160,000-ton ion-exchange membrane caustic soda plant; the hydrogen compressor is a water ring pump with an inlet pressure of 10 kPa and an outlet pressure of 110 kPa. I would like to ask for advice from experts.

This is a normal switch; is there any problem? One point to emphasize: the valve operation is adjusted slowly based on pressure.

It can easily trigger a chlorine-hydrogen pressure difference interlock, resulting in system shutdown.

So one word for slow. The electrolytic chlorine-hydrogen pressure difference is controlled manually via DCS; in this case, the chlorine pressure does not fluctuate due to changes in hydrogen pressure, thus preventing interference between them and avoiding any cascading effects. Hydrogen pressure switching is all done via programmable valves. Take your time. If adjusting the on-site manual valve, it requires personnel with extensive experience and a good sense of touch to operate it. Additionally, before switching, the electrolytic hydrogen vent valve can be used to release some hydrogen first, providing a margin for adjustment during the switching process to account for any fluctuations.

In fact, when switching a water ring pump (hydrogen compressor), the main issue is the large pressure difference fluctuation that occurs at the moment the inlet of the standby hydrogen compressor is opened; everything else is relatively fine. Before making the switch, it is necessary to train the staff carrying out the operation, explaining the key points of the switch and the emergency response measures. Experienced managers should be present both on-site and at the DCS to monitor every step of the switch process; there should be no major problems.

This post was last edited by nanren2 on 2017-3-10 at 12:46. Actually, it’s a question that seems ordinary on the surface but has quite a lot to it! To avoid fluctuations, it is not advisable for some manufacturers to open exports and then directly initiate imports! My shutdown procedure is as follows: 1. Check that the compressor is in good condition, that the power supply, mechanical seal water, etc., are all normal, and that everything is ready for shutdown 2. Fully open the single-unit reflux; open half of the discharge valve of the separator behind the unit, and open the nitrogen filling valve in front of the unit. 3. Start the compressor, check whether its operation is normal, and carry out nitrogen displacement at the same time! Once the oxygen content in the nitrogen meets the required standards, the inlet pressure is adjusted to match that of the system using the nitrogen pre-filter and post-filter! 5. Slowly open the inlet valve to connect with the system, then close the nitrogen valve at the front of the machine; hydrogen is used to displace nitrogen. Once the parameters are within the specified range, close the vent valve at the back of the machine. 6. Slowly close the individual return valve, gradually raising the pressure at the outlet behind the unit to the pressure in the external pipeline network; once the pressures are equal, slowly open the outlet valve. 5. Set the system’s main return valve to manual mode, while setting the return valve of the machine that is shut down to automatic mode. Slowly close the return valve of the compressor that has just been started, thereby gradually increasing the load. The compressor that is about to stop will automatically and gradually open the return valve in order to reduce the load! 7. When the opening degree of the return valve of the compressor to be shut down reaches over 70%, switch it to manual mode, and reset the main system return valve to automatic mode. Manually open the compressor return valve gradually until it is fully open! If the opening degree of the large reflux valve in this process is too small, the reflux valve of the compressor that has just been started can be appropriately reduced! 8. Close the inlet and outlet valves that are to be shut down; after draining the air from behind the machine, open the nitrogen supply at the front of the machine to carry out nitrogen purging until the conditions are satisfactory, after which close the valves! 9. Turn off the seal water after shutting down the machine! Although the caustic soda plant reduced the impact on the electrolyzers by adding gas tanks! However, the quality of the hydrogen compressor switch has a significant impact on the operation of the polyvinyl chloride plant that uses caustic soda It mainly affects the synthesis of hydrogen chloride! The above operations are for liquid ring compressors; this method results in very little system fluctuation, but it is rather complicated!

This switch is a bit difficult, but it can be done.

First, balance the operating units so that their outlet pressures are equal (generally, the outlet valves are quite large, resulting in significant pressure fluctuations; it is difficult to achieve balance without experience, and modifications may be necessary later on). Switching after balancing is very easy. Last year, our company faced issues that required unit switching; valuable lessons were drawn from that difficult and lengthy switching process. Thanks to the recent modifications, the switching of the hydrogen compressor is now very smooth.

1. Before making the switch, adjust the chlorine large reflux manually. 2. When opening the inlet valve of the standby unit, reduce the hydrogen large reflux slightly; wait until the pressure stabilizes before proceeding to the next step. 3. There must be one person at the inlet and reflux valves of the standby unit, and another person at the inlet and reflux valves of the unit that is currently in operation; both people should operate the valves based on the inlet pressure. 4. The DCS adjusts the large reflux valve based on the chlorine-hydrogen pressure difference.

It seems pretty simple. Why does the inlet pressure of the backup hydrogen compressor fluctuate? Turn the reflux fully on, open the inlet, close the reflux; adjust it to the same level as before based on the pressure behind the pump, and then slowly open the outlet. Try following my steps; it’s very simple

This post was last edited by aldd7611 on 2017-8-27 14:46. No way! As long as the pressure balance between the standby unit and the main outlet pipe is maintained, the rest of the switching process is smooth. Steps: 1. Check the status of the standby machine; start the standby machine normally ； 2. Slowly open the outlet of the backup unit (be sure to do it slowly). This can be achieved by installing a small balance pipe; this is the most crucial step :) Once the standby unit is at the same pressure as the system, slowly open the outlet completely. The remaining steps involve opening the inlet of the standby unit and enabling the return flow for the unit to be switched over ； Turn off the return flow of the standby machine, and turn off the inlet of the machine awaiting switching ； Finally, proceed with the operations at the switch outlet. {:1_90:} The speed control of opening and closing the valve is good, no issues.