Are the pressures before and after the compressor anti-surge valve the same?
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Valves generally serve to reduce pressure. Is the pressure before and after the anti-surge valve in a centrifugal syngas compressor the same, and by how much does it differ?
This post was last edited by tczxs on 2010-4-2 01:28. I think it should be different, right? Should the surge valve be kept open at all times? Really? It will only open near the surge zone, right? The pressure shouldn’t be the same in that case; throttling is still necessary. What’s the pressure difference? Don’t you have a pressure gauge?
Of course it’s different! The exact difference depends on how anti-surge is implemented.
Under normal conditions, surge in centrifugal compressors occurs due to a decrease in the inlet flow rate, such that the volume of gas being compressed is less than the flow rate corresponding to the surge point on the performance curve for that operating condition. Generally, a partial backflow approach can be employed: some of the process gas is routed back from the compressor outlet to the inlet, thereby enabling the compressor to meet the requirements of low-load operation while also ensuring that the flow rate remains above the minimum limit. Under normal operating conditions, the anti-surge valve is closed. The pressure difference across the valve should generally be the pressure difference between the compressor’s outlet and inlet. Specifically for the methanol synthesis gas compressor, as mentioned above, it depends on the specific anti-surge solution. Since I have no experience working in methanol synthesis plants, I can only guess that its anti-surge scheme is similar to that of ordinary centrifugal compressors. The pressure difference across the valve is the differential pressure between the compressor inlet and outlet. For example, the inlet pressure of the syngas compressor is 2.7 MPa (G), and the outlet pressure is 5.8 MPa (G); my understanding is that the pressure difference when the valve is in the fully closed position is 3.1 MPa. Syngas compressors typically use multi-stage compression, and if a certain stage is prone to surge, it may be possible to route flow back to the inter-stage area or draw air from there back to the inlet. But this one looks quite strange. Hehe.
It’s closed under normal conditions; it definitely differs. At a certain degree of opening, it is also necessary to consider the extent of the valve’s opening. When the valve is open only slightly, the throttling effect is significant and the pressure-reducing effect is obvious; as the valve opens further, the throttling effect changes, and once it reaches a certain level, this throttling effect gradually decreases. At that point, there is no longer any pressure-reducing effect, and the pressure difference becomes very small.
Of course it’s different; the pressure difference is simply the pressure difference between the inlet and outlet of the compressor.
Agree with the view on the sixth floor; the pressure difference before and after the valve is the difference between the inlet and outlet pressures.
When it is fully closed, it is the pressure difference between the inlet and outlet of the compressor. After the valve is opened, the pressure just before the valve is close to the outlet pressure, but slightly lower than it ； The pressure behind the valve is close to the inlet pressure, slightly higher than it. There is a gradient. . . . Is studying this useful for production?