Basic knowledge of distillation columns

Thread Content

Basic knowledge of distillation columns: The material flow process in a distillation column. 1. After the material enters the distillation column via the feed line or the oil sparging line, the liquid level on the trays in the feed section rises above the overflow weir; from there, it descends layer by layer to the bottom of the column through the downcomers, thereby establishing a liquid level； 2. Once the liquid level is established, the material enters the distillation tower via the feed line and exits it through the bottom discharge line. The distillation tower is heated using heating equipment such as steam exchangers, heat transfer oil exchangers, and reboilers. The light components in the material vaporize first and rise upward through the floating valves on the tray; during this ascent, they exchange heat with the material on the tray due to the presence of padding oil, resulting in condensation ； 3. As the temperature at the bottom of the tower increases, the heavier components in the material begin to volatilize as well. The temperature of the rising gas phase increases along with the temperature at the bottom of the tower; even after heat exchange on the tray due to the oil layer present, some light components remain in the gas phase and do not condense (the DCS shows that the tray temperature gradually rises from the bottom upward). When this rising gas phase comes into contact with the cold trays, some of its components condense ； 4. When the rising gas phase reaches the top of the tower, it passes through heat exchange equipment (air cooling, water cooling, etc.) to be forced to condense and enter the reflux tank. Once a certain liquid level is reached, the liquid is pumped back into the tower via a reflux pump. The cooled material overflows from the top and exchanges heat with the rising gas phase on the tray surfaces. Heavier components in the gas phase condense since they do not reach their boiling point, while lighter components in the liquid phase vaporize again as they reach their boiling point. Under certain conditions such as temperature and pressure at the bottom of the tower, a relative dynamic equilibrium is achieved ； 5. Once reflux is established and phase equilibrium is reached on the trays, the temperature of the distillation column trays decreases gradually from bottom to top; the components on the trays also become lighter. The temperature on the trays can indicate the boiling point of the material present on that tray ； 6. Depending on the requirements of the product, the desired component can be extracted from the corresponding tray in the distillation column. When the amount of extraction changes, the composition of the trays in the distillation column will change accordingly; by controlling other parameters of the distillation column, the product can be made to meet the required standards ； Basic knowledge of distillation columns 1. Distillation columns can be classified by structure into: the feed section, the stripping column section, and the rectification section. 2. The dry point of the overhead product in the fractionation tower is controlled by the extraction ratio. (When the distillation precision meets the requirements) 3. The principle of a distillation tower is to separate materials based on their differences in boiling points. 4. Overpressurization in the tower occurs when there is too much gas phase inside it, while flooding occurs when there is too much liquid phase inside it. (Foam entrainment is caused by an excessive amount of vapor phase.) Note: The terms \"excessive amount of vapor phase\" and \"excessive amount of liquid phase\" are relative to phase equilibrium. 5. Three types of equilibrium in the distillation tower: mass balance (the amount of material entering is equal to the amount leaving), phase balance (the composition of the gas and liquid phases on the tray remains relatively stable), and heat balance (the heat absorbed by the distillation tower is equal to the heat removed from it). 6. Reboil ratio: The ratio of the flow rate of the reflux liquid returning to the tower from the tower top to the flow rate of the product at the tower top.