Ammonium Sulphate and Co-Combustion with Peat – Two Strategies to Reduce Gaseous KCl and Chlorine in Deposits during Biomass Combustion

Combustion of a biomass with an enhanced content of chlorine (Cl) can result in operational problems including deposit formation and superheater corrosion. The strategies to reduce such problems include co-combustion and the use of additives. The positive effects of such measures are mainly due to sulphation of the alkali chlorides (KCl for biomass) to less corrosive alkali sulphates or capture of released alkali (K) in components such as potassium aluminium silicates. A mixture of wood pellets and straw pellets was fired in a 12 MW circulation fluidised bed (CFB) boiler. PVC was added to the fuel in order to achieve a further enhanced reference level of gaseous KCl during certain tests. Two strategies were applied to decrease the risk for superheater corrosion by reducing gaseous KCl and content of chlorine in deposits. The strategies were sulphation of KCl by injection of ammonium sulphate and co-combustion with peat. During co-combustion of biomass with peat both sulphation of KCl and capture of released K in ash components can be of importance. The results were evaluated by means of several advanced measurement tools including IACM (on-line measurements of gaseous KCl), deposit measurements (chemical composition in collected deposits, initial corrosion), ash analysis (chemical composition in fly ashes). The overall performance was better for ammonium sulphate, which significantly reduced gaseous KCl. Meanwhile almost no chlorine was found in the deposits. Only a minor reduction of gaseous KCl was obtained during co-combustion of biomass with peat although the chlorine content in the deposits was greatly reduced