Questions about pressure and temperature
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This post was last edited by tmj509 on 2009-10-10 at 11:56. I would like to ask the experts: at a certain operating temperature, when the operating pressure is lower than the saturated vapor pressure at that temperature, will the temperature of the material at this operating pressure be higher than the temperature corresponding to the saturated vapor pressure (that is, the boiling point at that pressure)? I work with distillation towers, and I’ve observed that at a certain temperature, when the operating pressure at the top of the tower is lower than the saturated vapor pressure of the material, the temperature at the top of the tower is still higher than the temperature of the saturated vapor at that pressure. For example: the temperature of the material at the top of the tower under current operating conditions is 80 degrees, with a pressure of 2 kilograms. However, the saturated vapor pressure at 80 degrees is 3 kilograms, and the saturated vapor temperature at a pressure of 2 kilograms is 70 degrees. Currently, this is causing the temperature at the top of the tower to drop significantly under the operating pressure. Why does this situation occur? I hope all of you experts will be kind enough to share your insights. Thank you. . .
The temperature is too high, resulting in only a gas phase existing in the upper part of the tower; in the case of a plate tower, a dry plate phenomenon would occur, thereby eliminating the separation effect. This can be addressed by increasing the reflux flow rate, or by reducing the heat input from the feed and the reboiler.
1. No, that is to say, there are changes in all of them; it might be that there are issues with other control parameters
I disagree with your view. There is a connection between the reboiler and the reflux rate; a decrease in the energy supplied to the reboiler inevitably leads to a reduction in the reflux rate. While reducing the feed amount can alleviate the situation, it cannot eliminate this phenomenon, and it also affects the continuous discharge of product
The amount of gas volatilization is too high; there is no liquid at the top of the tower, so distillation cannot take place； Reduce the gas phase outlet; if there is a valve for regulating it, close the valve slightly ； If there is no valve, the gas is cooled by reducing the amount of coolant used
Check if there is a possibility of overheating.
If the production load is not below the designed minimum load, it is recommended to follow these procedures: 1. The mismatch between the top pressure and temperature is caused by supercooling of the vapor at the tower top; it is suggested to increase the reflux rate； 2. Reduce the amount of coolant used in the tower top condenser; if coupled cooling is employed, system adjustments are required ； 3. Another possibility is excessive operation of the tower; by reducing the system’s feed rate, the operating conditions of that tower can be adjusted gradually to see if this improves the situation. Looking forward to your good news!
At a certain operating temperature, when the operating pressure is lower than the steam saturation pressure at that temperature, the material will evaporate. Evaporation requires heat; therefore, the temperature of the material at this operating pressure should be higher than its temperature at the saturation steam pressure.
7th floor – with supercooling at the top of the tower, the temperature at the top naturally decreases. Moreover, our tower is not operating at all near the design specifications; the designed output volume from the top of our tower should be over 10,000, but currently it’s only around 3,000~~~ Anyway, thanks for your suggestion