Technical Description
BHS-vacuum belt filters are continuously operating, pneumatically driven horizontal vacuum filters. A circulating belt, moving in cycles, is the filter medium. The suspension is fed continuously or in batches onto the belt, the filtrate is sucked away from below. The filter cake forms on top of the belt and under-goes further treatment in the form of washing, extraction, suction drying or pressing. With very little vacuum loss, the belt is stationary during filtration process. When the belt moves forward, the vacuum trays are vented so as to ease strain on the belt.
Vacuum trays
The vacuum trays are divided into zones corresponding the length of belt feed. Supporting grids with large open sections are provided in the vacuum trays to support the belt.
Filtrate drain
Each individual zone in the vacuum trays is separately connected to the filtrate manifold. The filtrate manifold is divided up in line with the zones for filtrate separation. Rapidly opening and closing shut-off valves cut out the vacuum when the belt advances and vent the filtrate chamber.
Belt conveyance
The continuous, circulating filter cloth belt is moved in cycles by pneumatic cylinder and conveyer roller. While the belt is stationary, vacuum is applied to the trays, holding the belt in place. The length of cloth moved forward corresponds exactly to one zone length and is taken from the belt storage device. The return movement is completely free from strain.
Suspension delivery
The suspension is delivered from a stationary distributing facility. An oscillating delivery unit can be provided for heavily sedimenting sus-pensions.
Cake washing
Washing media are delivered by spray systems or distributing channels. The delivery units can be positioned with precision on the vacuum trays.
Cake discharge
Part of the cake is removed during forward feed, the remainder when the extraction roller travels back. A mechanical scraper removes any cake re-sidue still adhering to the cloth.
Cake pressing
A pressing plate is pneumatically or hydraulically pressed onto the cake for one cycle unit. Compressed air or hot air is additionally blown through the cake.
Drying
Following the normal filtration, washing and dewatering stages, it is possible to apply a variety of drying systems to dry the product.
Confildry
The Confildry version consists of heatable upper rams and heatable vacu-um trays. Hot gas can also be drawn through the cake. This produces a high level of heat transfer, resulting in efficient drying.
Criteria / demands
The BHS vacuum belt filter can be used to good effect where the following criteria need to be met:
- Several consecutive process steps
- Enclosed gastight production
- Fully automatic operation
- Temperature up to 95°C
- Dewatering by mechanical expression up to 6 bar
- Filter cake drying
Encased filters
To meet customer specifications, various types of encased filters are available:
- simply hood type
- with closed hood over the entire filter
- closed box type
- gas- and pressure tight box type
- pharmaceutical type
Normally, an encased box type will be used here, with particular attention focused on surface quality (Ra up to 0.8µ), processing directives (GMP) and the use of permissible materials (FDA).