Two strategies to reduce gaseous KCl and chlorine in deposits during biomass combustion — injection of ammonium sulphate and co-combustion with peat

Combustion of a biomass with an enhanced content of chlorine can result in operational problems including deposit formation and superheater corrosion. The strategies applied to reduce such problems include co-combustion and the use of additives. In this work a mixture of wood pellets and straw pellets was fired in a circulating fluidised bed boiler. Two strategies were applied to decrease the risk of superheater corrosion by reducing gaseous KCl and content of chlorine in deposits: 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 potassium in ash components can be of importance. The results were evaluated by means of IACM (on-line measurements of gaseous KCl), deposit probe measurements (chemical composition in collected deposits, initial corrosion) and ash analysis (chemical composition in fly ashes). The best overall performance was achieved with ammonium sulphate, which significantly reduced KCl. Meanwhile almost no chlorine was found in the deposits. Only a minor reduction of gaseous KCl was obtained during co-combustion although the chlorine content in the deposits was greatly reduced. The resistance to initial corrosion was improved during both injection of ammonium sulphate and co-combustion with peat.