Influence of pressure and CO 2 in fluidized bed gasification of waste biomasses

An autothermal fluidized bed reactor was used to research the influence of pressure (0 – 2 bar g ) on the gasification process of different types of biomasses. The tested feedstocks were bark and lignin while softwood pellet was used as a reference fuel. A mixture of O 2 /CO 2 /H 2 O was used as a gasification agent. The impact of the application of CO 2 on the yield of H 2 in product gas was determined. Resulting product gas was characterized by a high content of CO which makes its use for applications based on chemical synthesis very difficult without extensive upgrading or supply of H 2 from external sources. CO 2 proved to improve carbon conversion efficiency (CCE) of the gasification process and to be an option for its chemical sequestration (negative carbon footprint). A slight modification of conventional indices used to evaluate efficiencies of gasification systems (CCE and water/ carbon ratio) was proposed, to take into account the impact of the additional source of carbon fed into the reactor. The increase of system pressure led to changes in the composition of the product gas in line with predictions of Le Chatelier ’ s principle. The influence was predominantly visible in higher yields of CH 4 and lower overall production of product gas. For higher hydrocar- bons (CxHy ), the trend was unclear. A set of stable gasification parameters were achieved for each pressure level and a standard gasification temperature of 850 °C, except for gasification of lignin performed at 2 barg . A proposed explanation for the problem is the combined effect of the increasing concentration of ash in the fluidized bed and its low characteristic melting temperatures. Due to the obtained experimental findings, a new ash agglomeration index was formulated