Why are the pipelines from the vacuum furnace to the vacuum tower thick and straight?
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The oil transfer line that leads from the vacuum furnace to the vacuum distillation column is different from that of ordinary atmospheric distillation furnaces; it is thick and straight. May I ask everyone: why is it designed this way? Are there any considerations?
A straight oil line experiences less resistance and a lower pressure drop compared to a bent pipe. Thick pipes are mainly used to reduce the fluid velocity within the pipe, thereby lowering the pressure drop. The purpose of reducing the pressure drop is also to lower the temperature drop in the oil transfer line. Another part is related to the issue of thermal stress compensation
Low temperature drop, low pressure drop, low thermal expansion!
http://bbs.hcbbs.com/thread-198800-1-1.html for reference
The vacuum level in the vacuum distillation column is achieved through the energy consumed by the steam at the top of the column or by the mechanical vacuum pumping system; therefore, controlling the pressure drop in the oil transfer line of the column allows for maximum utilization of the vacuum generated within the column, as well as energy savings.
The outlet of the vacuum distillation column is a gas-liquid mixture, and since the vacuum level in the column is low, the volume of the gas phase is large. To control the pressure drop in the oil transfer line, it is necessary to design this line with a larger diameter.
On one hand, it is the straight pipe that controls the pressure drop; on the other hand, a larger diameter provides sufficient space for vaporization of the vapor-liquid mixture, thereby reducing the load on the condenser.
The furnace outlet oil transfer line consists of two parts; one of them is called the high-speed oil transfer line, which is the section where the oil from each furnace tube flows before it converges. The linear speed in this section is high, and it is responsible for compensating for the amount of expansion due to deformation. The pipeline after convergence is called the low-speed transfer line; its purpose is primarily to reduce pressure drop. Since a decrease in pressure leads to rapid vaporization and cooling, this pipeline has a low flow rate in order to keep the liquid flowing and prevent coking. This pipeline is inclined at a certain angle, as straight sections present less resistance than bends. Moreover, the length of these straight sections is kept as short as possible. One of the key elements of the actual vacuum distillation technology is the vacuum furnace – reducing the pressure drop from the vacuum furnace to the vacuum tower allows for a lower temperature at the same vaporization rate, thereby reducing cracking.
Please refer to the Technical Q&A on Atmospheric and Vacuum Distillation Units.
From a process perspective, the oil transfer line under reduced pressure is thicker in order to reduce pressure drop and ensure a certain vaporization rate; it is also straighter to minimize pressure drop