Catalyst unit slurry issue
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This post was last edited by akzo2008 on 2009-9-3 at 22:22. Since the overhaul and restart of our plant’s heavy oil catalytic unit in December last year, its operation has been normal, with a yield of around 81%. However, in the past two to three months, this yield has dropped significantly, currently standing at only 77–78%. The solid content in the slurry is between 11–20 PPm. The valves in the re-refining pipeline have worn out, and there are large fluctuations in the pressure drop in the riser. There are also significant fluctuations in the initial separation pressure drop in the reaction settler. No catalyst has been removed over the past few months; as a result, the amount of slurry has increased, and the reaction temperature has reached 520 degrees, which leads to an increase in the amount of dry gas, and even the presence of liquid in it. What causes this phenomenon? I suspect it’s a problem with the nozzle; we’re using CS nozzles. Have they worn out? I’m not sure. The raw material is Changqing residue oil, and it was also found that the nitrogen oxide ratio in the regenerated flue gas in February was three times higher than before. So far, no new ammonia has been added, but the ammonia nitrogen level remains at around 5 kilograms per hour. Analysis shows that the raw material contains basic nitrogen; could this cause problems with the nozzles? Everyone, please help analyze it.
The high solid content in the slurry may be due to poor centrifugal separation, resulting in a longer residence time for oil and gas. I suspect there is coking at the centrifugation unit.
What is the pressure drop of the regenerative slide valve, and could it be caused by coking in the lift pipe?
Other parameters have not changed much, and the nozzle pressure drop remains unchanged; it is likely that the pressure sensing wire of the instrument is blocked
I think there might be several reasons (not necessarily all of them): 1. Raw material issues – the raw materials become heavier, which reduces their catalytic cracking efficiency and thus leads to a decrease in the yield of light oils； 2. Insufficient heat removal from the regenerator limits the increase in the device’s processing capacity. Inadequate heat removal leads to excessively high temperatures in the regenerator, which causes coking or deactivation of the catalyst, resulting in a decline in its catalytic efficiency and a decrease in yield ； 3. Frequent adjustments have a certain impact; frequent changes in temperature can cause coking in the lift pipe or distillation column ； 4. The feed temperature might be too low, resulting in coking near the nozzle; increasing the nozzle temperature appropriately can help.
Personally, I believe that your system’s inability to replenish fresh catalyst fails to meet the demands associated with wear and degradation, which leads to a series of chain reactions caused by an excessive amount of catalyst fine powder in the system. As for the reasons, there are too many to list them all; you can check out the relevant discussions on the forum! It is recommended to increase the rate of freshing agent addition appropriately and remove the existing catalyst from the replacement system.
Fresh catalyst has been continuously added, with a consumption of around 1.4; since the problem arose, no catalyst has been removed.
The purpose of the desulfurizing agent is to reduce the amount of fine catalyst particles in the system; otherwise, it will cause problems, affecting the operation of the equipment and the yield of the product!
Based on your description, it’s possible that there is a problem with the coarse rotation in the settler, which is causing the cyclone effect to be reduced. The main problems with the rough spinner are as follows: the detached lining may block the bottom of the rough spinner as the catalyst circulates, preventing it from functioning properly ； It is recommended to perform a thermal examination of the device to check for any red patches there. Another issue is whether the system has experienced a shutdown of feed or severe fluctuations, which have caused the coke particles within the system to detach due to temperature changes, thereby blocking the coarse spin section ； Was the connection area between the leg and the ash hopper inspected during the maintenance in the previous cycle? It is not known whether there is any wear there that could be causing abnormal operation of the coarse spinner. To ensure the safety of the equipment, it is recommended to carry out maintenance as early as possible; otherwise, if the solid content in the slurry system remains high for an extended period, it will lead to thinning of the walls of the pipes in the entire slurry system, which is detrimental to subsequent operations and creates many potential problems.
It’s possible; this could also cause that phenomenon. But thermal testing can only detect issues with the lining of the vessel wall; how can initial rotation problems be identified?
There is a problem with the rough spinning; coking may be occurring. Catalysts can also experience poisoning