2 replies to this topic

[biqbal]

I am a new member to this forum and fresh to chemical engineering (2 yrs of experience as unit engineer). I havent had much exposure in process design side. Any help would be appreciated in how to do to actual calculations

I have an existing TTG tank (currently out of service) that I need to size PV vents, emergency vent and nitrogen regulator. Tank is approx 500 bbls in volume 15 ft OD and 16.67 ft Height, Fixed roof. Fill rate =150 gpm and empty rate also 150 gpm. This is pretty much all the info I have for the tank. It has been out of service for a long time and dont have any other info.

There is a PV vent on the tank that has the following settings:
size 6"
settings vacuum: 0.479 oz
opening pressure: 1" wc

1. I need to verify above sizing for PV vent is adequate or not for the service
2. What information and equations do I need to size emergency vent
3. what info and equations do I need to size nitrogen regulator.

Please reply in detail step by step. Thanks again for your help.

Sincerely,
iqbal

[AlertO]

hi bigbal

the working of PV valve comes from the requirement of breath-in and breath-out during tank operation. Have you ever been familiar to API 2000?

Anyway, i try to give you the information.

• if you want to verify the existing PV valve, you have to calculate the breath-in and breath-out rate which is describes on API2000. Then you have to compare with the PV valve capacity at that existing allowable overpressure.
• Emergency vent is normaly sized based on the wetted area of the tank during fire scenario. This is also calculated as described in API2000 too.
• The sizing of PCV for nitrogen blanketing is calculated like general control valve sizing. the flow rate refers to the required breath-in rate. the pressure drop the calculated from the minimum inlet pressure to the valve minus the maximum operating pressure in the tank (this will give the worst case for sizing). Then you can calculate the CV of your valve.

Moreover, the operating pressure, the set pressure of PV valve and the set presssure of emergency vent should be at the proper setting value to avoid the acting of this device at normal operation and spending too much nitrogen comsumption.

hope this can help you.

[proinwv]

Agreed, and I add that the operating pressures including the band for each component must keep the tank pressures within MAWP and MAWV.

I do not believe anyone will reply "step by step in detail". You need to be able to do that yourself.

Read API 2000; search this forum for valuable information that has been repeated here many times by experts in the field.