Sharing of catalytic cracking shutdown experiences
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:) During the shutdown of catalytic cracking units, have you encountered any special emergencies? Please share any special experiences you have. Everyone is welcome to participate actively. Our installation is about to stop operating
Before shutting down, it was suddenly discovered that the slurry discharge line was blocked. . . . Finally, a new one was laid
1. The manhole of the settler should not be opened too early, as coke lumps can catch fire on their own. 2. Ensure that the catalyst is completely removed; when opening the regenerator manhole, expect catalyst to flow out. 3. The slurry system should be thoroughly flushed with paraffin oil to facilitate line cleaning. 4. The desulfurization system must have plans to prevent hydrogen sulfide.
The most important thing is to ensure the linear velocity of the medium in the settler, in order to prevent a large amount of catalyst from reaching the fractionation tower.
Before shutting down, ensure that all oil return lines are unobstructed, especially those in the crude oil and heavy oil systems.
Critical accidents encountered during the shutdown of the catalytic unit: 1. After the temperature in the primary settler dropped to 150 degrees, steam was replaced by air, but the temperature did not rise; subsequently, when the manhole of the settler was opened, spontaneous combustion occurred. 2. Inadequate pipeline cleaning led to accidents during hot work.
Generally, a planned shutdown should not pose any major problems. As long as the scale inhibitors in the slurry system are applied continuously, the lines will not get clogged, and there will be no leaks or other issues, thus preventing safety accidents. In short, with careful planning, everything goes smoothly.
Last year, when operations were halted and the distillation tower was opened, ferrous sulfide caught fire spontaneously; fortunately, it was extinguished in time. In the future, be sure to wash the tower carefully, waiting until it has cooled down before opening it.
The problem of spontaneous combustion of ferrous sulfide can be addressed by passivation washing, using a low-concentration potassium permanganate as the passivating agent; circulating water through the tower helps to remove heat, and this approach proves to be quite effective!
When removing the catalyst, a vacuum pump can be used to extract any remaining catalyst from the reactor, which saves time and effort.
1) Pay attention to the temperature of the settler; if there are many coke lumps inside, the temperature read by the thermocouple may not reflect the actual temperature inside. It is necessary to check the condition inside the settler once its manhole is opened to see if the coke lumps are burning, in order to prevent damage to the equipment. Be careful when conducting this inspection. 2) The dry gas liquid separation tank presses out the liquid before the system pressure drops.