Corrosivity of flue gases during co-firing Chinese biomass with coal at fluidised bed conditions

Five Chinese fuels (one AlSi rich coal with low S content (LSC), one sulphur rich coal with low AlSi content (HSC), two straws and one sawdust) were thoroughly analysed and burned alone and blended in a bench-scale fluidised bed reactor. Flue gases and mass flows of the elements in the fine fly ash (< 10 μm, including condensed vapours) were analysed. In addition, chemical equilibrium calculations were carried out. When burnt alone, both straws produced significant concentrations of alkali chlorides, which cause corrosive deposits on superheaters. Both coals were capable of destroying alkali chlorides during co-firing. The destruction was based mostly on sulphation with HSC, and alkali aluminium silicate formation dominated with LSC. Bed agglomeration occurred in most of the experiments, but it will be discussed elsewhere.