Let’s discuss the experiences and lessons learned from starting up catalytic cracking units
Thread Content
During the start-up of catalytic cracking, operations such as introducing main gas for airtightness testing, heating the reactors, establishing three circulation paths, sealing the switchers, loading the catalyst, changing the catalyst, achieving fluidization in the reactors, and injecting fuel must be carried out. Once we started working, things were going well at first, but when it came to installing the catalyst, it just wouldn’t fit in. The reason is that proper catalyst filtration was not carried out during the shutdown for agent removal, allowing some impurities to end up in the equilibrium catalyst tank, which severely affected the progress of resuming operations. I believe that those working in catalytic cracking may also encounter various problems during operation, and I hope we can discuss them and share insights together.
During one start-up, while installing the catalyst, cracks were found in the inclined tube expansion joint; it was necessary to weld over the expansion joint, which caused a 6-hour delay in the start-up.
Just before feeding material into a certain unit was to begin, the compressor needed to be warmed up. It was discovered that there was a temporary blind plate still in place at the discharge end of the compressor casing; therefore, starting up the unit was postponed. The valve was closed to isolate the flow, and the blind plate was removed. After feeding material into the reactor, it was vented through a flare. Fortunately, it was possible to stop the flow of material; otherwise, the operation would have had to be halted. During the shutdown period, the records related to the blind plate were incomplete.
During the heating up of the auxiliary burner at a certain installation’s startup stage, blockage in the lower half of the gas annular burner caused the gas to burn unevenly, which resulted in the top part of the furnace being burned through during the heating process; this forced another shutdown for repairs.
Shortly after feeding, the oil and gas **lan pad suffered a severe leak. Emergency shutdown. Later, we had to pack the boxes after feeding the material in. It has become a major problem for our device.
During one start-up, the additive could not be added either; upon further inspection, it was found that the catalyst tank had been pressurized incorrectly – pressure was applied to the fresh additive tank, so of course the catalyst could not be added. A very basic mistake. The operator is careless and lacks a sense of responsibility.
The balancing agent removed from the two vessels certainly won’t be very clean; whether the addition of the agent proceeds smoothly depends mainly on cleaning the pipeline by removing the flanges of the large feeding lines before starting up. We have also experienced situations where the additive was used for 16 hours. After switching to air, the steam failed to be drained, causing jamming at the packing gland of the check valve, preventing it from moving; it took 3 hours to resolve the issue. Leaks from the large blind flanges for oil and gas are a common issue; every time we start up operations, we fill the gaps around the flanges with packing, and then tighten the clamps with bolts – which works well. It avoids daily worries.