RO pressure with regards to temperature

[metzger1]

we have a Lapierre turbo 600 and in the manual it gives all this technical info about how the sap temp affects the processing, and how warmer or colder sap will effect the life of the membrane, but it doesn't give any simple parameters for the novice to understand where we should set the pressure in accordance with sap temperature in order to give the membrane a longer life. I have called them, but the techs I end up getting speak broken English, or keep giving me long formulas that I don't understand. There has got to be a rule of thumb... like if the sap temp is within this range, then it's best to run the pressure in this range, and if it's warmer go lower and if it's higher go higher....or something like that. Does anyone have a simple formula in this area? Thanks

[bowhunter]

I'm a retired Chemical Engineer and have studied RO, but haven't operated one in maple sap application. If you don't get any good advice from others on the forum, I would be happy to look at the manual/technical info and try and interpret some of it for you. I have a pretty good understanding of how RO works with the affects of temperature, pressure and sugar concentration. If you send me a scan of the technical pages on temperature and pressure I'll do my best to give you some guidance. I assume they have either tables of data or they have curves showing the impact of pressure and temperature.

Dave

[metzger1]

thank you bowhunter, and yes there is both tables of data and curves. Here is a link to the manual. The info I was referring to starts on page 25 http://www.sugaringequipment.elapierre.com/down/203.pdf
thanks again for any insight you might be able to offer

[bowhunter]

I looked at the manual and some other sources online and they really don't give you very much information, but here's what I can tell you:
- The membrane design specifications are set at a pressure of 225 psi and 13 degrees centigrade or 55.4 degrees F. This is where the manufacturers sets the expected performance.
- They have provided a temperature correction factor table so that you can tell if the membrane isn't performing as expected. In rough terms you lose about 1.4% of permeate flow per 1 degree drop in sap temperature. So let's say your system was designed to remove 7.5 gallons per minute of water with a total flow of 10 gallons per minute of sap through the unit at 225 psi and 55.4 degrees F. If the sap temperature is really 38 degrees F you will only get about 70% of 7.5 gallons per minute or 5.3 gallons per minute of permeate flow at 225 psi.
- Unfortunately they don't provide any factors to adjust for pressure. They only say that the relationship between pressure and permeate flow is linear. I was not able to find any data on the relationship between pressure and flow for these bigger membranes online, but I do have some pressure curves for some of Dow smaller filmtech membranes. So here's my guidance:

1. I would generally recommend you start with the lowest pressure you can get the desired water removal. Let's assume that's 75% as designed. This just requires the least amount of electricity to operate the unit. The unit was designed to operate between 250 psi and 400 psi. Above I said the membrane itself was designed around the conditions of 55.4 degrees F and 225 psi. All this really means is that you will have to operate the membrane above 225 psi because the temperature is below 55.4 degrees.
2. Based on pressure data I've seen for smaller membranes, I am pretty sure you should be able to recover the lost performance by increasing the pressure by 1 psi for every degree of temperature. So if you have the system set up to operate at 75% removal at 250 psi and 40 degree sap and the sap temperature drops to 35 degrees increasing the pressure to 255 psi should be adequate. One word of caution here is that there are many factors affecting performance and this may not be enough increase in pressure. I say this because the maximum design pressure is 400 psi which is well above what you would expect to be required to get the desired performance.
3. I would recommend staying at or below 75% on permeate flow. In other words at 600 gallons per hour of sap flow do not routinely exceed 7.5 gallons per minute of permeate flow. That should insure longer life on the membrane. Make sure you do the cleaning when the performance drops by 15% as recommended. If you wait too long to clean them they will become so fouled that they will have to be replaced.

I'm sure this isn't that clear so don't hesitate to ask for more clarification. Unfortunately the membrane manufacturers don't share their pressure data because it's part of what's called intellectual property and is probably protected by patents. I wanted to get back to you as quickly as I could because I know the season is almost over.

Dave

[metzger1]

Sorry I took so long to write back and thank you bowhunter, but the sap has been running well here for the last week and I finally got a break. Your information has been helpful. I have actually also been trying to read the manuals Dow has online with regards to their membranes and it is very difficult to get real world answers, although it was helpful in learning more about cleaning them. Unfortunately, advice that I got 2 years ago from a man giving a seminar at Leaders open house has probably caused my membrane to deteriorate prematurely. He said to rarely use soap to wash the membrane and to use multiple hot water only washes instead. We did that last season, and our performance dropped and we have struggled to get it back, and after reading the Dow manual it is clear to me, that sparing the soap washes was a huge mistake, and is likely what has caused our performance drop. We are trying to get it back, but I am not sure if we will be able too. Any advice on this would also be appreciated.

[bowhunter]

I don't know if you saw this or not. It's a nice presentation by H2O innovation on RO operation and cleaning. They have a lot of details on the cleaning process. Also some of the guys with homemade RO's are having pretty good success with a 5% food grade hydrogen peroxide wash, but I don't know if it would be that effective on the commercial RO units. My guess is that it's not effective because few if any of the RO manufacturers recommend it's use. I think the key to longevity is to measure the performance following the manufacturer's recommendation and cleaning when the performance first drops. I think between this presentation and your manual you have all the information you to monitor the performance. http://maple.h2oinnovation.com/wp-content/uploads/2011/04/H2O_Innovation_Maple_Membrane_Training_2011_ENG.pd f

[Sunday Rock Maple]

Regarding the hot water damaged membrane --- Lapierre will test and clean any manufacturers membrane during the off season for a little less than $200. At least that way you'd either know it's bad, or have it back to specs for the start of next year.

[metzger1]

Thanks bowhunter, that was very helpful. I see that they say that pressure does not effect the life of the membrane which is reassuring. And yes, we do have it cleaned and tested after each season, but by Dominion and Grimm as I prefer not to deal with Lapierre anymore. We dealt with them for many years and the service is terrible. They lost our membrane one year and it was into the next season before we got it straightened out and got it back and that was just one of many major problems. But yes, we do get it professionally cleaned and we get the report, which is why I know that we lost production capacity after the year we followed the no soap advice. Thanks all.