Estimation of dynamic and stationary loads due to safety valves discharge with biphasic fluid
Estimation of dynamic and stationary loads due to safety valves discharge with biphasic fluid
(OP)
Hello. I am working in a Project in which we have several safety valves. As it is well known, safety valves discharge creates transient forces on each change of direction due to the pressure wave generated when opening. Once the discharge is stabilized, there is also a stationary load at the point of discharge due to the "jet" effect.
When the valve discharges saturated or superheated steam the calculation of the stationary load can be found for example in Appendix II of ASME B31.1 and the transient loads can be calculated using papers like G.S.Liao's one "Analysis of Power Plant Safety and Relief Vent Stacks".
However, in the case we have biphasic fluid, these methods do not seem appropriate. I would greatly appreciate if somebody can give me a hand of how to calculate these forces (transient and stationary) in this case. Also, if anybody know of a software which calculate this, similar for example the way AFT Impulse does for water. Thanks in advance.
When the valve discharges saturated or superheated steam the calculation of the stationary load can be found for example in Appendix II of ASME B31.1 and the transient loads can be calculated using papers like G.S.Liao's one "Analysis of Power Plant Safety and Relief Vent Stacks".
However, in the case we have biphasic fluid, these methods do not seem appropriate. I would greatly appreciate if somebody can give me a hand of how to calculate these forces (transient and stationary) in this case. Also, if anybody know of a software which calculate this, similar for example the way AFT Impulse does for water. Thanks in advance.





RE: Estimation of dynamic and stationary loads due to safety valves discharge with biphasic fluid
Independent events are seldomly independent.
RE: Estimation of dynamic and stationary loads due to safety valves discharge with biphasic fluid
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Estimation of dynamic and stationary loads due to safety valves discharge with biphasic fluid
RE: Estimation of dynamic and stationary loads due to safety valves discharge with biphasic fluid
Normal practice is to knock out and hold the liquids in a flare scrubbing pot before sending the gas on to the vent. In fact great effort is made to keep liquids out of a vent or flare line. I would suggest that you do it that way. If you can't, make the pipe strong enough so that you don't have to vent to keep the pressure lower than its design limit.
http://www.exterran.com/Products/production-equipm...
Trying to handle liquids and gases in a highly dynamic venting situation can get dangerous very quickly. Sooner or later the pipe will most likely move a lot.
Independent events are seldomly independent.
RE: Estimation of dynamic and stationary loads due to safety valves discharge with biphasic fluid
RE: Estimation of dynamic and stationary loads due to safety valves discharge with biphasic fluid
Fine, but why can't you vent it after it's flashed. Must it flash inside the vent pipe?
No. I probably wouldn't believe them, if there were any.
Independent events are seldomly independent.
RE: Estimation of dynamic and stationary loads due to safety valves discharge with biphasic fluid
First,make sure you actually have two phase flow. If your shell is at high temp and under pressure it may well just evaportate and you end up with "heavy" gas with only very fine particles.
HX tube rupture is often dealt with by bursting discs which require large diamter short vents with little in the way of bends. Your HX should be equipked with ESD valves to rapidly close and reduce flow from the broken tube and not
Other forms of two phase flow in vent lines, as BI says, are normally designed out as the impact, literally, of high veleocity liquid slugs or particles is such that it is not safe or economic to build it that way.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Estimation of dynamic and stationary loads due to safety valves discharge with biphasic fluid
again, thanks for your interest. Based on above, conclusions could be:
1.- Avoid 2 phase flows whenever possible. There seems not to be a good method to work with 2 phase fluids
2.- In case one has a discharge which creates flashing, try the vent pipe to be as short as possible or try to separate the two phases as near as possible from the relief device or the point where the flashing may happen (knock out drum or similar)
RE: Estimation of dynamic and stationary loads due to safety valves discharge with biphasic fluid
You really...ly...ly... don't want liquids flying out the vent, or possibly over-fueling, or extinguishing a flare.
Independent events are seldomly independent.
RE: Estimation of dynamic and stationary loads due to safety valves discharge with biphasic fluid
Kevin
RE: Estimation of dynamic and stationary loads due to safety valves discharge with biphasic fluid
Independent events are seldomly independent.