AIR-CO2 GASIFICATION OF BIOMASS PELLETS IN A PILOT-SCALE DOWNDRAFT GASIFIER

摘要

Biomass has the highest potential to contribute to a sustainable energy supply. Gasification is a process thatconverts carbonaceous materials, such as coal or biomass, into a rich gas in carbon monoxide and hydrogen by reactingthe raw material at high temperatures with a controlled amount of oxygen and/or steam. The use of air as gasifying agenttypically leads to a reduction of the CV of the syngas due to the dilution with nitrogen. The authors carried out a series oftest in a pilot-scale downdraft gasifier to identify the feasibility of CO2 gasification, partially replacing air with CO_2 as agasifying agent, using Miscanthus pellets to perform the experiments. The results showed that, between 650°C and750°C, the presence of CO_2 did not lead to a more efficient conversion of the carbon in the fuel. In fact, the injection ofCO_2 did not promote the CO formation in the gas, due to the initial high amount of CO_2 that was injected. This led to adecrease in the temperature of the process and to a low gasification rate for all the gasification reactions and for the char.Moreover, the char was not properly activated by the CO_2 and its high concentration also inhibited the CO formation.Furthermore, the high CO_2 concentration played a higher role than the catalytic effect of the alkali metals on the surfaceof the solid (char), leading to a reduction of the gasification rate.