Problem with my concentrate and permeate flows

[SmellsLikeSyrupNH]

Ok so here is my issue. I basically have redesigned my whole RO. I took a single membrane ProCon 265gph based system to a two membrane with a Goulds 7GB pump. This pump should do 10gpm. The 2 membranes are brand new Dow XLE 4040 plumbed in series. Everything seems to be nice and tight with no air leaks or liquid leaks anywhere. I’m feeding the system with a 7GPM irrigation pump. The way I’m reading the specs everything in this setup should be good to go. My issue is my concentrate line flows at least double the rate of my permeate. In my head this should be the opposite. Adjusting my PSI with my needle valve the closest I can get them to bring even is to run at about 175psi and even that really isn’t much better. I ordered 2 flow meters that will arrive today so I can get a more accurate reading on what’s coming out of both lines.

I can’t understand why I’m getting the results I’m getting. I would have suspected that I would take 2% and get it up at least to 5% or 6% after one pass. That’s not happening at all. I am certainly removing water, out of 275 gallons of sap last night I removed 160 gallons after two hours. That was running it while recirculating. I’m testing the permeate and concentrate and I’m get 0% sugar in the permeate. It just seems that I’m getting flows opposite of what I was expecting on performance and not reducing my water nearly as quickly as it should. The system seems to physically be processing the sap at a speed that’s expected, just not concentrating it properly. I believe I should be taking that 2% sap and it easily be hitting 6-8% after 1 pass and I’m lucky if it’s getting to 3.5-4%.

Do you have any ideas?

[Super Sapper]

There may be other issues but your membranes will only put out X amount of permeate at a given pressure no matter how much the total flow is. A larger flow will keep the membranes from fouling as fast but will only give you X amount of permeate at that pressure. If you are going in at 10 gpm and getting 7 gpm concentrate and 3 gpm permeate you should get 17 gpm concentrate and 3 gpm permeate at 20 gpm coming in.

[wmick]

I'm no expert... but it sounds like you have a very similar setup to what I'm putting together... Theres another thread, where Bowhunter helps me understand what flows I might expect....
Link below - Check it out...


http://mapletrader.com/community/showthread.php?34887-How-does-your-membrane-perform&p=375740#post375740

[SmellsLikeSyrupNH]

Thanks! I just replied to that thread, I have the same parts you are discussing but im getting no where near that 7% after 1 pass...im looking at MAYBE 3.5% on 1st pass from 2% sap. It just seems not enough pressure to push more water through ther membranes to create the permeate. Last night I took 275 gallons and ran it for 2 hours while recirculating and removed approximately 160 gallons of water before I finally got over 5% on my concentrate. Im really stumped.....



I'm no expert... but it sounds like you have a very similar setup to what I'm putting together... Theres another thread, where Bowhunter helps me understand what flows I might expect....
Link below - Check it out...


http://mapletrader.com/community/showthread.php?34887-How-does-your-membrane-perform&p=375740#post375740

[Bricklayer]

Do you have a recirc line? If so do you have a needle valve or valve controlling your recirc.?

[SmellsLikeSyrupNH]

In my head "recirc" was just running it a 2nd pass....im starting to see where I was wrong in that assumption. I do not have a "recirc" ability as currently setup. I may need to go that route and do some re-engineering :-(

[wmick]

Thanks! I just replied to that thread, I have the same parts you are discussing but im getting no where near that 7% after 1 pass...im looking at MAYBE 3.5% on 1st pass from 2% sap. It just seems not enough pressure to push more water through ther membranes to create the permeate. Last night I took 275 gallons and ran it for 2 hours while recirculating and removed approximately 160 gallons of water before I finally got over 5% on my concentrate. Im really stumped.....

I think maybe its just a little bit of misunderstanding on the term "one pass".... Are you recirculating from your concentrate tank or do you have a recirc line plumbed in before your needle valve? If you are recirculating from your tank, you will not be able to achieve your "one pass" goal. When they say "one pass" It is one pass through the "system".... Not literally one pass through the membranes.. Re circulation is required, if you want to get to a decent brix level...

Take a look at the piping diagram below... See how the recirc line Ts off from before the concentrate needle valve, goes through another recirc valve and re-enters the system before the pressure pump.... Is your recirc plumbed in this manner? If so, you should be able to dial your concentrate valve down to control your desired permeate to concentrate ratio and brix... (This is your "one pass" concentrate) The rest of your pump's flow capacity recirculates within the system, keeping your recovery rate in check as not to foul the membranes..
Pay attention to this "recovery rate"... As I understand it, this is very important for membrane health... If your membranes are passing 90 gph (45 each) of permeate, you need 300 gph of flow passing through the concentrate side of the membranes for a 15% recovery rate.
20919
PS - Dont be confused by the "product and waste" labels on the diagram... This diagram is not from a "maple" RO ... Its from a water purification setup.

[wmick]

In my head "recirc" was just running it a 2nd pass....im starting to see where I was wrong in that assumption. I do not have a "recirc" ability as currently setup. I may need to go that route and do some re-engineering :-(

Sorry - I was busy typing my long winded explanation while you left this post... Sounds like you're getting it...

[SmellsLikeSyrupNH]

Hahaha no worries!! I will review the diagram and see if it makes sense for me to make these changes.

Thank you!

[wmick]

If you are interested.... I intend to install a recirc pump within the high pressure side of my system... Not critical but just a personal choice... This, I think, will allow me to ensure that my recovery rate stays good (using a dedicated recirc pump)... Thus, allowing me to use the full capacity of the hi-pressure pump for production flow, (if I need it) rather than for recirculation.

20920

[Bricklayer]

Flow meters are definitely going to help as well. Make sure they are installed after the needle valve.
A dedicated recirc line t’d into your concentrate output from the last membrane before the needle valve and to a separate valve then to a flow meter then to the intake side of your hp pump will help you get higher first pass. As it recirc’s already processed sap and slows down concentrate out flow. This also slows down the intake of raw sap though so your not processing as much sap per hour but getting a little bit more % on the first pass.
I usually run my recirc wide open and squeeze my concentrate output down to 1-1.5 gpm at 250 psi this usually gets me to a little above 4% on 2 % sap. Using 1 4040 membrane. So you should be able to get to 4.5 or 5 with recirc using 2 membranes in series.

[wmick]

Hahaha no worries!! I will review the diagram and see if it makes sense for me to make these changes.

Thank you!

Curious how you made out with your RO, SmelllsLikeSyrupNH ??

I finally hooked power up to mine on the weekend, after some modifications and fixes.... Unfortunately, with used equipment, there are some unexpecteds... EG - 3 out of 3 pressure gauges are broken... at a closer look, the needles are all buried on the wrong side of the pin... Not sure what would ever cause that??.. Oh well... And the stock controller was faulting out on different error codes that I dont have time to mess with... So I removed the solenoid valves and wired the pumps directly... I also learned that if you want to use a dedicated "recirc pump", it needs to be something capable of producing some pressure... I underestimated the restriction that the concentrate side of the membranes would have for recirc... so my little grundfos circ pump did not provide enough flow... (wasn't sure at first, because I had just replaced the flow meter... and wasnt sure if it works or not) Plumbed recirc back into the inlet side of the pressure pump... and it is flowing much better.... Also learned that I need to get my feed tank up in the air to provide some head pressure for my feed pump, or it cavitates... Seems to run on water.... will try sap later this week, after fixing the gauges.

[SmellsLikeSyrupNH]

I ended up leaving it as it was because I was too busy to try and re-engineer it at this time. In the off season I have a vision of where I want this to go and I think I will be all set in the future.

Sorry to hear about the bad luck with the gauges and controllers. hopefully you got it all worked out.