To understand agglomeration phenomena of ash particles in a hot gas ceramic filter system, actual tests were carried out on candle filters with a 4MWth pressurized internally circulating fluidized bed boiler (PICFB) pilot plant. Coal ashes build up on the ceramic filters were analyzed by computer controlled scanning electron microscopy (CCSEM) and thermomechanical analyzer (TMA). The dust cake taken at 750°C did not show any sign of bridging or cleaning difficulty, while those at 950°C showed some difficulty in cleaning because of ash bridging between the adjacent ceramic filters. The initial deformation temperatures of the non-bridge dust were about 750 to 800°C. The index of R2O/(Al2O3+SiO2) (R2O = Na2O or K2O) for the non-bridge dust cake showed in the range of 1 to 25wt%, and the particle size of the potassium rich particles was in the range of 0.5 to 2.2μm. However, the index for the bridge cake approached to below 5% and the particle size of the potassium rich particles shifted to the larger range of 2.2 to 10μm. It was observed that weak sintering takes place by the reaction of potassium rich particles and the ash particles that adjoins the particles.

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