Use of CO₂ in Pressurized, Fluidized Bed Gasification of Waste Biomasses

This research discusses the results of experiments performed on a large-scale gasification installation to determine the influence of total system pressure and partial pressure of CO₂ on the efficiency of conversion and the quality of the produced gas. The three tested feedstocks were bark, lignin and a blend of bark and wheat straw, while softwood pellet (SWP) was used as a reference fuel. A mixture of O₂/CO₂/H₂O was used as a gasification agent. The tests were devised to validate the previously proposed process parameters, verify whether similar ash agglomeration problems would occur and compare the thermal behaviour of the feedstocks converted in close-to-industrial process conditions. An understanding of the effect of using CO₂ for gasification was further deepened, especially regarding its influence on the yield of H₂ and temperature profiles of the fluidized bed. The influence of gasification pressure was predominantly visible in higher yields of all hydrocarbons (including CH₄) and lower overall production of producer gas. At the process development unit (PDU), all tested feedstocks were converted at similar process conditions and no signs of potential bed agglomeration could be noticed. This opposes the findings observed in smaller-scale bubbling fluidized bed (BFB) tests. The discussion behind these discrepancies is also presented.