Pressure in a membrane filtration system

[kcoinoz]

Hello,

I am working in the water treatment industry and for some of our tests we are using a bench scale 'high pressure' (8-10 bar) membrane filtration system. For the moment, the system comprises a tank from which water is pump into a membrane cell. A part of the flow just flows through the cell (retentate) and the other part, due to a difference of pressure on each side, permeates through the membrane. There is a backpressure valve in the retentate line to allow a pressure build up in the cell and consequently permeation of the water. Both the retentate and permeate lines are then recirculated back into the tank.

For a new project we will work with volatile compounds in the water and consequently, to avoid losses, we would need to have the tank sealed and have no headspace in that tank. That's where I get confused... if the system is theoretically airtight and completely full of water then it won’t work anymore... I mean that there won’t be a difference of pressure across the membrane, needed for the permeation, as the pressure will be balanced in all the different lines... Is this right?
I hope all this is clear enough.

Thank you for helping.
Regards
K

 

[edgepflow]

The pump would produce a driving pressure to make flow. However, the volatile compounds may vapor lock the filters. A small vent line may help with this.

 

[batman394]

No you should be fine. Get a tank with a variable volume cover. Basically the lid has a gasket on the edges, and you can float it on top of the liquid up/down as you need to remove the head space.

In some membrane operations, the retentate line is fed back into the inlet of the pump. And they don't see a crazy pressure build up.