Multi Bed Filter
In Multi Bed Filters the filtering medium is a packed bed of sand, anthracite or diatomaceous earth or fibrous pores are formed in the interstitial spaces of the packing material.
The feed suspension travels into the filtering medium. In the course of migrating through filtering medium the suspended partials are trapped inside the pores by virtue of impertinent (i.e. the inertial retardation, combined the surface forces).
Because of the limited capacity of packed bed multi bed filtration is suited only for clarifying liquids that contain a very small amount of suspended partials. Typically less than 1% on the scale of total suspended solids.
Following are the impurities are generally responsible for causing difficulty in sugar industry.
Suspended particles with average size less than 0.5µm.
Phosphate particles which are often ultra fine & fragile.
Starch which is viscosity enhancing high molecular weight polymers.
Dextran another species which is more soluble in water
Multi Bed Filter may be defined as a granular filter for removal of suspended solids in liquor.
Media depth of at least 4 ft. at a filtration rate of 2 gpm /ft2is necessary. Course media in normally used to encourage deep penetration of solids into the media bed. This allows longer filtration run times; simultaneous air & water back washes are used to ensure cleaning of filter as required. IT removes 75-80% turbidity of clarified liquor.
Brief description of Equipment
It is a cylindrical pressure vessel that can hold a pressure 350 Kpa.In the upper part of the vessels there is a liquor distribution system comprises of half longitudinal cut 4’’ dia pipes have in 5 mm holes and attached to the central feed pipe .Blow this liquor distribution system there are six beds of different filtering media from fine to coarse. The liquor is filtered through media and collected in the bottom from where it is send to the filtered liquor tank.
The bed depth details are as under.