pre-heating sap before RO

[Brent]

In the current running thread about reaching high concentrations, several comments were made about re-circulating causing heating of sap.

In my communications with DOW techs they told me that membranes lose 3% of throughput for every 1 deg C that fluid temperatures go down. So we end up with rigs running at our cool/cold sap temps and losing 2/3 of the throughput that they achieve at 20C / 68F.

So I have been thinking about all the hot water coming out of the SteamAway. On my rig its about 5 gallons at 200F every 5 minutes. If I could preheat sap to 50 or 60F I could double the throughput of the RO. Temperature regulation would be important because as we know when cleaning, they tell us not to exceed 115F. Not sure if that limit is because of the acidic and basic solutions or just a high end limit for the membrane under any circumstances.

Anyway, the comments in the "high concentration" thread sounded like getting the sap warm was not good. If the sap goes directly from the RO to the head tank and is boiling within say 30 minutes, is it really going to result in that much more growth and darkening of syrup.?????
Maybe my preheating idea is DOA.

[sapman]

Brent, I think I like your idea. But I would live close to the edge, I think, and try to only have a few minute cushion of sap in the head tank. Say a couple inches of concentrate. This would keep one on their toes! But if it gained a lot, might be worth it.

Now realistically, I'm not sure how much heat you could transfer flowing say 6-9gpm of sap, on my ro, and pulling off only 1gpm of hot water.

[Bucket Head]

Hi Guys,

If you could heat the sap to where you wanted it, it would come down to how fast you could get it boiling from there to kill the bacteria. Bacteria multiplies extremly fast from 50 degrees on up. Its something like (or very close to, if I'm remembering right) from 50 degrees and higher the bacteria multiplies 100% every twenty minutes. Dr. Tim would know the exact numbers I'm sure, but it is just an incredible increase of bacteria once it hits a certain temperature. There would be no room for errors, breakdowns, late-arriving hired help or any other type of delay once that sap came out of the RO!

Steve

[Cider Hill Maple Farm]

Steve,
I've been pondering the same idea as Brent, but this brings up another concern I have about bringing the sap up to a boil to kill off the bacteria. Right now I'm boiling on a 2'x3' sectioned pan that I built with a preheat pan in back and above. That seems to work fine and both boil great, but I added a coil inside the arch and recirc. cold sap to a stainless tank off the side, then control flow into the preheat to keep the boil going. The recirc. sap temp. gets to 160 F in the tank before it hits the evap. I was going with idea of using this to pre heat before an RO (That I'm in the building design phase still), but the bacteria problem is on my mind now. My rig doesn't have the best evap. rate going so I have a lot of hot idle sap. This is the whole reason I want to build an RO and increase the size of my evap. with a flue pan,floats and ect. What do you or anyone else think?????

Thanks, Shawn C.

[twobears1224]

get and hookup two plate heat exchangers to heat and cool the sap and you,ll be set. dairy supply companys sell then.

[Snowy Pass Maple]

Has anyone tried using a UV sterilizer ahead of the RO unit and then preheating?

I would think that this would help considerably. I'm working on a small RO design now and have been looking at adding a small UV unit based on comments from older threads discussing the bacteria problem. I've seen a UV suggested many times, but couldn't find anyone trying it yet.

[Brent]

I got excited about it in the first couple of years. Then eventually found that for whatever reason, we were making very light and occasionally medium syrup. The idea of using UV
is to reduce the bacteria that cause the sugars to invert and make darker syrup. Since we can't make dark syrup, we gave up on that idea. People who seek out a small syrup producer, at least around here, want a more robust darker syrup. Maybe this year with one year older pipeline, we'll finally get some true dark stuff.

[Cider Hill Maple Farm]

I got excited about it in the first couple of years. Then eventually found that for whatever reason, we were making very light and occasionally medium syrup. The idea of using UV
is to reduce the bacteria that cause the sugars to invert and make darker syrup. Since we can't make dark syrup, we gave up on that idea. People who seek out a small syrup producer, at least around here, want a more robust darker syrup. Maybe this year with one year older pipeline, we'll finally get some true dark stuff.

Brent did you give up on the UV and RO or just the UV? I have a feeling if I make light syrup ( Fancy ) we might have the same results with our folks we give the syrup to, most of us like the dark amber around here as well, heck I'll drown a stack with B+ any day!!

[Big John]

We run a 3600 cdl machine and cold sap goes through way better. we shoot for 18-22 brix.

[wiam]

I believe Glenn Goodrich in Cabot runs all his sap through uv lights before the ro. He makes a lot of light syrup.

[Brent]

Shawn we just dropped the idea of the UV. Still running the RO. If you put sap through an RO and boil it immediately is generally gives you lighter syrup because the sap does not stay in the pans boiling so long. Darkening, in the 50 words or less explanation, is the result of microbes making invert sugars, that darken syrup the longer it boils.

[Bucket Head]

Shawn,

I don't think 160 degree sap would be good for an RO. Their only supposed to go up to about 115, and thats for the wash cycle. Going back to the bacteria concern at 160, is'nt that the temperature of pastuerization? And its only 20 degrees away from the reccomended bottling temp. I would think at those temps. you would be minimizing the bacteria. However the bacteria issue would not be an issue with a bigger RO and evaporator. You could proccess sap pretty quick, even with only running the RO on the "cold" sap that was collected that day. I do plan on running my sap through a good sized U.V. unit this year after gathering. Only because my father and I will gather sap for several days and boil when we have enough or on the weekends. I'm looking for a little advantage in sap qaulity due to the storage time. I'm not trying to get more of any one grade, I'm trying to get a better grade than what I would have had if the sap had set without any bacteria reduction going on.

Steve

[Brent]

Shawn, you have no info in you post or your signature about how many taps you're running, but there is a big disconnect when you talk about running and
RO with a real small (likely flat bottom) evaporator.
Tell us a little more about what you're doing.

Steve is right. 160 degrees is death for an RO membrane. As I said in my openning post, controlling the temp not to go to 115 degrees will be a challenge. And when you get
an RO going with a sizeable evaporator, the last thing you need is another manual system to run. Chinese Fire Drill is something that comes to mind.

[Snowy Pass Maple]

Having perused the many UV and previous hobby RO threads a bit this evening, I think using a UV module would be good insurance to keep a small scale RO running cleaner (targeting 50-100 gal permeate/day - looking at using two 100 GPD Filmtecs) - especially when considering that I have a day job and won't boil daily. And I'd like to keep the option of warming the sap if necessary - ideally, I would want to heat just enough to get the system up to the point where I'm pump-limited with the aquatec 8800. The heat cost per gallon to warm a few degrees (assuming UV keeps it stable) should be fairly negligible as it takes very little energy to heat the water a few degrees as compared to bringing it all the way up to the boiling point and then vaporizing - and if it markedly increases the RO output, that may be a very worthwhile cost tradeoff.

I was thinking about trying the UV inside the RO circulation loop which would help keep knocking back and microbial development as it runs. I've also gathered that the preferred method is to put the UV somewhere after a 1-5 micron filter - beyond that, not sure if most RO users use it in the circulation loop or on the sap source line?

The other consideration I have is that I'm going to practice on maple using sap from ~15 taps - but my primary objective for this system is birch with potentially quite a few more taps. Last year I made a half gallon or so of birch syrup using multiple freeze concentration cycles followed by a non-boiling slow concentration on my indoor woodstove. This was a lot of work, and I think could be a very good application for a hobby RO - while 5% maple may not get people as excited as double digits, getting to 5% with birch would be awesome compared to the alternatives!

The other big wildcard here will be that birch seems to have a ton more mineral content which may present some more challenges for the RO; it's also notoriously easy to darken and degrade, so I would love nothing more than to have a problem with birch syrup that is too light - I'm not sure that is possible :lol:

[Teuchtar]

I like Brents idea about pre-warming the sap. The Lapierre manual refers to Dow Filmtecs relationship between sap temp and throughput. Can we hear it from people who have done this and measured flow at cold sap temperatures, and at warm ? What is the measured permeate flow at similar pressure/sugar level between cold (34F) and warm (75F).
Lapierres temperature correction chart shows a doubling of permeate flow between those two extremes. So if I can heat the sap to 77 ahead of the membrane, then straight to the evaporator, can I double RO rate and still not have excessive darkening without need for UV?

[Brent]

Right on ... but how to regulate the temperature to aobut 75 deg. ????
It gets expensive real fast if we let it get out of control to maybe 150 deg

[Snowy Pass Maple]

The heating solution could vary wildly depending on one's scale - but for a hobby sized producer, I'm thinking that hot domestic water could provide a source with a safe upper bound temperature around 115-120F. Could be as simple as having a well tank of warm water that you run a coil of tubing feeding the RO through.

If you know about how much sap you're going to process in recirculation and you know the temp of the sap and domestic hot water, then you can quickly calculate how much water the tank should have.

While the hot water costs money, if a modest use of it lets you double your RO output, you may conclude it's a great way to deal with those really high sap run days without buying a much more expensive RO system.

In my case, the hot water costs very little as the thermal solar starts kicking in more and more in the coming weeks!

Agree with Brent that for a continuous flow system, you'd have to really think through a lot more about what happens if the flow stops or slows down. But a recirculation loop with a finite heat source would not have that risk. Which is why I'm curious to see if UV could help make this whole concept viable!

[Cider Hill Maple Farm]

[QUOTE=Brent;177017]Shawn, you have no info in you post or your signature about how many taps you're running, but there is a big disconnect when you talk about running and
RO with a real small (likely flat bottom) evaporator.
Tell us a little more about what you're doing.

Steve is right. 160 degrees is death for an RO membrane. As I said in my openning post, controlling the temp not to go to 115 degrees will be a challenge. And when you get
an RO going with a sizeable evaporator, the last thing you need is another manual system to run. Chinese Fire Drill is something that comes to mind.[/QUOTE



Sorry guys about the misleading and lack of info!! I am running a small rig right now, but in the future I plan on a much much bigger unit. I added the stainless coil in the arch to boost the temp. before it hit my preheat pan to keep that guy boiling as well. It made quite a difference in the evap. rate on the small unit. I was concerned about bacteria that I could be growing in that tank before it hit the preheat pan. I didn't plan on running this extreme temp. through the RO, but to use this method to temper the fresh gathered sap in the storage tank to the recommended operating temp. How many taps? Well not to many yet, but the means are there for plentiful number on a tubing system in different locations. This hopefully a business I'm going to build for my 11 year old son, I've been a pipefitter/welder/fabricator for 23 years now so I'm building everything from scratch. Anymore questions guys please feel free to do so.

Thanks for your input ,
Shawn

[oneoldsap]

I have to think it'd be alot cheaper to operate a UV light than it would be to heat sap . I'm from the school where we keep sap as cold as possible before boiling . There's enough work to do in the sugarhouse without adding more . There's got to be a downside to heating sap upstream from the RO , or everybody would be doing it ! If anyone tries it , please post your results .

[Snowy Pass Maple]

I have to think it'd be alot cheaper to operate a UV light than it would be to heat sap . I'm from the school where we keep sap as cold as possible before boiling . There's enough work to do in the sugarhouse without adding more . There's got to be a downside to heating sap upstream from the RO , or everybody would be doing it ! If anyone tries it , please post your results .

You're right that UV is way cheaper - I am suspecting that the UV is a pre-requisite to even think about warming the sap while processing on the RO. I'm approaching the heating question from the many previous threads of folks trying to push a smaller hobby RO to do more - people that aren't big enough to justify buying a much larger RO system.

As to why everyone isn't doing it - I haven't yet seen any threads where someone has used UV with an intentional preheat either way - but a lot of good ideas and experiments from other small producers have inspired me to take a stab at it! I also didn't realize how much success people have had with the smaller units in what look like some very recent first attempts to scale down - really enjoyed reading through the threads from Gary, Brent and Boulder Trail.

[Bucket Head]

I suppose 75 degree sap would help the RO performance, but I would rather try and spend the time and energy trying to make that happen and monitoring it elswhere. I strive to get the best quality sap to my machinery and then let it do its designed job. But, the size of your operation and the amount of free time one has dictates how much experimenting can be done.

Filtering fresh sap and UVing it when its the cleanest and clearest its going to be is best. However, keep in mind that sugar molecules alter the path of UV light rays. This is why a "total kill" can be acheived with water but not maple sap. This is documented fact. I am unsure of the effectiveness of the UV in ROed concentrate. Due to the increase in sugar, I would think for it to have any noticable effect, the sap would have to be circulated very slowly (and probably recirculated many times) inorder for as much bacteria to be treated with the reduced effect of the light. And even after doing that the bacteria count might still be at a level that would create an unwanted grade of syrup. The tried and true way of decreasing bacteria is UV treating sap when it comes in, fresh, so it has the least amount of living bacteria while its stored, ROed and boiled. Oh yeah, and cleaning, rinsing, flushing, etc. your gathering and holding tanks, pumps, hoses, gathering pails, etc. You introduce a staggering amount of bacteria into fresh sap when its mixed with whatever was left behind in the equipment. I rinse out my gathering tank and flush the pump and hoses after each gathering. Yeah, its a little extra time and trouble, but have you ever stuck your head in a tank that had a little leftover sap in it that sat in the sun a day or two? That smell was bacteria that got put into the next load of sap that was gathered!

Steve

[Snowy Pass Maple]

All the points mentioned above are good points, and things I'm considering carefully in thinking about running this experiment as they have come up in many threads I've been reading.

I wouldn't think of getting near 75 for a small recirc RO system - I think Brent may have been considering going straight from the RO into the boiler where that is probably much safer.

I was thinking that if I tried the UV / warm RO / recirculation approach, I'd go to perhaps 50 F at most, by which point some of the larger home membranes should work reasonably well. It sounds like somewhere between 32-50, people find a very sharp drop-off in performance - above 50, the performance curve charts don't show any sharp changes so I don't see any reason to push it. I can't find curves going much below 50 though - there it's more just what I've read from others' experience.

I was also looking at oversizing the UV a good bit recognizing that the sap is a more challenging use - the cost only goes up $12 between units rated for 1 gallon per minute and 4 gallon per minute unit so I can't see any good reason to skimp on that.

I haven't yet found a chart looking at microbial growth rates as a function of temperature or how one monitors this (other than smell/taste!) - if anyone knows of documented links on the web, I'd be interested in checking them out!

From what I can see reading old threads is that some of these small homemade systems were probably recirculating already up to 40 F - and if they are achieving that without using UV and just thorough warm water rinses after each use, I would have to think a well-sized UV would let you push a little bit higher and get to a very nice operating point.