Inerting Styrene Storage Tank

[RJB32482]

We have a styrene storage tank that gets both pumped into and out of for polystyrene production. The tank is inerted with 0.5 psi of a nitrogen blanket. It looks like the blanketing system has malfunctioned during a shutdown. So we might have a situation for running with the blanketing system off. Concerns of mine are:
- don't know if there is a dip tube in the tank to help prevent static from free falling liquid.
- any codes that state that styrene needs inerted (even during colder months)

Does anyone have a method using temperature to see if the vapor space in the tank will reach above the LEL of styrene? I think I remember it has to do with vapor pressure of styrene at the certain conditions and has to correlate with LEL?

Also any other concrens I have to look at?

Thanks.

 

[djack77494]

RJB,
I believe the purpose of your nitrogen blanket is to prevent the ingress of oxygen, not necessarily because of fear of an explosion, but more of fear of uncontrolled & unexpected polymerization initiated by the oxygen. I don't believe that you can refer to any codes that would deal with this; just keep the tank's pressure adequate.
Doug

 

[Latexman]

RJB32482,

Is your styrene inhibited with TBC? If so, you must have some dissolved oxygen in the styrene for the inhibitor to work. The Limiting Oxidant Concentration (LOC) value for styrene when using nitrogen as a diluent in air is 9% oxygen (by volume). The purpose of the LOC value is to ensure sufficient inert gas (such as nitrogen) is used to dilute the oxygen concentration in air so that the mixture
cannot become flammable. It is common practice to blanket an inhibited monomer that requires dissolved oxygen with a nitrogen/oxygen mixture with the oxygen < the LOC and NOT with pure nitrogen.

There are other important design guidelines and operating procedures associated with styrene. I recommend reading Nova Chemical's Safe Handling Guide for Styrene.


Good luck,
Latexman