Ceramic Filters
Ceramic hot gas filters are high temperature equipment items for the continuous removal of particulates from air or other hot gases. The equipment consists of ceramic filter elements installed in custom-built vessels fitted with proprietary mechanical parts.
Ceramic Filter Element
Ceramic filter elements comprise mainly alumino-silicate ceramic fibres. This material has two key properties:
- it is very refractory making it resistant to high temperatures and corrosive gases
- it is a very thin fibre, which is ideal for constructing the low density, high surface area structures that make the best filtration media.
Ceramic filter elements are generally vacuum formed to the industry standard design; a 1000mm long tube, flanged at one end and closed at the other. It can withstand a temperature of 900 degC and can resist almost all chemical attack.
Element Installation
The elements hang vertically from the header plate, which separates the clean and dirty compartments of the filter vessel.
In use the hot gas is sucked through the filter medium from outside to inside, depositing the particles on the outer surface of the medium. The solids form a continuous layer, or cake, on the surface of the element. At controllable intervals a sharp pulse of compressed air or gas is blown back down the inside of the filter element causing a momentary reversal of flow. This reversal causes the accumulated solids to be detached from the outer surface of the filter elements as agglomerates or flakes. The solids fall into the hopper section of the vessel from where they will be discharged. The pictures show filter elements that have just been cleaned - it can be seen that the cake has detached in patches.
Ceramic Filter Designs
The design of a ceramic filter is constrained by the need to be able to remove the solids from the elements by reverse pulse cleaning and to be able to discharge the solids from the vessel. Reverse pulse cleaning (see data sheet) requires the elements to be in rows so that the pulse can be applied to more than one element at a time - rows are typically 8 - 20 elements long. Discharge of solids from the vessel requires a hopper section at the bottom tapering to a valve or seal allowing solids to pass intermittently to a removable container.