FAQ

The BHS pressure plate filter provides for pressure filtration, cake washing, drying, reslurry and automatic discharge as well as heel filtration in an enclosed and pressure vessel.

As shown in Figure 5, the motors on the top of the filter operate at different frequencies and the plates gently vibrate for cake discharge. The plates vibrate in the vertical and horizontal planes and the solids are conveyed in an elliptical pattern to the outside of the vessel. Gas assist helps in the discharge process. There are no rotating plates; gears or bushings and mechanical seals are not required.

Figure 5: Cake Discharge in the Pressure Plate Filter

BHS examines the cake structure and process parameters to determine the optimum technology. The major difference between the two technologies depends on the cake structure that is formed. Some cakes are better handled in the horizontal and some in the vertical.

Cake Thickness and Filtration: The candle filter is limited to cake structures that can be formed to about 5 – 20 mm. The pressure plate filter can handle cakes up to 75 mm. Both units can conduct filtration up to 150 psig.

Filter Media: The candle filter uses only synthetic media with a clean removal efficiency from 1 –3 micron range and finer down to 0.5 microns. The pressure plate filter can also use metal media. For the pressure plate filter, the clean micron range removal efficiency is also 1 – 3 microns and finer.

Cake Washing: If the process requires washing to remove the API from the solids, then generally the pressure plate filter is a better alternative. If washing is not as critical, then the candle filter may be the optimum technology for clarification and recovery.

Heel Filtration: The remaining liquid in the vessel (liquid heel) after filtration or washing can be removed from the candle filter or pressure plate filter by circulation, heel filter in the cone of the vessel, or additional heel filter plates in the pressure plate filter.

Cake Drying: The candle filter can produce cakes with approximately 10% moisture. This moisture level depends upon the specific cake but the moisture lower limit is that moisture just above the cake cracking point. The pressure plate filter can produce bone dry cakes.

Cake Discharge: Both designs can easily discharge most cakes equally with no residual heel.

Clean-In-Place (CIP)/ Steam-In-Place (SIP): Both units conduct CIP / SIP operations in identical manners by filling and circulating cleaning fluids while blowing gas in the reverse direction to the filtration direction, which crates a turbulent mixture or a quasi-ultrasonic cleaning effect. The pressure plate filter further enhances this operation with plate vibration.

Spinning disk filters are also commonly used for clarification. While these units overcome some of the special handling requirements of manual filters, they add mechanical complexity to the process as well as special cleaning requirements. Spinning disk filters require drive motors, gear box assemblies (including gear box housing, gear reducers, bearings, shaft bearing arrangement and bushings, torque loadings, etc.), mechanical seals (either single or double with special maintenance and cleaning) and unique installation concerns such as center of gravity due to the spinning plates, static and dynamic balancing and bearing lubrication and design to ensure no exposed threads and cleanability issues, and overall maintenance of these components.

The BHS units use vibrating plates which eliminate motors, gears, rotating seals, etc. and many of the operational issues of the spinning units.