2800 gallon steel storage tank

[SnowTraveler]

I may have an opportunity to purchase a brand new 2800 gallon ASME storage tank, already pre-fabbed with legs. I would have to build a building to house it in, which I do not mind, as I may be able to buy the tank for a very reasonable price. I currently have an Econoburn 150 with 500G storage, the addition of the 500G allowed me to run much, much better than without storage. My question to you folks here is would you consider 2800 gallons too much? I believe I could get it up to temp, even in very cold weather, as my house is very well insulated. Your thoughts on this will be appreciated.

 

[MrEd]

Just curious...what is a "very reasonable price"? Would this be pressurized? If so you are going to need to budget well north of a grand, maybe $1500 just for expansion tanks if they are bought new...

That said, if I had an opportunity to get one at a "very reasonable price", I'd probably be trying to figure out how to put it to use myself...

 

[SnowTraveler]

I have to bid on it from my employer, as it is surplus from a project and will most likely sell for near scrap value. I can only imagine what they paid for this tank. I inquired about it and received a very positive response about the ability to purchase it. I would then have to arrange for transport and rigging, but I have connections there. I am hoping to hit a home run here. The tank will be pressurized and I will need some helping sizing the expansion tanks and maybe some links on where to buy them.

 

[mpilihp]

Gee maybe you could use your current 500 gal for expansion tank?

Gonna take alot of insulation to wrap that thing up!

 

[MrEd]

Off the top of my head, you are probably going to want something on the order of 3 - 86 gallon expansion tanks (please get someone more qualified than me to size them). When I was looking at a 1000G tank, I came up with around 86 gallons, 2800 is almost three times as much, so 3X the number of tanks. I think they will run you $500 a piece.

Maybe if you get enough storage you can just make one big fire in the fall and be done with it!

 

[free75degrees]

For expansion. maybe you could just keep the top foot or so of the tank filled with nitrogen or some other inert gas?

 

[Sting]

Take it to a certified welder and have him chop a good big section out of it -- or whack it in half weld in two new ends and sell one of your two new tanks!

 

[leaddog]

I may have an opportunity to purchase a brand new 2800 gallon ASME storage tank, already pre-fabbed with legs. I would have to build a building to house it in, which I do not mind, as I may be able to buy the tank for a very reasonable price. I currently have an Econoburn 150 with 500G storage, the addition of the 500G allowed me to run much, much better than without storage. My question to you folks here is would you consider 2800 gallons too much? I believe I could get it up to temp, even in very cold weather, as my house is very well insulated. Your thoughts on this will be appreciated.

go for it and use your 500gal for expansion. You will want to insulate it very very well and it should work well . I have 1300 gals now and I'm going to put in 2000.
leaddog

 

[EForest]

I have 3k of storage and use a 500 gal propane tank for expansion with no trouble.
I burn every other weekend for DHW presently. Go for the big tank and add a DHW coil.
You won't regret it.

 

[MrEd]

Using a propane tank for expansion, hmmmm...how is this possible? Don't you need a bladder or something in the expansion tank? How would one pipe a expansion tank made from a propane tank?

When someone first mentioned it, I thought they were joking...now it seems it is a serious suggestion. Smaller propane tanks are easy to come by - so how do you hook it up and how does it work?

 

[SnowTraveler]

Thanks for the comments guys, I intend on using my existing storage for expansion and leave it where it is. I am now considering burying the 2800 gallon tank right next to the house. It is carbon steel with epoxy paint as an exterior coating. What are my insulation options? I have a friend that runs a residential spray foam business, I am considering setting the tank in the excavated area and have him spray it real good, then back fill. Suggestions on this idea would be appreciated. Also, how do you use a non-bladder tank for expansion?

 

[jebatty]

No bladder needed, but you do need to monitor the amount of water collecting in the smaller tank. It will be sealed, so will allow water in up to equal water/air pressure in tank. The air gradually will be dissolved into the water, so at some point the tank will become water logged. Need a sight glass or another means to monitor level, and then need to force air into the tank (or remove water and let air in) and start over again. There is a post on this forum showing how to use such a tank as an expansion tank.

 

[free75degrees]

The air gradually will be dissolved into the water...

Doesn't this mean that you would be repeatedly adding oxygen to the water, causing rust?

 

[Redox]

The air gradually will be dissolved into the water...

Doesn't this mean that you would be repeatedly adding oxygen to the water, causing rust?

Correct. Just about any gas will dissolve into water. If you used nitrogen, there would be no oxygen to cause rust, but you would have to maintain the nitrogen bubble. Doesn't everyone have a nitrogen cylinder laying around?

Chris

 

[jebatty]

Someone may know how often air needs to be added to the tank, but I'm guessing not often and the rust problem from additional O2 is small. But you can control this with sodium sulfite, an O2 scavenger. Someone else may know what the ppm for sodium sulfite should be, and I think the range is pretty broad. There are testing kits for this. OWB's commonly have a similar issue due to their open storage, so with sodium sulfite I think this is quite manageable.

 

[SnowTraveler]

I will look for the previous post regarding the expansion tanks. I can get N2 no problem. If I fill and bleed my system of air, then completely pad/inert the expansion tank with N2, how do you regulate the overall system pressure? I would assume that the makeup water regulator to 12 psig would remain and operate as normal, with the N2 "bubble" absorbing expansion? Do I have that concept correct? I would assume that several feet of water level in the expansion tank would be appropriate with N2 on top.


From Redox: "Just about any gas will dissolve into water. If you used nitrogen, there would be no oxygen to cause rust, but you would have to maintain the nitrogen bubble".

How quickly would the N2 dissolve into my large volume of water? I don't want to be constantly worrying about maintaining the N2 bubble.

 

[Bob Rohr]

define the job you want the tank to do.

Job one would be overflow parking for days when you have more fire then load. Job two would by coast time. How long you could run without firing the boiler.

You need to define the operating temperatures of your emitters. If you have high temperature emitters like baseboard 180F, or fan coils 160F, remember you need to keep that tank very hot to provide much buffer. a low temperature radiant would best leverage buffer capacity allowing a drawdown to maybe 90- 100F so an 80 degree operating range.

first determine the load of your building at design day. Figure your coldest day and indoor temperature required.

tank volume would be 3 X .70 X 36.2 X 7000- 40,000 X 3 divided by 8.33 X (180- 140)

So 3 cubic feet of oak, burned at 70%. x density of the wood X btu/ lb. wood fuel value (20% moisture) 40,000 BTU load at burn time X burn time

Divided by gallon of water weight x (highest tank temperature- lowest useable temperature)


The coast time would be 8.33 X volumne X delta T 180- 140 divided by the 40,000 load

Keep in mind you will have jacket and piping loss, no amount of insulation can stop heat flow, just limit the transfer.

At design days does you boiler have enough HP to charge a buffer? Will the juice be worth the squeeze considering the time, space and $$ to make it all work?

Personally I think 1000 gallons is about the realistic upper limit, unless you have a lot of solar array or other "free" energy to harvest and store?

hr

 

[leaddog]

We're going to use tanks for expansion tanks and use nitrogen. You do have to monitor the level and watch the water level. any leaks and you will lose air pressure but should work well. They used to do it all the time with well water systems but the air would disolve in the water and you had to keep adding air. with nitrogen you won't get oxygen in the water. I'm going to get the nitrogen from my welding tanks.
leaddog

 

[termite]

When I was thinking about expansion for my system I wondered why you couldn't put some "balls" in the tank that would compress as the water expanded. These balls would have to be able to withstand high temps for a long time. You would need enough of them to keep pressure around 20-25 psi at full temp. They would need to be constructed of something that would prevent migration of oxygen.

The precharge on them, I assume, would be the feed valve pressure.

I don't know of anything that fits the bill. Even if balls that meet the specs exist there would be no way to service them if one broke inside the tank.

An option I was considering was buying a replaceable bladder for an expansion tank and fitting it to my storage tank. I still think that would work but the bladders are very expensive and I found a deal on a regular expansion tank.

 

[free75degrees]

When I was thinking about expansion for my system I wondered why you couldn't put some "balls" in the tank that would compress as the water expanded. These balls would have to be able to withstand high temps for a long time. You would need enough of them to keep pressure around 20-25 psi at full temp. They would need to be constructed of something that would prevent migration of oxygen.

That's a really cool idea. I think it could work, although there is no reason they'd have to be spherical. How about an uninflated inner tube, stick it through a hole in the tank, keeping the valve sticking out, then inflate it inside the tank with the valve sticking out. If it ever implodes you just fish it out and use a new one.

 

[SnowTraveler]

Here is a pic of tank, negotiations are in progress.

 

[Redox]

Here is a pic of tank, negotiations are in progress.

Wow, that is a big sucker! How long will your boiler have to run to heat that thing up to a useable temperature? 2800 gallons may be bordering on overkill. You might want to try filling it half way up and pressurizing it with air or nitrogen to see how it does. You wouldn't need an expansion tank at all if you did it that way.

Just thinking out loud here...

Chris

 

[Bob Rohr]

E (energy required) = 8.33 (gallons) (Th- Tc)

8.33 (2800) (180 -550)

To take 2800 gallons from 55 to 180 if my math is right 2, 915, 500 BTU

if the boiler has an output of 100,000 it would take 29.5 hours. That does not take into account any heat loss from the tank and piping, etc. It could take 35 hours or more.

hr

 

[SnowTraveler]

I am indeed considering pressurizing it with N2 to eliminate the need for add on expansion tanks. A lot of decisions still need to be made, but location will be less than 20' from my boiler as I will bury it next to my house, adjacent to my basement boiler room. This process is going to take some time, but I will post pictures as the project advances.

 

[Grapenut]

What are your thoughts on insulatioon?