High-temperature corrosion due to lead chloride mixtures simulating fireside deposits in boilers firing recycled wood

•A mixture containing PbCl2 and K2SO4 is more corrosive than PbCl2 mixed with SiO2.•Highly corrosive K-Pb-Cl mixture was formed when PbCl2 and K2SO4 was mixed.•Corrosion detected already below deposit's first melting temperature.•A solid phase with composition of K3Pb2(SO4)2Cl observed for the first time.•A solidus projection for KCl-FeCl2-PbCl2 mixture was calculated.

One of the biggest operational concerns in recycled wood combustion, is the risk for formation of low melting, corrosive deposits. The deposits present on low-temperature heat transfer surfaces (material temperature < 400 °C) are composed of alkali metals, chlorine, sulphur, heavy metals or, as is often the case, a mixture of these.K2SO4 is commonly regarded as non-corrosive, but there have been indications that K2SO4 may worsen the PbCl2 induced corrosion. Consequently, a more detailed study with these compounds was of very high interest. This paper reports the results obtained from 24-hour isothermal laboratory corrosion tests with PbCl2 mixed with either K2SO4 or SiO2. The tests were carried out at 350 °C using low alloy steel (16Mo3). The interaction between PbCl2 and K2SO4 was investigated in a furnace with a temperature gradient.As a result, a mixture of PbCl2 and K2SO4 is more corrosive than PbCl2 mixed with SiO2. Corrosion was noticed below the deposit's first melting temperature. However, for a mixture of FeCl2, KCl and PbCl2, the first melting temperature is below 350 °C which could explain the high oxidation rate observed below the first melting temperature of the deposit. A solid phase or a mixture of phases with the composition of K3Pb2(SO4)3Cl was observed in the tests with SEM/EDX for the first time.