Instructions for Handling Oxygen Pump Interlock Trip Incidents

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Accident sequence: On March 6, 2009, the anti-surge valve BV9004 of the 271A booster (the flow control valve for the transition from stage 2 to stage 1 of the booster) suddenly opened fully, resulting in no flow from the booster to the expander. This caused the expander to shut down due to low speed interlock. As the amount of air flowing to the heat exchanger decreased, the liquid oxygen pumps P9601/2 also shut down due to the oxygen pipeline temperature TIAS9302 falling below -20°C, which led to the shutdown of the distillation system. In light of this incident, the following precautions have been established for future operations: 1. Stop supplying nitrogen to external systems and keep the distillation system in a vented state ； 2. The plate exchanger must not experience cold flow; the operating conditions can be adjusted by modifying HCV9605, HCV9302, and V9603, while taking care to prevent surging of the unit during these adjustments. 3. To prevent overpressure in the upper section of the distillation tower, it is possible to appropriately reduce the settings of HCV9601 and HCV9602; if the pressure in the upper section becomes too high, V9451 can be opened to release pressure. 4. If the HCV9305 control panel cannot be used, immediately apply manual pressure using the handwheel to prevent the heat exchanger temperature from dropping too low, which could damage the heat exchanger and pipelines. After the instrument forced interlock is released, the HCV9305 handwheel can be reset ； 5. At the site, open the expander blowout valve and the volute drain to check for the presence of liquid. If liquid flows out, continue to allow it to drain to prevent large amounts of liquid from evaporating and damaging the equipment. Before starting the expander, first open the outlet valve at the expansion end, slightly open the inlet valve, and open the blowout valve. Check again to ensure that there is no liquid in the blowout valve; only after confirming that there is no liquid should the expander be started.