Abstract
Currently, biomass is limited to low percentages of feedstock in UK co-fired power stations because of the severe corrosion which ensues and the resulting increase in shutdowns and maintenance costs. Recent field trials in power stations that use 100% biomass fuels indicate specialist coatings can provide protection of superheater tubes in these highly corrosive combustion environments.
This paper summarizes the results of several projects evaluating the use of thermal spray coatings and ceramic sealants to protect superheater tubes from the corrosion arising from the combustion of biomass fuels with high chlorine content, including attack by molten chloride salts. Several trials were carried out on uncoated samples under simulated biomass burning and molten salt environments to establish baseline corrosion. On site trials have shown that these coatings reduce oxidation and chlorination, double superheater tube life and allow plants to operate at higher temperatures with improved efficiency. The performance of the coatings correlates to coating composition, coating density and to the use of sealants which prevent ash-build up, solid particle erosion and may also reduce the diffusion rate of aggressive gaseous species through the coating. The performance of similar coatings exposed to laboratory tests simulating on-site corrosion is correlated to the biomass-fuelled power plant experience. The work has implications not only for biomass combustion, but also for co-firing and waste incineration plants.
