High temperature corrosion of boiler waterwalls induced by chlorides and bromides. Part 1: Occurrence of the corrosive ash forming elements in a fluidised bed boiler co-firing solid recovered fuel

In waste fired boilers high temperature corrosion has often been attributed to zinc and lead chlorides. In addition, bromine induced high temperature corrosion has been earlier observed in a bubbling fluidised bed (BFB) boiler co-firing solid recovered fuel (SRF) with bark and wastewater sludge. In Part 1 of this work a measurement campaign was undertaken to determine the occurrence of Cl, Br, Zn and Pb in the fuel, in the combustion gases as well as in the deposits on the boiler waterwalls. It was observed that Cl, Br, Zn and Pb originate to a large extent from the SRF, they are vaporised in the furnace, and may form waterwall deposits. This, complemented by fluctuations between oxidising and reducing atmosphere resulted in rapid corrosion of the waterwall tubes. Concentrations of Cl, Br, Zn and Pb in the fuel, in the furnace vapours and in the deposits are reported in this work. As there is lack of published data on the bromine induced high temperature corrosion, laboratory scale corrosion tests were carried out to determine the relative corrosiveness of chlorine and bromine and these results will be reported in Part 2 of this work. Furthermore, the forms of Cl, Br, Zn and Pb in the combustion gases as well as in the waterwall deposits were estimated by means of thermodynamic equilibrium modelling and these results will also be discussed in Part 2.