Treatment of riser blockage
Thread Content
In a refinery in the north, after the catalytic unit was successfully restarted for operation in winter and the catalyst was transferred to the lift column, the regeneration slide valve was temporarily shut down for other reasons. However, due to a leaky regeneration slide valve, a small amount of catalyst entered the lift column. The outlet of this lift column led to a bed reactor used for reducing olefins. Because of the cold weather, the temperature of the steam used for stripping was insufficient, and there was no circulation; as a result, water condensed and froze in the upper part of the lift column, causing it to stop flowing and become blocked. When attempts were made to transfer catalyst again, it became clear that fluidization was no longer possible. What should be done in such a situation? Are there any effective solutions?
Adjust steam and air to control temperature and carry out fluidized coking; hehe, for reference only
Personally, I think work should stop. Then disassemble the lift pipe and settler, as well as the regenerator manholes for maintenance. If this situation is handled recklessly and work starts, there will still be hidden risks in the future. . Take it apart to check whether the lining, various nozzles, and cyclones have frozen and cracked or deformed. . . .
If it stops moving, just rinse it with water
During feeding, the temperature of the lift pipe dropped, and in such cases, water had to be used for flushing. The effect is okay.
Where on earth is this place where the temperature remains so low in March? The diameter of the lift pipe should be at least 600 mm or more. It’s probably not due to freezing; it could instead be caused by catalyst and sludge. The safest and fastest way is to shut down the reactor-reformer system, install blind flanges on the oil and gas pipelines, and then remove the catalyst. Otherwise, if the issue isn’t handled properly, it can cause blockages in the legs of the settler, leading to the catalyst flowing into the distillation unit, which would create additional problems that would also need to be addressed.
We have encountered this situation as well, but back then our facility was small, with an annual processing capacity of only 200,000 tons. The solution taken at the time was to close the large valve at the inlet of the fractionator and to fill the regenerator with catalyst. After confirming that no catalyst was leaking from the bottom of the lift pipe (at that time the slide valve wasn’t sealing properly, but once the regenerator was filled with catalyst, further leakage stopped). ), a high-pressure water gun was used to flush inside through the vent valve at the bottom of the lift pipe; what came out was only thin sludge. Once the passage was cleared, air and steam supply were resumed immediately. The nozzles, pressure guiding pipes, and steam pipelines were carefully inspected to ensure they were unobstructed, after which fluidization of the two reactors was initiated. At first, the circulation rate was kept low and the temperature was raised gradually; condensate was drained from the bottom of the lift pipe several times (circulation was stopped during these drainage operations). Once the temperature rose, feeding could be resumed for normal production. This is only a temporary solution for special situations; it’s not ideal. The best approach is still to strengthen prevention measures.
As soon as the catalyst starts to leak in, there might still be some ways to deal with it, such as increasing the exhaust volume at the bottom of the lift pipe. If the pressure drop in the lift pipe gradually decreases, that’s fine, but continuing in this manner carries significant risks; operating in such conditions is likely to lead to problems. The most important thing when starting up a catalytic reactor is to be careful, and to follow the established procedures. Before changing the catalyst, experienced operators will definitely pay attention to both the pressure drop and density in the lift pipe. Additionally, the large vent valve of the lift pipe should be opened before the catalyst change: this is done to remove condensed water and to check for any leaks in the regeneration slide valve; if leaks are detected, they need to be corrected promptly, and the catalyst also needs to be removed at that time.
It’s recommended to stop for now; the top of the riser is definitely covered with catalyst and sludge, and the situation is quite serious. After parking, rinse it with water or enter through the manholes at the top and bottom of the lift cylinder to carry out the treatment.
It must be the catalyst and sludge; I agree with the above statement – it’s best to stop and rinse it with water