I need the help of experts regarding a compressor issue
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Today, my supervisor asked me two questions regarding the new hydrogen compressor. It’s a reciprocating type of compressor, and he asked why the cylinders of the first and second stages (which are cylindrical in shape) differ in shape from those of the third and fourth stages (which are square in shape). He also asked why the buffer tanks at the compressor outlet are getting smaller, with the buffer tank at the exit of the fourth stage being the smallest. Could anyone help explain this? I’m not an expert in equipment, so I can’t figure out this issue
I’ll take on the task myself; I’d appreciate it if the experts here could give me some advice
With constant inlet flow, the volume of the gas being compressed becomes smaller and smaller; as a result, the diameter of the cylinder and the volume of the buffer tank decrease. But the pressure will increase, and the risk will rise significantly. Our 4M65 has an outlet pressure of 22.6 Mpa; it features three stages of compression, and the outlet buffer tanks for these stages are designed in a spherical shape.
Well, I’ve learned it. May I ask what considerations are behind the different shapes of cylinders?
The volume of the buffer tank is due to process-related reasons – the mass of hydrogen compressed by each stage of the pressper per unit time remains constant; with each stage of compression, the density of hydrogen increases, its volume decreases, and the pressure rises. Cylinder cross-sectional shape? Could you confirm that the internal structure of the cylinder is square? ——Theoretically, rectangular materials are less resistant to forces compared to circular materials of the same size. Perhaps for reasons such as ease of installation, it is designed with a circular cross-section for the inner wall and a square shape for the outer shell. Anyway, since the cylinder volume is smaller, the difference in material usage isn’t significant
The question regarding the volume of the buffer tank has already been answered. Regarding the shape of the first and second cylinders as well as the third and fourth cylinders, the internal structure of these cylinders is the same; the difference lies in their external shape. I remember a teacher mentioning that compressor cylinders come in two types: cast and forged. Cast cylinders have a simple manufacturing process, but their strength is low and they cannot withstand high pressures; forged cylinders are more difficult to manufacture, but they possess higher strength. Cast cylinders can be formed in one casting process; they are cast into a cylindrical shape according to the mold design, which requires less material. For forged cylinders, additional cutting and polishing may be necessary on the outside, while making them square might be simpler and more convenient. This is just my guess; I’ll need to consult the expert to find out for sure. Please let me know once you have an answer so I can learn from it
The question regarding changes in the volume of the buffer tank has already been answered. Regarding the issue of different cylinder shapes, regardless of their external form, their internal cross-section is always circular. I wonder if the external shape is related to the manufacturing process of the cylinder. Since the pressure in the first and second cylinders is low, cast cylinders that are relatively simple to manufacture, inexpensive, but also have lower strength can be used; they can be molded in one go directly according to the shape of the mold, and less material is required for cylindrical shapes ； If the pressure in cylinders of grades 3 and 4 is high, forged cylinders can be used; these are more difficult to manufacture and more expensive, but they have higher strength and can withstand greater pressures. After being forged, forged cylinders may have irregular external shapes that require machining and polishing. If a cylindrical shape is intended for them, the amount of work required would be significant, so it is simpler to machine them into a square shape. This is my speculation; I’ll need to ask the teacher to confirm whether it matches the actual situation. If the person who asked the question knows the correct answer, please let me know. Thank you
“Why do level 3 and level 4 (square ones) have different shapes?” ? Are you referring to the appearance? ? It should be the shape of a cooling water jacket interlayer, right?
Well, yes, it’s cylindrical inside; the difference in appearance is due to the number of primary and secondary air valves (there are 4 valves in total for intake and exhaust), is it for aesthetic reasons during installation?
Cylinders are cast, while squares are forged. Forging requires much higher pressure levels than casting; lower pressures are sufficient for grades 1 and 2, so casting is used in those cases. Higher pressures are needed for grades 3 and 4, hence forging is employed, and of course the prices differ as well