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(1) Evaporation can be classified into atmospheric evaporation, pressure-driven evaporation, and vacuum evaporation based on the operating pressure during the evaporation process. For most solutions with no special requirements, normal pressure, pressurized, or reduced-pressure operations can all be used. However, for the evaporation of heat-sensitive liquids such as antibiotic solutions and fruit juices, it is necessary to carry out the process under reduced pressure in order to ensure product quality. The advantages of vacuum evaporation are: ① The boiling point of the solution decreases; under conditions where the temperature of the heating steam remains constant, the average temperature difference for heat transfer in the evaporator increases, thereby reducing the required heat transfer area ； ②Due to the decrease in the boiling point of the solution, low-pressure steam or waste heat steam can be used as the heating steam ； ③The solution has a low boiling point, which prevents the denaturation or decomposition of heat-sensitive materials ； ④Due to the low temperature, the system has low heat loss. On the other hand, due to the reduced boiling point, the viscosity of the solution is high, which decreases the heat transfer coefficient for evaporation; simultaneously, vacuum evaporation requires additional equipment and power to create the vacuum. (2) Based on whether the secondary steam is used as heating steam for another evaporator, the evaporation process can be divided into single-effect evaporation and multi-effect evaporation. If the secondary steam from the previous effect is directly condensed without being reused, it is called single-effect evaporation. The evaporation process in which secondary steam is directed to the next evaporator as heating steam, and multiple evaporators are connected in series to allow the heating steam to be reused multiple times, is called multi-effect evaporation. (3) Batch evaporation and continuous evaporation: Based on the mode of the evaporation process, it can be divided into batch evaporation and continuous evaporation. Intermittent evaporation refers to evaporation operations with batch feeding or discharging. The characteristic of batch operation is that, throughout the process, the concentration and boiling point of the solution in the evaporator change over time; therefore, batch evaporation is a non-steady-state operation. Generally, intermittent evaporation is suitable for small-scale, multi-product operations, while continuous evaporation is suitable for large-scale production processes.