Materials for fluidized bed heat exchangers

In order to increase the steam parameters in combustion units, several new approaches have been proposed. New materials have been tested, but they seldom have been a sufficient solution. Metallic coatings sprayed on superheater tubes have been noted to reduce erosion and corrosion in selected cases. New plant designs have been tested. However, most of these solutions have at least one special feature, which prevents using them as a general solution applicable to all new boiler units. Fluidised bed combustion units, and especially circulating fluidised bed (CFB) combustors have gained reputation as one of the most feasible means of solid fuel combustion. These units have one major benefit over other technologies: possibility to utilise the re-circulated solids for heat generation. This allows using fluidised bed heat exchangers (FBHE), which are one of the most promising novel solutions to improve the efficiency of solid fuel combustion units. Selecting optimal materials for such heat exchangers is not straightforward due to several special demands, such as high heat flux and continuous erosion.