According to the different evaporation operating pressures, the evaporation process can be divided into normal pressure, pressurized and reduced pressure (vacuum) evaporation. For most solutions without special requirements, normal pressure, pressurized or reduced pressure can be used. However, the evaporation of heat-sensitive liquids, such as antibiotic solutions, fruit juices, etc., needs to be carried out under reduced pressure in order to ensure product quality. The advantages of reduced pressure evaporation are: ①The boiling point of the solution decreases. Under the condition of a certain heating steam temperature, the average temperature difference of the evaporator heat transfer increases, so the heat transfer area decreases; ②As the boiling point of the solution decreases, low pressure steam or Waste heat steam is used as heating steam; ③The boiling point of the solution is low, which can prevent the denaturation or decomposition of heat-sensitive materials; ④Due to the low temperature, the heat loss of the system is small. But on the other hand, due to the lower boiling point and the higher viscosity of the solution, the heat transfer coefficient of evaporation is reduced. At the same time, vacuum evaporation requires additional equipment and power when evaporating under reduced pressure.

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