Formation and behaviour of chlorine compounds during biomass combustion

The combustion of herbaceous biomass leads to significant emissions of chlorine compounds and to depositions in the boiler due to the chlorine content in the fuel. In the present work, the formation and behaviour of chlorine compounds during combustion has been investigated. It is shown that chlorine, bound as KCl in the biomass, is released as KCl vapour at temperatures above 750 degrees C. In the boiler section, KCl condensates which leads to emissions of aerosols in the flue gas. Furthermore, deposit formation in the boiler occurs which is mainly attributed to thermophoresis. Beside KCl, HCl is formed in lower concentrations. At high temperatures in the furnace, HCl can form Cl-2, which can lead to the formation of chlorinated hydrocarbons. However, only low concentrations of chlorinated hydrocarbons are found in the flue gas at good combustion conditions. The combustion of herbaceous biomass leads to comparable low PCDD/F emissions as wood although it has a far higher chlorine content.