Simulation and process analysis of hydrogen-rich syngas production by chemical looping reforming of biomass pyrolysis volatiles based on decoupling strategy

Abstract

The biomass chemical looping gasification process involves various complex reaction processes, including pyrolysis, gasification, and reforming, which occur within the same reaction space. These reactions exhibit intricate interactions, posing challenges for achieving targeted control. Consequently, some issues arise, such as low carbon conversion, high tar yield, and difficulties in attaining auto thermal operation. The biomass pyrolysis chemical looping re-forming process, employing the decoupling strategy, aims to achieve an independent regulation of pyrolysis and reforming reactions, thereby mitigating the issues mentioned above. The process underwent simulation using the Aspen Plus software, and the model’s validity was confirmed by comparing it with the results of pyrolysis experiments. Using the established process model, the impact of pyrolysis reactor temperature, fuel reactor temperature, and steam-to-biomass mass ratio on process performance was examined. The results demonstrate the effective predictive capability of the established process model regarding the distribution of pyrolysis products within the temperature range of 400−600 ℃. As the pyrolysis temperature rises, the syngas yield exhibits a generally increasing trend, reaching its peak at 550 ℃ with a value of 1158.98 Nm3/kg biomass. At a pyrolysis temperature of 600 ℃, the heat demand of the reforming reactor is adequately met by the exothermic reactions of pyrolysis char and oxygen carrier oxidation without any surplus energy. Elevating the fuel reactor temperature augments the syngas yield but diminishes the H2-to-CO ratio and energy efficiency of the syngas while also necessitating a substantial increase in the circulation rate of bed material for achieving auto thermal operation. Steam serves as an effective regulator for controlling the H2-to-CO ratio in syngas. The pyrolysis chemical looping reforming process generates syngas with an H2-to-CO ratio of 2.0 when the steam-to-biomass mass ratio is 0.45, lower than the ratio needed for the biomass chemical looping gasification process. Consequently, taking into account the syngas yield and process performance, the recommended operating conditions for the pyrolysis chemical looping reforming process are as follows: a pyrolysis reactor temperature ranging from 550 to 600 ℃, a fuel reactor temperature of 700 ℃, and a steam-to-biomass mass ratio of 0.45.

Keywords

• chemical looping
• gasification
• biomass
• aspen plus
• decoupling