Thermal Inbreathing for elevated temperature atmospheric tanks

[itdepends]

I've seen a number of threads on venting requirements for atmospheric tanks.

Having perused API 620 and API 2000 I'm still stuck regarding the therma inbreathing requirments for tanks which fall outside the tables of API 2000 (>49degC).

API 2000 states that an engineering review should be conducted for uninsulated tanks with temperatures greater than this.

Has anyone done this before? At this stage I suspect it means I would need to calculate the rate of heat transfer from a cooling medium (e.g. rain shower) through the tank walls to the internal vapour. Once I had this- then calculated the rate of condensate formation (and thus inbreathing requirements).

All advice appreciated.

Cheers

 

[JStephen]

Sounds like you're on the right track to me.

I see that API-650 bases thermal inbreathing requirements on a temperature change of 100 degrees F per hour. If you're just somewhat over the recommended limit, it might make more sense to scale results off the temperature differential rather than actually doing the heat-transfer calcs. The problem I foresee is difficulty in finding really good information on weather changes.

If your vent size turns out to be unreasonable, you might consider increasing the design vacuum.

In a flat-bottom tank, design vacuum can be limited by the shell, by the roof, or by the floor. The roof design is based on snow load, and if you can reasonably conclude that maximum snow load and maximum cooling rate cannot occur at the same time, then the roof snow load could be converted to allowable vacuum load. Flat bottoms are not built to resist uplift, but if a minimum amount of liquid is always present in the tank, then the allowable vacuum on the floor can be increased. This leaves the shell, which for small tanks, may be adequate for more vacuum than the 5 PSF typically designed into them.

 

[Montemayor]

itdepends:

I've done this exact application on several hot crude oil storage tanks as late as 24 months ago. I used an Excel workbook that I developed for this purpose as well as for all other tank venting and relief applications.

You are correct in suspecting that you're going to have to consider partial vacuum conditions as a credible and possible hazard. This is the actual intent of the API recommendations for an engineering review under these type of storage temperatures. You're on the right track.

Art Montemayor
Spring, TX

 

[TD2K]

Art, did you start off with the method in, I believe, Appendix C of API 2000 (used to generate the original table values in API 2000) and adjust it for your temperatures or did you use another approach?

I'd be interested in how you did this.