Fuel Tank Water Storage

[tenthbuzz]

Kinda of new here. Been watching for a while. I am considering a boiler install this year and I am wondering if a farm style fuel tank would work for water storage on a non pressurized system. There are a lot of these tanks available locally in different sizes.

 

[hobbyheater]

Kinda of new here. Been watching for a while. I am considering a boiler install this year and I am wondering if a farm style fuel tank would work for water storage on a non pressurized system. There are a lot of these tanks available locally in different sizes

In most cases the boiler will have to be run under pressure to prevent corrosion to the inside of its water vessel. The heated water to the storage tank will have to go through a flat plate heat exchanger the size to be determined by the output of your boiler .(broken link removed to http://www.ebay.ca/itm/FHPE-Flat-Plate-Heat-Exchanger-30-Plate-WVO-SVO-/280783203797?pt=LH_DefaultDomain_0&hash=item415ffbadd5) The heat exchanger will allow your storage tank to remain unpressurized.

On the storage tank - for example 1000 gallons when heated from 120 to 185 degrees creates around thirty gallons of expansion and this expansion water will have to be stored somewhere. If you have easy access to one of these tank, mount a 50 gallon drum just above the storage tank and fill both with water and vent the top of the 50 gallon drum so there is no pressure. If the static pressure created by the 50 gallons in the drum does not make the storage tank bulge you are a go.

 

[tenthbuzz]

In most cases the boiler will have to be run under pressure to prevent corrosion to the inside of its water vessel. The heated water to the storage tank will have to go through a flat plate heat exchanger the size to be determined by the output of your boiler .(broken link removed to http://www.ebay.ca/itm/FHPE-Flat-Plate-Heat-Exchanger-30-Plate-WVO-SVO-/280783203797?pt=LH_DefaultDomain_0&hash=item415ffbadd5) The heat exchanger will allow your storage tank to remain unpressurized.

On the storage tank - for example 1000 gallons when heated from 120 to 185 degrees creates around thirty gallons of expansion and this expansion water will have to be stored somewhere. If you have easy access to one of these tank, mount a 50 gallon drum just above the storage tank and fill both with water and vent the top of the 50 gallon drum so there is no pressure. If the static pressure created by the 50 gallons in the drum does not make the storage tank bulge you are a go.

Thanks for all the info Hobby Heater, I am learning new things already. I guess that I would then circulate the storage water through a second flat plate exchanger tied into my existing propane boiler loop. If so would I be losing lots of efficiency from the 2 exchangers? Both would be in heated areas.

 

[Mark Holden]

the tank will need fittings welded; make sure you have someone who is willing to do that, and knows how to weld a fuel tank without blowing himself up.
There could be some difficult insurance issues as you're in the US.
Even I, a fairly nutty guy who has welded quite a few fuel tanks, would be hesitant to work on one of those at a normal wage.

 

[hobbyheater]

Thanks for all the info Hobby Heater, I am learning new things already. I guess that I would then circulate the storage water through a second flat plate exchanger tied into my existing propane boiler loop. If so would I be losing lots of efficiency from the 2 exchangers? Both would be in heated areas.

With the flat plate exchanger between the boiler and storage, it is difficult to get storage up to max temp (180 - 190 range) without having the fire in the boiler cycle and when the boiler cycles, this is where your combustion efficiency drops as compared to a complete batch burn. But having a storage tank that cannot operate at 2 -3 psi static pressure is a price you will have to pay.
For simplicity, my choice would be to put heat exchangers (coils) inside the storage tank; one for the heating side and the second for DHW.
http://www.ahona.com/ this company makes these coil type heat exchanger that would thread into 3" or 4" pipe flange into the storage tank.
http://www.boilersupplies.com/tankheaters/index.html This is a website where you can see some examples of coils.

 

[Bob Rohr]

Coils in tanks ate certainly the easiest way to build a HX. With copper coils you would get great thermal transfer, copper is an excellent conductor.

The secret to plate type heat exchangers is they have two pumped flows. Turbulent flow breaks up the boundry layers that you get with a coil in water that is not moving. Yes it does take and additional pump to pipe them but the heat exchange is much better than a coil in still water.

The copper tube side arm HX that many OWF companies sell are poor performers for the same reason, they depend on a thermosiphon to move the heat transfer.

You should be able to size the plate type hx to get within 5 degrees A side to B side. It does take more HX surface to get a "close approach" tight temperature, and the larger sized HX should eliminate any boiler shore cycles also.

Below is a good article that describes various DHW devises and pros and cons.

There is a big movement towards plate or tankless style heaters to eliminate standby loss, but also legionella potential with a tank of below 130 stored water, as is the case with modern DHW tanks that have had their temperatures limited for scald potential reasons.

hr

www.pmmag.com/Articles/Column/BNP_GUID_9-5-2006_A_10000000000001189359

 

[maple1]

The secret to plate type heat exchangers is they have two pumped flows. Turbulent flow breaks up the boundry layers that you get with a coil in water that is not moving. Yes it does take and additional pump to pipe them but the heat exchange is much better than a coil in still water.

The copper tube side arm HX that many OWF companies sell are poor performers for the same reason, they depend on a thermosiphon to move the heat transfer.

Agree wholeheartedly about tankless coils. When using hot water with ours in the summer, sometimes the hot water out of the taps will cool off to barely warm enough (or cooler), before the aquastat senses the temp drop & kicks the oil burner on - just in time to heat the water in the boiler, but after the need has stopped. It doesn't take long for a coil to cool off in water that is not circulating around it, and unless the aquastat is right next to the coil, it takes a while for the aquastat to sense it. That can all be avoided, of course, by raising your boiler temp - but that also raises the amount of stand by heat losses tremendously.

On the sidearm, I am hoping to make a good performer out of the one I just got in my setup. I think the thermosiphon effect can be an advantage if it can be set up right. It can quietly do its thing charging up my 80 gallon electric hot water tank in periods of non-use (like overnight, or middle of the day when nobody is home) to hopefully hotter temps than required, then there is lots of hot water on hand when needed as running through a mixing valve on the way to the taps will extend the 80 gallons even further. All with no added pumping/controlling complexity. I have yet to put that to the test though, but am working on it...

 

[infinitymike]

the tank will need fittings welded; make sure you have someone who is willing to do that, and knows how to weld a fuel tank without blowing himself up.
There could be some difficult insurance issues as you're in the US.
Even I, a fairly nutty guy who has welded quite a few fuel tanks, would be hesitant to work on one of those at a normal wage.

Could you fill the tank completely with water to "push" the fumes out, then drain some down just below where you need to weld? Or even better, could you weld with water right up against the fitting?

 

[Bob Rohr]

Agree wholeheartedly about tankless coils. When using hot water with ours in the summer, sometimes the hot water out of the taps will cool off to barely warm enough (or cooler), before the aquastat senses the temp drop & kicks the oil burner on - just in time to heat the water in the boiler, but after the need has stopped. It doesn't take long for a coil to cool off in water that is not circulating around it, and unless the aquastat is right next to the coil, it takes a while for the aquastat to sense it. That can all be avoided, of course, by raising your boiler temp - but that also raises the amount of stand by heat losses tremendously.

On the sidearm, I am hoping to make a good performer out of the one I just got in my setup. I think the thermosiphon effect can be an advantage if it can be set up right. It can quietly do its thing charging up my 80 gallon electric hot water tank in periods of non-use (like overnight, or middle of the day when nobody is home) to hopefully hotter temps than required, then there is lots of hot water on hand when needed as running through a mixing valve on the way to the taps will extend the 80 gallons even further. All with no added pumping/controlling complexity. I have yet to put that to the test though, but am working on it...

Those side arms work fine, probably thousands of them installed. Recovery can be slow, sometimes all day for an 80 gallon tank.

Watch out for tank over-heating issues. If the HW tank gets too hot it can trip out the ECO on gas fired water heaters or the "red" pop thermal over load on electric tanks. My electric over-heat thermal pop, trips if the solar warms my tank to 165F. I suspect manufacturers have backed off the temperature on those safetys over the years, I remember running tanks to 180F in the past.

Gas fired tanks have ECOs, (energy cut out") switches built into the aquastat. I believe they shut off fuel supply if the tank reaches 190F. or lower and need to be replaced if they trip.

You are wise to invest in a top quality, listed 3 way thermostatic device for the tank output. Look for a ASSE 1017 that works on temperature and pressure changes.

 

[nate379]

It doesn't weld good with water around it like that. Sure in a pinch you do what you have do (water main is leaking or something), but the water pulls the heat from the weld.

I would just fill it with some soap and water a few times to clean it out and then weld it. Less worry if it was diesel and not gas too.

BUT a fuel tank won't last long with water in it. The insides are usually bare steel and it'll rust fast. I suppose if the tank was cheap enough, could just replace it now and then though.

Could you fill the tank completely with water to "push" the fumes out, then drain some down just below where you need to weld? Or even better, could you weld with water right up against the fitting?

 

[Mark Holden]

I've welded tanks full of water, it's the favored method. sometimes it isn't practical, like if it weighs several tons and you can't roll it around to get the fitting to the top.
I've even welded leaks while water was coming through from the other side; this is fairly normal when welding old barges at the shipyard. Just crank up the heat and push. Theoretically, you're not supposed to do this [hydrogen enbrittlement the textbooks say], but in practice it's fine for low stress items. I mean, if it were a serious pressure vessel that kind of thing wouldn't do. Of course that's only for a crack, you can't weld a fitting while water blasts out around the edges like a firehose.
Water pulling heat from the weld isn't a problem, you just turn up the power. I've welded with water on the other side of the plate, could hear it boiling as I worked. I've done it with diesel too, welding braces to the outside of a full tank. I waited until it was full, I wouldn't do that if it were empty.
I have used inert gas in the tank while welding; nitrogen and another time CO. I let it bleed through the tank as I worked. Lots of black smoke came out. There was diesel in the bottom of both those tanks at the time.

Once I worked on a tank with a really large manhole at one end; I just took the cover off and blew air through with a fan to clear the fumes as I welded a 2" filling pipe through the top. There was an inch of diesel in the bottom, and the tank was 3' wide and 6' long. I figured if the fumes would blow with it open like that, nothing would happen. I just didn't stand near the opening while I worked!

But I would never weld on a fuel tank that had simply been cleaned with soap and water; I've been warned that that's how people blow themselves up, and I take those warnings seriously.

For a gasoline tank, I would only weld when full of water. even ex-LPG isn't as dangerous.

As for corrosion, all of these tanks are the same material, mild steel. ex-lpg and other ex-fuel tanks are all the same stuff. A vented tank will have to have some sort of anti-corrosion chemical added. A closed [pressurized] system will soon turn anaerobic [the water goes black] and then be fine. That's how regular central heating systems work.

 

[nate379]

Why the hell is it that no matter than I say, someone has to one up me with how I'm wrong and they are a pro this that or the other?

 

[hobbyheater]

Why the hell is it that no matter than I say, someone has to one up me with how I'm wrong and they are a pro this that or the other?

I know how you feel. It must be where we live!

 

[Mark Holden]

Sorry...
If it makes you feel any better, I'm not really professional, just a very experienced amateur.

 

[jebatty]

There have been lots of prior posts on using fuel tanks in open systems, especially used fuel oil tanks like homeowners have, about 250 gal or so. My first attempt at storage used 3 of these, in use one heating season. I also mig welded fittings on the tanks. My welding is very amateurish and I had pinhole leaks. I sealed one leak with silicon by smearing it on the inside of the welded fitting.

Corrosion may be a big issue. I didn't use any water treatment, as I figured that even though the system was open (vented to let expansion air in and out), air movement would be minimal and corrosion rust would soon stop, not so. My fill water had pH slighter higher than 7.5 or so, that is, acidic, and corrosion was major and fast. One tank soon developed a leak through the shell. I suggest paying lots of attention to water treatment and corrosion prevention if you decide to use a fuel tank in an open system.

All heat exchangers, plate, coil, sidearm, etc., become less effective at a given flow rate as in-out delta-T temperatures close. There also are lots of posts on this topic. My only experience is with plate hx's, as the storage tanks I have used had no feasible access to install coils, and I may not have used coils anyway due to cost.

In short, I was not at all satisfied with fuel tank open storage. Maybe mostly due to my mistakes. But after the first season I bought a used 1000 gal LP tank, cleaned it, used fittings it came with for 2 heating seasons, and then had 2" fittings welded on by a pro welder, which now I have used for 2 heating seasons and ready to start the 3rd season this year. I don't use this for dhw as no need for that in my installation. For a 2nd "in short," my system now works about as perfectly and trouble free as I could imagine. Perhaps others have open systems about which they would say the same thing.

Whatever your decision, I hope it works well for you. Mistakes can be expensive and even dangerous, depending on the circumstances.

 

[infinitymike]

Sorry...
If it makes you feel any better, I'm not really professional, just a very experienced amateur.

Well I'm glad for experienced amateurs. I guess I wasn't completely wrong.

 

[Mark Holden]

Jebatty, is your new tank also open?
LPG tanks are much ticker than unpressurized tanks they use for oil; it could be that it just takes longer to rust through. Did you check the ph, etc?
It's a problem I've been giving a lot of thought to. I haven't found any affordable anti-corrosive chemicals here in southern Portugal. I'd prefer a sealed system but for the cost of the huge expansion tank it would need.

 

[Fred61]

I started with a 500 gallon steel oil tank and coated the inside with a two part epoxy that was touted as a special coating for water tanks. After one heating season, I re-entered the tank and found that the coating had cracked and separated in several places and had lifted off most of the surface. I replaced it with a 500 gallon stainless chemical tank that was so in-expensive I couldn't pass it up.
I did a post mortem on the oil tank and found what appears to be electronic corrosion. Deep pits on the bottom and within four inches from the top. It wouldn't have lasted another season. I had treated the water but it did not appear to have done any good.
I'm curious if a sacrificial zinc annode would have changed anything. I'm actually thinking about installing one on my stainless tank which has been in service for two seasons.

 

[Mark Holden]

Fred; I looked into this subject for my work on fresh water barges.
An electrochemical cell will spontaneously form on the surface of mild steel immersed in water, even fresh water. I found that an aluminum anode had very little effect, only protecting the metal for a couple of feet, but a magnesium anode had a protective effect for about 6 feet. It depends on the chemical makup of the water, and I don't know what happens in rusty water that we
Anodes will work, but without a good coating, they won't last long. What they do well is protect tiny areas where the coating is compromised.
I have to say, I never liked epoxy coatings for just the reason you gave. Some friends of mine love the stuff, and say their boats can stay in the water for 10-20 years without maintenance.These are 50-100 ton barges.
What did you treat your water with?
As far as I know, you don't need an anode to protect a stainless tank; but I gather others on the forum have stainless tanks, so I'm interested to hear real experiences. Stainless is protected by an oxide layer that forms on the surface, and in the absence of oxygen you can get corrosion. A lot depends on the alloy of the tank. Stainless water heater tanks I've seen don't have anodes.
I've welded on a small stainless tank; it was tough, since the metal was thin and I don't have a mig / tig machine. I did it with stick.
Glass coated steel water heater tanks use anodes; I think those anodes would be a good choice for other coated steel tanks, but the tanks will need an internal coating for sure if there's going to be any oxygen in the water.
Anaerobic water will absorb oxygen if exposed to the atmosphere, so I don't think there's any halfway state; a system is either open or closed.

 

[Fred61]

I treated the water with a product from Qualichem Technologies but I don't remember the part number nor the name of the product.
The wall of my stainless tank appears to be thicker than the standard milk or brewery tanks I've seen. I didn't measure them because the top rim is supported with a substantial piece of angle welded around the top.
Although I've had a welder plugged in for thirty years in my shops, I weld so infrequently I still consider my welds to be in the "bubble gum" class. I had a local shop weld in fittings for return water and for wells in the top, center and bottom of the sidewalls as well as fittings for the sight glass. I have a snorkel that vents through the top and is directed to the outside of the house in order for the tank to breath and keep the moisture out of my basement. My house is very tight and any moisture hangs around for a long time. Approaching the need for an air to air exchanger.
Do you think those barges would last 20 years if the water they are in, went from 130 to180 on a daily basis?
I'm wondering if I should take the time to inspect the tank before too many years pass to see what's happening in there. Although I did the insulating so I can re-enter and built the top cover in two pieces, it's still a pain.

 

[Mark Holden]

I don't expect those barges to last 20 years in the water that they're in, unless the owner takes them to the shipyard in between. I should add that they're already more than 100 years old, and are riveted steel with bitumen at the seams. I don't think epoxy will stick there.
I don't think there's any point in looking in your tank; if there is any crevice corrosion going on, it will be nearly imposable to see.
It's unlikely anyone made a big stainless tank from low grade material; those tanks are made for either food or chemicals, and either way they would have used 320 or better. It'll be fine, I think we can all envy you for that.
I've been told of some anti-corrosive additives, use this or use that they tell me, but I'm skeptical. Rust has cost me too much money in the past; it never sleeps the Dutch say. But if someone [or better, several people] tell me of something they used for years, and it works, I'll give it serious consideration. If it's cheaper than a closed system.

 

[nate379]

I'm not saying I'm a pro at everything or never wrong, very far from, but I think all can understand my frustration?

Yes you can weld with water on the other side, or heck in water even, but it doesn't weld decent WITHOUT having specific equipment that can crank the heat and shield the weld properly... none of that the average "hobbyist" weldor will have.

So without typing way too much, this is very much correct: "It doesn't weld good with water around it like that. Sure in a pinch you do what you have do (water main is leaking or something), but the water pulls the heat from the weld."

 

[jebatty]

Mark Holden: Jebatty, is your new tank also open?
LPG tanks are much ticker than unpressurized tanks they use for oil; it could be that it just takes longer to rust through. Did you check the ph, etc?

My new tank is pressurized. The first year I did my own water treatment, primarily with sodium hydroxide (aka lye aka caustic soda) to raise the pH. Then I moved the Tarm and tank to my new shop and I treated the entire pressurized system with chemicals from Wood Boiler Solutions. I don't recall at the moment the final tested pH, but it was above 9. Both with my treatment and the WBS treatment, boiler water has remained clear in color and no evidence of corrosion anywhere. The open system was deep orange colored in short order and lots of rust-type corrosion was occurring.

All plumbing is black iron and copper, brass valves, except in-floor is pex.

I also have a water filter on system supply to a plate hx and mixing valve which supplies 100F water to my in-floor heat. After a year, when I changed the filter, the filter was nearly the same color as new and it did not appear that it was filtering anything out of the system water. The same is true when I drain a few ounces of water from the boiler - nearly clear in color and no change after two years of operation following the WBS treatment. I used the filter to protect the plate hx from potential clogging.

I tend to think in a closed, pressurized system, the most important factor is pH. I see recommendations on pH from 8.5 to 11 in the literature. Low pH, i.e. acidic water, is very corrosive in my experience, and in an open system may quickly lead to a major system failure.

 

[maple1]

So I've got this jar of stuff called 'PH Booster' for our swimming pool. Doesn't seem to take a whole lot of it sprinkled around to raise the PH of our small 5000 gallon pool a bit. Says on the side 'contains sodium carbonate'. What bad things would happen if that were used to raise boiler & tank water PH? Thinking it must be on the harmless side if its made for water you'd be swimming in.

 

[jebatty]

I used sodium carbonate initially. My water pH was about 6.5, and it took a lot for little effect. I then switched to sodium hydroxide, mixing and adding small batches at a time. It was very effective at raising pH. Be cautious with sodium hydroxide, as it can cause serious burns or worse. Wear eye and hand protection at the minimum.