DIATOMITE FILTER - AID
It is a mineral of vegetable origin. It represents the accumulation of an enormous number of fossil diatoms. Diatomite is called miraculous mineral because of its lightness, porosity and its uniquely honeycombed structure which makes it an ideal filtering medium. And because of its inherent stability and the absence of most trace elements, Diatomite is ideal for use by processor who has very high purity requirements such as the food, beverages and pharmaceutical industries, etc.
Filtration using diatomite is a two step operation. First, a thin protective layer of filter aid, called the precoat, is built up on the filter septum by recalculating filter aid slurry. After precoating, small amounts of filter aid (body feed) are regularly added to the liquid to be filtered. As filtering progresses, the filter aid, mixed with the suspended solids from the unfiltered liquid, is deposited on the precoat. Thus, a new filtering surface is continuously formed. The minute filter aid particles provide countless microscopic channels which entrap suspended impurities but allow liquid to pass through, without clogging.
The first step in the use is to build up a “precoat” of filter aid on the filter septum.
The purpose of the precoat is
- To prevent the filter septum from becoming clogged by impurities, prolonging septum life.
- To give immediate clarity.
- To facilitate cleaning of the septum at the end of the cycle.
Precoating is accomplished by circulating slurry of filter aid and filtered or clear liquid between the filter and the precoat tank. Since most of the filter aid particles are smaller than the openings in the septum, they must from the precoat by bridging these openings. These bridges can be upset by air bubbles, sudden changes in pressure, or vibrations, causing the filtrate to become turbid until the upsetting influences have been corrected. If flow distribution in the filter is good, the filter may be filled with clear precoat liquid and concentrated slurry of filter aid may then be pumped or educated into the filter followed by recirculation.