Role of Alkali Hydroxides in the Fireside Corrosion of Heat Transfer Surfaces, a Practical Approach

Fireside corrosion of heat transfer elements in biomass combustion has been widely studied. Several parameters have been detected to contribute the material loss of heat transfer surfaces. The role of fuel is the most significant, but it has to be kept in mind that if sufficiently high steam parameters are selected, corrosion can take place as oxidation even with the best solid fuels available. With proper selection of steel, corrosion rates can be decreased, but it is not possible to totally prevent corrosion reactions. One of the specific aspects in corrosion found in biomass combustion is the presence of deposits. The cases in which corrosion is only due to gas-to-solid reactions are rare, because the concentrations of harmful substances seldom reach levels that are sufficient to allow mass transfer rates required for significant degradation of steel. When a deposit is formed, the composition of the deposit depends on several factors, such as the temperature and the composition of the flue gas, aerosols, and small particles. Depending on the deposit composition close to the metal surface, there may be a risk of partially molten components in the deposit, which may cause rapid corrosion reactions due to the high mass-transfer rates solid-liquid reactions allow. These molten components can be different forms of salts and their mixtures. Due to the nature of the high temperature corrosion, it is very difficult to predict when the melt is formed, and thus the