Catalytic cracking compressor inlet butterfly valve
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A few days ago, the FCC unit where I used to work was shut down for repairs. During the process of restarting the unit and stabilizing the gasoline flow, a malfunction in the V203 level gauge caused gasoline to flow back into the compressor inlet through the inlet pipeline. This led to leakage at the flange of the safety valve, and when the gasoline came into contact with high-temperature, medium-pressure steam, it flashed and caught fire. The positioners of the DN200 and DN250 flare valves were damaged, as well as the instrument signal wires. After replacing the positioners and signal wires and attempting to restart the unit, the compressor developed problems; there were issues with the rotor, likely due to liquid present in the system at low speeds (2000 rpm). The question is: the DN500 butterfly valve at the inlet is closed during normal shutdown – so how does the liquid get inside the compressor? Could it be caused by a fire?
It’s very likely; I don’t know if you have conducted pressure tests on it. Check whether its operating pressure is correct. This is because ordinary sealed butterfly valves use polytetrafluoroethylene material for sealing. If exposed to high temperatures (such as cleaning with superheated steam or burning by an open flame), it will deform, resulting in a reduced sealing effect or leakage. In summary, I think it is possible that the fire was the cause. But the specific reason can only be determined after you have completed the calibration of the valves. Additionally, I suggest that a liquid level display be added to V203, so that such issues can be avoided. Because this is an issue that instrument operators must pay attention to.
V203 has two sets of level indicators: a glass plate along with double flanges. However, the glass plate is no longer functional (scale has accumulated inside it, making it impossible to see the liquid level). At that time, the level gauge for the dehydration hopper at the bottom of V203 (a float-type gauge) stopped working due to a broken wire, which caused gasoline to flow into the compressor inlet. I would like to know whether it is possible for the DN500 inlet butterfly valve to open after the signal wire became short-circuited, in the event of a fire
It seems it won’t work. As mentioned in the second comment, PTFE has deformed, which makes rotation difficult. But this is just a speculation; one can try to manually rotate the valve body
From a safety design perspective, when the signal line is short-circuited, the inlet valve closes and the flare valve opens
Butterfly valves do not have good sealing performance, and are inferior to gate valves. If there is liquid in the pipeline, it is normal for it to enter the machine