Calculation of Constant backpressure, superimposed pressure and variab
Calculation of Constant backpressure, superimposed pressure and variab
(OP)
Dear Experts,
I'm designing a system consists of at least 15 PSV's where most of them designed for fire case. All the PSV's are conventional spring loaded types, the flare header is purged with nitrogen with a contant pressure of 0.1 psig.
How to calculate constant backpressure, variable backpressure and superimposed backpressure.
Thanks in advance,
Timewrap.
I'm designing a system consists of at least 15 PSV's where most of them designed for fire case. All the PSV's are conventional spring loaded types, the flare header is purged with nitrogen with a contant pressure of 0.1 psig.
How to calculate constant backpressure, variable backpressure and superimposed backpressure.
Thanks in advance,
Timewrap.





RE: Calculation of Constant backpressure, superimposed pressure and variab
JAC
RE: Calculation of Constant backpressure, superimposed pressure and variab
RE: Calculation of Constant backpressure, superimposed pressure and variab
I want to bring to your attention that this safety system is related to a petochemical plant where there are no significant or large Hydrocarbon inventories are nearby. Hence it is safe to assume that there is no pool fire and fire is restricted to one location only. In this scenario, there will be only one PSV going up in the event of fire. The system design will be based on the biggest PSV.
Does this makes it easier to calculate the superimposed backpressure?. Can I assume that the N2 presure of 0.1 psig is the constant backpresure on all the PSV's?
Thanks in advance,
Timewrap.
RE: Calculation of Constant backpressure, superimposed pressure and variab
Greenche is correct about the effect of back pressure on capacity. High Back Pressure does indeed restrict the relieving capacity of the PRV.
JAC
RE: Calculation of Constant backpressure, superimposed pressure and variab
My intitial question was how to calculate the different types of backpresures when designing the flare system. Your answers seems to throw some light on the issue but the initial questions still remain answered. This is a new system, I do not have aceess to Flarenet, I have to specify backpressures to the PSV vendor for correct sizing.
In your opinion what are the baic data in terms of backpressure a vendor requires for a PSV design. This is assuming that this is a new sysrtem, the only data you have is PSV sizing scenarios and rated capacities of each valves. How to approximate diff. BP's during initial design.
Thanks in advance,
Timewrap.
RE: Calculation of Constant backpressure, superimposed pressure and variab
RE: Calculation of Constant backpressure, superimposed pressure and variab
If there are two or more valves with different set pressure relieving into the same header. These valves are all sized for fire case and the header sizing is based on the fire case as well.
How would you recommend to calculate the back pressure on each valve?
Is the flare header sizing based on 10 % of the lowest set pressure valve if all the valves are conventional spring loaded??
Thanks in advance,
Timewrap.
RE: Calculation of Constant backpressure, superimposed pressure and variab
If you are talking about calculating backpressure with multiple RVs relieving, see my first post in this thread.