Urgent! Urgent! Urgent! ! ! The one-way damping valve at the main fan outlet will not open
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Today, the catalytic cracking unit was put into operation. After starting the backup main fan, the instrumentation technician adjusted the one-way damping valve at the outlet of the main fan (Lanlian ZHY800 butterfly type one-way damping valve); once it was closed, the one-way damping valve could not be opened again. This fault occurred once on the 14th; during that inspection, the entire valve was taken apart and no abnormalities were found: 1) There were no foreign objects stuck in the valve disc, and 2) The pneumatic actuator was inspected as well, with the cylinder piston moving normally and no sticking observed. After disassembly, use force to move the valve plate; then reconnect the pneumatic actuator. Once the switch functions properly, put it into use. Today, before starting the catalyst fluidization process, I was concerned about the instruments, so I checked and adjusted the one-way damping valve again. It worked fine when opened for the first time, but after being closed the second time it wouldn’t open anymore. On-site, the pneumatic actuator was removed, and a winch along with large pipe wrenches were used to try to force the valve disc shaft to move and open the valve, but the valve disc didn’t budge at all. To find the cause, it is possible that the problem lies in two aspects: 1) The electric butterfly valve located downstream of the check damper is not sealed properly, allowing air leakage; as a result, the back pressure at the valve disc of the check damper is not sufficient to keep it open ； 2) The copper sleeves at both ends of the valve plate shaft of the one-way damping valve seize due to heating (air leakage in the electric butterfly valve causes a temperature of 105 degrees Celsius in that area) ； This issue hasn’t been resolved yet; we’re considering what to do, otherwise the third unit can’t be started either. It’s urgent! Urgent! Urgent! Could someone from Haiyou help analyze the reason? Has anyone encountered this situation? Thank you!
The problem is solved! ! Today, based on the two reasons analyzed, factors such as back pressure and thermal expansion were taken into consideration (and since the air leakage rate of the electric butterfly valve was uncertain, removing it could severely affect the main airflow, so it was not possible to remove the check damper). Therefore, a DN100 hole was made online in the pipeline between the check damper and the electric butterfly valve. Once the hole was created and pressure was released, the check damper opened easily, and the problem was finally resolved. However, this incident serves as a lesson: in future maintenance tasks, the overhaul of the check damper must always be included in the maintenance plan :lol