Does a methanol tank need a flame arrestor?

[PetroBob]

A 9000 gallon methanol tank located at an oil & gas facility, would you, or would you not include a flame arrestor on the tank vent? All instrumentation will be Ex rated. I believe the only potential source of ignition would be lightning strike.

 

[Latexman]

Is there a conservation vent or PVRV?

Good luck,
Latexman

Technically, the glass is always full - 1/2 air and 1/2 water.

 

[e43u8]

PetroBob,

Methanol is a liquid with high vapor pressure (around 3 psia @25 C and 12 psia @60 C). Then it is normally stored in a pressure vessel/drum (rather than in atmospheric tank), let say with design pressure of 3-4 barg, along with the N2 gas blanketing to avoid continuous waste of the Methanol vapor through the vent. Therefore API 2000 isn't applied for such storage facility...
Also the depad valve on the tank would relieve the methanol vapor of overpressure due to normal process upset to the flare network. Hence there would be no need to the flame arrestor on the tank vent which might be opened just during maintenance...

 

[bimr]

It is considered to be good engineering practice to do so, but may not be explicitly required.

http://www.aiche.org/sites/default/files/cep/20131216_1.pdf

 

[bimr]

A link to storage guidelines:

http://www.methanol.org/Health-And-...ty/Methanol-Safe-Handling-Manual-English.aspx

 

[PetroBob]

Thanks folks for the useful comments and reference documents. I am reviewing a design which, at present, has an atmospheric tank and gooseneck type open vent; which I am concerned about. There is no nitrogen blanketing in the design at this point. Reading API 2000 & the methanol handling manual which you attached bimr, it seems that, as a minimum, tank venting should be through a PVRV, and consideration should be given towards having a flame arrester as well.

Another question: What materials of construction are typically used for methanol tanks? The existing design is double walled carbon steel, but we are considering whether a coating as corrosion protection is needed or not.

 

[bimr]

What kinds of drums are recommended for methanol storage, only steel or are some plastics acceptable?

There are no standard or universal answers for questions regarding materials selection for methanol storage. The following information is provided as general guidance only. Mild steel is usually selected as the construction material for methanol storage containers. If moisture and trace amounts of inorganic salts are expected to exist within the container from time to time, then one should consider upgrading from carbon steel to 316 L stainless steel, or even a titanium or molybdenum stabilized grade of 316 L stainless steel. Many resins, nylons, and rubbers, such as neoprene, nitrile (Buna-N), and ethylene propylene (EPDM), are suitable for methanol service, though some are more appropriate in flowing applications and others for static service. One important consideration is that plastic storage containers are more susceptible to physical damage than metal ones (e.g., if dropped or hit by a forklift). Pure anhydrous methanol is mildly corrosive to lead and aluminum alloys, and more so to magnesium, and platinum. Methanol-water solutions can be corrosive to some non-ferrous alloys depending on application and environmental circumstances, including copper alloy, galvanized steel, and aluminum alloy components, and some plastics and composites. For more information on methanol storage consult Chapter 3.2 of the Methanol Institute’s Methanol Safe Handling Manual.

 

[gr2vessels]

The design and manufacture, safety requirements, etc are regulated by the rules of NFPA 30, Handling of Flammable and Combustible Liquids. The storage tank design is regulated by UL 142 and the vent has to be fitted with flame arrestor. Additionally, the tank has to be provided with an emergency vent sized for fire case, with no flame arrestor. There is a requirement for secondary containment, typically in form of double skin storage tank and other features to safeguard the tank.
Typical construction of an 9000 gal Methanol Storage Tank is a horizontal vessel, SS internal skin and CS outer skin, on saddles. However, vertical double skin storage tank is also feasible.
Cheers,
gr2vessels