Vent sizing for underground storage tank. 3

[zamu]

Greeting folks,
I am sizing the vent for underground storage tank operating at atmospheric pressure to hold the produced water (having oil content of 10 ppm and few other impurities). I have used API 2000 for this pupose.
My concern is that tank is designed for future N2 blanketing. does it has any impact on it?
Thanks in advance

 

[ash9144]

You need to consider flow rate of nitrogen blanket to size vent. Usually in a blanketing system there is some type of outlet pressure control to limit nitrogen flow rate for cost reasons. I have to say I am puzzled why you would put a nitrogen blanket on a water tank.

 

[zamu]

Thanks Ash9144,
In future the tank should be used for N2 blanketing.
So the concern is to size the vent in such a way that the tank can be used for both puposes.
Can you explain a bit more what i need to cosidered for N2 blanketing?
what are outlet pressure control limits?
API 2000 can used to size the vent for this pupose?
Regards
Zamu

 

[JimCasey]

with an underground tank you won't to need to worry about fire sizing or even thermal effects. Just size the vent to handle the flow in and flow out of the tank. The N2 blanketing system should also be sized to replace and volume of liquid taken from the tank, and it should shut down when any liquid is being added to the tank. Any inflow will displace the tank atmosphere out the vent.

 

[CMA010]

If you want to size your vent for the future blanketing you will have to include failing open of the nitrogen regulator.

 

[djack77494]

API2000 will give you methodology to calculate the RATE of vent gases flowing into/out of your tank. You must use this information in conjunction with the tank's design pressure (I hope it's not "atmospheric") and a calculation of hydraulic losses through your assumed vent pipe size and layout. Calculate pressure drop both at maximum inflow and maximum outflow conditions to determine the maximum pressure and maximum vacuum that your tank will "see". Hopefully these values are within the design limits of the tank; if not increase vent pipe size and try again.

 

[maddocks]

I agree wholeheartedly with CMAO10 - you need to consider the failure of the N2 blanket regulator in your vent sizing. Suggest you discuss with vendors - blanket regulator selection can be difficult and you'll never hear the end of it if you put in a reg that wanders and causes frequent venting. Not that I've ever done that.... ha,ha