[Travesh]

Hi All,

Please assist with the following. An atmospheric amine sump tank (13 % by weight monoethanolamine) is to be purged with nitrogen. The outflow of liquid is controlled via gap control. Please confirm if oxygen has to be excluded from the vapor space (Note that the flammability is relatively low). Should purge rate be based on the higher of maintaining an inert atmosphere, and preventing vacuum formation due to pump out rates?

Thank you.

Regards,

[Art Montemayor]

Travesh:

MEA solution degenerates in the presence of Oxygen (or air). Its flammability is of no concern. What is of concern is the corrosive by-products of its degradation and the high cost of the MEA makeup. Those are the prime reasons for blanketing any MEA solution storage vessel with nitrogen.

Note that I said “blanketing” – not “purging”. There is a big, big difference in those words and the operations they describe. By blanketing, I mean maintaining a positive vapor pressure of nitrogen over the liquid in the tank. This is done with a regulator that maintains a slight, positive pressure of nitrogen in the tank’s vapor space. Once you pump the MEA solution out, you will lower the liquid level and lessen the vapor pressure. This will activate the regulator to add more nitrogen to the tank. This system is simple and works without complex problems.

The only problem that occurs is when you have to pump in more MEA solution. Since you initially have a low liquid level, you have a lot of nitrogen already inside the tank. Upon increasing the liquid level by pumping in more MEA solution, you will compress the existing nitrogen blanket. The nitrogen regulator unfortunately can’t take the nitrogen back, so the tank can over-pressurize (over it’s MAWP – Max. Allowable Working Pressure). In order to avoid any over-pressurization, you must have a relief device – such as a Protectoseal Breather Vent (http://www.protectoseal.com/pvcvents.html).

Depending on how fast you pump out, you also may need a vacuum breaker device that can be combined with the above as a pressure and vacuum relief device.

[proinwv]

Travesh and Art,

Let me add that I recommend in all cases a vacuum vent for protection. They are inexpensive, can be combined with the pressure vent Art recommends and are really necessary.

Few tanks can tolerate negative pressure. Any failure of the blanketing regulator to provide an adequate amount of gas in a timely manner can result in a negative tank pressure. Further, the lower the blanketing gas pressure, the more risk.

[Travesh]

Art & Paul,

Thank you greatly for your valuable responses. These have assisted me tremendously. I am always impressed with the topics & contributions on this website.

Best regards.

[Qalander (Chem)]

At times if
secure Gas backing-in Vaccume breaking system is not in-place and functional

serious catastrophic or mega loss damages may result due to equipments crashing under vaccume or implosions etc.

Hope this helps/supports a little bit, in my humble way.