Trace element behavior in the fluidized bed gasification of solid recovered fuels: A thermodynamic study

Gasification of biomass and recycled fuels is of particular interest for the efficient production of power and heat. Trace elements present as impurities in the product gas should be removed very efficiently. The objective of this work has been to develop and test thermodynamic models for the reactions of trace elements with chlorine and sulfur in the gasification processes of recycled fuels. In particular, the chemical reactions of trace elements with main thermochemical conversion products, main ash components, and bed and sorbent material are implemented into the model. The possibilities of gas cleaning devices in condensing and removing the trace element compounds are studied by establishing the volatilization tendency of trace element compounds in reducing gases. The results obtained with the model are compared with the measured data of trace elements of gasification experiments using solid recovered fuel as feedstock. Some corresponding studies in the literature are also critically reviewed and compared. The observed discrepancies may be attributed to differences in thermodynamic databases applied and experimental arrangements. The method of removing gaseous trace elements by condensation is already in use in the 160 MWth waste gasification plant in Lahti, Finland.