Strainers continuous operation

A feed pump transfers the product to the atomizer either directly or via a constant-head feed tank. The feed tanks are of sufficient volume to permit continuous operation and to smooth out possible interruptions and variations in the supply of the material. It is quite usual for two holding tanks to be used alternately, thus assuring constant product supply to the dryer. The feed strainer or filter is important because all matter likely to jeopardize the performance of the dryer through partial or total blockage of the atomizer must be removed. Demineralized water or clean condensate is usually required for use in cases of feed blockage. 

An obvious disadvantage of a permanent strainer of the types just described is the need to shut down the plant flow so that they may be cleaned. Where continuous operation is required in a pipeline service, duplex strainers can be used in an integral unit with the provision to isolate one element at a time for cleaning, or even having multiple strainers in one unit (as shown in Figure 3.6). Individual strainer elements or baskets are then made accessible via cover plates with static seals (usually 0-rings). 

The duplex or multi-basket strainer must stiU be watched to check for the need to swap baskets. Self-cleaning strainers may be used as an alternative to dual or multiple strainers where continuous operation is critical in the process system. Two methods of self-cleaning are illustrated in Figure 3.7 - one uses a brush and the other a scraper. Brush cleaning is suitable for most applications, with scraper types more specifically suited for handling high-viscosity products. 

The Metafilter is widely used for filtering domestic water, beer, organic solvents and oils. The filtration characteristics of clay-like materials can often be improved by the continuous introduction of a small quantity of filter aid to the slurry as it enters the filter. On the other hand, when the suspended solid is relatively coarse, the Metafilter will operate successfully as a strainer, without the use of a filter bed. 

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