Vacuum drum filters operation modes

One of the oldest filters applied throughout the chemical processing industry is the rotary vacuum drum filter, which is illustrated in Figure 8. This machine belongs to the group of bottom feed configurations. Rotary drum filters are typically operated in the countercurrent mode of operation. The principle advantage of these machines is the continuity of their operation. 

The filter cake can be separated from the drum by means of the various discharge methods described previously for vacuum drum filters. Doctor blade and roller removal are preferred for reasons of construction space. The solid is removed from the volute in the surge chamber and transported to the laterally positioned discharge chute. Depending on the mode of operation and the consistency of the filter cake a pump, pressure lock or valve is employed for the final discharge of the solids from the pressure vessel. 

Filtration. Filtration can include filter presses, rotary drum vacuum filters (RDVF), belt filters, and variations on synthetic membrane filtration equipment, such as filter cartridges, pancake filters, or plate and frame filter presses. These processes typically operate in a batch mode when the filter chamber is filled up or the vacuum drum cake is exhausted, a new batch must be started. This type of filtration is also called dead-end filtration because the only fluid flow is through the membrane itself. Due to the small size of cells and their compressible nature, typical cell cakes have low permeability and filter aids, such as diatomaceous earths, perlite, or other mined materials are added to overcome this limitation. Moreover, the presence of high solids and viscous polymeric fermentation byproducts can limit filtration fluxes without the use of filter aids. 

Pressure filters are operated in the range of 30-60 psi and some times up to 100 psi. In contrast to vacuum filters, pressure filters normally operate in batch mode. The rate of cake buildup in batch operation is slow in comparison with continuous drum filters. The time required to dump the cake and clean and reassemble a pressure filter is called dead time. It is a significant element in determining the capacity of a pressure filter. 

FQtration with Filter Aids. A wide range of pressure and vacuum cake filters can be used with both precoat and body aid fihration. Most of these operate in the batch mode and include the filter press, the vertical and horizontal leaf filters with sluice or centrihigal disduuge and the vertical tubular fih . The rotary drum vacuum fitter works in a semi-batch shion in that the precoat is removed progressively as the fitration proceeds. 

---