How is the pressure control in each stage of a triple-effect evaporator used to create a pressure gradient across the three stages?
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This post was last edited by Desert Fish on 2016-3-30 at 14:12. I have a question: in a three-effect evaporator, the vaporization chamber of the third effect is connected to a vacuum pump to create a negative pressure, while the first and second effects are not connected to the vacuum pump. How is negative pressure achieved in such a case? How to achieve a three-effect pressure gradient? Please refer to the answers from experts in three-effect systems
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@Wang Tianze @jacques0920 @*nht1 @ylb913 @TalksOnChemicals @YoungEngineeringRager @WiseOne
This is easy to understand: a vacuum pump is used solely to remove non-condensable gases. It does not create a vacuum by removing steam; if that were the case, the vacuum pump would have to be extremely large. The reason for the creation of negative pressure is that the steam from the third effect condenses in the condenser; as the volume of the steam decreases sharply, the pressure drops. A lower pressure leads to a lower temperature, which is why the temperature in the third effect is the lowest (in fact, the closer it is to the temperature of the vacuum pump, the lower the temperature). By the same logic, the third effect consumes the steam from the second effect, which also leads to a decrease in the pressure of the second effect.
The steam systems of the three-effect evaporator are connected to each other, as are the systems for removing non-condensable gases. This creates a pressure gradient naturally. If you’re still not clear about this, you can add me on QQ: 2240388747 so we can discuss it together.
The steam system doesn’t seem to be working properly; condensate and non-condensable gases are the same. Is it possible that the pressure in the first two stages is adjusted through the valves on the non-condensable gas lines, in order to create a pressure gradient and a temperature gradient?
The negative pressure generated by steam condensation should be quite low; it’s mainly the vacuum pump that is used to remove the non-condensable gases
No, non-condensable gases are after all in small quantities; how could they have a flow rate and volume as large as those of secondary steam? Otherwise, why would the pressure drop?
Primary steam is generally isolated separately, while secondary steam is connected to it along with non-condensable gases. Under normal circumstances, there is no need to adjust the pressure or temperature gradients; what needs to be adjusted is the amount of evaporation, that is, the volume of primary steam and the amount of feedstock introduced!