3 replies to this topic

[mariona]

I’ve read many of the postings about relief valves for drums and didn’t find the answers that I’m looking for. If I missed something already available please forgive me I’m new to this forum. I’m a chemical engineer newly transitioning from semiconductor processing to bulk chemical industry.

I want a safe system for venting 55 gallon drums of methanol in indoor use. This is in an R&D setting. The maximum total quantity on hand would be 200 gallons; industrial grade warehouse with sprinklers. Is there a safe way to provide necessary ventilation without introducing water into the drums, and preferably without allowing continual methanol evaporation to the atmosphere, that be implemented at low cost?

The planned use would be 2 passive drums and 1 active drum. The drum openings are fitted with 2” threaded and 3/8” threaded connections and arrive with caps. The chemical supplier leaves headroom to accommodate normal expansion of the methanol at room temperature. The active drum would dispense at a rate of 0.2 gallon per minute. I’ve read postings in favor of the nitrogen blanketing, and references to API 2000 and NFPA 30, which I have not got copies of. Is it still recommended for such a small system?

What do you think of this alternative solution? (1) leave the passive drums closed until point of use (2) For the active drum, I would propose to create an air inlet line by reducing the 2” opening down to a 1/2” diameter line and using, inline from the drum, a flame arrester tube, a vacuum breaker valve and a dessicant filter. For the outlet, I would use a 3/8” opening with flame arrester and appropriate external pumps and motors. As backup, I was considering adding a higher breaking vacuum valve, a pressure monitor with alarm, and/or an overpressure relief valve.

Thanks in advance for any help and advice you can offer.

[Art Montemayor]

Mariona:

Yours is a practical application that occurs often in small pilot situations and R&D labs. However, we have to have a basic definition of the hazard that you are protecting against. All you have stated is that you require “safe venting” of the 55-gallon drums filled with methanol.

You specifically ask: “Is there a safe way to provide necessary ventilation without introducing water into the drums, and preferably without allowing continual methanol evaporation to the atmosphere?”

Yes, there certainly can be a safe way to ventilate the drums without introducing water into the drums. But if you have a requirement to vent methanol vapors, there is no other available sink that I can identify except the atmosphere around your facility. That is what venting does.

I believe what you haven’t defined is the venting scenario that you want to design for: an indoor pool fire within your laboratory building that could envelope the 55-gallon drums in a fire. This is definitely a hazardous scenario for the methanol storage and everything in the immediate surroundings. If you indeed have a credible and possible pool fire scenario within your laboratory and you are storing methanol there, then you should have facilities and equipment to mitigate a disasterous fire and possible explosion of methanol vapors. I am going to assume that you do have that possible scenario.

Firstly, I would NOT “STORE” full methanol drums within the R&D labs. I would store them in a hazardous area, free of static, and other ignition or fire sources. This would be probably an external, independent, locked shed that is sheltered and kept cool – much like a paint locker in a process plant. Only the one methanol drum in service would be kept inside the laboratory while it is in service. It would be exchanged with a full drum when it would be depleted. This drum in service would be in a diked, protected and isolated area of the lab where a local fire can be segregated and fought quickly and successfully without affecting the rest of the lab. The drum can be piped up to a PSV that would relieve the excess vapor pressure generated in the event of an indoor fire. The PSV would discharge to the outdoors, away from the R&D building. Unless it is used at night also, this service drum would be disconnected at night and stored with the remaining full drums in the external storage shed.

I don’t understand what you intend to do by having the service drum “blanketed” with Nitrogen. Unless you really need the Nitrogen vapor pressure to help the NPSH of your methanol pump, I wouldn’t do it. In the event of a pool fire, the Nitrogen will not deter the expansion and generation of methanol vapors in the drum. The drum will still overheat and “pop” its PSV if the fire persists. There is little you can do to save the methanol and the drum if it is exposed to a pool fire EXCEPT putting out the fire itself. And putting out the fire should be the first and foremost priority. The PSV is there to save the personnel and the drum from an explosion or rupture of the drum. That is the principle and spirit of API 2000 and you should use it if you need to protect against a fire scenario. The API 2000 principles apply to drums just as they apply to API storage tanks.

You don’t furnish a schematic or PFD of your proposed installation, so I am unable to see how you propose to install a pump to your 55-gallon drum. I presume that your tank would be vented with your process so that you don’t pull a partial vacuum within the drum as you draw the methanol inventory down with the pump. If you are able to do that, it prevents you pulling a vacuum on the drum. If you can’t vent the drum to process, then you may need the Nitrogen blanket – but not as a fire deterrent, but rather as a pressure assist for your transfer pump. This is readily done by simply applying a nitrogen regulator to the drum and setting the vapor pressure inside the drum to several inches of nitrogen pressure. The maximum amount of pressure that you can apply should be verified and confirmed with your methanol vendor.

I hope this experience helps out.

[riven]

In a laboratory setting (where our limits are 200kg/100m2 ventilated lab space)we use denios chemcial cupboards. For the sizes you suggest you would require something like the attached
http://www.denios-us...ge_Cabinets.pdf
These are fireproof, have a bund to contain overflow and have extraction vents where any vapours are removed from the cupboard etc etc. In our company (large R&D energy) we only use these in outdoor areas. This typically takes care of storage issues.

The question really is though is why you are dispensing directly from the drum. Typically we transfer contents for a drum to a mechanically designed feed vessel (for pressurized services) or other container. We do not use the delivered drums in the process. This is because these drums are not designed for pressurized service and are thus not gaurnteed to be involved in a process.

[proinwv]

Possibly I can learn something from this. I have been aware of these issues in the past but never have become involved.

My questions are:

1. Do these drums have actual pressure and vacuum ratings? Lacking that information, a system could cause more harm than good.

2. I am not aware of any appropriate P/V venting valves for these small sizes. Are they available?