Air separation oxygen production area: [Weekly Topic] Week ** of 2011——What actions are required in the event of an emergency shutdown of the air separation unit?
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In the event of an emergency shutdown of the air separation unit, what actions need to be taken to resume production as quickly as possible? To facilitate the discussion, I will provide a brief description of the process; or you can also talk briefly about your own process. It involves a turbine driving two units, or electric drive, with molecular sieve purification followed by compression in a pump using liquid oxygen and liquid nitrogen
Let me get started – make sure that impure products do not enter the users or storage tanks!
Instrument air interruption: Measures: 1. Open the backup instrument air valve, and the device will be able to resume operation. 2. If it does not function properly, shut down the device. 3. If the device continues to operate, the purity of the product should be checked, as well as the degree of regeneration and cooling of the molecular sieve purifier. If it is not normal, corresponding adjustments should be made.
In the case of an emergency shutdown of the air separation unit, the product outlet valve must be closed; to speed up restart, it is possible to omit draining the tower
When an air separation unit shuts down urgently, the first thing to determine is the cause. If it can be restored in a short time and conditions permit, start the instrument air compressor first to supply instrument air to the entire plant ； Then, immediately activate the liquid nitrogen backup system to supply nitrogen to the subsequent system ； Open the relief valves of all products and close the discharge valves ； At the same time, it is necessary to close the inlet and outlet valves of the expander, and also pay attention to controlling the liquid level in the pre-cooling system, among other things. If production is to be resumed as soon as possible, it is necessary to first identify the cause; thereafter, the pre-cooling system and the purification system can maintain pressure ； The distillation system can maintain pressure while keeping the liquid level stable. This way, it starts faster. The above are my personal views; please point out any shortcomings.
When stopping the operation, try to pump liquid nitrogen into the upper tower so that the main cooler operates beyond its range; this prevents a rapid drop in the temperature of the main cooler when starting up again, thus allowing for a faster restoration of purity
Unit handling: To stop the machine manually, press the emergency stop button on the DCS or the on-site emergency stop button; to bring the rotor to a stop as quickly as possible, open the atmospheric safety valve to break the vacuum. Confirm that the inlet guide vanes of the air compressor are closed and the outlet vent valve is open; confirm that the inlet valve of the booster is closed and the anti-surge valve is open. Confirm that the turbine emergency shut-off is closed. Monitor and record the idle time of the unit; engage the barring gear when the turbine speed is zero. Stop the extraction steam turbine and cease shaft seal air supply.
Turn off the seal gas for the cryogenic tank. Stop the crude argon pump, liquid oxygen pump, and liquid nitrogen pump; drain the liquid after shutdown. It is correct to feed liquid air into the upper column, but when the main cooler exceeds its operating range, the liquid still needs to be drained to a location where it can be monitored.
Close the product delivery valve. Liquid nitrogen reflux valve at the lower tower – opened to allow air in and prevent overpressure, from the night sky to the upper tower. The inlet and outlet of the expander are closed. Molecular sieve pressure holding. Pre-cooling prevents the liquid level from rising, ensuring the proper operation of the sealing gas
1. Stop the gas supply and shut down the product compressor. Open the vent valve on the pipeline. 2. Liquid delivery valve. 3. Stop the argon pump and close the inlet and outlet valves. 4. Close the nozzle, expansion turbine outlet valve, and fully open the expansion turbine bypass valve. 5. Close the air inlet valve V101. 6. Open the oil bypass valve fully. 7. Switch to instrument air. 8. Close the air compressor make-up valve, or close the relevant exhaust valve. 9. Stop the purifier. Check the degree of regeneration and cooling of the molecular sieve purifier. The purifier timer stops. 10. Pump stopper. Drain the water from the cooling tower. 11. Transfer the liquid level from the lower column to the upper column. 12. Decide whether to stop the circulation water pump depending on the situation. Stop the fan.