A mechanical questions on distillation tower 1

[strackma]

We are working on dei-butanizer tower>

24" diameter
44 feet (vessel)

As we had seen at internal pressure design as ASME S VIII Div I. design was solved using a 24" pipe SCH 10.

Is it possible that minimal internals sizings require thickness bigger than our calculated value ?

What criteria must be used selecting feed pipe and what is turndown ratio? Where I could obtain feed pipe diagrams (not founded)?

Thanks for time and help

strackma!

 

[TD2K]

I don't understand what you mean by "minimal internal sizing require thicknesses bigger than our calculated value". The calculated value is based on the tower's design pressure, how would internals affect that?

If you are talking about whether your trays will fit in a tower constructed of 24" sch 10, you need to look at the vapor and liquid flow rates from your process simulations or calculations as well as the type of trays you expect to use and use that data to estimate the tray diameter required. Glitch/Koch puts out a valve tray design book which goes through estimating tray diameters.

Feed distributor sizing and type is typically a function of the feed rate and the feed quality. Your feed distributor will be different if you have an all liquid feed versus a two phase mixture.

 

[unclesyd]

I think you will run into mechanical problems with you column. Being only 1/4" thick and I assume C/S limit yourself to essentially no corrosion allowance, maybe 1/32" until you are under the minimum allowed.
I would look very close at the support, full of liquid, and wind loading.
A column this thin will not take any external forces from piping and shouldn’t be used as an anchor point.
Any welding on the column is probably going to cause local problems with warping.
Nozzles are going to be problem, especially a large one.

I would look at Sch 20 as a minimum from a mechanical standpoint, though you should be able get a Sch 10 shell to work I don’t think it would sell.

 

[MJCronin]

strackma,

You are not suggesting a "bottom supported tower" are you ?

If you are suggesting a Schedule 10S -24" diameter verical tower at 44 feet height, I feel that you are way over your head. If this tower is not supported at a couple of locations along its length and located inside of a building, it will not last long.... A bottom supported distilation tower of these dimensions is out of the question.

The mechanical design and integrity of bottom-supported distillation towers is different than many other pressure vessels. Wind and other mechanical loadings typically control the vessel wall thickness, not pressure. Leave the ASME VIII tower design to the experts, contact a fabricator !!!

Two good references to begin to understand what is involved are "Pressure Vessel handbook" - Megusy

http://shop.store.yahoo.com/pennwell/presveshan11.html

and the "Pressure Vessel Design Handbook" by HH Bednar
(~$62.00) on Amazon

"Unclesyd" and "TD2K are on the right track.......a complete, competent mechanical design includes carefull process and mainteneance considerations also....

Give us more details about your tower...


My thoughts only


MJC

"There comes a time in the affairs of man when he must take the bull by the tail and face the situation." W.C. Fields

 

[pmureiko]

What is your vessel design pressure / MAWP? It should be high enough to contain material in case of cooling loss and other overpressure scenarios. I'm guessing something on the order of 100 psig would be good.

Also I would consider just using random packing. It is cheaper than trays and good liquid distribution can be easily achieved because of the small column diameter.

The voice of experience can be seen in the good repsonses TD2K, Unclesyd, and MJCronin. They may have prevented an unsafe design from being built.

 

[Hookem]

One must additionally consider the internal pressure that exists in the bottom of the tower when the tower is erect and filled with fluid, e.g., water as when subject to field hydrotest, or circulating fluid (in the case of non-operating or pluggage of liquid outlet downstream equipment).

One must additionally consider the wind loading that exists at all heights of the tower.

One must additionally consider the load of ladders, platforms, relief valves, piping, piping supports, lifting lugs, skirts, etc. - besides above mentioned corrosion allowance.

DO NOT attempt vessel design if you do not either have the time to learn how to do it right, nor the expertise.

I have many spreadsheets that will do this right, and am available to consult. chesney@uei-houston.com; or tpcenginer@aol.com.

 

[PAN]

It is also very difficult to install and replace your internal parts (support ring, tray and etc.) for vessel diameter 24".