Influence of O2 during Sulphation of KCl in a Biomass Fired CFB Boiler

Sulphur/sulphate containing additives, such as elemental sulphur (S) and ammonium sulphate ((NH4)2SO4), can be used for sulphation of the alkali chlorides (mainly KCl) during biomass combustion. A more efficient sulphation of KCl is achieved for ammonium sulphate compared to sulphur. The presence of gaseous SO3 is thus of greater importance than that of SO2. The concentration of O2 and the presence of combustibles could also have an impact on the sulphation efficiency when injecting ammonium sulphate. This paper is based on results obtained during co-combustion of wood chips and straw pellets in a 12 MW circulating fluidised bed (CFB) boiler. Ammonium sulphate was injected at three different positions in the boiler and they were in the top of the combustion chamber, in the cyclone inlet, and in the cyclone. The sulphation of KCl was investigated at three air excess ratios (λ= 1.1, 1.2 and 1.4). Several measurement tools including, IACM (on-line measurements of gaseous alkali chlorides), deposit probes (chemical composition in deposits collected), and gas analysis were applied.