Backpressure issue in liquefied hydrocarbon pipeline expansion lines
Thread Content
If a safety valve is installed on the liquefied hydrocarbon in the liquid phase, its purpose is to prevent the formation of a closed section in the pipeline as a result of external temperature effects； The outlet of the safety valve is connected to the gas phase of the liquefied hydrocarbon sphere tank. The problem is that if the set pressure is set at 3 MPa, the design pressure of this pipeline is 3.1 MPa ； However, the gas phase pressure of the spherical tank generally varies within the range of 0.8 to 1.2 MPa ； In this case, the back pressure of the safety valve is 0.8–1.2 MPa. So how should this safety valve be selected? Is it reasonable to set it at 3MPa + 0.8～1.2MPa? Does back pressure affect the set pressure?
Choose a safety valve with a bellows to reduce the impact of pressure.
This is a bit of an over-the-top idea – what could the setting pressure of a safety valve have to do with back pressure? It’s like asking what connection there can be between how quickly a kitchen knife can be sharpened and the material of the cutting board. On the other hand, it is still related to the selection of safety valves; a high back pressure and a small pressure difference can affect the discharge rate of the safety valve after it activates. To ensure an adequate discharge volume, it is necessary to consider using safety valves with a larger diameter, or to install two or more safety valves.
Why not connect the safety valve outlet to the flare line?
Agreed; backpressure-balanced and Daofa control methods can be considered when making the selection.
It’s a waste to pass the flame on; in that case, it will end up in the tank. The tops of those tanks are likely equipped with BOG recovery systems as well. There’s nothing wrong with the design, and the set pressure of the backpressure valve and safety valve isn’t an issue either. As long as the backpressure is maintained accurately (whether it’s a constant or variable backpressure), the safety valve manufacturer can select an appropriate valve.
Back pressure affects the discharge volume; the safety valve will enlarge, independent of the set pressure
From the perspective of safety valves, the set pressure has little to do with the back pressure. However, according to your description, the design pressure of the pipeline is 3.1 MPa; if it is set at 3 MPa plus the pressure in the spherical tank as you mentioned, then there is no need for a safety valve anymore, as this value already exceeds the design pressure of the pipeline. . . . . .
Hello, do you have Teacher Gao’s number?
That’s correct; the set pressure (opening pressure) depends on the design pressure of the equipment to be protected, while back pressure affects the flow rate, that is, the size of the diameter.