RO without head tank

[jrgagne99]

Is anyone out there running an RO with direct feed to their evaporator, i.e. no head tank? If so, I would like to know your experiences with this configuration. The most concentrate I've had in my head tank this year has been about 2 inches of depth. It's hardly worth it, especially with having to climb up into the loft at the end of the night to clean the head tank. So I'm considering pluming the RO output directly to my steamaway, at least as an optional flow-path.

[maple flats]

It may work, but I see having no head tank as a recipe for disaster. Do you have a wood fired evaporator, or oil? If oil, maybe, but still not a good idea in my opinion, if wood you better have an Oh S*^it back up plan!

[BSHC]

are you saying you ran all year with only 2 inches in the head tank? I hope as maple flats said you had a backup plan in case the ro quit.

[ecp]

Its funny you bring this up because I have said for a while if someone were to put a water depth sensor on a piggyback/steam away with a signal that can modulate a valve on the RO concentrate line that should work perfect. You would get the highest concentrate for your evaporation rate and not have the added expensive of a tank plus cleaning the tank every time. Personally I would never go that route because there are days that we start the RO and go to dinner, and I like having a consistent concentrate feeding the evaporator so that things are not going up and down all the time. My other idea was a brix reader and a valve with VFD's on the RO so that you could get that consistent feed at a consistent concentration, but I don't know if the agricultural market is ready for a change like that.

[jrgagne99]

Dave and BSHC: In case the RO quits, my backup is the ~10 gallons of concentrate bubbling away in my steam away. Plus whatever condensate I happen to have on hand, which is generally at least one 5-gallon pail once things get rolling. More than enough to avoid disaster, with the ~20 minute burn down time on my wood fired rig..

ECP: I like your idea, but my system (avatar photo and described in signature below) is entirely manual control-- not even any floats. So automated concentrate flow rate, which is relatively complicated I think, probably wouldn't be a good choice for me to start adding automation.

For now, I think I will keep the head tank, but will plumb in a branch line that bypasses the tank and directly feeds the evaporator.

[ecp]

You could always try the VFD option on your pressure pumps so that you could match the flow rates. That would still be manual but maybe serve better in matching the flow rates.

[jrgagne99]

I suppose I could try that. But my simple minded approach to modulate concentrate flow is to just use my main needle valve. I've done this on rare occasions when I need to feed in sap quickly. It works for me, partly because I have poor-man's internal recirculation on the RO. The recirc restriction valve basically sets the membrane pressure and keeps it pretty steady, even if I say double my concentrate outlet (at a reduced percentage). It's because the recirculation flow is several times more than the concentrate outlet flow- so tweaking the conc outlet isn't really changing the total flow over the membranes.

[jrgagne99]

Update... I've been feeding the evaporator directly off the RO this year, (no concentrate tank) and so far it is working pretty well. Only minor occasional adjustments to my concentrate output are needed. In the end, it saves me a trip upstairs at the end of the night to clean the concentrate tank. Not a big deal, but I'll take it.

[maple flats]

You have more nerve than I do.

[ennismaple]

I like to maximize my concentrate Brix and adjust when I start up the evaporator to try to run out of concentrate about when my last fire goes on. Doesn't have to be perfect but it takes the worry out of boiling. Rinsing the concentrate tank takes 5 minutes, cleaning a burnt pan takes many hours or $$$ if it's ruined.

[jrgagne99]

Not too much nerve required. If the RO breaks, my safety net is the steam-away volume, which is more than enough to feed the evaporator until the fire dies down. Not to mention buckets of steamaway condensate if stuff really goes south.

[DrTimPerkins]

...my simple minded approach to modulate concentrate flow is to just use my main needle valve.

Our Lapierre HyperBrix RO is set up to do that. Dial in the Brix you want on the meter and it adjusts the needle valve to keep it at that level. However we don't feed the evaporator from the RO directly. It goes to a refrigerated bulk tank instead. Typically we stock up 750-1000 gal of 35 Brix concentrate before we boil -- about once every 4-7 days. Real nice to NOT have to boil daily.

[maple flats]

Yes, but to do that you refrigerate the 35% concentrate to about 25F. Maybe you forgot that point? I doubt it, Dr Tim!