A NOVEL COAL-BASED HYDROGEN PRODUCTION SYSTEM WITH LOW CO_2 EMISSIONS

摘要

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 H2 production process and a CO_2 cryogenic capture process are well integrated to gain comprehensive performance. In particular, through sequential connection between the PSA H2 production process and the CO_2 capture unit, the CO_2 concentration of PSA purge gas that entering 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 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 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 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. What's more, the energy consumption of CO_2 recovery is expected to be reduced by 20-60% compared to that of traditional CO_2 separation processes. Further analysis on the novel system indicates that synergetic integration of the H2 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.