A modified two-stage sorption-enhanced steam gasification of biomass process for H2 production

Abstract

A modified two-stage sorption-enhanced steam gasification of biomass (SESGB) process for H2 production is proposed and studied using a dual fixed-bed system. This process can be controlled independently for each stage, enabling the catalytic gasification and reforming processes to proceed at their respective optimal temperatures. In this process, CaO is alternately circulated, i.e., when the CaO sorbent in the second stage needs to be regenerated it is replaced by the CaO acting as a catalyst in the first stage, which reduces the regeneration frequency of CaO by half. In the first stage, tar can be almost completely removed by catalytic thermal cracking of CaO. In the resulting tar-free atmosphere, the CaO sorbent in the second stage can maintain a rapid carbonation rate. As a result, the concentration and yield of H2 can be as high as 70.5 vol% and 600.7 mL/g-SB, respectively, while the sorbent/carbon ratio is as low as 0.82. The conventional one-stage SESGB process, by contrast, requires sorbent/carbon ratio as high as 3.82 to obtain syngas with H2 concentration above 70 vol%. Compared with the one-stage process, this two-stage process is more effective in removing tar, increasing H2 concentration and yield as well as reducing CaO consumption.