Hydrogen production from biogas by the combined process of chemical looping water splitting and sorption enhanced reforming process: process analysis and design

Abstract

The integrated sorption-enhanced chemical looping reforming and water splitting (SECLR-WS) process was proposed for hydrogen (H2­­) production from biogas using iron oxide as the oxygen carrier and calcium oxide (CaO) as a carbon dioxide (CO2) adsorbent. The simulation of the SECLR-WS process was based on a thermodynamic approach and was performed using an Aspen Plus simulator. The sensitivity results showed that the H2 yield (mole of H2/mole of CH4), H2 purity in the fuel reactor (FR), and CH4 conversion could be improved by increasing the steam feed to the FR to CH4 (SFR/CH4) and CaO to CH4 (CaO/CH4) molar ratios. The molar concentration of carbon monoxide (CO) in the high-purity H2 stream could be reduced by increasing the pressure in the steam reactor (SR). The H2 yield in FR of 3.11 and in SR of 0.66 were obtained at the optimal operating condition at TFR of 606.9 oC, SFR/CH4, SSR/CH4, Fe3O4/CH4, and CaO/CH4 molar ratio of 2.35, 2.33, 0.92, and 1.94, respectively. The performance of the optimal designed SECLR-WS process was compared with a sorption-enhanced chemical looping reforming (SECLR) and a chemical looping water splitting (CLWS) processes. The thermal efficiency of the optimal designed SECLR-WS process was further improved by heat exchanger network design based on a pinch analysis. In addition, the energy and exergy analyses of the optimal designed SECLR-WS process were conducted to identify the part of the inefficient energy usage of SECLR-WS process. The results indicated that the highest exergy destruction was occurred in the FR and SR due to the occurrence of several reactions in these units. The exergy efficiency of 76.83 % and 75152.8 kW exergy destruction can be obtained from the SECLR-WS process.