Experts, I have several questions regarding the steam in the amine liquid regeneration towers; I would appreciate it if you could help answer them. Thank you
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1. Issue regarding the temperature at the bottom of the regeneration tower: The temperature at the bottom of the tower is 120 degrees. Is this the temperature of the lean liquid phase in the tank at the bottom of the tower? Does this temperature need to be below the boiling point of the lean solution? Is 120 degrees appropriate at a bottom pressure of 120 kPa? The absorbent is a 30 wt% MEA aqueous solution. 2. The issue of reboiler temperature: Can saturated steam at 0.35 MPa be used as the heat source for the reboiler? Is the temperature of the vapor from the reboiler, which carries the depleted liquid back to the tower, higher than the temperature at the bottom of the tower? Is most of the vapor in this lean liquid steam water vapor? Is this return steam superheated or saturated? 3. The issue of steam returned to the tower: That is, for a feed rate of 1 t/h of amine solution, how many kg of reboiler steam is required to be returned to the tower? We have no reflux; we plan to draw off all the vapor from the top of the tower. After being drawn off, it condenses in the gas-liquid separator, and the liquid phase is returned to the system after passing through the rich-lean liquid heat exchanger (this approach is used because our plant is small and handles a small amount of amine solution). The rich liquid enters at the top of the tower, with a feed temperature of 90 degrees. 4. Heat transfer within the tower: The steam returning to the tower moves from bottom to top, heating the rich liquid in the packing section; does the rich liquid flow from top to bottom to the bottom of the tower, where it is heated to a temperature of 120 degrees? As the steam flows upward, does it condense into the rich liquid? Is the amount of steam reduced by this significant? 5. Pressure issue in the tower: Is the pressure of 120 kPa at the bottom of the regeneration tower the pressure of the gas phase above the liquid level of the lean liquid in the bottom tank? How is this pressure controlled to be achieved? The pressure at the top of the tower is higher than that at the bottom. Is this due to the decrease in steam temperature, the reduced condensation of steam in the packing section, and the pressure drop resulting from gas flow in that section? 6. Design question: When calculating the diameter of a packed tower, are the operating temperature and pressure of the regenerator taken as the bottom temperature and bottom pressure of the tower?
1. The temperature at the bottom of the tower is the temperature of the lean liquid phase, and theoretically it should be below the boiling point of the lean liquid. At a bottom pressure of 120 kPa, a temperature of 120 degrees is appropriate, but the decision should be made based on a comprehensive consideration of the properties of the amine solution and the operating conditions. 2. The heat source for the reboiler can be saturated steam at 0.35 MPa, but this needs to be determined based on actual conditions. The temperature of the steam returning the lean liquid to the tower is generally higher than the bottom temperature of the tower, as it is necessary to transfer the amine molecules from the lean liquid back into the rich liquid. Most of the steam returning to the tower is water vapor, but it also contains a small amount of amine gas. The steam returning to the tower is generally superheated. 3. The amount of steam required to return to the tower needs to be calculated based on specific conditions; it is recommended to engage professional engineers for the design and calculation. 4. It is possible for the rich liquid to flow from top to bottom to the bottom of the tower where it is heated to 120 degrees, but this depends on factors such as the packing design and operating conditions. As steam rises, it will condense in the rich liquid phase; however, if the liquid phase is evenly distributed within the tower, this will not have a significant impact on the amount of steam. 5. The pressure at the bottom of the regenerator refers to the pressure of the gas phase above the liquid level of the lean liquid in the bottom tank; this pressure can be controlled by adjusting the opening degree of the bottom discharge valve and the steam flow rate. 6. When calculating the diameter of a packed tower, the operating temperature and pressure should take into account the average temperature and pressure throughout the entire tower, rather than just the temperature and pressure at the bottom of the tower. At the same time, factors such as the properties of the filler and the fill ratio also need to be considered. It is recommended to hire professional engineers for design and calculations. .
1. Normally, a bottom temperature of 120 degrees refers to the temperature of the lean liquid phase in the bottom tank of the tower. This temperature must be below the boiling point of the lean liquid in order to prevent it from vaporizing at the bottom of the tower. At a bottom pressure of 120 kPa, a temperature of 120 degrees can be considered appropriate. When the absorbent is a 30 wt% MEA aqueous solution, the boiling point of the lean liquid at atmospheric pressure is approximately 100 degrees. 2. Saturated steam at 0.35 MPa can be used as a heat source for the reboiler. The temperature of the vapor from the reboiler, which carries the lean liquid undergoing evaporation, generally needs to be higher than the bottom temperature of the tower in order to maintain the temperature within the tower. Most of the vapor in the lean liquid is water vapor, but it may also contain a small amount of ammonia vapor. The steam returning to the tower can be superheated or saturated, depending on the process conditions. 3. To calculate how much reflux steam is required by the reboiler, it is necessary to know parameters such as the reflux behavior of the amine solution in the tower and the vapor-to-liquid ratio of the reflux stream; these parameters must be determined based on the specific process conditions. Generally, the flow rate of the vapor returning to the tower needs to be adjusted according to actual conditions in order to maximize the mass transfer efficiency within the tower. 4. As the return steam flows upward within the tower, it heats the rich liquid; thereafter, the rich liquid flows from top to bottom to the bottom of the tower, where it is heated to a temperature of around 120 degrees. As the steam flows upward, eddies and vortices are formed due to the gaps between the packing, the presence of a liquid film, or other factors; the steam then condenses in the liquid-rich area. However, this does not result in a significant reduction in the amount of steam, as the steam flow rate is high. 5. Under normal conditions, the pressure of 120 kPa at the bottom of the regeneration tower refers to the pressure of the gas phase above the liquid level of the lean liquid in the bottom tank. This pressure can be controlled by adjusting the outlet gate valve or other methods. The pressure at the top of the tower is slightly lower than that at the bottom, mainly due to pressure losses caused by the decrease in steam temperature and the condensation of steam in the packing section. 6. When calculating the diameter of a packed tower, factors such as the operating temperature and pressure of the regeneration tower need to be taken into account, but these factors generally are not exactly equivalent to the bottom temperature and bottom pressure of the tower. The specific calculation method needs to be determined based on the design requirements and process conditions.