【Weekly Topic】Production Technology: What are the factors that affect changes in the liquid level at the bottom of a distillation tower? May 31, 2011~June 5, 2011

This post was last edited by shmily327 on 2011-5-30 09:29. 1. Changes in the amount of product extracted from the tower bottom； 2. Variations in the amount of material added ； 3. Changes in the reflux volume at the tower top ； 4. Changes in the amount of vapor heated, as well as the temperature and pressure, in the tower bottom or reboiler ； 5. The impact of whether the level gauge is functioning properly.

1. There is a problem with the reboiler, causing the bottom temperature of the tower to decrease or increase. 2. If the feed rate is too high or too low, the distillation tower will operate under overload or underload conditions. 3. The recovery rate is too high or too low. 4. Changes have occurred in the materials. The reflux is too high or too low. 5. The condenser has failed. 6. The reflux pump or the bottom extract pump has failed. 7. DCS signal failure.

1. Changes in the temperature at the bottom of the tower； 2. Changes in feed rate or temperature ； 3. Changes in the amount extracted from the bottom of the tank ； 4. Changes in steam volume and temperature for bottom stirring ； 5. Changes in the properties of the feed material ； 6. Failure of the pump ； 7. System pressure changes ； 8. Failure of the bottom material control valve or level detection system ；

(1) Change in the composition of the reactor liquid: By reducing the reactor temperature while keeping the pressure constant, the gas-liquid equilibrium composition at the bottom of the tower is altered, resulting in an increase in the amount of reactor liquid and in the concentration of light components within it. With the extraction of the kettle liquid remaining unchanged, it will cause the level of the kettle liquid to rise. When this phenomenon occurs, the normal kettle temperature should be restored first; otherwise, a large amount of light components will be lost. (2) Changes in feed composition: When the content of heavy components in the feed increases, according to material balance, the volume of liquid in the reactor will increase. In such cases, it is necessary to increase the discharge rate of this liquid; otherwise, the liquid level in the reactor will rise. If the normal discharge rate of the reactor liquid is maintained while raising the reactor temperature to keep the liquid level at a normal level, this will cause the heavier components to reach the top of the tower, resulting in a decline in the quality of the product at the tower top. (3) Change in feed rate: As the feed rate increases, the discharge volume of the reactor liquid should increase accordingly; otherwise, the level of the reactor liquid will rise. (4) Failure of the adjustment mechanism: When the adjustment mechanism fails, it should automatically switch to manual adjustment, and maintenance personnel should be contacted at the same time. (5) At the beginning of operation, due to the small amount of liquid on the trays, proper gas-liquid contact has not yet been established; as a result, a large amount of light components easily enter the bottom of the tower. The amount of these components that can be vaporized in the bottom of the tower is not sufficient to meet the heat requirements within the tower at that time. Therefore, for a tower that has just started operation, the heating vessel should be preheated appropriately before feeding begins. Once a liquid level is observed in the vessel, an appropriate amount of heat should be supplied; otherwise, it will be difficult to raise the temperature of the vessel, the liquid level inside it will rise too high, the volume of liquid discharged from the vessel will increase, and as a result, more of the light components in the liquid will be lost.

Reply 1# sun-rock: 1. Influence of reflux ratio; 2. Influence of feed condition; 3. Amount of feed; 4. Feed composition; 5. Top draw rate; 6. Bottom draw rate or improper waste discharge from the reactor bottom; 7. Amount of cooling at the tower top

1. Changes in feed rate, 2. Changes in the composition of the feed, 3. Changes in the amount of reflux, 4. Accuracy of the bottom of tower level gauge, 5. Changes in the temperature of the bottom reboiler, 6. Changes in the amount of liquid drawn from the bottom of the tower.

1. Changes in the amount of feed added depending on its feeding condition； 2. Influence of the reflux ratio R ； 3. Changes in the reflux volume at the tower top ； 4. Changes in the amount of product recovered from the tower bottom ； 5. The level gauge gives inaccurate readings ； 6. DCS control system failures, etc.

The stability of the liquid level at the bottom of the tower is one of the important conditions for ensuring the smooth operation of a distillation tower. Only when the liquid level in the bottom of the tower is stable can heat transfer at the bottom of the tower be maintained stable, which in turn ensures stability in aspects such as the temperature at the bottom of the tower, the flow rate of vapor rising within the tower, and the composition of the liquid at the bottom of the tower; this facilitates the proper operation of the tower. The adjustment of the reactor liquid level is mostly controlled by the amount of liquid removed from the reactor. As the level of the liquid in the tank rises, the discharge volume increases; as the level drops, the discharge volume decreases. There is also a method of controlling the liquid level in the reactor using the heat dose supplied to it; as the liquid level rises, the heat dose increases. But knowing only this is not enough; it is also necessary to understand the factors that affect changes in the level of the reactor liquid in order to take targeted actions. The main factors affecting the change in the level of the reactor liquid are as follows. (1) Changes in the composition of the reactor liquid: By lowering the reactor temperature while keeping the pressure constant, the gas-liquid equilibrium composition at the bottom of the tower is altered, resulting in an increase in the amount of reactor liquid as well as the concentration of light components in it. With the extraction of the kettle liquid remaining unchanged, it will cause the level of the kettle liquid to rise. When this phenomenon occurs, the normal kettle temperature should be restored first; otherwise, a large amount of light components will be lost. (2) Changes in feed composition: When the content of heavy components in the feed increases, according to material balance, the volume of liquid in the reactor will increase. In such cases, it is necessary to increase the rate at which this liquid is removed from the reactor; otherwise, the liquid level in the reactor will rise. If the normal discharge rate of the reactor liquid is maintained while raising the reactor temperature to keep the liquid level at a normal level, this will cause the heavier components to reach the top of the tower, resulting in a decline in the quality of the product at the tower top. (3) Change in feed rate: As the feed rate increases, the discharge volume of the reactor liquid should increase accordingly; otherwise, the level of the reactor liquid will rise. (4) Failure of the adjustment mechanism: When the adjustment mechanism fails, it should automatically switch to manual adjustment, and maintenance personnel should be contacted at the same time. (5) At the beginning of operation, since there is less liquid on the trays and good gas-liquid contact has not yet been established, a large amount of light components tend to enter the bottom of the tower. The amount of these components that can be vaporized in the bottom of the tower is not sufficient to meet the heat requirements inside the tower at that time. Therefore, for a tower that has just started operating, it is necessary to preheat the heating vessel appropriately before feeding material. Once a liquid level appears in the vessel, an appropriate amount of heat should be supplied; otherwise, it will be difficult to raise the temperature of the vessel, the liquid level inside it will rise too high, the volume of liquid discharged from the vessel will increase, and as a result, more of the light components in the liquid will be lost.

1. There is a problem with the reboiler, causing the bottom temperature of the tower to decrease or increase； 2. Changes in feed rate or temperature, with the feed rate being either too high or too low, resulting in overloading or underloading of the distillation tower ； 3. Excessive or insufficient extraction volume from the bottom of the pot ； 4. The steam volume and temperature for stirring at the bottom of the tank are either too high or too low ； 5. Changes in the properties of the feed material ； 6. Failure of the pump ； 7. System pressure changes ； 8. Failure of the bottom material control valve or level detection system ； 9. Changes in the material cause excessive or insufficient reflux. 10. The condenser has failed. 11. The reflux pump or the bottom extract pump has failed. 12. DCS signal control failure.

Reply 1# sun-rock: The main reasons affecting the level change of the boiler liquid are as follows. (1) Changes in the composition of the reactor liquid: By lowering the reactor temperature while keeping the pressure constant, the gas-liquid equilibrium composition at the bottom of the tower is altered, resulting in an increase in the amount of reactor liquid as well as the concentration of light components in it. With the extraction of the kettle liquid remaining unchanged, it will cause the level of the kettle liquid to rise. When this phenomenon occurs, the normal kettle temperature should be restored first; otherwise, a large amount of light components will be lost. (2) Changes in feed composition: When the content of heavy components in the feed increases, according to material balance, the volume of liquid in the reactor will increase. In such cases, it is necessary to increase the rate at which this liquid is removed from the reactor; otherwise, the liquid level in the reactor will rise. If the normal discharge rate of the reactor liquid is maintained while raising the reactor temperature to keep the liquid level at a normal level, this will cause the heavier components to reach the top of the tower, resulting in a decline in the quality of the product at the tower top. (3) Change in feed rate: As the feed rate increases, the discharge volume of the reactor liquid should increase accordingly; otherwise, the level of the reactor liquid will rise. (4) Failure of the adjustment mechanism: When the adjustment mechanism fails, it should automatically switch to manual adjustment, and maintenance personnel should be contacted at the same time. (5) At the beginning of operation, since there is less liquid on the trays and good gas-liquid contact has not yet been established, a large amount of light components tend to enter the bottom of the tower. The amount of these components that can be vaporized in the bottom of the tower is not sufficient to meet the heat requirements inside the tower at that time. Therefore, for a tower that has just started operation, the heating vessel should be preheated appropriately before feeding begins. Once a liquid level is observed in the vessel, an appropriate amount of heat should be supplied; otherwise, it will be difficult to raise the temperature of the vessel, the liquid level inside it will rise too high, the volume of liquid discharged from the vessel will increase, and as a result, more of the light components in the liquid will be lost.