Based on what parameters can it be determined that catalyst bridging has occurred?

1. Regeneration line bridging: The inventory in the regenerator increases, while the inventory in the settler decreases; the density of the regeneration risers or inclined tubes rises, the pressure drop across the regeneration slide valve drops significantly, the density at the bottom of the lift pipe reactor decreases greatly, and both the reaction temperature and pressure drop rapidly； 2. Bridge erection in the raw catalyst line: The inventory in the settler increases, while that in the regenerator decreases. The density in the stripping section and the raw catalyst standpipe or inclined pipe rises, and the pressure drop across the raw catalyst plug valve or slide valve drops significantly. In catalytic units with a coaxial arrangement of these two reactors, the density of the raw catalyst sleeve is low, and the pressure drop across the sleeve distributor is small.

An intuitive way to determine this is that the pressure drop across the spool valve is zero, but it is very small. In other aspects, such as reaction temperature, regeneration temperature, and the inventory levels in the two reactors, there are significant changes; to go even further and consider phenomena downstream, there are even more, which will not be repeated here.

Definition of catalyst bridging: When catalyst is transported downward through vertical or inclined pipes, the normal flow of catalyst within the pipes is disrupted, resulting in catalyst blockages and other issues. At the sites of blockage, the catalyst may collapse slowly or a small amount of it may flow, but the flow rate of catalyst is much lower than that under normal conditions. The packing density of catalyst above the blocked areas increases continuously, while there is no catalyst in the lower sections. In such cases, the blockage cannot be resolved on its own, and this phenomenon is defined as bridging.

Catalyst “bridging” phenomenon: (1) The inventory in the stripping section increases rapidly, while the inventory in the regenerator decreases； (2) Abnormal changes in the density of the raw material riser and the pressure drop across the raw material plug valve ； (3) Regenerator temperature drops ； (4) Settler density, centrifugal leg density, and reserve increase. Cause analysis: (1) The differential pressure between the two devices changes in a pulsed manner, resulting in large fluctuations in the catalyst circulation rate ； (2) Remove the loose steam (air) plugs from the standby risers; the steam may contain water, or the amount of steam (air) may be too high or too low ； (3) Degradation of the fluid properties of the chemical agent (severe carbon accumulation in the unreacted catalyst, oil contamination in the unreacted catalyst, changes in the proportion of different components in the catalyst sieve analysis, etc.) ； (4) Blockage by foreign objects, such as cinders or detached lining, blocking the raw oil riser ； (5) Mechanical failure of the plug valve or malfunction of the instruments ； (6) Large fluctuations in fluidization air flow for the sleeve and the raw catalyst riser distributor ； (7) The spent catalyst contains oil, causing the regenerator to overheat; coking occurs in the spent catalyst standpipe ； (8) Severe carbon buildup, failure to address it in a timely manner, overheating of the regenerator, rapid expansion of the raw material riser, jamming of the raw material plug valve, resulting in an interruption in catalyst circulation ； (9) If the steam quality in the raw feed riser is persistently substandard or contains excessive water, scaling occurs near the loose areas and accumulates over time, eventually narrowing the flow path in the raw feed riser or even causing bridging. Solutions: (1) Stabilize the differential pressure between the two vessels; if necessary, switch from pressure control to manual operation, and change the plug valve to manual control as well ； (2) Address blockages, drain condensed water, adjust steam (air) flow, replace orifice plates, and switch media ； (3) Adjusting the amount of stripping steam and the amount of material used for loosening, dealing with carbon accumulation, replacing the catalyst, and other such measures ； (4) Reduce the processing capacity, change the opening degree of the plug valve in a short time to adjust the differential pressure between the two units, address the clogged area; if necessary, cut off the feed for treatment or even shut down the operation ； (5) Manual plug (sliding) valve, open the plug (sliding) valve ； (6) Steady-sleeve fluidization air ； (7) Operate smoothly and strictly follow the process specifications ； (8) Ensure the quality of the loose steam (air), and strictly prevent water contamination ；