Small Scale RO - Parallel or series design

[dmichel]

Good evening everyone. This is my first year at making syrup and I'm loving it. I have about 100 taps outs with a small 18x60 evaporator. I'm keeping up but just barely. This summer I plan to build a small sugar shack, get prepped to run some tubing, and I'm considering building a little RO system. Not looking for anything huge, probably something capable of 100 to 150 gpd of sap processing. I've been looking at the designs online and they look fairly straightforward. The one question I have is whether there any advantage to running membranes in series or in parallel? I've seen both designs on the forum, but no discussion about which is the preferred method. Does anyone have an opinion on this? Is one better for any reason or are they essentially the same?

Thanks,

[Paperman]

Can we assume you are planning to use small under sink homeowner RO cartridges? Through put is better on parallel and sugar content is high on series. Depends on pump and your expectation of the system.

[5 Oaks]

I am going to be using the design posted here. https://sites.google.com/site/mattatuckmadnessmaplesyrup/home/homemade-reverse-osmosis-system

I am going to use a 6 membrane system, I plan to put them in 2 rows, 3 on top, 3 on bottom. Wish I could answer your question. I'd think there would be not much difference. Just remember every fitting and the more tube used is a PSI loss. (one thing I learned in the fire academy)

[DrTimPerkins]

Any single membrane can only concentrate to a certain degree depending upon the membrane properties and the RO properties (pump and design of system). You can't take a single membrane system and have it concentrate sap at 2% to 25%.....just not going to happen. And typically the higher you try to concentrate, the lower your concentrate flow output and the higher the pressures that are required.

Assuming your pump(s) can handle it, then membranes in parallel will increase the amount of sap processed per hour to a given concentration. It is basically running like running two separate systems, and the effect is additive. For example, if you produce 10 gal concentrate per hour with one membrane at a certain concentration, you will produce nearly 20 gal per hour with two (10 gal + 10 gal = 20 gal).

When the membranes are placed in series, the concentrate from the first membrane is the feed material for the second. In that case, you end up with lower flow, but the sugar concentration is higher.

Larger RO configurations are designed to operate in different configurations, and are often hybrid parallel/series machines. So a 5 post RO might have 3 running in parallel feeding two more posts in series with the first three posts, or a 3 x 2 configuration. It gets complicated, but it all depends upon how fast you want to process sap and how high you want your concentration to go and how much concentrate you wish to produce per hour. Generally there are trade-offs.

[Diesel Pro]

Probably larger than you need, but a single 4x40 at 250 psi should suit you well and have plenty of capacity for expansion. This past weekend we made 31 pints finished syrup. I used maybe a gallon and a half of gasoline (generator for RO) and well under 1/4 face cord of dry split poplar.

On a typical cook day (I'm a weekender) I start with 200+ gallons of sap and concentrate it to around 10-12%. It takes around 7-8hrs to get there depending on the temp (usually low 30's) but the boil goes fast. Get the sap up to room temp and it should go much faster.