The change of the sealing of the large pressure cylinder side of the new gas air compressor

After the inspection, the vibration of the high-pressure cylinder was still very large. When the speed was 7226r/min and the flow rate was 30,000m3/h, the radial vibration of the three sections reached 1143m. The unit was forced to stop again after about 500 meters on September 21st. The high-pressure cylinder core inspection found that the end cap of the shaft end seal of the fourth section fell off, but the damage was not serious, and a screw was sucked into the four-stage first-stage impeller flow passage. At the same time, it was found that the fifth stage separator of the high pressure cylinder was damaged due to the breakage of the connecting screw.

After careful analysis of the structural form of the shaft end seal, it is considered that there are some defects in the original design and it is improved to avoid such accidents from happening again.

Reasons for damage The structure of the shaft end seals at both ends of the high-pressure cylinder is basically the same as the cause of the damage. The three-stage shaft end seal is taken as an example for illustration, and its structure is as simple as shown.

The shaft end seals at both ends of the high pressure cylinder of the carbon dioxide compressor are sealed by a labyrinth. The shaft end seal is fixed to the three-stage flange of the high-pressure cylinder with the screw 1 of the high-pressure cylinder, and the end cover of the shaft end seal is fixed to the shaft end seal by the screw 2. During operation, the CO2 gas from the droplet separation tank of the two-stage intercooler is entrained with unremoved moisture. Since the temperature of the CO2 gas coming out of the separation tank is very low (generally 42) and the pressure is high, it is easy to react with water to form carbonic acid. The CO2 gas with carbonic acid enters the three-stage inlet of the high-pressure cylinder, and the carbonic acid has a corrosive effect on the bushing of the first-stage impeller of the three-stage high-pressure cylinder rotor; on the other hand, it also corrodes the shaft end seal and its end cap. The same situation can also occur at the four entrances. This has been verified during the previous inspections.

The structural diagram of the three-stage shaft end seal of the original design high-pressure cylinder under the corrosive action of carbonic acid, the outer surface of the end cap of the shaft end seal will form many corrosion pits, and the CO2 gas will enter the corrosion pit near the end cover connecting screw 2 Stopping the ground. Over time, the connecting screw 2 will loosen until it falls off, and the end cap will fall off. The detached screws are sometimes sucked into the flow path of the impeller and the stationary member along with the air flow, which deteriorates the dynamic balance of the rotor and also affects the flow of gas in the flow path. The detached end cap will be attached to the inlet of the three-stage first-stage impeller, which will affect the unit's load and increase the two-stage outlet pressure. If the end cap and the impeller are rubbed, the high temperature generated by the friction will melt the aluminum end cap, and the molten droplets will enter the flow path of the impeller and the stationary part and solidify on it as the airflow passes, which will make the unit The operation deteriorated rapidly and was forced to stop.

The defects and improvement measures of the original design can be known from the above analysis: the connecting screw 2 of the end cap of the shaft end seal is easy to fall off during operation, which is the main cause of such accidents. It is conceivable that if the shaft end seal and its end cap are made in one piece, the connection screw is removed, and the problem is completely solved. The main problem with this retrofit is how the shaft end seal is fixed to the three-section flange. There is still a distance from the end of the shaft end seal exposed on the outside of the flange. It is conceivable to machine a groove in this position. The shaft is locating with a circlip (GB894188), and the position of the previously installed screw 1 is modified. pin. The reconstructed structure is as shown.

The improved high-pressure cylinder shaft end seal structure is simple. 1) The modified shaft end seal structure is simpler, the processing and installation are more convenient, and the axial positioning is accurate and reliable.

2) In order to ensure the accurate installation position of the circlip for the shaft, it is required that the groove of the shaft end seal is processed after the test is determined.

3) The large amount of water in the three-stage and four-stage inlet gas of the high-pressure cylinder of the carbon dioxide compressor is also a safety hazard. From the perspective of equipment, the bushing material of the three-stage and four-stage first-stage impeller has been changed from the original 2Cr13 to 1Cr18Ni9Ti to improve its corrosion resistance. At the same time, it is necessary to control the impurity content in the aluminum (ZL302) used for the shaft end seal to ensure the material quality. From the technical point of view, the separation tank should be drained frequently, and the liquid level in the separation tank should be strictly controlled.

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