PSV on Anhydrous Ammonia Storage Tank

[MP2012]

Need to size PSV on Anhydrous Ammonia Storage Tank. Is fire case is credible scenario for Anhydrous Ammonia? Thanks for your inputs.

 

[Latexman]

What jurisdiction is this tank under? If U.S., this standard says consider fire exposure:

OSHA 1910.111 - Storage and handling of anhydrous ammonia

Good luck,
Latexman

 

[MP2012]

Thanks Latexman. It is in Canada, Don't know what is Table H applies to in the standard you mentioned. For fire case, should I follow API procedure? Appreciate if you could guide me more in this regards.

 

[GHartmann]

Table H applies to the required size of the relief valve as determined by the surface area of the vessel. The Table has as its basis the API case for fire assuming 100% of the surface is wetted.

Unfortunately you have to convert the flow rate in air to equivalent flow rate of ammonia to utilize the API relief valve sizing forumulas.

Another standard that is utilized is "The Compressed Gas Association" CGA G-2.1 which essentially replaced ANSI K61.1.

The OSHA 1910.111, and CGA G-2.2 / ANSI K61.1 are very similar.

I like the ANSI K61.1 because it calculates the required relief valve capacity in terms of lb/h of ammonia rather than SCFM of air.

Good luck

 

[GHartmann]

It also looks like you have some Canadian standards that refer to:

Agricultural Ammonia Institute pamphlet, Standards for the Storage and Handling of Anhydrous Ammonia

http://canlii.ca/en/ca/laws/regu/crc-c-1146/latest/crc-c-1146.html

I would be surprised to find the sizing requirement different from OSHA or K61.1, but I don't have any access to the AAI pamphlet.

 

[MP2012]

Thanks GHartmann
I don't have ANSI K61.1 or equivalent CGA G-2.1. Appreciate if you could provide it.
I need procedure to size or specify PSV based on Anhydrous Ammonia Storage Tank Size

 

[GHartmann]

Unfortunately these type documents are copyright protected and cannot be posted on this forum.

You will get the correct size if you use the API case for wetted fire assuming the tank area is 100% wetted. You will need the latent heat of vaporization of ammonia to complete the calculation.

Here is a source to guide you futher:

http://www.tannerind.com/PDF/blue-anhy-amm.pdf

 

[don1980]

Before proceeding with calculation based on fire exposure, consider whether or not you have a source of fire. Ammonia won't cause a pool fire. Do you have any flammable liquids that might spill and flow around this ammonia tank?

 

[MP2012]

Thanks Ghartmann for your comments.

I talked to Fabricator regarding it and he mentioned that it's a two port spring loaded valve which is slightly different than API orifice designate PSVs. I did calculation using API method, which gives me Orifice Size J. There is already one tank installed on site, which has different PSV than what I Calculated. Appreciate your inputs.

 

[GHartmann]

Sorry for the multiple posts.

Another way to make the calculation is to size the relief valve using the values from OSHA 1910.111 in SCFM of air.

Then using that size, determine the quantity of ammonia that will pass through the same relief valve.

The formula for weight from ANSI 61.1 is:

W = (34500 x F x A^0.82) / L

F = Environmental factor = 1.0
A = surface area ft2
L = latent heat of vaporization BTU/lb
W = lb/h

Good luck!

 

[Latexman]

Since it's not U.S., the OSHA standard has no jurisdiction. Determine your local, regional, and federal requirements. If none, the OSHA standard does have some guidance value. If your security is good, you can avoid the parts that were put in place to limit the amount of ammonia someone (i.e. an illegal drug maker) can steal.

Good luck,
Latexman

 

[GHartmann]

From what I understand, the Canadian regulation references the Agricultural Ammonia Institute pamphlet.

The AAI had input into and sponsored the CGA G-2.1 / ANSI K61.1 , but somewhere along the way withdrew the sponsorship (1999 K61.1 forward)

OSHA 1910.111 incorporates much of ANSI K61.1

Thus, the Canadian regulation will be very similar to OSHA.

But, as already stated this needs to be verified.

 

[MP2012]

Thanks everyone for your valuable input.

 

[MP2012]

My understanding for PSV for Anhydrous Ammonia Storage is not orifice size based on API 526. It is a speciality item as shown here in the attached vendor catalogue. It is based on surface area of tank.

Please correct me if I am wrong. Thanks

 

[Latexman]

Don't read too much into that good marketing/sales catalog the vendor has put together. Someone had to size those PSVs in the catalog, and I guarantee you they used/followed API 526. It's just that all those messy calcs. are transparent to you. That's what the vendor wants. He wants you to not shop around and buy his product. It may be a good product at a good price, but maybe it's not.

Also, I don't think a PSV Engineer can fully delegate safety to a vendor. There has to be check and balance.

Good luck,
Latexman

 

[GHartmann]

We had a discussion on another thread about these same valves and whether they would satisfy the ASME requirements (may not be applicable in Canada). The general conclusion was they would not.

Latexman is correct. On page D9 in the catalog is the capacity required by ANSI K61.1 which specifies the capacity in SCFM of air (this table has as its roots the API fire calculation for wetted area). Then the vendor has gone off and done some more calculations to determine the area of his valves. Since these valves are not "typical" relief valves they may use some different formulas than specified by API.

I think what you need to do depends on what type facility you have and how big your tanks are.

A small nurse tank at fertilizer distributor might be OK with the REGO valves. However, if you are in a big chemical facility or power plant, you might want to have a more typical ASME style relief valve.

I would ask REGO if they comply with the OSHA guidelines and CGA guidelines as to the relief valve requirements (they are very specific in the regs).

Sorry if seems I am beating this to death. Just trying to keep you out of trouble.