Vertical diaphragm press cycle

Figure 6.4 Schematic diagram of the single sided, vertical diaphragm press cycle (end view of one chamber shown and cake discharge omitted), (a) Filtration via pump and/or diaphragm (b) compression deliquoring (c) displacement washing (d) gas deliquoring.

Figure 1.36 Schematic and photograph (Larox), of the vertical diaphragm filter press. A more detailed schematic of the diaphragm press filter cycle is shown in Figure 6.4.

The vertical filter press, like the horizontal press, is strictly speaking a batch operating filter, but is more correctly called a semi-continuous filter, because the cake is discharged from all of the compartments at the same time. When the filtration cycle starts, the plate assembly (Figure 3.73) closes, and slurry is fed to all of the compartments at the same time. Cakes form on top of the filter medium in each compartment. Once filtration is complete, diaphragms are forced hydraulically down on the cakes to dewater them. Then the diaphragms are relaxed, wash water is introduced, and the cakes squeezed once again, followed by a compressed air blast to dry them further. At this point, the plate assanbly opens, and the continuous band of filter medium advances... 

These include the cost of labour, the cost of replacing components and the rent and rates on the area of land. A comparison of the latter is very unfavourable to diaphragm cells where almost twice as much land is necessary because of the low current density and the need for evaporation plant. Membrane and mercury cells have similar land requirements because the former are packed together closely in a filter press and to some extent the electrodes scale vertically. All the processes are largely automated and hence the difference in labour costs is likely to arise because of a variable incidence of component and pipework failure. Certainly the need to replace diaphragms on a routine cycle increases the labour costs for the diaphragm cell process. 

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