Sintering Behavior of Coal Ash Build up on Ceramic Filters in a Hot Gas Filtration System

Abstract

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. A coal ash build up on the ceramic filter was used in this study. The ash was treated at 850, 900, 950 and 1025°C in an atmosphere of air for 5 minutes in order to make agglomerated particles at known conditions. These samples analyzed by computer controlled scanning electron microscopy (CCSEM) and thermo-mechanical analyzer (TMA). The samples treated at 850 and 900°C showed little sign of agglomeration, while those at 950 and 1025°C produced some agglomerate powders. The index of R₂O/ (Al₂O₃+SiO₂) (R₂O=Na₂O or K₂O) for the samples decreased with increase in treatment temperature, and the particle size of the potassium rich particles in the sample shifted to the larger range of 2.2 to 10m. The shrinkage of ash layer measured by TMA was less than 1% at the exposure temperatures of 750 to 800°C and c.a. 2% at that of 850°C after 40 hour tests. However, it exceeded over 3 to 6% at a temperature above 950°C after 40 hour tests. This result showed that heavy agglomeration of ash particles starts from the potassium rich particle suirounded by ash particles and produce a little amount of liquid in ash layer above 960°C, which was also confirmed by thermodynamic equilibrium calculation.