Problems with starting centrifugal carbon dioxide units

Thread Content

Our newly installed carbon dioxide unit is of the two-cylinder, four-stage type, with an inlet pressure of 0.17 MPaA and an outlet pressure of 16 MPa. The rated speed is 10,000 rpm. When we started the machine, we opened all the outlet vent valves; these valves were not closed even after the speed exceeded the critical value. As a result, during the first start-up, at 8500 rpm, the temperature of one of the thrust bearings in the high-pressure cylinder exceeded 110 degrees (an alarm was triggered at 105 degrees, and the machine stopped automatically due to the interlock system set at 115 degrees). There are no abnormalities with the repair tiles. The same procedure was followed a second time; the outlet vent was closed only after the anti-surge valve of the low-pressure cylinder became energized. The speed of the low-pressure cylinder was 9800 rpm, and the temperature of the thrust bearings was 96 degrees. I would like to ask whether it is possible to reduce the flow rate at the vent valve before reaching the critical point; this way, both the high-pressure side and the low-pressure side of the high-pressure cylinder can do work simultaneously, and the axial thrust exerted on the thrust bearings will be much smaller. As for the surge problem, as the relief valve is closed, the pressure at the outlet of the low-pressure cylinder will increase to some extent, but the volume of air passing through the anti-surge valve will also increase, so there should be no issue ； The high-pressure cylinder should also be fine, right? I hope everyone can give me some advice.