Hi everybody,
I want to design two industrial vacuum distillation systems.
The dimension of my distillation tanks are as follow:
(1) A Horizontal Cylinder Tank with 200 cm length and 200cm diameter (total volume = 6300 liter)
(2) A Horizontal Cylinder Tank with 400 cm length and 290cm diameter (total volume = 26500 liter)
The material for both systems is Black Iron Sheet. The pressure and the temperature I want to work at are in the range of 0.1-0.07 mbar and 200-350 degree of centigrade.
But I don’t know what wall thickness for the distillation systems is safe?
By the way, I am an organic chemistry expert, so I don’t know much about design of distillation systems (which is an engineering problem).
The simple answer is you don't! I have been designing and operating vacuum distillation systems for over 30 years and have not been required to calculate this once. You specify the vessels be vacuum rated. Typically, I specify the vessels be rated for 150psig/FV. This takes care of several things. One the vessel manufacturer does these calculations routinely and ASME code stamps the vessels for a slight fee more. In addition, the 150 psig typcially doesn't require any additional material and allows you to use smaller relief devices since the vessel is now rated for 150 psig. For extremely large vessels, it may be worth backing down slghtly on the positive pressure rating (have the vessel fabricator calculate what the pressure rating will be if it is designed for full vacuum and pay the extra fee to have a code stamp on the vessel.
If you want to re-purpose existing vessels, then there are various rating programs you can purchase that will help you with your calculations.
Honestly I don't think it is critical, I'm no mechanical engineer either, but I guess anything over 4-5 mm will be plenty. Your real problem though will be the welded seams - you need a really good welder and probably some special welding techniques.
But at low pressures (high vacuum), shrinkage can happen for tanks. I am afraid of this problem, so I have to calculate the correct amount for the wall thickness.
1.25 inches of thickness. The following link can be useful
http://www.hooperwelding.com/news/crude_vacuum_tower/
For both of them? But I know that in larger containers, thicker wall sheets should be used. could you tell me how did you calculate the required thickness?
Just chipping in.
Even under any slight vacuum inside, the shell must be designed for external air pressure of 14.7 psi/1 bar.
Use the ASME formula
P_ext = 2.A.E/(3.D0/t)
where A is an MOC (material of construction) factor, E is elasticity modulus, D0 is vessel dia, and t is vessel thickness.
Assume some sensible thickness (t), and then from an appropriate material chart you need to determine A (ASME Code, Section 11, Part D, Subpart 3, Fig G) and then calculate P_ext. By few trials, you should be able to get a thickness for which P_ext > 14.7 psi.
You also need to use few vacuum stiffener rings as reinforcement over the shell.
Have a look at this link for all formulae.
http://www.engineersedge.com/material_science/pressure_vessel_external_pressure_calculations_9857.htm
The simple answer is you don't! I have been designing and operating vacuum distillation systems for over 30 years and have not been required to calculate this once. You specify the vessels be vacuum rated. Typically, I specify the vessels be rated for 150psig/FV. This takes care of several things. One the vessel manufacturer does these calculations routinely and ASME code stamps the vessels for a slight fee more. In addition, the 150 psig typcially doesn't require any additional material and allows you to use smaller relief devices since the vessel is now rated for 150 psig. For extremely large vessels, it may be worth backing down slghtly on the positive pressure rating (have the vessel fabricator calculate what the pressure rating will be if it is designed for full vacuum and pay the extra fee to have a code stamp on the vessel.
If you want to re-purpose existing vessels, then there are various rating programs you can purchase that will help you with your calculations.
Andrew is correct, the supplier/fabricator should ensure that the vessels are appropriately designed if you inform them that they are to be used for vacuum service.
Ion Laurentiu Tobos purpose seems to be in the range. I believe the thickness should be between 3- 5 mm. to be in safety side, take the larger one e.g., 5 mm
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