A novel conceptual solar-driven biomass chemical looping gasification (BCLG) system was theoretically and experimentally investigated. The air and fuel reactors in the state-of-the-art BCLG systems were replaced with a steam reactor and a directly irradiated solar fuel reactor in the proposed system, respectively. Metal oxides were circulated between the steam reactor and the solar fuel reactor as the oxygen carrier. The solar-driven BCLG exhibits two advantages over its conventional counterparts: (1) the syngas yield is raised as the high-temperature process heat is provided by high-flux solar radiation rather than biomass combustion, and (2) two streams of fuels, hydrogen and syngas, can be mixed to achieve a desirable carbon-to-hydrogen ratio for carbon-neutral liquid fuel synthesis via FischerâTropsch process.
A zero-dimensional thermodynamic model was built to determine the theoretical solar-to-fuel energy conversion efficiency. First law and second law analyses were conducted to examine the effect of various pivotal parameters, including the reaction temperatures in both reactors, the ratio of oxygen carrier to biomass, the solar concentration ratio, and the heat recovery effectiveness, on the overall performance of the proposed system. A proof-of-concept experiment was also conducted in a cavity-type packed-bed solar reactor under concentrated solar radiation emitted by Singaporeâs first 28 kWe high flux solar simulator. The results indicated that the solar chemical looping gasification of biomass is a viable method for producing syngas and hydrogen in separate streams, which can be subsequently combined in a specified proportion for downstream chemical processing.
