l/d ration of vessel

[nstress]

Hi all

DOes ASME SecVIII has anything to say about the L/D Ratio to be used for a vertical vessel? I am designing a continuous blow down tank in a boiler system.I am just wondering if there is any guideline to find out the optimum L/D Ratio


thanks for your time and help

 

[deanc]

Perhaps ASME SecVIII Div 1 Appendix G will give you a start

 

[EGT01]

The optimum L/D ratio may depend on the parameter you want to optimize such as cost, plot space, vertical height, process requirements such as liquid holdup or vapor-liquid separation, etc.

See if you can get a copy of the following article from Chemical Engineering Progress (CEP), AIChE publication.
W.Y. Svrcek and W.D. Monnery, "Design Two-Phase Separators Within the Right Limits", CEP, October 1993. They give a table of L/D guidelines based on vessel operating pressure.

[tt]Vessel Op. Press., psig L/D
0 < P <= 250 1.5 - 3.0
250 < P <= 500 3.0 - 4.0
500 < P 4.0 - 6.0[/tt]

Once you find dimensions to meet your process and location needs, think about tweaking the size to minimize longitudinal and circumferential welds or cuts needed to fabricate the vessel. Maybe plate thickness is already factored into the table above based on operating pressure.

If nothing else, check some of the references given by the article. The article references API RP-521 and checking it, they go through an excercise to optimize a horizontal knock-out drum that maybe you could generally follow to sizing a vertical drum.

 

[davefitz]

There is a cookbook calculation you can use for designing blowdown tanks- it is offered by the national board of boiler and pressure vessel inspectors. Just don't look into its mthjods and assumptions too carefully- but it seems to be used in the power industry often.