Working Principle and Operating Procedures of Gasoline Hydrocracking Fractionator
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I am currently learning to be a chief operator for gasoline hydrogenation. I’m not entirely clear about the working principle and operation of distillation towers. Our distillation towers are mainly used to separate light gasoline (with a boiling point of around 60°C) from heavy gasoline (with a boiling point of around 200°C). First, what determines the separation ratio, and how is it calculated? Secondly, keeping the bottom temperature constant, reducing the top temperature can increase the reflux rate, decrease the amount of light gasoline produced, and lower the sulfur content in light gasoline ； The opposite is true. However, in practice, the method of adjusting the reflux rate and output volume by changing the top temperature of the tower (with a single change amount of 0.3–0.5°C) in order to control the sulfur content in light gasoline is not effective. For example, the top temperature is 70°C, the reflux rate is 60 t/h, and the output volume of light gasoline is 21 t/h. But here’s the problem: when the top temperature is gradually reduced to 68°C, the reflux rate and output volume hardly change; in some cases, the reflux rate even decreases. Why is that? I hope experts can help. Also, I would like to improve my skills in chemical engineering English; are there any textbooks you can recommend?
I’m not clear on the details; it seems like you have a misunderstanding. Firstly, the control of the distillation tower is adjusted according to the requirements of the product, and it is the product that determines who decides on the cut ratio. Chemical engineering basics: The higher the boiling range, the higher the sulfur content; less light gasoline is extracted from the top of the distillation tower when the boiling range is lower, and thus the sulfur content is lower. Changes in the top temperature, with constant material and bottom temperatures, are controlled by the reflux temperature and reflux rate. By reducing the extraction of light gasoline, the reflux flow increases. An increased reflux flow leads to a decrease in the top temperature, and this lower top temperature results in the components entering the reflux tank becoming lighter, which in turn causes the reflux flow to decrease slightly, until equilibrium is reached. When the distillation effect is good, the boiling range of light gasoline is controlled by the amount extracted.
First, the cutting ratio is primarily determined by the operations in the hydrogenation section; if the sulfur content in the light components is acceptable, it’s advisable to carry out more cuts at higher points, but in this case the temperature rise in the reaction section must be taken into account. Most of the olefins have gone up, which results in less heat release; this indirectly affects the operation of the hydrogenation section. Secondly, the factors that affect the top temperature include reflux rate, bottom temperature of the tower, feed temperature, etc.; therefore, addressing the issue by considering these influencing factors seems to indicate that your approach is a bit reversed
Thank you very much for your reply. Are there any textbooks that can be used to learn about the practical aspects of oil refining, such as the principles of distillation columns and the challenges involved in their operation?
There doesn’t seem to be anything specific regarding distillation towers; you might want to take a look at \"Technical Q&A on Hydrorefining Units\" – it’s very suitable for those who are just starting to learn this subject. Many things cannot be learned from textbooks; it’s necessary to observe and accumulate experience through actual operations
It is important to understand that what is required is the operation of the distillation column, not its design; the quality of the product obtained at the top of the column is adjusted by controlling the top temperature and the reflux rate. In practice, however, the reflux ratio often deviates significantly from the value specified in the design. Secondly, what is your method for reducing the top temperature? A decrease in the top temperature leads to an overall reduction in the load at the tower top, which may result in a decrease in the amount of vaporization and, accordingly, a reduction in the reflux flow. The low-temperature or feed temperature can be appropriately increased to reduce heat removal in the middle section, and this, combined with air cooling for temperature reduction, enables the adjustment of the quality of the product at the top of the tower.
The cutting ratio mainly depends on the downstream equipment; if light gasoline is to be used in etherification, the dry point of the light gasoline generally needs to be controlled
Separation is carried out based on differences in volatility, or in other words, differences in boiling points