Tank Emergency Vent - Capacity Charts 1

[Justice100]

I have a tank filled with cryogenic hydrocarbon. The emergency relief vent (weighted pallet with hinge, something like this -

https://www.protego.com/products/detail/ER_VH.html)

is set at 130 mbar with 20% allowable accumulation and there is an inlet line 10m long (required as double walled tank). The tank is to be repurposed for a different cryogenic HC.

I have calculated the emergency sizing case relief rate but I am struggling with the relief vent capacity charts. The capacity charts are in air at standard conditions but my relief fluid and relieving conditions are very different so I assume I use API 2000 equation D.35 to convert my relief rate at sp +20% to air at standard conditions. I can then use the capacity charts. Is this the correct approach? Also, how can you account for the inlet line DP? Similarly how do you account for pressure losse due to inlet/outlet piping for a PVRV using these charts?

 

[don1980]

Regarding your first question about conversion, use the Protego sizing tool that's posted on their website. It does this conversion for you, and reports the necessary size.

Regarding the question about inlet and outlet piping on a low-pressure vent devices, this piping pressure loss reduces the dP that's available for the vent device, thus reducing its capacity. So, you'll need to size the vent device based on this reduced dP. The best design for these vent devices is to install them directly on the tank nozzle, without any inlet or outlet piping. With such installations, the pressure drop from the tank to the vent device can be ignored, as long as the tank nozzle isn't smaller than the inlet to the vent device. So, I suggest you first evaluate why there is piping on the inlet and outlet sides of this emergency vent. I'm puzzled why this is thought to be necessary - doesn't make sense to me. But if we assume that it is necessary, then subtract the piping pressure loss from the set pressure. Then size the device using this "pseudo set-pressure".

 

[Justice100]

Thanks Don, very much appreciated.

Regards the inlet pipe it is required as it is a double containment tank so needs to go through the outer and inner roofs.