Migration And Catalytic Characteristics Of Biomass Alkalis During Coal And Biomass Co-pyrolysis

Co-gasification of coal and biomass is an effective way to alleviate energy crisis and reduce environmental pollution, thus it has a good prospect for development. However, biomass contains a significant higher amount of volatile alkali metals, it may enhance coal char gasification, on the other side lead to serious problems such as slagging, agglomeration, deposition, and heated side corrosion. Therefore, in order to reduce the negative effect caused by biomass alkalis and enhance catalytic effect of biomass alkalis, it is necessary to study the migration and catalytic characteristics of biomass alkalis during co-gasification. In this thesis, the release and migration characteristic of biomass alkalis during pyrolysis under different time was investigated firstly. Then the effect of coal char component and structure on biomass alkalis migration during co-pyrolysis was investigated in a fixed bed reactor. At last the catalytic properties of biomass alkalis migrated to coal char was investigated. The main results are drawn as follows:(1) Biomass alkalis mainly release into gas phase at devolatilization stage during biomass pyrolysis. It was also found that the release rate of potassium was slower than sodium during biomass pyrolysis. The alkalis content was nearly unchanged during Jincheng anthracite coal pyrolysis. At the early stage of coal / biomass co-pyrolysis, few biomass alkalis could migrate to coal char and the content of alkalis retained in biochar was almost unchanged. At the late stage of coal / biomass co-pyrolysis, the alkalis retained in biochar reduced gradually, and the alkalis migrated to coal char increased gradually.(2) Biomass alkali metals can migrate to coal char during coal / biomass copyrolysis process. The migration process of biomass alkalis during copyrolysis could be that volatile biomass alkalis was adsorbed on coal char surface firstly, and then reacted with coal char components. The volatile biomass alkalis mainly reacted with minerals and oxygen-containing functional groups in coal char.(3) The migrated biomass alkalis by reaction with oxygen-containing functional groups in coal char showed excellent catalytic effect, while the migrated biomass alkalis by reaction with minerals in coal char would lose their catalytic activity. The catalytic effect of biomass alkalis mainly depends on the mineral content in co-pyrolysis coal char. More specifically, the catalytic effect of biomass alkalis on coal char gasification become better with the decrease of mineral content in coal char.