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Dear All,
I am New and wants your help.
I have to design a tank for sulfuric acid as per API 620.
API 620 says...
The tanks described in this standard are designed for metal temperatures not greater than 250 F and with pressures in their gas or vapor spaces not more than 15 pounds per square inch gauge.
I am quite unsure ... what should be design pressure in this case.
I have having
liquid = Sulfuric acid
Tank dimensions = 30' (Dia) X 15' (H)
Sp. Gr. = 1.9
Do I have to consider the pressure as H . (rho) . g
To calculate internal pressure.
Regards
GE
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Api 620
Started by vishal3992, Nov 30 2008 03:56 AM
3 replies to this topic
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#2
fallah
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Posted 30 November 2008 - 05:14 AM
(rho)*g*H is used for calculating the thickness of the tank's shell plate.
Limitation of 15 psig is applied for gas or vapor space between tank roof and liquid surface and determines thickness of the roof and also strength of the roof to shell connection.
Limitation of 15 psig is applied for gas or vapor space between tank roof and liquid surface and determines thickness of the roof and also strength of the roof to shell connection.
#3
djack77494
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Posted 01 December 2008 - 04:56 PM
GE,
I see no reason why you would choose designing your tank to API620 as opposed to the less stringent API650 for this service. The tank's design pressure could be fairly low, though I believe in reserving a bit of design pressure "to work with". You are dealing with concentrated sulfuric acid, a very hydroscopic substance. So, you will want to exclude water vapor (i.e. humidity) from the tank's vapor space. A Vent Dessicator would permit tank breathing to and from the atmosphere while restricting air ingress. However, I like to provide a generous allowance for the pressure loss across such a device. Should you locate this device at a location other than the top of the tank, hydraulic losses would occur. Your tank's design must take these pressure differentials into account, while still maintaining the tank within its design pressure envelope. (BTW, reiterating what fallah has stated, the design pressure refers to the pressure at the top [vapor space] of the tank.) I know Art Montemayor has described this several times in past postings. [Just make sure that the tank designer is fully aware of the density of the tank's contents.]
I see no reason why you would choose designing your tank to API620 as opposed to the less stringent API650 for this service. The tank's design pressure could be fairly low, though I believe in reserving a bit of design pressure "to work with". You are dealing with concentrated sulfuric acid, a very hydroscopic substance. So, you will want to exclude water vapor (i.e. humidity) from the tank's vapor space. A Vent Dessicator would permit tank breathing to and from the atmosphere while restricting air ingress. However, I like to provide a generous allowance for the pressure loss across such a device. Should you locate this device at a location other than the top of the tank, hydraulic losses would occur. Your tank's design must take these pressure differentials into account, while still maintaining the tank within its design pressure envelope. (BTW, reiterating what fallah has stated, the design pressure refers to the pressure at the top [vapor space] of the tank.) I know Art Montemayor has described this several times in past postings. [Just make sure that the tank designer is fully aware of the density of the tank's contents.]
#4
Art Montemayor
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Posted 01 December 2008 - 09:38 PM
GE:
I cannot put enough stress and importance to what Doug is passing on to you as sound and smart advice on the design and employment of storage tanks for sulfuric acid.
Please, before you do any designing and calculating, go to:
http://www.csb.gov/completed_investigations/docs/DS-MotivaIR-090602.pdf
Read this official report carefully and digest every word you read about what tragedy happened in a sulfuric acid tank farm because of pure negligence and ignorance in what sulfuric can do to a tank - if allowed to do so. Sulfuric CAN be stored safely in steel tanks - but it must be always protected from absorbing atmospheric moisture and creating a dilute and corrosive sulfuric solution. It is imperative that you design for a safe and conservative inert blanket for the tank. And to do that, you must design in as large a "dead band" as you possible can in order to have a broad instrument control range in working pressure. I have posted many Excel workbooks on the subject of protecting storage tanks and also a workbook on the Motiva disaster. If you search our Forums you will locate these workbooks and perhaps they will help you in your project.
Again, heed what Doug has advised you to do.
I cannot put enough stress and importance to what Doug is passing on to you as sound and smart advice on the design and employment of storage tanks for sulfuric acid.
Please, before you do any designing and calculating, go to:
http://www.csb.gov/completed_investigations/docs/DS-MotivaIR-090602.pdf
Read this official report carefully and digest every word you read about what tragedy happened in a sulfuric acid tank farm because of pure negligence and ignorance in what sulfuric can do to a tank - if allowed to do so. Sulfuric CAN be stored safely in steel tanks - but it must be always protected from absorbing atmospheric moisture and creating a dilute and corrosive sulfuric solution. It is imperative that you design for a safe and conservative inert blanket for the tank. And to do that, you must design in as large a "dead band" as you possible can in order to have a broad instrument control range in working pressure. I have posted many Excel workbooks on the subject of protecting storage tanks and also a workbook on the Motiva disaster. If you search our Forums you will locate these workbooks and perhaps they will help you in your project.
Again, heed what Doug has advised you to do.
