Experimental study on hydrogen production by lignite gasification in supercritical water fluidized bed reactor using external recycle of liquid residual

Abstract

The technology of supercritical water gasification provides a novel way to convert high-moisture lignite to hydrogen-rich products directly. According to the energy analysis of the whole system for supercritical water gasification, the energy recovery of liquid residual played a key role in the energy efficiency improvement. Moreover, previous research findings showed that some chemical compounds such as phenols and formic acid contained in liquid residual can be recycled to increase the yield of hydrogen. Therefore, an external recycle of liquid residual was used in the supercritical water fluidized bed system to recover not only the heat energy but also the chemical energy by re-gasification of the liquid residual. Besides, the separation of gaseous products from the system enhanced the gasification process. Hydrogen production experiments were operated in this system and the influence of operating temperature 470–550°C, pressure 23–27MPa, concentration 3–35wt% and cycling flow rate 0–70g/min were studied. The experimental results showed that hydrogen yield and carbon gasification efficiency reached 32mol/kg and 82%, respectively, at 530°C.