the filter cloth in the first few seconds
the filter cloth in the first few seconds
In broad terms drum filters are suitable to the following process requirements:
Slurries with solids that do not tend to settle rapidly and will remain in a uniform suspension under gentle agitation. |
Cakes which do not require long drying times to reach asymptotic moisture values.
Cakes when a single washing stage is sufficient to remove residual contaminants from the cake or yield maximum recovery of .
that generally do not require a sharp separation between the mother and wash filtrates. Some complex valves, however, enable atmospheric purging of the sectors and internal piping to facilitate a sharp separation of filtrates.
Filtrates that are acceptable with a low quantity of fines that pass trough the in the first few seconds of cake formation. Broadly, and depending on particle size and cloth permeability, the filtrate may contain 1000 to 5000 ppm insolubles.
The selection of a suitable type of mechanism depends largely on the release characteristics of the cake from the filter media and will vary from process to process. Scraper discharge mechanisms will suit cakes that release readily and roller discharge mechanism are better for thixotropic cakes.
A drive with a variable speed that rotates the drum at cycle times that normally range from 1 to 10 MPR.
An agitator that keeps gently the slurry in suspension and reciprocates between the drum face and tank bottom at 16 or so CPM.
A tank with baffled slurry feed connections, an adjustable overflow box to set a desired drum submergence and a drain connection. The tanks are normally designed for an “apparent submergence” of 33-35% however on certain applications 50% and more is possible. With these special designs the tank ends are higher in order to accommodate stuffing boxes on both the drive shaft and valve end trunnion.
On applications where cake washing is required, 2 or 3 manifolds with overlapping nozzles are mounted to a pair of splash guards bolted to the tank ends. The position of the manifolds and the quantity of wash liquid are adjustable depending on the wash characteristics of the cake.
Optional controls may be used to automate settings such as drum speed, applied wash liquid and drum submergence for a desired cake thickness or throughput. The monitoring of drum submergence controls the slurry feed valves so an adjustable overflow weir is not necessary except for a fixed connection in case of emergency.
The flow scheme of a Rotary Drum Filter Station will generally look like this:
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