Release of inorganic trace elements during gasification of wood, straw, and miscanthus

The release of alkali metals, chlorine, sulphur and heavy metals during gasification of four different types of biomass was investigated. The samples were two types of wood (clean and waste wood), miscanthus, and straw. Experiments were conducted in two different setups; in a tube furnace which could be considered as batch experiments, and in an atmospheric lab scale fluidised bed reactor with continuous fuel feed. Molecular beam mass spectrometry was used for on-line analysis of the hot gas. The experimental results reveal that the release of inorganic species like HCl, KCl and H2S is strongly dependent on other inorganic constituents in the samples, e.g. Si and Ca. In general, the release from herbaceous biomass is much higher than from woody biomass. With the exception of zinc released from miscanthus at temperatures above 900 °C, no heavy metals could be detected. The measurements were accompanied by equilibrium calculations using FactSage 5.5 and the FACT database which are in relatively good agreement with the experimental results.

► On-line analysis of hot gas by molecular beam mass spectrometry.
► Release of HCl, KCl, and H2S strongly depends on ash composition.
► Release from herbaceous biomass much higher than from woody biomass.
► Very low concentration of gaseous phosphorous species due to formation of phosphates.
► Almost no significant release of heavy metals.