PSVs Venting to Tank
PSVs Venting to Tank
(OP)
There is a PSV set at 1440psi piped to a 400bbl tank through a 2" line. The maximum gas rate through the PSV would be about 10 mmscf/d. The tank is venting through two 8" vents.
Does anyone know how I could calculate the pressure in the tank the instant that the PSV vents gas to the tank?
Does anyone know how I could calculate the pressure in the tank the instant that the PSV vents gas to the tank?





RE: PSVs Venting to Tank
Then you need to decide how much pressure you feel safe putting on the tank (it should be a pretty small number).
Then you need to look at the length of the 8" vents. If it they are longer than about 3D, then you need to do a pipe flow calc using the dP you decided was safe above. If the vents are shorter than 3D then you need to do a nozzle calc with the dP to get the flow rate up the vents.
If the two vents can move significantly more than what you calculate then you are fine (i.e., the maximum pressure won't approach the safe value). When I get pushed into a corner and have to do this kind of calculation I typically use a safety factor of 2 (i.e., can each pipe move the entire volume by itself at the maximum dP?).
David Simpson, PE
MuleShoe Engineering
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
RE: PSVs Venting to Tank
It just seems like with that amount of gas there might be a pressure surge greater than 1 psi the instant that the PSV pops. Does that make sense?
RE: PSVs Venting to Tank
Have you ever watched the end of a vent pipe during a blowdown? It starts out kind of raggedy and then within a few seconds it coalesces into a teardrop shape with the center of the teardrop being very dense. That teardrop is formed by the standing wave that is choking the flow. If you look a foot or so past the teardrop it looks like the stream has dissipated (it hasn't, but it has slowed below 0.6 Mach and is no longer exhibiting velocity enhanced density or compressible flow). At the point that the stream seems to disappear it is no longer dangerous to steel. That point is usually within 2-3 ft of the end of the pipe. Same thing would happen in your tank.
David Simpson, PE
MuleShoe Engineering
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
RE: PSVs Venting to Tank
RE: PSVs Venting to Tank
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek