Tubular Backpulse Filters
Tubular back pulse filters consist of large number of filter candles, housed in a vertical cylindrical filter shell. The filter candles are covered with a filter medium. The filter candles are suspended from a tube sheet, which is clamped between the filter shell and the upper reservoir.
The raw liquid enters into the shell, and flows outside-in through the filter medium to the upper reservoir. The impurities cannot pass through the filter medium and are collected on the outside of the filter candles. Over time these impurities build up a thick layer -the filter cake – and with that the resistance for the liquid to pass increases. When the required pressure reaches a certain level the filter cake has to be removed from the candles. For this cleaning step a back-pulse is performed.
The back-pulse is an automatic cleaning cycle during which the feeding of raw liquid is stopped and the pressure inside the shell is released. The filtered liquid which is held in the upper reservoir flows back, inside-out, through the filter candles and rinses the filter cake from the surface of the candles.
The released filter cake with the accumulated solids are collected in the conical bottom of the shell and are discharged after each filter cycle or, in case of limited cake thickness, after a pre-determined number of cycles.
Depending on the type of filter medium used and the characteristic of the filter cake, different types of back pulse systems can be chosen:
- Open top systems with atmospheric back pulse
- Closed top systems with compressed air or nitrogen for stronger back-pulse action
Open top system:
The upper reservoir is open to the atmosphere. This construction has many advantages as it allows a free view on filtered liquid and the performance of the individual candles, and provides easy access for maintenance. The level of the liquid contained in the open upper reservoir provides sufficient pressure to rinse off the filter cake from the candles. Read more..
Closed top system:
During the back pulse step, low pressure compressed air or gas is forcing the filtered liquid in a reversed flow through the candles, forming a thin layer of liquid between the cake and the filter medium. The filter cloth or membranes expand slightly and the accumulated solids are removed from the membrane surface. Read more.
The filter medium on the outside of the filter candles is the most important part of the filter. ProFilco prefers to use its Porous PTFE Tefflux Membranes, but can offer suitable alternatives including pre-coat systems to suit any application. In any design the filter medium is installed on a non-metallic filter tube with an open structure, providing the inner support and allowing unobstructed and even flow over the full surface of the filter medium,
For most applications ProFilco promotes the use of Tefflux multiple tube pPTFE membrane technology.
ProFilco can also equip its tubular back pulse filters with pre-coat candles or standard membrane candles.