【Q&A Question 013】2017.01.13
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This post was last edited by 955559 on 2017-7-21 at 12:56. [Q&A Question No. 013] 2017.01.13: How to deal with excessive temperature rise in the hydrogenation reactor bed? The reference answers will be visible after responding; points are awarded by identifying the key points. (Unless otherwise specified, all questions and answers are based on hydrogenation units.) 1. To address excessive temperature in the reactor bed, one approach is to increase the amount of cold hydrogen used. 2. Reduce the temperature at the furnace inlet appropriately and increase the capacity of the recycle hydrogen compressor. 3. If control becomes impossible, it is necessary to immediately switch to alternative feedstock and stop feeding low-quality oil into the unit. 4. In severe cases, it is required to shut down the burners in the heating furnace; the air cooling system for the high-pressure section should be activated to prevent overheating and excessive liquid levels, as well as to avoid bubbling of the high-pressure liquid, which could cause false liquid level readings. 5. Effective liquid removal is necessary at the compressor inlet, and it is advisable to disable the recycle hydrogen desulfurization tower to avoid contaminating the solvent. Summary thread of Q&A questions from 2017 (updates ongoing): http://bbs.hcbbs.com/thread-1657793-1-1.html Summary thread of daily questions from 2017 (updates ongoing): http://bbs.hcbbs.com/thread-1657794-1-1.html Summary thread of Q&A questions from 2016 (already updated): http://bbs.hcbbs.com/thread-1597792-1-1.html New Normal Cup – 2016 HaiChuan Top 10 Selections – Please recommend candidates: http://bbs.hcbbs.com/thread-1654112-1-1.html Third phase of the HaiChuan Outstanding Management Members selection contest: http://bbs.hcbbs.com/thread-1655902-1-1.html (Source: HaiChuan Chemical Industry Forum)
1 Reduce the reactor outlet temperature. 2 Inject emergency cooling hydrogen
First, the approach of increasing cold hydrogen can be adopted, along with appropriately reducing the outlet temperature of the furnace and increasing the displacement of the hydrogen circulation pump. Secondly, it is still not possible to control an immediate switch to another raw material in order to stop the feeding of low-quality oil. In severe accidents, the heating furnace shuts down and feeding is stopped; the high-pressure system should be switched to large-scale air cooling to prevent overheating and liquid formation. It is advisable to shut down the desulfurization tower, and the bypass system should be adjusted to operate in a circulating mode.
Cut off the feed and increase the hydrogen circulation rate
In the event of a sudden rise in temperature in the reactor bed, one possible solution is to increase the amount of cold hydrogen used; reduce the temperature at the furnace inlet appropriately and increase the capacity of the recycle hydrogen compressor. If the situation still cannot be controlled, it is necessary to immediately switch to another feedstock to stop the supply of low-quality oil to the unit； In severe cases, the heating furnace shuts down, and large-scale air cooling is employed to prevent overheating and excessive liquid levels. It is also necessary to avoid bubbling due to high liquid levels, which could result in false liquid level readings. Efficient liquid removal must be ensured at the compressor inlet, and the circulating hydrogen desulfurization tower should be disabled to prevent solvent contamination. The new hydrogen compressor should be controlled manually to prevent the system’s hydrogen pipeline network from being overwhelmed
Reduce the reaction temperature, inject cold hydrogen, increase the flow rate of circulating hydrogen, reduce the feed amount, and shut down the furnace
Runaway temperature occurs in exothermic reactions; from a thermodynamic perspective, higher temperatures accelerate the progress of these reactions. Once the heat balance within the reactor is disrupted, and the heat generated exceeds the amount of heat that can be removed, heat starts to accumulate, causing the temperature to rise. This in turn increases the reaction rate, leading to further heat accumulation and an intensification of the reaction – a vicious cycle that results in runaway temperature. At that point, the temperature rises extremely rapidly; I’ve seen it with my own eyes – the speed is just too fast. It’s worth mentioning that for every 12-13 degrees increase in temperature, the reaction rate doubles! The most effective way to prevent excessive temperature rise is to relieve pressure promptly, stop feeding material, and discharge both the pressure and the material into the flare – this removes heat while also stopping the reaction; it is essential to act quickly and decisively.
Fly temperature should trigger the immediate shutdown of feed, with maximum circulation of recycled hydrogen to ensure optimal gas flow within the reaction bed; if this cannot be controlled, pressure relief is the only way to remove the heat generated by the reaction. . .
1. To address excessive temperature in the reactor bed, one approach is to increase the amount of cold hydrogen used. 2. The temperature at the furnace inlet should be reduced appropriately, and the capacity of the recycle hydrogen compressor should be increased. 3. If control becomes impossible, it is necessary to immediately switch to another feedstock and stop feeding low-quality oil into the unit. 4. In severe accidents, it is required to shut down the burners in the heating furnace; the air cooling system in the high-pressure section should be activated to prevent overheating and excessive liquid levels, as well as to avoid bubbling of the high-pressure liquid, which could cause false liquid level readings. 5. Effective liquid removal must be ensured at the compressor inlet, and it is advisable to disable the recycle hydrogen desulfurization tower to avoid contaminating the solvent.
The refined reactor has a different chemical reaction from the cracking reactor, and it has a different impact on the molecular structure of the feedstock. It can be said that the possibility of a runaway temperature in the refined reactor is extremely low, unless the inlet temperature of the reactor is very high and there is an imbalance in the feed. If the reaction temperature becomes too high due to an interruption in the circulating hydrogen, adjusting the temperature at the hydrogenation reactor inlet and the feed rate promptly will suffice. If nothing else works, shut down the furnace, stop feeding material, and perform an emergency venting