The evaporation process can be divided into atmospheric pressure, pressurized and reduced pressure (vacuum) evaporation depending on the evaporation operating pressure. For most solutions without special requirements, normal pressure, pressurization or decompression can be used. However, for the evaporation of heat-sensitive liquids, such as antibiotic solutions, juices, etc., in order to ensure product quality, it is necessary to carry out under reduced pressure. The advantages of evaporation under reduced pressure are:

       1. The boiling point of the solution is lowered, and under the condition that the temperature of the heating steam is constant, the average temperature difference of the heat transfer of the evaporator is increased, and thus the heat transfer area is decreased;

       2. due to the lower boiling point of the solution, low pressure steam or waste heat steam can be used as heating steam;

       3. The solution has a low boiling point to prevent denaturation or decomposition of the heat sensitive material;

       4. The heat loss of the system is small due to the low temperature. On the other hand, since the boiling point is lowered, the viscosity of the solution is large, and the heat transfer coefficient of evaporation is reduced. At the same time, when the pressure is evaporated under reduced pressure, the vacuum is required to increase equipment and power.