Experiment 2

Experiment 2 - 2 FILTRATION Plate and frame separation of...

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23 2. FILTRATION: Plate and frame separation of calcium carbonate and water Background The plate and frame filter, or filter press, is one of the most widely employed filter designs. It consists of two end filter plates to which the filter medium is attached. Between the two end plates are frame plates and wash plates. Feed slurry is pumped into the frame plates and filtered solids collect there. Wash plates have a filter medium on both faces and have a particular port arrangement to enable slurry washing procedures. The number of frame plates and wash plates can be altered so that the separation area and solids capacity of the filter meets a range of demands. All of the plates are held pressed together to form a seal which enables the filter unit to be operated at pressure, this pressure being the driving force for the filtration or washing/drying processes. The plate and frame filter is batch operation and usually requires dismantling for the recovery of solids at the end of the filtration cycle. It also allows washing of the filter cake in–situ. The Armfield UOP12 Filtration Unit uses a press made from 5 plates, two end plates, two frame plates and a wash plate. The filter medium has nominal pore size of 63 μm. While this size allows reasonable filtration rates, it also necessitates the use of precoat/filter aid to recover particles much smaller than 63 μm. Theory The general equation for filtration is developed from first principles for flow through porous media. The theoretical development is performed excellently by Bennett and Myers (3 rd Edition, pages 224-244). In brief, for an incompressible filter cake (possibly weak assumption for these conditions), the filtration equation giving the instantaneous relationship between upstream filter pressure and flowrate is: (1) ….where P = pressure upstream of filter unit, Pa V = volume of filtrate collected, m 3 Q = flowrate of filtrate, m 3 /s … and K 1 is a constant which is strongly dependent on the characteristics of the cake building up in the filter according to: 2 1 ) 1 ( A s m s K (2) Q K V K P ) ( 2 1
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24 … where: s = mass fraction of solid in original slurry = liquid density, kg/m 3 = liquid viscosity, kg/m-s = constant specific cake resistance, m/kg m = ratio of wet cake to dry cake A = filtration area, m
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Experiment 2 - 2 FILTRATION Plate and frame separation of...

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