TMP or Flux as Control
TMP or Flux as Control
(OP)
Generally speaking, is it better to control membrane systems (water filtration) on constant TMP, or constant flux? I have seen a lot of systems where the permeate is throttled, so TMP and flux change inversly proportional to each other as the membrane fouls. I am designing a system with some automatic control on the permeate side.
Does anyone have experience controlling the TMP or Flux rate of the system? Is there any difference in performance?
Does anyone have experience controlling the TMP or Flux rate of the system? Is there any difference in performance?





RE: TMP or Flux as Control
brennans7
RE: TMP or Flux as Control
I am thinking to keep flux constant and let TMP vary between backpulses.
Is there an argument for keeping TMP constant and letting flux vary?
RE: TMP or Flux as Control
Sounds like you plan on running in a batch configuration. What is the size of the process tank and what will be the membrane configuration (number of tubes in series and number of passes)? Also membrane area? What concentraion factor are you hoping to attain? Is this a supported membrane?
To approach your question more directly, all of the UF wastewater systems I have ever commissioned have kept the the pressures constant over the course of the run. Not many work the other way (constant permeate rate). Having said that, really the determining factor is whether or not this is to be a batch concentration or continuous (no concentration) process. Due to the viscosity changes from concentration and pressure limits on most membranes constant TMP is the way to go. By increasing the driving force for permeation as you go all you really due is increase the fouling rate.
RE: TMP or Flux as Control
The industries I serve do operate very much on constant flow principles. The products are, however, disposable, and the membrane can be taxed and put to its functional limit. If you're using so-called clean-in-place systems, try not to push it too hard. Preserve the life and avoid premature replacement.
ChemE, M.E. EIT
"The only constant in life is change." -Bruce Lee
RE: TMP or Flux as Control
The current system design is for constant flux. This makes it easier to sell a X gpm system because the flow rate is constant and prevents some problems on the front end (like larger EQ).
I have the feeling that constant TMP would make the system run at a more steady state. TMP seems to be the main driving force for fouling, and if it were held steady, the fouling trend would be less variable...