Domes for methanol tanks - venting as per API 650?

[dkf]

We started a study to transform 200.000 barrels external floating roof oil tanks in fixed roof ( via aluminium dome )plus internal flating roof tank to contain methanol.
Dome venting design is being conducted as per API 650 in Roof vents 3.10.8
Once methanol has a much wider explosivity range ( from around 3 to 33 %) when compared to hydrocarbons generally stored in atmospheric tanks, questions are:
A- Are we using correct code for venting design?
B- What would be expected atmosphere mixture concentration in confined space under dome if using API code?
C- Does enyone have field experience, actual measurements of resulting methanol atmosphere concentration in similar tanks?
TIA
dkf

 

[JoeTank]

I suggest that you check with the dome manufacturers such as Temcor or Conservatek.

Joe Tank

 

[dkf]

Thank you for suggestion JoeTank
We posed this question to Temcor local sales people and they claim that they do not have experience with methanol.
Other major dome manufacturer was already inquired,and did not answer the yet.
It seems to me that dome manufacturers do not care for that small details.
Does anybody know if venting is to keep atmosphere in the lean side or in the too rich side of explosive mixture?
Regards
dkf

 

[IFRs]

I have installed over a hundred internal aluminum floating roofs in methanol service. Use API 650 Appendix H. Use circulation vents per Appendix H. The vents keep the atmosphere between the IFR and the tank roof lean. Actual measurements? - no but I have checked the LEL on many and it is always below 10% unless there is a problem with the IFR seals or the vents. This is a common situation.

 

[dkf]

IFRs, thank you for information.
Are any of mentioned tanks situated in tropical site?
Our yearly average temperatures are around 25°C peaking over 40°in summer. And days with no wind and high humidity are not uncommon.
Compared to gasoline tank would methanol vaporize more or less?
Regards
dkf

 

[IFRs]

In the USA Texas, Louisiana and more. Elsewhere Taiwan, Singapore and more. The vaporization is a function of it's vapor pressure. At 60 DegF, Gasoline is around 6, Methanol is around 1.3 so I'd expect lower emissions from a Methanol tank than a gasoline tank. You may want to go to the US EPA web site and look in the air emissions section. See them at

http://www.epa.gov/ttn/chief/ap42/ch07/index.html