RO

[Acer]

What pressure & flow do I need to get decent permeate flow at 10-12% sugar on a single stage home made ro? looking at xle4040 membrane.
was thinking 1.5 horse booster pump would do it but flow is only 4.3gpm@200psi.

Other way to slice it is what %brix can i concentrate to on 200psi?

Dean

[Russell Lampron]

Dean,

With that membrane you should only run it at about 200 psi. It will do a nice job of concentrating at that pressure. If your RO has recirculation you can slow down the concentrate flow to get what about 10% out of it in one pass. If it doesn't have recirculation you will have to run the concentrate at a higher flow rate so that the membrane won't clog up on you.

[Acer]

Thanks Russ,

Dug around and it looks like 10% sucrose solution exerts about 100psi osmotic pressure. So 200psi @10% sugar would leave 100psi to force water through the membrane. That pump sound a little under gunned for the xle4040 or ok?



Dean

[Russell Lampron]

Dean,

The XLE membrane is designed to work with low pressure. The 1.5 hp pump may be a little small but I would give it a try. It does have the capacity at 4.3 gpm to do more than double what the membrane will flow. My RO is rated for 150 gallons per hour and uses the same size membrane.

[Teuchtar]

Russ
I presume your 150 gallon Lapierre has a built-in concentrate recirculation feature which re-enters the HP pump mid stream.
If I'm right, whats the recirc flowrate ? Seems to me that Dow Filmtec advise to have something like 6-8 gpm through the concentrate side of the membrane otherwise fouling will reduce the permeate flux.
On my homemade RO, I just couldn't stop the fouling until I raised the flowrate up to 6 gpm. Now I can go for much longer, but still need some experimentation to get the right recirc flow. I had to install an additional pump to do this. This has the added benefit of reducing flow through the HP pump, so it can reach a higher pressure.
Now I can get 300 psi on the membrane tank with less heating of the concentrate. I'd like to go for higher pressures, but already touching the rated pressure of the tank. Maybe I'll tack on a second membrane instead.
Duncan

[WMF]

The recirc flowrate on these modern RO's is very high, probably beyond what the membrane manufacturers spec out but the membranes seem to hold up.

The best way to measure recirc flow is with a differential pressure guage across the membrane vessel. I think Filmtec specs out 10 psi max pressure drop across an element.

[Russell Lampron]

What my RO has is a jet pump bolted right onto the bottom of the pressure vessel. I think it is just to spin the high pressure sap before it goes into the membrane. It probably creates a tornado like thing that scrubs so to speak the face of the membrane to keep it from clogging. It is more of a circulation pump than a recirculation pump.