Production Technology [Weekly Topic]: Questions and Answers on Multi-stage Compressors (2011-01-31~02-06)

1. Avoid excessive exhaust gas temperature. 2. Reduce power consumption. 3. Improve the cylinder volume utilization rate. 4. The compressor structure is more rational, reducing the stress on the piston; the compression temperature at each stage remains within the allowable range ； The total power consumption of the compressor is minimal ； The machine structure should be as simple as possible to facilitate manufacturing ； Reliable operation

Usually, due to the large pressure difference between the inlet and outlet of the compressor, it is necessary to gradually increase the pressure to meet the final pressure requirements, which simplifies the design of the machine; however, this increases the cost of the machine itself.

High exhaust pressure, high compressor input power

Advantages: 1) Reduces exhaust temperature. By using multi-stage compression, the pressure ratio for each stage can be reduced, and inter-stage intercooling can be applied to keep the suction temperature of each stage low (usually similar to that of the first stage). As a result, the exhaust temperature of the gas after compression is **reduced, which helps to save power consumption. By using multi-stage compression, intermediate coolers can be installed between the stages; this allows the compressed gas to undergo isobaric cooling after each stage of compression in order to reduce its temperature before it moves on to the next cylinder. As the temperature decreases and density increases, it becomes easier to compress further, which can **save energy consumption** compared to a single compression. 3) Improve the cylinder volume utilization rate. Multi-stage compression is employed, with each stage having a very low compression ratio; the gas remaining in the clearance volume expands slightly to reach the intake pressure. This allows the effective volume of the cylinder to increase, thereby improving the utilization rate of the cylinder’s volume. 4) Reduce the maximum gas force on the piston. When the compression ratio is high, multi-stage compression is used; the gas pressure increases step by step, while the diameter of the cylinders decreases at each stage. As a result, in the lower pressure stages, the gas pressure acting on the larger piston area is low, whereas in the higher pressure stages, a higher gas pressure acts on a smaller piston area. As a result, the forces acting on the motion mechanism at all levels are relatively small. If the various levels are allocated reasonably as well, the force acting on the moving parts can be further reduced.

Happy New Year! The advantages of multi-stage compression are: 1. The compression ratio per stage is low, the piston stroke is short, and the equipment is simple to manufacture. 2. Hierarchical compression is employed, with cooling available during the process to prevent additional energy loss caused by heat generation during gas compression, resulting in high efficiency.

Reasons for using multi-stage compression: 1. To prevent the exhaust gas temperature from becoming too high. 2. Reduce power consumption. 3. Improve the cylinder volume utilization rate. 4. The compressor structure is more rational. 5. Reduce the maximum gas force on the piston.

1. Reduce exhaust temperature. 2. Save power consumption. 3. Improve the cylinder volume utilization rate. 4. Reduce the maximum gas force acting on the piston.

Multi-stage compression can achieve a higher outlet pressure; to obtain the same outlet pressure, using single-stage compression would require a much larger volume of equipment and pose greater manufacturing challenges.

1. Reduce exhaust temperature. When the exhaust pressure of the compressor is high, if single-stage compression is still used, the pressure ratio will be very large, resulting in an exhaust temperature that is far above the allowable level and preventing the machine from operating properly. If multi-stage compression is used, the pressure ratio for each stage can be reduced, and inter-stage intercooling can be applied to keep the suction temperature of each stage low (usually similar to that of the first stage). As a result, the exhaust temperature of the gas after compression will **decrease** ； 2. Save power consumption. By using multi-stage compression, intermediate coolers can be installed between the stages; this allows the compressed gas to undergo isobaric cooling after each stage of compression in order to reduce its temperature before it moves on to the next cylinder. As the temperature decreases and density increases, it becomes easier to compress further, which can **save energy consumption** compared to a single compression. 3. For media that are prone to phase changes under compression, multi-stage compression must be employed, and the liquid must be completely removed from the tanks between stages; otherwise, it can cause fatal damage to the compressor. Furthermore, for centrifuges: compared to single-stage compression, multi-stage compression reduces the size of the equipment and simplifies control under the same flow rate conditions ； Especially for centrifuges with very high pressure ratios, multi-stage compression must be used to account for anti-surge considerations. For reciprocating engines: improve the cylinder volume utilization rate. Due to manufacturing, installation, and operational factors, a clearance volume within the cylinder is always inevitable. This clearance volume not only reduces the effective volume of the cylinder directly, but the high-pressure gas remaining in it also has to expand to the intake pressure before the cylinder can start drawing in fresh air, which further reduces the effective volume of the cylinder. It is easy to understand that the greater the pressure ratio, the greater the maximum gas force acting on the piston within the clearance volume. When the compression ratio is high, if single-stage compression is used, the higher final pressure acts on a larger piston area, resulting in a greater force being transmitted to the moving mechanism. In multi-stage compression, the gas pressure increases stage by stage, while the diameter of the cylinders decreases at each stage. As a result, in the lower pressure stages, the gas pressure acting on the larger piston area is low, whereas in the higher pressure stages, a higher gas pressure acts on a smaller piston area. As a result, the forces acting on the motion mechanism at all levels are relatively small. If the various levels are allocated reasonably as well, the force acting on the moving parts can be further reduced. As the residual gas expands more, the effective volume of the cylinder becomes smaller. The above content is based on Haichuan: http://bbs.hcbbs.com/thread-231360-1-1.html

1. The entire compression process can be carried out in several stages across multiple cylinders, so that the pressure increase of the gas in each cylinder does not become too high; as a result, a multi-stage compressor can achieve a higher volumetric efficiency. 2. By using intercooling, the temperature of the gas at the end of compression is reduced, which also decreases the power consumption of the compressor.