API-650...paper stock storage tank...height/diameter ratio?

[sarcazmo]

Hello,

I am in the engineering department of a paper mill, and I am trying to get a handle on the cost of a storage tank for 350,000usgal of 5% OCC paper stock. Our mill is short on real estate, so my manager is asking me to look at putting it in some pretty tight spaces, which would dictate a small diameter (< 35'). My question is, does API-650 or any other standard give limits, or rules of thumb for height/diameter ratios for steel tanks?

Also, at 5% +/- consistency, a high density storage tower design may have to be employed here. Would any of you know of any standards that might apply to this, or of any reasonable height/diameter ratio to shoot for in this design? Agitation may become a factor at this point, too.

Thanks very much,
Sarcazmo

 

[MJCronin]

sarcazmo,

In response to your questions:

1) No, API 650 does not resrtict the height/diameter ratio...usually, it is economics that dictates, but I see that you are in a restricted space.. For your 350,000 gallon tank, I get about a 48 foot shell at 35 feet diameter..... This is well within the &quot;normal and reasonable range&quot; for flat bottomed tanks. Realize that your shell wall thickness will taper as you go up the tank.

About the highest &quot;aspect ratio&quot; tanks that I have seen were shop built tanks 10 foot diameter and 38 feet high ( about 3.8 to 1)

Give some thought to allowing 3 to four feet minimum all around the tank. Decide upon the method of support for the tank ( Ring wall !??) and also consider performing a study of the ground to support the tank weight. Will the tank need agitation or a sloped bottom ? What kind of coatings will be required ? You should have a really good idea about materials and coatings if this is your process....

Based on my experience, the foundation and coatings questions can strongly affect the tank cost.

Good luck

MJC

 

[sarcazmo]

MJCronin,

Thanks for your reply. Believe it or not, my manager has asked me to look at places that would allow as little as 27' in diameter, which push the required height into the 90' tall range which I think would be pushing the limits of reason. And if, as you say (and I strongly agree, by the way) I allow a few feet around the tank for maintenance and regular access, then it will resemble our boiler chimney more than a tank! But, I guess as a manager he has to look at all possible options. I have difficulty getting estimates on a tank that's 25' in diameter and 110' tall, though!

Fortunately, our mill site is a good one for ground conditions - typically only 5-6 feet to 'refusal', so the bedrock is close at hand. The tank would definately require a sloped bottom, and agitation in the dilution zone at the bottom, or the contents would bridge. We have enough trouble with previously installed storage tanks, and I don't want my name on anything like that! It would also have to be insulated, so the 'system' costs will quickly dwarf the tank costs.

Thanks again,
Sarcazmo

 

[bmoj]

Do not forget seismic requirements in your design. If you are in an earthquake zone a tall tank it may not work or not be cost effective.

You could also talk to tank vendors, such as CBI Horton, who have made these tanks before and know what can or cannot be done. bmoj@telus.net
The Project Doctor

http://www.geocities.com/projdoc

 

[butelja]

Nearly anything is POSSIBLE. But a 27'D x 90'H tank would have some difficulties. The foundation design to resist the seismic and wind moments (not to mention dead weight) would be a challenge. Also, the tank's shell will need to be thicker than you think near the bottom to avoid buckling under the moment loading of seismic and wind. It is very likely not the most economical solution.

I would also have a concern with regards to the dynamic stability if only API 650 is used in the design. It is very possible that the tank could have lateral vibration problems if they are not considered in the design. The normal range of D/h for API 650 tanks precludes this problem, so API 650 doesn't address it. Someone who builds tall steel stacks and/or tall vertical vessels should be consulted if you are serious about such a tall skinny tank.