Design basis for bottom and top temperatures of distillation columns

The design bottom and top temperatures of a distillation column are determined based on the conditions of the utility systems and the properties of the feed materials, such as the heating source for the column bottom and the cooling medium used for column top cooling.

What is the difference in boiling points between n-butane and isobutane? The temperatures at the top and bottom of the tower are primarily determined by the requirements for the separation precision of the products at those positions.

The boiling points differ by over ten degrees; both are below 0 degrees. The bottom of the distillation tower is controlled at around 68 degrees, while the top is controlled at around 45 degrees

I just don’t quite understand: in a catalytic fractionation tower, there are gasoline-like components and rich gas components coming from the top of the tower, and the temperature at the top is much lower than the boiling point of gasoline. Is it true that to ensure the purity of the product obtained from the top of the distillation tower, the temperature there needs to be close to the boiling point of the substances at the top?

This is true for pure components; if the component being taken from the top of the tower is pure, then the temperature at the top of the tower is the bubble point temperature of that component at the corresponding pressure. For gasoline, it is a mixed composition containing C5 light components; the dry point of gasoline (corresponding to the heavier components) does not correspond to the tower top temperature.

It is related to the operating pressure; the separation of n-butane and isobutane requires pressurized operation. If circulating water is used for cooling at the top of the tower, it is necessary to ensure that the components at the top remain in a liquid state at temperatures below 30°C. The high operating pressure results in higher boiling points.

As explained in the answers for floors 6 and 7, this is a pressurized distillation process, with mixtures at both the top and bottom of the tower; therefore, the operating temperatures at these levels are determined by the separation accuracy required

Firstly, for a distillation column, there is a separation requirement, which refers to the specifications of the products at the top and bottom of the column. Knowing the product specifications at the top and bottom of the tower allows one to determine the bubble point and dew point. Starting with the tower top, condensation occurs at the tower top. If the bubble point temperature of the components at the tower top is too low, it is clear that the cooling water available from utility systems may not be sufficient for cooling; in such cases, cryogenic fluids are required, or the condenser equipment needed becomes very large, resulting in high costs and significant space requirements. Therefore, generally the column pressure is increased to raise the bubble point of the components at the top of the column, which is sufficient to meet the requirements for using cooling water. At this point, the temperature and pressure at the top of the tower are determined. Turning to the base of the tower, the separation requirements dictate that the tower must have a minimum number of theoretical plates, which is equivalent to the tower height. Then, by calculating the pressure drop for each tray in the tower, it is possible to determine the pressure at the bottom of the tower. Once the pressure and composition at the bottom of the tower are known, the temperature there can be determined as well~ The process is roughly as described above~

It was clearly said on the ninth floor: learn *

Circulating water is generally used as the cooling medium at the top of the tower; since refrigerants cannot be utilized, the temperature at the top of the tower is usually kept around 50°C. This applies to pressurized towers. The bottom temperature of the tower should be determined based on the separation requirements.