What are the reasons for catalyst loss during shutdown for repairs?

Please, the original poster, explain how to shut down the device – was the catalyst removed? Is the bed stuffy? Wait, to facilitate discussion among sea friends.

The reactor must not have been turned on when the operator stopped work, right? During startup and shutdown, significant temperature changes can cause the coke lumps at the cyclone riser to fall off and block the material legs, or it can also lead to coking and blockage of the cyclone material legs. However, there is a high possibility that the coke clumps will fall off and cause blockages, or that they will jam the flap valve. Personal opinion, for reference only.

Flue gas leakage occurred in the double-acting slide valve area of the unit, and some expansion joints were torn, posing a serious threat to the safe operation of the unit; after discussion, operations were halted for repair welding. The original plan was to shut down for three hours due to a blocked regenerator, but delays caused by a shortage of materials resulted in operations resuming only after 12 hours. During this period, after the supplementary welding was completed, burning oil was injected into the device to raise the temperature of the regenerator; all steam flow to the regenerator was stopped during the bed shutdown. Since the temperature drop was not particularly severe, no desulfurization treatment was carried out. The oil injection in the unit was functioning properly, and operations were able to resume fairly quickly. However, the solid content remained high; even 12 hours after oil injection, around 2 a.m., the solid content of the slurry discharged outside was still as high as 30. The slurry pump used in the unit is an imported model from the United States, with a flow rate of 500 cubic feet per hour. The operation of the pump and the volume of slurry circulation were both normal, and no large-scale additives were used. Nine hours after oil injection, the catalyst level increased, but it decreased again after 11 hours. That’s the basic situation. If you need to know any other information, please ask and I’ll do my best to provide it.

The reactor wasn’t turned on, hehe； The temperature of the regenerated dense phase decreased from 630 to around 435. Based on the linear speed of the settler, it is not very likely that the coke lumps will detach from the material leg. As for the wing valve getting stuck, it could lead to a significant increase in the pressure drop across the material leg; or there might be no material seal in place – it’s hard to say for now.

The maintenance is now complete, and the unit is operating smoothly. Upon opening the reactor and settler, no coking blockages or stuck flap valves were found. It is estimated that during the bed shutdown, catalyst loss occurred due to pressure or fluctuations in the material flow rate. Based on the subsequent shutdown for maintenance, the reverse and regeneration systems were functioning normally, and the resumption of operation confirmed that the typical phenomena associated with catalyst loss did not occur.

When the bed level of the second catalyst bed in the regenerator of a certain unit is high, a large amount of catalyst is lost, with a catalyst consumption of 2.0–2.5 kg/t. The system can only operate at low bed levels or even at zero bed level, resulting in the unit operating in an uneconomical manner characterized by low processing capacity, high catalyst consumption, and high energy consumption. After analysis, the reasons are as follows: 1. Damage to the fluidization air distribution pipes in the second catalyst bed or damage to the centrifugal separator; 2. Operation with the bed empty for external heat extraction, which caused flue gas to flow back into the second catalyst bed, resulting in disturbance of the bed layer and loss of catalyst; 3. Incompatible catalyst model, requiring a new selection; 4. Increased density of the balancing agent, leading to insufficient headroom in the annular space of the second catalyst bed and unstable bed layer fluidization

It is possible that the large temperature changes inside the settler during the bed sealing process caused the coke particles to fall off; these particles are then gradually burned in the regenerator during operation. However, small coke particles can still affect the efficiency of the cyclone separator. In reality, during the shutdown process, those small cinder blocks likely fell off already.

This is possible, because during the subsequent shutdown, when the sliding valve was opened, it was found that there were cake-shaped coke pieces about 20*20 cm in size inside, located right on the ship-shaped distributor

Loss of catalyst is, in my opinion, the biggest problem in catalytic cracking. In the two catalytic units I work at, loss of catalyst has caused the oil slurry pumps to wear out, the pre-heating lines to leak, the elbows to leak, and the blades of the flue gas turbine to get damaged after just ten days of use, among other issues.

The catalyst from the reactor ended up in the distillation tower

So you stopped the inspections later and found no abnormalities?

Yes, from the inspection results, there are no problems, and that’s what puzzles me as well. Logically, with such a high solid content, there shouldn’t be any problems when opening the two devices, but that’s not the case at all – it’s hard to understand why. It’s possible that catalyst deposition in the sampling area is the cause, but even after replacing the sampling port with one that was closer, the problem persisted. I wonder if anyone else has encountered this situation?

This is likely what actually happened. No major changes occurred in the other parts; only the solid content changed. This indicates that during the shutdown and bed immobilization period, due to the reduced flow rate of the catalyst and fluctuations in the bed level, the catalyst escaped from the coarse spiral. Our settler uses UOP technology – I’m not sure whether other UOP technologies have encountered this issue as well

During shutdown for repairs, catalyst loss is inevitable; the challenge lies in controlling the amount of loss. At this point, it is uncertain whether the feed rate can be reduced, with some of the catalyst being transferred to the hot catalyst tank.

Add operating instructions for the slurry pump, respond to my own commitments; hope it’s not too late, hehe. Part 1: Preheating preparation 1.1 Once the slurry pump has been overhauled and installed, the fitter confirms that preheating is possible. 1.2 Fill the pump bearing housing with 46# lubricating oil. If there is lubricating oil in the bearing housing, it is necessary to check whether the oil has deteriorated and replace it if needed. Keep the oil level at 1/2 to 2/3 to ensure proper lubrication. 1.3 Verify that the cooling water flow is unobstructed ； Lead the sealing oil to in front of the valve ； The cooling steam is drained at the lowest point before the valve. The pressure gauge hand valve is fully open. 1.4 Turning the shaft: Manually turn it several times to ensure it rotates freely. Due to the effects of inertia, bearings, and mechanical sealing surfaces, there is a certain amount of resistance during rotation. If friction occurs, the pump must not be started until the cause is identified. Part 2: Preheating of the slurry pump 2.1 Ensure that the inlet and outlet valves of the slurry pump are closed; open the manual valve for flushing the mechanical seal, and keep the seal oil pressure at no more than 5 kg/cm2. 2.2 Open the first and second valves of the re-refining oil pre-heating line fully, and use the last valve to control the flow rate for pre-heating. The speed of the entire preheating process should be strictly controlled at ≤65°C/h; please operate according to the on-site thermometer. Every increase of 65°C constitutes a stage, and in each stage it takes at least one hour for the pump body to reach equilibrium in temperature with that of the heating medium. When preheated to 150°C, the cooling steam is turned on, with its pressure controlled at 0.07–0.21 kg/cm2 (refer to the pressure gauge on site). 2.3 The housing is gradually heated to 275–285°C following the procedure above. When this temperature is reached, at least one hour of holding time is required before starting the pump. Note: For newly installed pumps, at around 250°C, it is necessary to use a torque wrench to tighten the pump’s bolts to the torque values specified in the drawings, while also aligning the coupling thermally. 2.4 Once the shell temperature reaches the required level, open the inlet valve of the slurry pump slowly to prevent the pump from running dry; then turn on the slurry pre-heating unit and contact a fitter to carry out thermal alignment. 2.5 For the operation of the standby pump, the flushing oil must remain on (with the pressure maintained at around 3.0 kg/cm2) to prevent particles in the medium from entering the sealing chamber, and to ensure that the standby pump meets the startup requirements. Part 3: Starting the slurry pump 3.1 When the pump reaches its operating temperature of 275–285°C and the entire system is ready for operation, close the inlet and outlet valves of the shell preheating line, and adjust the pressure of the mechanical seal flushing oil to no more than 9.8 kg/cm2. 3.2 Check on-site to ensure that the cooling water and steam are functioning properly, and verify that there are no leaks at any sealing points; take corrective actions if any leaks are found. At the same time, contact the fitter and electrical maintenance staff to arrive. 3.3 Perform manual turning of the shaft to check for any sticking, excessive weight, or uneven weight distribution. 3.4 Open the outlet valve slightly by 10%, wait for a few minutes to allow the residual air in the outlet pipeline to be removed. With all maintenance personnel present, inform the control room operators to prepare to start the pump. 3.5 Start the motor and slowly open the outlet manual valve to full open. Pump maintenance personnel on-site check whether parameters such as pump body vibration, displacement, acceleration, and motor vibration meet the required standards. The operators in the control room monitor whether there are any abnormalities in the motor temperature. Part 4: Shutdown of the slurry pump. The method for shutting down a new slurry pump is basically the same as that for shutting down an existing crude slurry pump. There is only one thing to note: when the pump needs maintenance, after its temperature drops to the ambient temperature, shut down the other auxiliary components of the pump following the reverse procedure to starting it.