Acid relief valve

[ChemStel]

Can anyone point me in the right direction to a guide for sizing of a relief valve / bursting disc. API2000 seems to be directed to the petrochemical industry or flammable materials.

My application is the boiling of nitric acid in a 200 litre vessel by immersion heating. There are no flammable materials in the vicinity, so I am not looking at fire case. I'm assuming the worst case is vapour expansion.

The normal working pressure is 70mBar (g). The design pressure of the vessel is 1Bar (g). I would set the relief valve at this pressure of 1 Bar(g). But, most relief valve data sheets from suppliers ask what the over-pressure is. I don't quite understand the concept of over-pressure. Should the relief valve set pressure be lower than the design pressure of the vessel to allow for some over-pressure?

Thanks in advance

 

[devaxrayz]

Stel,

following your thread above, depends on what you are trying to do, i think your condition can be accessed using one of this two solution.

1. you might want to use a Pressure Safety valve (PSV) or Pressure Relief valve (PRV)... if you do so, you are referring to wrong API standard. for sizing a PSV use the API 520 part 1. PSV available in market can be setted as low as 5 psig while you want to set it at 1 barg (14.7 psig) so it is applicable. Depends on what case do you expect (blocked outlet, fire case, power failure, heat control not working so there is vaporization, etc) you can determine what is the fluid type relief at the PSV (gas/liguid/two phase) and select the proper formula to size your PSV.
What the suplier ask about the overpressure is how much psig you allow the pressure to be above your design pressure when the PSV is relieving. It is usually 10% of the design pressure if you install only one PSV (please check in API 520)

2. you maybe want to install a pressure vent with ot without vacuum vent. This the what API 2000 address for (Tank venting). This is generally used to release pressure acummulated during filling up and vacuum generated during emptying the tank. altough it is also can be used for another case. however this Pressure vent is not intended for liquid purposes. One you can do if you want to use this vent, you should calculated what is your relief (vent load) at your case - vaporization of the acid- and tell the vendor about your load, your prefered setting and your tank design pressure and they will size it for you. There is also some vendor (protectoseal for example) which will give you the sizing software so you can size it by your self.
The venting has what its name overpressure, its because ussually the vent reach its full capacity above from it setting pressure. You should consult the vendor about your setting pressure if you dont want the relief pressure to reach the tank design pressure. But if it was a pressure vessel, generally it is OK if the vessel relief slightly above its design pressure since its should already hydrotested at 1.35x design pressure.


In both equipment above, i recommend u use the PSV instead of pressure vent and since your working pressure is so far from the design pressure, it will be more safer if you set the PSV below the design pressure thus the setting pressure + its overpressure will be at your design pressure.


Another thing you should also consider is that your fluid is acid so it will determine what is your relief equipment material and where to discharge it.

-rayz-




-rayz-