Pre-lift section issues

First, check whether you have a pre-cooler; this is the most crucial factor as it affects catalyst fluidization and the reaction temperature. Prone to bridging or collapse

It can indicate the effect of fluidization (whether it is normal)

By measuring the density in the pre-lift stage, we can assess the fluidization condition of the catalyst; if the density is high, it may be due to insufficient pre-lift mass or inadequate driving force； If the density is low, together with the pressure drop across the regeneration spool valve and the density before the spool valve, it is determined whether there is bridging in the regeneration line, voiding, or insufficient driving force in the regeneration line. In short, this point serves as an analysis point for production monitoring. This is just my personal opinion; please correct me if I’m wrong.

As a supplementary point: during the shutdown of the unit, this density value can also be used as an indicator to determine whether the agent has been completely removed.

Does the height have an impact on raw material conversion and coking at the nozzle?

It has an impact. The density there is too high, the lifting capacity is insufficient, the radial distribution is uneven, the catalyst circulation rate is inadequate, and there is poor contact between the feedstock and the catalyst, resulting in a decrease in conversion rate. If it is too low, the cause needs to be examined; if the density decreases due to bridging or voiding in the regeneration circuit, the same principle applies to the decrease in circulation volume. If the pre-lift medium is too large, resulting in an excessively high line speed in the pre-lift section, this will also reduce the reaction time and affect the conversion rate. As for the impact of coking at the spray outlet, in my opinion the main reason is the atomization effect of the nozzle; too high or too low a density there also has an influence, but it depends on the specific situation. Of course, in extreme cases, the lifting force is insufficient, the lift pipe gets clogged, and the injected crude oil cannot be vaporized due to contact with the high-temperature catalyst, which may lead to coking above the nozzle. In short, the counter-reaction is not influenced by a single variable, but rather by the interrelationships among multiple variables. This is my personal opinion for reference only; please correct me if it is inappropriate.