Thermodynamic modelling of hydrogen production in sorbent-enhanced biochar-direct chemical looping process

Hydrogen (H-2) has been widely considered the clean energy carrier of choice for emerging renewable energy generation technologies. However, H-2 is a secondary fuel mainly derived from natural gas. Over the past decades, research on developing H-2 production technology that reduces carbon emissions has gained momentum due to increasing atmospheric levels of carbon dioxide (CO2). This study proposed a new sorption-enhanced (SE) and biochar-direct (BD) integrated chemical looping system for hydrogen production from biomass gasification, using iron oxide as an oxygen carrier, calcium oxide (CaO) as a CO2 adsorbent, and biochar as a reducing agent. In this study, a thermodynamic model with the proposed sorbent-enhanced biochar-direct (SE-BD) chemical looping hydrogen production (CLHP) process has been developed using an Aspen Plus simulator. The effect of important process parameters, including the reactor temperature, the syngas composition, and the molar feeding ratios of iron oxide/syngas, biochar/syngas, and CaO/syngas on the performance in terms of product gas composition, iron oxide conversion, H-2 yield, H-2 purity, and reactor heat demand has been evaluated. The simulation results show that the addition of biochar significantly enhances the overall hydrogen yield compared to the conventional CLHP process; whereas the addition of CaO-sorbent was found to significantly improve the H-2 purity. Moreover, the exothermic lime carbonation further reduced the thermal requirements of the process. In addition, this thermodynamic simulation demonstrates that the sorbent-enhanced biochar-direct chemical looping hydrogen production (SE-BD-CLHP) process can achieve a wide operating window for complete iron oxide (Fe3O4) reduction by adjusting the CaO and biochar feeding ratio.