Thermodynamic analysis of the novel chemical looping process for two-grade hydrogen production with CO2 capture

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 an oxygen carrier and calcium oxide (CaO) as a carbon dioxide (CO2) adsorbent. In the SECLR-WS process, the biogas feed is partially oxidized using iron oxide and CO2 is captured by CaO in the fuel reactor (FR) to produce H2-rich syngas. The iron oxide is re-oxidized in the steam reactor (SR) to generate a high-purity H2 stream and CaO is regenerated in the calcinator. The simulation of the SECLR-WS process was based on a thermodynamic approach and was performed using an Aspen Plus simulator. The effects of key parameters such as the steam feed to the FR to methane (SFR/CH4) and iron (II, III) oxide (Fe3O4) to CH4 (Fe3O4/CH4) molar ratios on the process performance in terms of H2 yield and purity, and CH4 conversion were investigated. The results showed that the H2 yield, H2 purity in the FR, and CH4 conversion could be improved by increasing the SFR/CH4 and CaO/CH4 molar ratios. A total H2 yield of 3.8 and a H2 purity in the FR of 97.01 mol% can be obtained at the FR and SR temperatures of 610 and 500 °C, and SFR/CH4, CaO/CH4, Fe3O4/CH4, and SSR/CH4 molar ratios of 2.2, 1.66, 1, and 2.87, respectively. The molar concentration of carbon monoxide (CO) in the high-purity H2 stream could be reduced by increasing the pressure in the SR and the amount of CO2 in the biogas feed stream negatively affected the performance of the system. In addition, increasing the Fe3O4/CH4 molar ratio can improve the heat demand in the FR.