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Abstract: In Part 1 of the work a measurement campaign was carried out to determine the occurrence of corrosive ash components in a bubbling fluidized bed (BFB) boiler combusting solid recovered fuel (SRF). It was found out that the main ash-forming elements that had been vaporized and subsequently condensed from the gas phase were Na, K, S and Cl together with minor amounts of Zn, Pb, Cu, and Br. Both, Cl and Br were found in the corrosion front of the waterwalls prior to the measurement campaign. In this work, the forms of ash forming elements in the combustion gases and in the waterwall deposits of the examined boiler were predicted by means of thermodynamic equilibrium modeling. Laboratory tests were also carried out to estimate the degree of corrosion of boiler steels under bromine containing deposits. A mixture of ZnBr2 and K2SO4 was selected for high temperature lab-scale corrosion testing since Zn, Br and K as well as sulfates were present in the deposit and it was possible to compare these results to previously published results with ZnCl2–K2SO4 mixtures. The comparison showed that more severe material degradation was caused by the ZnBr2 containing salt than by the corresponding chloride and corrosion was significant already at 400°C. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: Iron and aluminium sulphates are added to processes producing sewage sludge (SWS), and SWS also contains aluminium silicates. These compounds can destroy alkali chlorides and prevent Cl deposition on superheaters. Sulphation of chlorides requires formation of SO3 in the furnace. Raw and digested SWSs were mixed with a fuel containing bark and recycled fuel (REF). Combustion experiments were conducted with a pilot-scale bubbling bed reactor, and concentrations and deposition of critical elements (Cl, Na, K, S…) in the furnace were measured. Change of the iron and aluminium sulphates added to the SWS to phosphates and hydroxides evidently reduced the power of the sulphur to form SO3. Nevertheless, addition of SWS to the biomass feedstock effectively decreased alkali chloride concentration and Cl deposition, and the alkali sulphates found in the fine fly ash confirmed the contribution of sulphation to alkali capture. The importance of aluminium silicate reaction in alkali capture was indicated. [Copyright &y& Elsevier]