[Q&A Question 232] 2016.12.08
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【Q&A Question 232】December 08, 2016: What are the effects of excessive reaction temperature rise? The reference answers will be visible after responding; scoring is granted by identifying the key points. The reaction temperature rise is primarily controlled by adjusting the outlet temperature of the heating furnace and the amount of cold hydrogen between the catalyst beds. The hydrogenation process is a highly exothermic reaction, and as the reaction progresses, more and more heat is released. Therefore, in industrial hydrogenation units, there is a temperature rise in the catalyst bed along the reactor axis. When the reaction temperature rises too high and is not properly controlled, it may lead to the following consequences: (1) the formation of a high-temperature reaction zone inside the reactor. The reaction stream undergoes intense reactions in the high-temperature zone; large molecules continue to break down, releasing more heat that raises the temperature further. This vicious cycle leads to a temperature runaway accident. (2) As the operating time increases, the catalyst gradually becomes deactivated. When the reaction temperature is raised to compensate for this, the catalyst in the high-temperature zone reaches its maximum design temperature prematurely, forcing a shutdown. At this time, although the catalyst in the low-temperature zone at the top of the reactor still has high activity, it is not fully utilized, resulting in reduced efficiency of the plant. (3) It is unfavorable for product quality and selectivity. In the hydroprocessing reactions, hydrogenation denitration and aromatic saturation are governed by thermodynamic equilibrium; when the reaction temperature is increased to a certain level, the equilibrium conversion rates decline, resulting in reduced denitration and aromatic saturation levels as well as a decrease in product quality. In hydrocracking reactions, high reaction temperatures accelerate secondary reactions, resulting in a decrease in the selectivity for middle distillate oils and an increase in gas yield. Summary post of Q&A from 2016 (updated up to December~~~~) http://bbs.hcbbs.com/thread-1597792-1-1.html Seeking sponsors for the “2016 Haichuan Top 10 Members Selection Contest” http://bbs.hcbbs.com/thread-1628108-1-1.html (Source: Haichuan Chemicals Forum)
The reaction temperature rise is primarily controlled by adjusting the outlet temperature of the heating furnace and the amount of cold hydrogen between the catalyst beds. The hydrogenation process is a highly exothermic reaction, and as the reaction progresses, more and more heat is released. Therefore, in industrial hydrogenation units, there is a temperature rise in the catalyst bed along the reactor axis. When the reaction temperature rises too high and is not properly controlled, it may lead to the following consequences: (1) the formation of a high-temperature reaction zone inside the reactor. The reaction stream undergoes intense reactions in the high-temperature zone; large molecules continue to break down, releasing more heat that raises the temperature further. This vicious cycle leads to a temperature runaway accident. (2) As the operating time increases, the catalyst gradually becomes deactivated. When the reaction temperature is raised to compensate for this, the catalyst in the high-temperature zone reaches its maximum design temperature prematurely, forcing a shutdown. At this time, although the catalyst in the low-temperature zone at the top of the reactor still has high activity, it is not fully utilized, resulting in reduced efficiency of the plant. (3) It is unfavorable for product quality and selectivity. In the hydroprocessing reactions, hydrogenation denitration and aromatic saturation are governed by thermodynamic equilibrium; when the reaction temperature is increased to a certain level, the equilibrium conversion rates decline, resulting in reduced denitration and aromatic saturation levels as well as a decrease in product quality. In hydrocracking reactions, high reaction temperatures accelerate secondary reactions, resulting in a decrease in the selectivity for middle distillate oils and an increase in gas yield.
This post was last edited by RSchufaqi on 2016-12-8 08:08 (1) A high-temperature reaction zone is formed inside the reactor. The reaction stream undergoes intense reactions in the high-temperature zone; large molecules continue to break down, releasing more heat that raises the temperature further. This vicious cycle leads to a temperature runaway accident. (2) As the operating time increases, the catalyst gradually becomes deactivated. When the reaction temperature is raised to compensate for this, the catalyst in the high-temperature zone reaches its maximum design temperature prematurely, forcing a shutdown. At this time, although the catalyst in the low-temperature zone at the top of the reactor still has high activity, it is not fully utilized, resulting in reduced efficiency of the plant. (3) It is unfavorable for product quality and selectivity. In the hydroprocessing reactions, hydrogenation denitration and aromatic saturation are governed by thermodynamic equilibrium; when the reaction temperature is increased to a certain level, the equilibrium conversion rates decline, resulting in reduced denitration and aromatic saturation levels as well as a decrease in product quality. In hydrocracking reactions, high reaction temperatures accelerate secondary reactions, resulting in a decrease in the selectivity for middle distillate oils and an increase in gas yield.
The reaction temperature rise is primarily controlled by adjusting the outlet temperature of the heating furnace and the amount of cold hydrogen between the catalyst beds. The hydrogenation process is a highly exothermic reaction, and as the reaction progresses, more and more heat is released. Therefore, in industrial hydrogenation units, there is a temperature rise in the catalyst bed along the reactor axis. When the reaction temperature rises too high and is not properly controlled, it may lead to the following consequences: (1) the formation of a high-temperature reaction zone inside the reactor. The reaction stream undergoes intense reactions in the high-temperature zone; large molecules continue to break down, releasing more heat that raises the temperature further. This vicious cycle leads to a temperature runaway accident. (2) As the operating time increases, the catalyst gradually becomes deactivated. When the reaction temperature is raised to compensate for this, the catalyst in the high-temperature zone reaches its maximum design temperature prematurely, forcing a shutdown. At this time, although the catalyst in the low-temperature zone at the top of the reactor still has high activity, it is not fully utilized, resulting in reduced efficiency of the plant. (3) It is unfavorable for product quality and selectivity. In the hydroprocessing reactions, hydrogenation denitration and aromatic saturation are governed by thermodynamic equilibrium; when the reaction temperature is increased to a certain level, the equilibrium conversion rates decline, resulting in reduced denitration and aromatic saturation levels as well as a decrease in product quality. In hydrocracking reactions, high reaction temperatures accelerate secondary reactions, resulting in a decrease in the selectivity for middle distillate oils and an increase in gas yield.
Increasing the temperature speeds up the reaction rate, but at excessively high temperatures, the equilibrium conversion rate of hydrogenation decreases
The consequences of excessive reaction temperature rise can be very serious. In mild cases, there is an increase in by-products; in severe cases, an explosion may occur.
1. It can easily cause the catalyst to become pulverized. 2. The internal components are prone to cracking.
Excessive reaction temperature rise can lead to high bed temperatures, triggering overheating and coking incidents; moreover, high operating temperatures will **reduce the catalyst’s service life**.
(1) A high-temperature reaction zone is formed inside the reactor. The reaction stream undergoes intense reactions in the high-temperature zone; large molecules continue to break down, releasing more heat that raises the temperature further. This vicious cycle leads to a temperature runaway accident. (2) As the operating time increases, the catalyst gradually becomes deactivated. When the reaction temperature is raised to compensate for this, the catalyst in the high-temperature zone reaches its maximum design temperature prematurely, forcing a shutdown. At this time, although the catalyst in the low-temperature zone at the top of the reactor still has high activity, it is not fully utilized, resulting in reduced efficiency of the plant. (3) It is unfavorable for product quality and selectivity. In the hydroprocessing reactions, hydrogenation denitration and aromatic saturation are governed by thermodynamic equilibrium; when the reaction temperature is increased to a certain level, the equilibrium conversion rates decline, resulting in reduced denitration and aromatic saturation levels as well as a decrease in product quality. In hydrocracking reactions, high reaction temperatures accelerate secondary reactions, resulting in a decrease in the selectivity for middle distillate oils and an increase in gas yield.