Slowing RO output to match evaporator

[twofer]

We are currently recirculating our sap up to 6-8% and then shutting down our 600GPH RO since we don't have a second tank large enough to pump the concentrate into. Our evaporator will do ~80 gallons per hour. My idea is to reduce to the pressure on the RO and then pass the concentrate into the head tank for the evaporator. In order to do this we would have to reduce the concentrate output to ~1.3 gallons per minute.

What I would like to do is reduce the pressure on the RO so that the permeate is at 2GPM and the concentrate is at 1.5GPM so we are still removing water while we are evaporating. Would throttling down a 600GPH to this rate cause any harm?

[twofer]

In case anyone finds this thread in the future I will update with my first nights results since no one responded and my stubborn butt decided to forge ahead without any expert advice. :)

We recirculated up to 6% and then set the permeate to 2.5 GPM and the concentrate to 1.5 GPM and redirected to the evaporator. The RO seems to run just fine at that low of a flow rate.

Not sure if there are any long term problems to running an RO like this but my initial thoughts are that it is just fine.

[Jeff E]

I was told by a CDL rep that running the concentrate at such low flow rates can cause the membrane to plug prematurely. If your pressures are lower, 300ish, you are probably OK though.

[rayi]

I was at a dealer rescently and he says to start your RO and pump into a head tank. Then start your evaporator with sap The way he wants it connected ther RO will flow into the evaporator or if it is producing too much it will flow into the head tank. When I asked about running it thru for a second pass he said NO. Seems he feels the sap gets too hot between the two passes and microbs get started. Now up until that time I had never seen an RO so I may be the second to last person to listen to. I think the salesman would be the last

[twofer]

I was told by a CDL rep that running the concentrate at such low flow rates can cause the membrane to plug prematurely. If your pressures are lower, 300ish, you are probably OK though.

So far we've ran twice like I described and the pressure settles in ~250 psi at 2.4 GPM permeate and 1.4 GPM concentrate.

Running this way we have been recirculating for two hours and then sending to the head tank at the reduced flow for two hours. It's working out really well and cutting way back on the boiling. Wish I had done this earlier in the year when we had a couple boil until breakfast sessions. :)

[Jeff E]

sounds like it is working well. keep it up and have fun!

[ennismaple]

I'm glad this is working for you on your RO. On ours, at 5.5GPM permeate flow and at 440 psi membrane pressure we get about 3.25GPM concentrate flow. If we lower the concentrate flow any more the pressure really spikes.