Regarding the residence time of vacuum residue
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The external design of the vacuum distillation tower is narrow at both ends and wider in the middle; reducing the diameter at the bottom of the tower helps to shorten the residence time of residue oil within the tower, thereby minimizing coking at the bottom. So, what is the residence time of vacuum residue in the vacuum distillation tower? Please calculate your own shutdown time by yourself. I’ve seen some people say it’s 1 minute; is there any evidence for that? Study* study*.
I know it’s to reduce the duration of stay, but I’m not sure exactly by how much. Looking for similar information as well
Calculate volume, calculate flow rate, calculate time – and you’ll know it
The time I calculated refers to that of my setup. Are there any sources that indicate what the acceptable range for the residence time is? Or do the design firms determine the size of the tower based on a certain value for the residence time when designing such setups?
Primarily, under negative pressure, the thermal cracking tendency of high-temperature vacuum residue is relatively strong; moreover, in such conditions it is easy for the reaction to proceed in a cracking direction. Therefore, it is necessary to control the residence time. This is clearly explained on page 154 of the technical questions and answers related to atmospheric and vacuum distillation units, where it is recommended that the residence time not exceed 1 minute.