Gasification characteristics of steam exploded biomass in an updraft pilot scale gasifier

•Decomposition temperatures were lowered in TGA (thermo gravimetric analysis).•Boudouard reaction is effective in gasification.•Water gas shift reaction is suppressed in steam gasification.•Significantly high CO content was obtained in syngas.•More CH4 and more phenolic tar were observed in syngas.

Pretreatment of biomass becomes more and more important due to the large scale application of biomass having low energy density. In this paper, steam exploded biomass pellets (Black pellets) and unpretreated biomass pellets (Gray pellets) were gasified with air and steam at an updraft HTAG (High Temperature Agent Gasification) unit.Decomposition characteristics of pellets were first analyzed with TGA (thermo gravimetric analysis). Early decomposition of hemicellulose and cellulose were seen with Black pellets around 241 °C and 367 °C respectively. Introducing CO2 led comparatively high mass loss rate with Black pellets.Gasification of Black pellets resulted in syngas with high CO and hydrocarbon contents while Gasification of Gray pellets resulted in high H2 content of syngas. LHV (lower heating value) of syngas was high around 7.3 MJ/Nm3 and 10.6 MJ/Nm3 with air gasification and steam gasification respectively. Even with significantly low syngas temperature with gasification of Black pellets, only slightly high total tar content was seen compared to that of Gray pellets gasification. Phenolic compounds dominated the tar composition.In general, steam gasification of Black pellets seems to be more feasible if syngas with high energy value is desired. If higher H2 yield is preferred, gasification of unpretreated pellets likely to be more attractive.