The excellent particulate removal efficiency of ceramic candle filters has prompted
efforts to develop a more durable and economical alternative to existing ceramic candle
filters. Porous ceramic candle filter elements were successfully fabricated from calcium
aluminate cement, calcined fireclay aggregate, and organic pore formers using refractory
concrete casting techniques. Methods used to characterize the porous ceramic filter
elements included determination of pore size and distribution, permeability, resistance
to alkali attack, and mechanical strength. Various pore formers and casting, curing, and
sintering conditions were examined to produce highly permeable and structurally sound
filter elements.
The optimized fabrication procedure produced porous ceramic candle filter elements
with pore diameters between 20.3 to 43.1 tlm, porosities of 38 to 60%, and pressure
drops of 3 to 24 mbars at a face velocity of 100 mjh. These characteristics are
comparable to existing ceramic filters which are noted for their > 99% collection
efficiencies of submicrometer-sized particles, but short-term durability in advanced coal
combustion clean-up systems. Test specimens of the alumino silicate refractory concrete
proved more durable by showing no severe attack following exposures to
alkali-containing atmospheres at 700-1000°C. The strength of the cast samples ranged from 200 to 1139 psi depending on the relative densities and pore formers. Porous fliter
elements with different porous structures, permeabilities, and shapes can be easily
produced with this technique.
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