I’ll ask gently…
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The surface of the catalyst to be used in catalytic cracking units is a high-temperature catalyst covered with coke. In our units, this temperature is around 550°C, while the ignition point of coke is approximately 500°C. Yet when we retrieve the catalyst to be used, the high-temperature catalyst does not catch fire on its own; we’re not sure why Is it due to an insufficient amount of coke, or is it cooled down rapidly as soon as it comes out?
Spontaneous combustion refers to the phenomenon in which a combustible material catches fire in air without the presence of an external ignition source, due to self-heating or external heat. When the catalyst is released, it is quickly cooled, and the temperature does not reach the ignition point of the coke, so it will not catch fire on its own.
Once, the sampling port for the slurry was blocked; in the evening, we used a steel bar to clear it, and when the passage was restored, the slurry came out, and it was clearly visible that it burned like coal once it emerged. During the day, the burning may not be visible, or if the amount is small, there isn’t enough heat to cause spontaneous combustion.
After being released, the coke was quickly cooled, failing to reach the auto-ignition temperature.
There is little combustible material attached to the catalyst, so it should burn. It’s just that this burning occurs at a very fast rate. So it can’t be seen.
Sometimes spontaneous combustion does not necessarily produce flames, or there may not be much burning material involved, which can also result in a lower temperature