Issues related to expanders

“Start up the system by cycling the inlet valve at the pressurization side. . . . ” No way

Hehe, it’s not clear why the inlet valve on the pressurization side needs to be rotated to start the machine. Starting the expander at intervals is done to maintain stable pressure and flow levels in the equipment, thereby ensuring a safe startup of the air separation unit and preventing either too low pressure or overpressure in various parts.

1. Starting the expander: First, it is started by using an emergency shut-off valve for a trial run, with all other valves open and the inlet guide vanes at the expansion end at a certain degree of opening； Secondly, start the machine by rotating the inlet valve on the pressure-boosting side; once a certain speed is reached, immediately open the return valve on that side. That driving method is better; what are the advantages? The expander uses an adjustable nozzle for operation, while the emergency shut-off valve is either fully open or fully closed. . . If the expander is started using an emergency shut-off valve? Be careful of excessive airflow causing the expander to run away. . . . Once a certain speed is reached, the reflux in the pressure-increasing section should be turned off; after that reflux is stopped, the nozzle can be activated again to increase the pressure. . . Therefore, both of the owner’s two-week driving methods are harmful to the equipment. . . 2. Why is it necessary to wait for a certain period of time between starting the two expanders at the beginning of cooling? First, start the expander; the air compressor unit also needs to maintain pressure. If the pressure isn’t stabilized once one unit is started, how can the next one be started? Second. The air at the outlet of the exhaust expansion machine is not very cold, which can easily lead to overpressure in the subsequent systems. .

Reply to 4#: It was me. At first the nozzle was at a low opening degree; after the emergency shut-off valve was activated, a restart was carried out. Once a certain speed is reached, open the nozzle and close the return valve at the pressure-boosting end to apply load.

Since the valve positioner is controlled by DCS signals, there can still be cases where the DCS values do not match the actual valve opening. Doing so merely to save time is a risky approach. If it must be done, it is recommended to check before starting up whether the DCS-set signal corresponds to the actual opening. The cost of this approach is that someone will have to climb to the top of the expander to check the valve position; considering the time required for that, it’s still faster to use the nozzle. If the speed drops suddenly after using the nozzle, someone should be on hand to monitor the situation. If the speed starts rising rapidly, an emergency shutdown device should be used to close the quick-shut valve and ensure the safety of the unit.

Expansion machine startup steps 1. First, supply cooling water 2 to the cooler at the pressure-increasing end of the expander. Introduce it into the sealer, supply cooling water from the oil cooler, and start oil pump 3. Check whether the interlock signals are functioning properly, as well as whether the emergency shut-off valve is in good condition. 4. Open the air inlet and outlet valves on the pressure-boosting side. 5. Ensure that the pressure at the second stage of the compressor is normal. 6. 7. On the DCS, select “Expander Defrosting” and reset the expansion machine’s interlocks; finally, initiate the expansion machine (with the emergency shut-off valve open). Open the air inlet and outlet circuits at the expansion end on-site. 8. After the expansion machine starts, use the reflux valve at the pressure-boosting end to control its speed to just below the critical speed level, in preparation for starting up the machine. 9. All subsequent operations should be carried out in close coordination with those performed on the compressor. Any corrections or suggestions are welcome