Tank Design Question

[Gooserider]

Thought I'd toss this one in as a question for folks planning storage, either making their own tanks, or purchasing one... All else being equal, what is the preferred shape for a storage tank - Tall and skinny, or short and wide? As an example, if one were getting a 1,000gal propane tank, would it be better to have it on it's side or standing on end? (If one wanted to stand it on end, how hard would that be to do?)

I hear lots of talk about stratification where it is considered good to heat the top of the tank more than the bottom, would that be aided by having a taller tank?

How much difference would it be in strain on the bottom / sides of the tank if one were building a wood frame, or concrete tank to use say 8' high walls instead of 4' high, assuming the same volume of water?

I'm guessing here, but I would think that there would be less load on the short/wide tank, but that you might get better stratification on a tall tank. It could also have a big impact on designing ones boiler space - a tall tank would have a smaller footprint, but would need a taller building?

Another thought I had for possible tanks - what about the tanks you see outside some factories and the like for cryogenic liquids (i.e. Liquid Oxygen) - I would assume they have really good insulation, but would that insulation be suitable for high temps? Also do those tanks ever / often become available as surplus?

Gooserider

 

[leaddog]

Taller would be better because of stratifcation, and round because of strength. I build my tank retanglar and it takes ALOT of braceing to hold it. It is only 5ft high and the forces are great. My son is going to build his in the ground and that will help with the forces and is going to go 8 or 10 ft deep.
The LO2 tanks would be great I think but have never seen one for sale. I think they are double walled and vaccum tanks.
I see that there is shipping containers that are tank containers and they would be great because they would be easy to fill with insulation but haven't found any for sale. If any one has a link email me.
I think that you really need atleast 4ft to get useful stratification.
leaddog

 

[Gooserider]

Thanks for the response, I figured it was a question I hadn't seen mentioned before, so I thought it would be worth asking... I know that round is better from a strength viewpoint, but it would seem to me that if you don't go with a pre-fab tank (like an LP tank) then it might be harder to build since most "home builder" supplies are pretty much flat, and it isn't easy to come up with something that would be both easy to build and round.

The other downside is possibly insulation - the board type products aren't real flexible, though I suppose one could go with a fiberglass blanket and cover that with some sort of foam box shell.

Gooserider

 

[Bob Rohr]

My first buffer tank was a 185 gallon used lp tank. I stood it on end in a couple pieces of 2" foam dished out with a grinder. The mounting legs I lag bolted to the wall for extra tip protection. It worked fine, but was a little light on capacity. I now have a 500 gallon but it was too tall to stand on end.

My EKO runs until the entire tank reaches 180- 185F.

The biggest drawback to old lp tanks is getting the smell out! It took months of de-gassing and a few flushes with Tide to clean out.

You can purchase new ones, of course. About a buck a gallon for used ones in my part of the woods.

hr

 

[jebatty]

If using a round tank with flat top and bottom, three considerations: 1) stratification; 2) radiated heat loss related to temperature, and 3) surface area as contributing to heat loss. Stratification clearly would be aided by height. I have nothing to contribute as to what height vs diameter is optimal for stratification, but intuition tells me that h:w ratio of 1 or more to 1 would be desirable.

Heat loss is going to come from surface area and from temperature. With regard to temperature, so in a sense while stratification is aided by height, the increased temperature at the top also will increase radiated heat loss (I think) while radiated heat loss from the bottom will be less (I think). But I think the ratio of heat loss to temperature is not linear, and much more radiated heat loss occurs as temperature rises. A mixed blessing here.

With regard to surface area as contributing to heat loss, some quick calculations with some rounding, assuming a round 1000 gal tank, flat top and bottom: a tank with about a 5' height and 6.8' diameter is close to minimum surface area, which should equate to minimum heat loss related to surface area:

D = 3'
H= 19'
S = 193 sq ft

D = 4'
H = 10.63'
S = 159 sq ft

D= 5'
H = 6.8'
S = 145.75 sq ft

D = 6'
H = 4.75'
S = 190 sq ft

With regard to standing a propane tank on end, only a guestimate here, but I think they are made very strong because they have to withstand pressures much greater than a low pressure boiler (<30 psi). So I doubt a structural problem with standing on end. More of a balance and support problem.

I'm looking at a 1000 gal, older LP tank, and the length is about 16'. To stand, balance, and support this on end would not be easy and would be very dangerous if it would tip. Assume the tank weighs 1000 lbs, the water in the tank will weigh 8330 lbs. Also, 9330 pounds resting on a very small area will take a good slap to support. If this would tip, a major safety disaster. I'll stay with horizontal.

Good luck on thinking this through.

 

[Willman]

After reading thru this thread I got the idea to check out well tiles. Roughly 3' dia. 3' ht. Pour a 6" well reinforced and insulated slab. Urethane or some reliable heat resistant sealant for the joints between sections. Use the polypropylene to line the inside, one vertical seam easily welded. Stack as many as you need to arrive at the size storage desired. Cover with the manhole top for access. Foam board the exterior. I will call the concrete product dealer on Monday. Easier to handle than a septic tank. Line them up for a cascade system. Could even be buried below the floor in the basement if the can fit thru the door.

 

[Gooserider]

After reading thru this thread I got the idea to check out well tiles. Roughly 3' dia. 3' ht. Pour a 6" well reinforced and insulated slab. Urethane or some reliable heat resistant sealant for the joints between sections. Use the polypropylene to line the inside, one vertical seam easily welded. Stack as many as you need to arrive at the size storage desired. Cover with the manhole top for access. Foam board the exterior. I will call the concrete product dealer on Monday. Easier to handle than a septic tank. Line them up for a cascade system. Could even be buried below the floor in the basement if the can fit thru the door.

Well tiles, or perhaps for a bigger cross section, those round concrete things they make manholes out of do sound interesting. But unless they are made with some serious amounts of rebar, I would be surprised if they would be strong enough. Concrete is a material that gets it's strength from compression, but a tank wall is almost all tension loading. However those well tiles look to me like they are mostly designed to deal with compression loading from dirt pressing in on them from the sides. While in theory, they might do OK if burried, I'm not even sure about that - after all, when full of water in a well, they are being equally loaded by the water at a nearly equal level on the outside, so again the loading would mostly be compressive from the dirt, not tension from the water weight.

While I have doubts about super insulating underground in any case, it would be even more problematic in our situation as it appears that the water table is only 3-4' down in at least some seasons of the year - at least, without a sump pump our 4' below grade basement would have mild water problems, so I assume that indicates where the water table is.

Gooserider

 

[Willman]

Concrete culverts must be strong enough. Nothing inside, they support a road above. I will ask about the well tile rebar when talking with rep. Tank doesn't have to buried. I would stand a culvert section up on a well insulated and reinforced slab and wrap with multiple layers of 1/2" blue or pink foam board with staggered joints. Then pour another layer around the outside to keep it from moving. Bore some holes in slab and culvert to pin with rebar. Would have to make a template for the correct location of pins. Probably worth doing with the well tiles. I live on top of a huge sand deposit so water table is not an issue.

Will

 

[Gooserider]

Concrete culverts must be strong enough. Nothing inside, they support a road above. I will ask about the well tile rebar when talking with rep. Tank doesn't have to buried. I would stand a culvert section up on a well insulated and reinforced slab and wrap with multiple layers of 1/2" blue or pink foam board with staggered joints. Then pour another layer around the outside to keep it from moving. Bore some holes in slab and culvert to pin with rebar. Would have to make a template for the correct location of pins. Probably worth doing with the well tiles. I live on top of a huge sand deposit so water table is not an issue.

Will

Not really... The load on a culvert is still all compression, with the dirt surrounding the culvert supporting it and distributing the load over a wide area. Most roads you could probably pull the culvert right out without loosing any strength, mostly the culvert is just there to hold the shape of the hole, and as long as the shape holds, there really isn't much load on the concrete. Trying to fill the upright culvert with water, all the stress is tension, trying to blow the concrete apart from the inside. Concrete is very strong in compression, but very weak in tension. If I were needing to build out of concrete, I'd either insist on some really specific engineering data from the precast outfit showing it was up to the load, or perhaps look at doing something with ICF's (Insulated Concrete Forms) using very large quantities of rebar wrapped around the outside edges of the forms for support.

Gooserider