Why is the temperature difference between the tower bottom and the tower top so large?

The temperature difference between the bottom and the top is related to the composition of the light and heavy components.

A difference of 20 degrees isn’t that big either. There’s a 30-degree difference between the top and bottom of us! ! ! ! This is mainly related to the height of the tower, the composition of the material, the reflux ratio, etc.

What was said on the second floor makes sense. For the operation of a distillation column, if there is no side stream extraction, it can be considered as a separation of two components. The temperature at the top of the column corresponds to the boiling point of the lighter component at that pressure, while the temperature at the bottom corresponds to the boiling point of the heavier component at that pressure. The magnitude of the temperature difference is mainly determined by the nature of the components.

Reasons for the influence of top temperature: 1. It is a zone where light components accumulate; its specific heat is low, so the temperature is low； If the feed contains a high proportion of light components, it will also result in a lower top temperature. 2. The reflux greatly reduces the temperature. 3. Effect of the condensant: With a higher amount of condensant, the top temperature decreases at the same reflux condition. Reasons for the influence of kettle temperature: 1. It is a zone where heavy components accumulate, with high specific heat, resulting in a high temperature ； If the feed contains a high proportion of heavy components, it will raise the temperature of the reactor. 2. High steam consumption leads to high reactor temperature. 3. Fluctuations in steam supply, high steam pressure, high temperature, and so on

Using terms commonly used in process simulation: light key components, heavy key components – related to these two types of key components!

Using terms commonly used in process simulation: light key components, heavy key components – related to these two types of key components!

There are many light components at the tower top, resulting in excessive reflux

The moderator is too unfair! I gave a detailed answer, yet only 1 point was given – it’s a waste of all my effort and experience

The top temperature is determined by the composition of the material at the top of the tower, as long as it meets the requirements for process separation.

To summarize, the temperature at the top of the tower is actually the dew point temperature of the gas at that level, while the temperature at the bottom of the tower is the bubble point temperature of the liquid there. Distillation takes place under controlled pressure conditions. Under such pressure conditions, let’s examine how the dew point and bubble point change with composition. The dew point refers to the gas phase; its English term is Dew Point. It denotes the system temperature at which liquid droplets begin to form in the gas phase (since we have already specified the pressure here; if we specify the temperature first, then the dew point corresponds to the pressure). Intuitively, if there are more heavy components in the gas phase, liquid droplets will form at a higher temperature, meaning it’s easier to reach the dew point, or in other words, the dew point is higher. Conversely, if there are fewer heavy components, the dew point is lower. For the top of a distillation tower, we generally want fewer heavy components, i.e., a lower dew point, which means a lower temperature at the top of the tower. The bubble point refers to the liquid phase; its English term is Bubble Point. It indicates the system temperature at which bubbles begin to form in the liquid phase (since we have specified the pressure here; if we specify the temperature first, then the bubble point corresponds to the pressure). Intuitively, if there are more light components in the liquid phase, bubbles will form at a lower temperature, meaning it’s easier to reach the bubble point, or in other words, the bubble point is lower. Conversely, if there are fewer light components, the bubble point is higher. For the bottom of a distillation tower, we generally want fewer light components, i.e., a higher bubble point, which means a higher temperature at the bottom of the tower. Therefore, a large temperature difference between the bottom and the top of the tower indicates good separation efficiency. In fact, the magnitude of this temperature difference can often be used to assess the performance of the distillation process. I’ve visited this forum many times, yet the moderator has never given me any points. Since this is an important concept, I’ve written a bit more in detail for everyone’s reference. Additionally, those who wish to learn more can read Professor Hu Ying’s book on Molecular Thermodynamics of Fluids or other books discussing vapor-liquid equilibrium. This post was last edited by kevin25 on 2007-12-29 03:03

It is also related to the relative volatility of the components

I’m not sure how it was divided evenly; the answer on floor 5 wasn’t very theoretical, but it was more practical.

From an operational perspective, I personally believe it is related to whether it matches the control of the reflux flow at the top of the tower and the steam consumption in the reboiler at the bottom of the tower.