How to determine the outlet pressure of a high-pressure safety valve
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I would like to ask the experts the following question: How is the outlet pressure of a high-pressure safety valve determined, and what is the basis for this? The specific parameters are as follows: the pressure at the inlet of the safety valve is 10 MPa. After passing through the safety valve, the fluid flows through a pipe approximately 20 meters long before entering a storage tank that is connected to the atmosphere. What is the pressure in the pipe downstream of the safety valve?
Just look at Bernoulli’s equation in the principles of chemical engineering to understand it. Before the safety valve opens, the pressure in the outlet pipe of the safety valve can be determined, starting from the storage tank ； The outlet pipe pressure is calculated starting from the throat diameter of the safety valve, at or after the safety valve opens.
Owner, what you mentioned is that the outlet pipe pressure should be calculated starting from the throat diameter of the safety valve, either at the time the safety valve activates or after that. Is it correct to understand that the pressure at the throat diameter is 10 MPa?
No. If considering a fire accident involving a single safety valve, the allowable discharge pressure at the inlet of the safety valve is 10X110% = 11 MPa. Regarding the original question, you can refer to http://bbs.hcbbs.com/viewthread.php?tid=109668&page=1#pid2276355 to find out how to determine the operating pressure in the pipeline downstream of the safety valve; before the safety valve activates, the pressure at its outlet is equal to atmospheric pressure ； After taking off, since the connected tank is also at atmospheric pressure, the pressure in the outlet pipeline of the safety valve is determined by the resistance generated by a 20-meter-long pipeline. If it weren’t for this 20m pipeline, the outlet pressure would actually be atmospheric pressure. As mentioned on the second floor, according to the white energy equation, the head at the inlet has actually been converted into exit velocity head; this explains why the inlet pressure is high while the outlet pressure is 0 – everything has been converted into velocity
Agree with what was said above: handshake :handshake
It can be said that there are certain variations in the pressure of the pipeline at the outlet of the safety valve. At takeoff, the pressure at the outlet = 10 MPa – pressure drop across the throat diameter ； After takeoff, the pressure at the outlet = discharge pressure – throat diameter pressure drop. The pressure drop of the system is incurred at the throat diameter and the pipe outlet (similar to a flow-limiting orifice plate), as well as along the pipe. A rough calculation can be done: the throat diameter and the pressure drop at the pipe outlet are calculated using a flow-limiting orifice plate ； The pipeline pressure drop is calculated based on the flow velocity.
The outlet pressure should equal the resistance of the 20m pipeline and that of the connected equipment, that is, the pressure of the tank
The storage tank can be considered to have a back pressure of atmospheric pressure (connected to the atmosphere)； Calculate the safety valve outlet pressure inversely
The pressure drop in the inlet section of the safety valve is less than 3% of the valve’s operating pressure, while the pressure drop in the outlet section is less than 10% of that operating pressure.