Application of the ChlorOut concept in a waste wood fired CFB boiler

Abstract: Boilers converting from sulphur rich fossil fuels to alkali and chlorine rich bio fuels often experience an increased super heater corrosion. This is partly due to the increased formation of KCl during combustion of bio fuels. The problem could, for instance, be handled with a sulphur containing additive to the fuel or to the flue gases. This diploma work was carried out at Vattenfall Power Consultant AB and it focuses on the so-called ChlorOut concept. The ChlorOut concept has been developed by Vattenfall to minimise deposit formation and corrosion. It consists of IACM, an instrument for on-line measurements of gaseous alkali chlorides, and a sulphate-containing additive that converts alkali chlorides to less corrosive alkali sulphates. The sulphate-containing additive is often ammonium sulphate, (NH4)2SO4. The main objective was to evaluate a ChlorOut installation in a CFB (Circulating Fluidised Bed) boiler in Germany. This boiler burns waste wood and has experienced super heater corrosion problems. IACM measurements showed very high levels of alkali chlorides in the flue gas. Results showed that adding (NH4)2SO4 reduced KCl measured by IACM and also the chlorine content in deposits in the super heater region. The deposits were collected by using temperature controlled steel rings on a deposit probe. The fast response for KCl from IACM enables controlling the flow of (NH4)2SO4 when fuel quality varies. The results indicated a reduction of the chlorine induced corrosion in the boiler when using the ChlorOut concept.