Interlocking actions for all rectifier shutdowns
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Hello, everyone! For the trough-type design of Beihua Machinery, there are generally two scenarios for its interlock action after all rectifiers stop operating: ① When all rectifiers stop, the interlock mechanism causes PCV-218 to open fully, while PCV-228 maintains a pressure difference of 4 KPa in the main pipe ahead of the scrubber tower ； ZV-219 and ZV-229 are both shut down; the hydrogen compressor and turbine have stopped! ②All rectifiers are shut down; PCV-218 is opened fully, and PCV-228 is set to a certain opening degree to limit the hydrogen emission rate and thus maintain the pressure difference ； ZV-219 and ZV-229 are both shut down; the hydrogen compressor and turbine have stopped! Of course, there are many other methods besides these two; some involve using gas tanks filled with hydrogen, while others use water seals to maintain the hydrogen pressure, etc. The rest will not be discussed here. The ideal scenario for these two approaches is that the valves can operate simultaneously; however, during normal operation, the hydrogen compressor and turbine generally stop more quickly, followed by the operating speed of the ZV switch valve, and lastly the operating speed of the PCV pressure control valve. From a process perspective, if simultaneous operation is not possible, the PCV pressure control valve should be opened first to prevent pressure buildup! Therefore, delays are used in most configurations; some of these delays can be viewed and set on the DCS operation screen, while others run in the background of the DCS program. I’d like to ask how everyone does it?
You forgot that the most important elements for controlling the pressure difference are the two control valves, PCV216 and PDCV226. Once PCV218 and 228 cause an interlocked shutdown, these valves should be opened fully; after the pressure difference stabilizes, the opening degree of valve 228 can be adjusted manually as appropriate.
I don’t think there will be pressure buildup, because control valves adjust more quickly than on-off valves. Generally, in the system, the valve heads 218 and 228 are smaller than those 219 and 229, and they operate more quickly; therefore, no delay is required.