2nd pass reduction percentages, if anyone knows.....

[SmellsLikeSyrupNH]

I have my new NextGen unit that says will process 200 gph and remove 25-30% of water per pass. If I start with a 275 gallon tank of 2% sap and run the permeate off to a separate tank and let the concentrate dump back into a 2nd tank what sort of reduction would or should I expect on that 2nd pass? Would it also be 25-30% It is warning me to not go above 8% BRIX but I don't think I will approach that with 2 passes.

So 1st pass I will remove lets say approximately 70 gallons of water (more than 3 hours of boiling time for me...new evaporator so im hoping its higher), what would I expect on that 2nd pass?

Thanks in advance......

Here is a diagram of what I plan on doing....permeate flow is not in the diagram. that will be going into 55gallon drums.
14982

[adk1]

Interesting. I will be interested in hearing what experienced sugar makers say that use ro machines. Only thing that I would say that I have learned is that the ro concentrates everything in the sap including bacteria so your essentially adding concentrated backteria into that loop and tank. Second thing is the concentrate tanks should be stainless because of that concentrating of bacteria

[bowhunter]

If you keep the pressure the same on each pass the water removed will be reduced on each pass as the sugar content increases in the concentrate. You should double the sugar concentration after two passes. It would probably take you more than 4 or 5 passes to get to 8% with 2% sap.

[maple flats]

You can do it that way, but (I have a different RO) I simply run mine into my head tank on my first pass, then I recirculate from the head tank back into the head tank.
I do 8% in first pass at 275 psi, then for second pass I back the pressure off to about 260 if I'll be there to check on it every several minutes, if I'm going to haul another load I'll usually turn the PSI down to about 230 or so.
Just watch what pressure your unit is designed to run at on the first pass, but then turn that down for the second pass. The PSI will climb shortly after starting a second pass, as it does, turn it back and you may need to do it a few times until you are fully in the higher sugar source, after that it climbs as the membrane gets coated, but not very fast. As it approaches your upper limit simply turn it back.
On mine I remove about 70-75% on the first pass and then it drops to about 60-40 and by a half hour to 3/4 hour it might be 50-50. When I'll be gone to haul more sap, I set it at 50/50 while it starts the pass, but once the unit is fully in the pass it it more like 25-30% permeate and the rest concentrate. Occasionally it shuts down on recirculate when it hits 300 PSI which is my high limit switch, but usually not unless I'm gone longer than usual.
To begin with you may not want to leave the RO unattended, but after you get comfortable with it, that will be a benefit, you can remove water while you're not there. I don't think I did that my first season, but by the second one I did.
To answer your question, it will not remove as much in the second pass, but it will still remove a good amount of water. Since your only easy way to know if it is not going higher than 8% will be the high pressure gauge, Start with a known amount of sap at a known sugar % and do the math to get 8% sugar (the easy one is 100 gal at 2% yields 25 gal at 8%, or you can double that). When you are at 8% adjust the valves to shut off on your high pressure limit switch. That is how I do it, but my upper limit is 15%.

[SmellsLikeSyrupNH]

Thanks Dave, I believe my unit is only rated to do 225psi....so I will not be able to get to those high of pressures, not sure I will want to with this smaller unit. I think right now I will just need to run it and see what it does. I got a refractometer so I'll be able to test my content while its running and prior to running. This is a LOT of new things for me this year. I will be able to switch things around if 3 passes is viable to recirculate....anything I can do to reduce that boiling time is going to be a huge help. I'll have close to double my taps of last year so I need to save those valuable hours.

Thanks again!!

[maple flats]

You must stay within the pressure range Next Gen tells you to use, but there should be similar comparisons, just that at lower pressure you squeeze less water out in a pass.

[DrTimPerkins]

I will be able to switch things around if 3 passes is viable to recirculate.

Keep in mind that each pass through an RO will warm the sap/concentrate by some amount. The higher sugar content and higher temperatures mean faster microbial growth and more rapid spoilage of the concentrate and darker syrup. After two passes you'd better plan to be boiling right away, and probably would not want to consider three passes, not only due to concentrate spoilage, but also because of membrane fouling....especially late in the season when the sap is coming in warmer.

[SmellsLikeSyrupNH]

Thanks Dr Tim, My plan will always be to go from the RO to the headtank and then to the evaporator. I don't like sitting on sap at all, so it will always go from collection to RO to boiling in one session.

[Sterling Maple]

It all depends on the pressures and flows you work at, how much water you remove. Working at maximum pressure, I can go from 2% to 20% with low out flows or 2% to 8% with high out flows. I love the 2 pass system as I have an Ultraviolet Light that disinfects the concentrate, so I am able to remove 75% of the water AND kill off the bugs. When I do the second pass, I maintain fairly high flows as I am not trying to squeeze as much water out. Not sure if this is applicable as I have one 16" post in series with three 8" posts. BTW, I think UV lights are great.

[DrTimPerkins]

It all depends on the pressures and flows you work at, how much water you remove.

Absolutely. The pressures will depend upon the machine settings (pressure set via the flow valves and capability of your pumps) and the temperature of the incoming sap and the condition of your membrane. When you have a multi-membrane system, it is also going to depend upon whether your machine is running in series or parallel (or both).

I believe that the theoretical max concentration for standard membranes is something like 4.7X the concentration of the incoming stream (for a single-pass through a membrane and not arranged in series). That would be at the ideal temperature and pressure, so it probably is not a good idea to try to go to that point.