Health & Environmental Research Online (HERO)


Print Feedback Export to File
2072440 
Technical Report 
Analyses of ashes from the Tidd PFBC advanced particulate filter 
Snyder, TR; Pontius, DH 
1995 
NTIS/02987481_3 
GRA and I 
GRA and I 
Early observations of the Advanced Particulate Filter (APF) at the Tidd PFBC Demonstration Plant led to the conclusion that tenacious ash deposits formed in the filter vessel and induced stresses that resulted in bent or broken ceramic candle filter elements. The proximity of these bent and broken candle filter elements to large, strong ash deposits emphasized the need to prevent or control the growth of these deposits, facilitate their on-line removal, and/or to develop filter design criteria to minimize their effects on individual filter elements. The chemical characteristics of the ashes collected in the Tidd APF combined with the environment within the filter vessel tend to cause ash deposits formed in the filter vessel to consolidate and strengthen. One theory that may explain the growth and strengthening of these deposits is based on the formation of eutectics such as various calcium aluminosilicate compounds. These eutectics form when primary coal ash particles come into physical contact with sorbent-derived ash particles which contain relatively large amounts of magnesium and/or calcium. Aluminosilicate compounds in the coal ash particles react with alkali metals in the sorbent ash particles to form eutectics that melt at relatively low temperatures. The surface tension of the near-liquid layer on the particles pulls adjacent ash particles closer together, thereby eventually consolidating the structure of the entire ash agglomerate. The optimum solution to the problems caused by the ash aggregates that have been consolidated and strengthened by pervasive eutectic formation is the removal of these aggregates from the APF before the eutectics have had enough time to develop. The approach that proved most successful in eliminating the deposits was the total bypassing of the cyclone upstream of the APF. This increased the size distribution of the particles forming the various ash deposits, thereby decreasing their inherent cohesivity.