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.