Why is vacuum pumping required in two-effect evaporation?
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Why is vacuum pumping necessary? Is it to lower the boiling point?
It’s not necessarily necessary to create a vacuum; if the material is not heat-sensitive, the pressure in the first stage can be increased, while the pressure in the second stage should be slightly positive. Of course, this also depends on the heat source – as long as its temperature is high enough
Reduce steam quality! Improve evaporation efficiency!
Since the heat source for the reboiler of the second-effect tower is the vapor at the top of the first-effect tower, i.e., the bubble point temperature, it is necessary to ensure that the dew point temperature at the bottom of the second-effect tower is lower than the bubble point temperature of the first-effect tower; therefore, pressure reduction is required to lower its dew point.
First, it is mainly about energy conservation and reducing steam consumption. Second, increase the temperature difference thrust to boost production capacity. These are the main two aspects, or it may be related to the properties of the materials, etc.
Are there also reasons that lower the boiling point of the concentrate?
Vacuum lowers the boiling point. For example, it boils at 90 degrees under normal pressure, but may boil at around 70 degrees in a vacuum
Steam is a rather broad concept; what it does is lower the boiling point of the medium, not its quality. There’s a summary downstairs that’s quite comprehensive; you can take a look at it!
Vacuuming reduces the pressure inside the first-stage crystallizer, allowing lower temperatures to be sufficient for boiling and generating secondary steam； At the same time, vacuum extraction also provides the power for the secondary steam from the first effect to heat the second effect. Generally, the second stage operates at atmospheric pressure, while the first stage has a vacuum level of 40 kPa.