Multi-element pressure filter

A multi-element pressure filter comprises a cyhndrical vessel inside which a number of horizontal or vertical porous elements covered by filter cloths are placed (see Figures 1.29 and 1.30). The process suspension, which may be toxic, volatile or flammable, is pumped into the vessel at pressures up to 500 kPa. The positive pressure induces cakes to form on the outer surfaces of the cloths and filtrate is transported away through the elements and a suitable manifold system. Either flat elements, in the form of square, circular or rectangular leaves, or tubular candles are used. They are spaced sufficiently to avoid the possibility of cakes touching on adjacent elements. The pressure... 

Figure 1.29 Cross-sectional views of vertical vessel, multi-element pressure filters with horizontal (left) and vertical (right) leaves. A detailed schematic of the typical filter cycle is shown in Figure 6.2.

Figure 1.30 Cross-sectional view of a horizontal vessel, multi-element pressure filter with vertical leaves showing the in situ and extracted positions of the filter leaves.

Multi-element pressure filters usually comprise a cylindrical vessel inside which a number of horizontal or vertical porous elements covered by filter... 

The two equipment simulation modules provide calculation sequences for more than 20 types of vacuum and pressure filters, potentially involving combinations of cake formation, compression, gas deliquoring and washing. Batch filters include single and multi-element leaf filters, filter presses and diaphragm and tube presses while continuous filters include the horizontal belt, drum, disc, table and tilting pan filters. The user is able to define filter... 

If filtration takes place at constant pressure then the equations presented for the tube press in Section 6.2.1.3 are also valid for the multi-element candle filter noting that = n,ndh where n, is the total number of candles in the filter. When filtration takes place at variable pressure then it is necessary to impose the pump curve characteristics to relate Ap and q and a numerical solution to equation (6.17) is generally required. For the special case of variable pressure/constant rate filtration with a positive displacement pump... 

Simulation of pressure filter equipment (Nutsche, multi-element leaf filters, filter presses, diaphragm, and tube filters)... 

Precoat filtration can be incorporated within a wide range of pressure filters including leaf, multi-element and plate and frame types (see Section 1.4.2). Up to 700 g m of precoat is typically filtered onto the filter medium prior to introduction of the feed suspension. The feed, which may also contain a significant addition of filter aid to improve cake permeability, is filtered until the filtrate flow rate is sufficiently low to warrant cake discharge in the normal way. It is not economical to recover the feed solids from the precoat, and it follows that washing of the solids is not practised. Moreover, the filter aid tends to abrade the pumps used to promote the filtration. Precoat pressure filtration is most often used for the removal of finer particles from dilute suspension where other potential processes would require too high an investment. 

Multi- (horizontal) element leaf pressure filter None 5C 8 8 8 29 1-100 <1-20+... 

Single leaf (pressure Nutsche) filter Multi-element (tubular candle) 6 6 6 6 8 -... 

Multi-element leaf and candle pressure filters... 

Number of tilting pans, plates, frames or chambers Number of candles or leaves in a multi-element filter Capillary number Dimensionless pressure Pressure in air phase. Pa... 

Multi (tubular) element leaf pressure filter (Sections 1.4.2.2 and 6.1.3)... 

The multi-pass filter test is the normally used method for evaluating filtration performance. It consists of circulating a highly contaminated fluid through the test filter at constant flow rate and temperature. As the filter element picks up contaminant particles, the differential pressure drop across it increases. The test is terminated at a predetermined differential pressure across the filter, and three basic performance characteristics are evaluated separation efficiency (against particle size), contaminant holding capacity, and clean-assembly flow or pressure drop performance. 

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