Why can’t the temperature in the catalytic cracking fractionation tower be too low

Maybe it’s afraid of curing! It should be fine though!

I really admire you; all your posts have missing words and spelling mistakes. Every post contains at least one spelling mistake; some have as many as 3 or 4.

If the temperature at the bottom of the tower is too low, the light components cannot be vaporized; in severe cases, this can cause the slurry pump to run dry

An excessively low bottom temperature does not result in a significant increase in the content of light components; the light components at the bottom of the tower are mainly introduced by the seal oil used in pumps and machinery, as well as by the oil used for instrument flushing. Because as long as the temperature of the baffle is not low, the light components rise as a gas. An excessively low temperature at the bottom of the tower is caused by too much reflux, which is not conducive to energy savings.

It depends on whether the feedstock for catalysis is distillate oil or heavy oil; the bubble point temperature of the slurry made from distillate oil is at the bottom of the tower, while that of the slurry made from heavy oil is one tray below. The control of the liquid phase temperature at the bottom of the tower (the bubble point temperature of the oil slurry) is determined by the feed to the unit.

Thank you to all the teachers for your help!!!!:kiss:

The distillation tower is fed with superheated gas phase, and its operation relies mainly on temperature control. The bottom temperature of the tower is controlled by the temperatures of the material flowing upward and downward from the bottom of the tower; a low bottom temperature indicates insufficient heat within the tower, usually due to excessive heat extraction. This has little effect on the amounts of light components such as gasoline, liquefied gas, and dry gas. However, some of the light and heavy diesel fractions will be forced back into the reprocessing process, resulting in a decrease in yield. The components sent back for reprocessing become lighter, the amount of reprocessing increases, and the volume of slurry rises rapidly. As a result, the liquid level at the bottom of the distillation tower increases quickly, and the amount of material discharged outside also increases. Yet if heavy fuel oil can be purchased at the price of light diesel, it will have little impact on economic efficiency. Moreover, the solid content of the slurry will decrease, which is beneficial for slurry pumps, heat exchangers, and control valves. Finally, I earnestly ask those who want to learn * to first check out a few relevant books on the forum.

There are so many experts; I’ve learned a lot

The steam ring at the bottom of the tower serves mainly not for stripping, but to prevent catalyst deposition. Many have switched to using re-refined oil stirring ring tubes placed at the bottom of the distillation tower, with a very low amount of stirring steam supplied. To reiterate, the bottom of the tower is a storage tank for slurry oil. The extraction temperature of the slurry in many units is lower than that in the reprocessing tank; can you say that the slurry is lighter than the reprocessed oil? By the way, regarding one question: if, during normal operation, the slurry pump suddenly stops working and no flow is generated. How do the liquid level and temperature at the bottom of the distillation tower change? Once you understand this question, the principle behind the bottom of a fractionation tower becomes clear as well.

Hehe, let me answer you, you clueless student! There are three disadvantages to a low temperature at the bottom of the tower. 1. It is not conducive to the utilization of heat sources at high temperatures, because the temperature at the bottom of the tower is low; with the oil slurry circulation rate and the temperature returning to the tower remaining unchanged, all the heat goes to the top of the tower. 2. An excessively low temperature at the bottom of the tower may cause the slurry pump to experience vacuum conditions, although this is a very unlikely possibility. 3. Low temperature results in high viscosity, which increases the power consumption required for transportation. Are you satisfied? However, the impacts are all very minor; some are even not observable.

As a supplementary point: too low a temperature at the bottom of the tower can increase the viscosity of the slurry, which in turn leads to a reduced flow rate. This can cause the pump to run dry, and the motor may experience overcurrent and thus shut down.

Too low a temperature at the bottom of the tower can lead to an increased residence time there, thereby raising the likelihood of coking； The viscosity of the slurry results in low flow rates in the pipelines, which increases the load on the pumps and causes the motors to trip due to overcurrent.

What was said above is quite comprehensive. The low temperature at the bottom of the tower prevents the full utilization of the high-temperature heat, resulting in an increased content of light components and a reduced yield of light oils. The presence of many light components in the oil slurry can easily cause the pump to dry out. On the other hand, an excessively low temperature at the bottom of the tower can lead to increased viscosity of the slurry, making it difficult to flow; moreover, the motor may experience overcurrent and thus shut down. However, this impact is minimal.

Thank you to the original poster for their help. My keyboard isn’t working well, so I make many spelling mistakes; I’m sorry if this is embarrassing for everyone, hehe. Thank you!!!!!!

The low temperature at the bottom of the tower is mainly due to a high circulation rate of the slurry. In order to ensure proper control of the light ends, once the temperature of the slurry on the tower trays is at the desired level, all the remaining slurry is sent back down into the tower. Objective: To prevent coking in the slurry pipeline and at the bottom of the tower by increasing the line speed and residence time at the bottom of the tower.