Air-CO2 and oxygen-enriched air-CO2 biomass gasification in an autothermal downdraft gasifier: Experimental studies

Abstract

The mounting CO2 emission and rapid depletion of fossil fuels are two significant challenges for sustaining growing energy requirements and keeping the environment clean. Biomass gasification using CO2 as a gasifying agent may be one of the alternative techniques to tackle such emerging problems. CO2 behaves as an inert gas at low temperatures and can be converted to CO at high temperatures. In the present study, air-CO2 and oxygen-enriched air-CO2 biomass gasification are successfully conducted in the autothermal reactor. The impacts of varying concentrations of CO2 and oxygen in the gasifying agent on the performance of the gasifier are analyzed. The CO2 content in the gasifying agent is varied from 0 to 45 vol% at two different oxygen concentrations (21 and 35 vol%). The reactor used is an Imbert-type downdraft gasifier with a thermal capacity of approximately 10 kW. The results reveal that the yield of CO in the producer gas increases compared to air gasification resulting in a higher heating value of the producer gas. However, the average temperature in the gasifier reduces with increasing CO2 percentage in the gasifying agent. Upon increasing the O2 fraction from 21 to 35 vol%, while keeping 30 vol% CO2 content constant, CO content is found to upsurge from 23.96 to 31.37 vol%. The inclusion of CO2 inside the gasifier promotes the endothermic Boudouard reaction that causes the conversion of CO2 into CO.