2 capture unit, the CO 2 concentration of PSA purge gas that enters the CO 2 capture unit can reach as high as 70%, which results in as much as 90% of CO 2 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 CO 2 is avoided. The adoption of cryogenic energy to capture CO 2 enables direct production of liquid CO 2 at low pressure and thereby saves a lot of compression energy. Besides, partial recycle of the tail gas from CO 2 recovery unit to PSA inlet can help enhance the amount of hydrogen product and lower the energy consumption for H 2 production. As a result, the energy consumption for the new system's hydrogen production is only 196.8 GJ/tH2 with 94% of CO 2 captured, which is 9.2% lower than that of the coal-based hydrogen production system with Selexol CO 2 removal process and is only 2.6% more than that of the coal-based hydrogen production system without CO 2 recovery. More so, the energy consumption of CO 2 recovery is expected to be reduced by 20―60% compared with that of traditional CO 2 separation processes. Further analysis on the novel system indicates that synergetic integration of the H 2 production process and cryogenic CO 2 recovery unit, along with the synthetic utilization of energy plays a significant role in lowering energy penalty for CO 2 separation and liquefaction. The promising results obtained here provide a new approach for CO 2 removal with low energy penalty.

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