Fouling in the backpass of a large-scale CFBC

The results of the investigations associated with fouling in the backpass of a commercial 415 MWt CFB boiler are presented in this paper. The boiler was fired with a mixture of hard coal, biomass, and coal slurry. After certain operation period a strong deposition on the heat transfer surfaces in the boiler convective section was detected. Analysis of the samples indicated that the solid structures on the heat transfer surfaces were very hard and mainly enriched in calcium and sulfur compounds. Detailed investigation and sample analysis indicated that the solid structures were formed mainly by ultrafine m-size solids. A special fouling probe was prepared and industrial tests were conducted in order to determine the effect of fuel type on deposit formation and the formation rate. It was found that the deposition was mainly associated with combustion of the coal slurry.