Seeking advice on setting pressure in Aspen
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There is a case: design of a continuous tray distillation column operating at atmospheric pressure, with the following design parameters. Feed composition: 63.2% water, 38.6% methanol (by mass)； Processing capacity: 55 t/h of water-methanol mixture ； Feed thermal state: saturated liquid phase feed ； Feed pressure: 125 kPa ； Operating pressure: 110 kPa ； Single-board pressure drop: ≤0.7 kPa ； Top distillate: Methanol content greater than 99.5% (by mass). Bottom residue: Water content greater than 99.5% ； (Mass fraction). Reflux ratio: user-defined ； Overall tower efficiency: ET=52%. Heat source: low-pressure saturated water vapor. The case specifies a condenser pressure of 110 kPa and a reboiler pressure of 130 kPa. Since the reboiler pressure is not given in the available information, how was 130 kPa determined? Was it assumed based on the fact that the heat source is low-pressure saturated water vapor? I would appreciate your advice, thank you!
Don’t you know your condenser pressure? You also know about pressure drop towers; by estimating the number of plates, you can determine the pressure in the reboiler at the bottom of the tower. The pressure at the bottom of a distillation tower is the highest. The pressure of the condenser (full condenser) is generally the pressure below the bubble point of the product at the top of the tower.
The operating pressure should be, under normal conditions, the pressure at the top of the tower； The plate voltage drop multiplied by the number of plates gives the total pressure drop of the tower. The operating pressure plus this tower pressure drop should equal the pressure at the bottom of the tower; it is sufficient that the reboiler pressure be greater than or equal to the pressure at the bottom of the tower. . .