Hydrocracking excessive temperature issue
Thread Content
In the book on hydrocracking operators, soaring temperature is explained as follows: since hydrocracking is a highly exothermic reaction, increasing the reaction temperature speeds up the reaction rate, thereby releasing more heat. If the reaction heat is not removed in a timely manner, it will lead to heat accumulation, causing the reaction temperature in the bed to rise suddenly, which results in the so-called \"temperature spike\". I would like to ask that since hydrocracking is an exothermic reaction, according to chemical equilibrium, an increase in temperature should inhibit the reaction, so why does it instead accelerate the reaction?
As the temperature rises, the reaction rate increases and becomes more intense; this is a kinetic issue. . You are referring to the issue of thermodynamic equilibrium; in actual production, it is controlled by complex factors such as dynamics and thermodynamics.
Hydrogenation reactions are exothermic reactions, while cracking reactions are endothermic reactions
The cracking agent is a bifunctional catalyst with hydrogenation and cracking capabilities. Furthermore, you can check that in a cracking reactor, reactions such as hydrogenation, cracking, isomerization, and polymerization mainly take place; these reactions are all exothermic (and this is evident in the behavior of such reactors). Chemical reactions are controlled in different ways at various stages, mainly through thermodynamic control and kinetic control (in other words, at a certain stage, one type of control dominates)
I’ve never seen a runaway temperature in hydrocracking units, but I have seen it happen in other types of plants. The temperature in the reactor bed rose from 240°C to 350°C in less than ten minutes – it’s really terrifying； It turns out that once thermal runaway occurs, the generation of heat increases exponentially; that’s why it is called thermal runaway rather than simply an increase in temperature ；
There were two incidents of emergency shutdowns; the temperature in the cracking reactor bed reached around 450 degrees (the normal temperature is around 400 degrees), and the reactor did not experience runaway temperature. Therefore, I believe that the reactor’s tendency to reach high temperatures is related to the ratio of raw materials (the ratio of fresh raw material to recycled oil), the activity of the catalysts in the reactor, as well as the amount of circulating hydrogen in the entire reaction system.