Explanation of reciprocating compressor issues
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I haven’t been here for a few days; the first page of the forum is filled with questions about the principle of reciprocating compressors. Not many people seem to understand this topic. Let’s pose a few questions; if you understand them, you won’t be confused about the principles of reciprocating compressors. 1. How is the discharge pressure of the final stage of a reciprocating compressor determined? 2. For a fully assembled 3-stage compressor, assuming it is a 2-4, 4-8, 8-16 stage compressor with a pressure ratio of 2 for each stage, what will happen to the outlet pressure when the inlet pressure decreases during operation? How is the inter-stage pressure distributed? How should the pressure ratio be allocated? 3: A compressor with 3 stages of compression; 2-4, 4-8, 8-16, with a compression ratio of 2 for each stage. When the system is started, the pressure is adjusted to 2. During the process until the pressure at the outlet reaches 16, how does the pressure change at each stage, and by how much? When does work start to be done at levels 1, 2, and 3 respectively? 4. All flow control systems can reduce the compressor’s power consumption, but variable-speed control systems and clearance control have an adverse effect on the compressor’s reverse angle. And the continuously variable adjustment system may have an adverse effect on the compressor crankshaft.
It would be better if these questions were accompanied by answers; otherwise, they are too technical and there are many things that are not clear. More content is needed in the follow-up! :)
1. It is determined by the back pressure of the system downstream of the compressor (the pressure after the outlet). 2. When the inlet pressure decreases, if the gas consumption of the system remains unchanged, the outlet pressure will also decrease; the exhaust pressure at each stage will drop as well, and the pressure ratio will adjust automatically. As for by how much the outlet pressure decreases, it is a result of the system’s feedback mechanism. If the outlet pressure remains constant, the pressure ratio per stage will increase, with the increase being smaller for the first stage than for the second stage, and even smaller for the third stage. 3. This is a complex dynamic process. Theoretically, with a back pressure of 16, after the compressor starts up, the inlet valve is opened and the return line is gradually closed. The pressure in the system begins to rise after the first stage of discharge; for example, the pressure at the 3rd stage outlet might be 4, while it’s 3 at the 1st stage outlet, 3.9 at the 2nd stage outlet. In other words, the pressure ratio increases first. When the outlet pressure is low, it is the earlier stages that do most of the work, while the later stages do less work, serving merely as a passage. 4. The flow regulation of reciprocating machines includes variable speed, stepless systems, clearance adjustment, and backflow adjustment; among these, the backflow adjustment at the final stage cannot reduce power consumption. Stepless regulation is currently the best method of control for high-power units (provided that the reverse angle meets the requirements).
Questions 1 and 2 were answered correctly; for question 3, the answer did not address the key point. 4. For stepless adjustment, it is necessary to verify not only the reverse angle but also current fluctuations, uneven rotation, and crankshaft lifespan.
Both the original poster and the one on floor 5 are experts. The variable flow control system isn’t as amazing as the manufacturers claim; choose it based on your own circumstances.