Juho Lehmusto

Studies on the Partial Reactions Between Potassium Chloride and Metallic Chromium Concerning Corrosion at Elevated Temperatures

Recovery of energy from biomass by combustion has become important due to reduction of detrimental CO2 emissions. It has been suggested that the reaction between KCl released during combustion and the protective Cr2O3-layer is the one responsible for starting the complex series of corrosion reactions. In this work, the overall reaction between KCl and Cr was studied through reactions with compounds such as Cr2O3, K2CrO4, and K2Cr2O7 known to participate in the overall reaction or to be formed during it. The reactions were studied in synthetic air with a DTA/TGA apparatus. Under the conditions studied, both KCl and K2CrO4 reacted with pure, metallic Cr as well as with Cr2O3. In the case of Cr, Cr2O3 was formed via the formation of K2CrO4. In reactions including Cr2O3 as reactant also K2Cr2O7 was detected. However, when used as a reagent, K2Cr2O7 reacted with neither Cr nor Cr2O3.

The Effect of Pretreatment on the Corrosion Resistance of Superheater Materials

In order to improve the power production efficiency of biomass-fired boilers, power plants must be operated at higher steam temperatures than nowadays. One of the main factors hindering the rise of the steam temperatures is the corrosive nature of the flue gases and fly ash towards the superheaters. In this study, the high-temperature corrosion resistance of three commercial superheater steels exposed to potassium chloride was compared. The focus was on the effect of pre-oxidation on the protective properties of different steels, whereupon various variables were used during the pre-oxidation.

Detailed Studies on the High Temperature Corrosion Reactions between Potassium Chloride and Metallic Chromium

Recovery of energy from biomass and various waste–derived fuels by combustion has become important due to reduction of detrimental CO2 emissions. Biomass does, however, release significant amounts of chlorine and alkali metals, as e.g. HCl(g), KCl(g), KOH(g) and NaCl(g), into the gas phase during combustion. The alkali chlorides may cause deposits on superheater tubes, which interfere with operation and can lead to corrosion and/or blockage of the gas path. To prevent and diminish the problems mentioned above, better and more detailed knowledge of the reactions between potassium chloride and the tube materials during combustion is needed. These materials commonly contain, among other metals, chromium, which is thought to protect the rest of the material since it forms a very dense but thin oxide layer on the surface of the tube material. It has been suggested that the reaction between solid or partly molten KCl and chromium oxide is the one responsible for starting the complex series of corrosion reactions. In this work, the overall reaction between potassium chloride and chromium was studied through partial reactions with compounds known to participate to the overall reaction or to be formed during it. The reactions were studied in synthetic air by heating sample mixtures in a DTA/TGA (Differential Thermal Analysis/ Thermogravimetric Analysis) apparatus. Selected samples were also studied and analyzed with a scanning electron microscope equipped with an energy dispersive x-ray analyzer (SEM/EDXA). Under the used conditions both potassium chloride and potassium chromate reacted with pure chromium and chromium oxide. In the case of chromium, chromium oxide was formed via the formation of potassium chromate. In reactions including chromium oxide as reactant also potassium dichromate was detected.

The effect of oxygen source on the reaction mechanism of potassium chloride-induced high-temperature corrosion

The role of two oxygen sources, air and water vapor, in the initiation of KCl-induced high-temperature corrosion was addressed with three different commercial alloys typically used in power plants....

Comparison of High-Temperature Oxidation Onset Behavior of Sanicro 28 Steel with KCl, NaCl and K2CO3

This paper presents results from a study regarding the influence of three alkali salts (KCl, NaCl, and K2CO3) on the initial high temperature corrosion behavior of high alloy stainless steel Sanicro 28 (Fe31Cr27Ni) at 535°C. It was found that all three salts were corrosive, however, with clear differences in terms of reaction initiation.