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How are the "plate evaporators" classified according to the evaporation process?

Views:　Date:2020-04-14
Propellent plate evaporator can be divided into the following three categories according to the evaporation process:
(1) Normal pressure evaporation, pressure evaporation and reduced pressure evaporation
According to the different operating pressure of evaporation, 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 decompressed operation can be used. However, in order to ensure the quality of products, the evaporation of heat-sensitive materials such as antibiotic solutions and fruit juices must be carried out under reduced pressure. The advantages of vacuum evaporation are:
① The boiling point of the solution decreases, and under certain conditions of heating steam temperature, the average temperature difference of heat transfer of the evaporator increases, so the heat transfer area decreases;
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 boiling point of the solution is low, which can prevent the denaturation or decomposition of heat-sensitive materials;
④ Due 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, when the vacuum is evaporated under reduced pressure, the vacuum requires additional equipment and power.
(2) Single-effect evaporation and multi-effect evaporation
According to whether the secondary steam is used as heating steam of another evaporator, the evaporation process can be divided into single-effect evaporation and multi-effect evaporation. If the secondary steam of the previous effect is directly condensed and no longer used, it is called single effect evaporation. If the secondary steam is led to the next evaporator as heating steam, multiple evaporators are connected in series, and the evaporation process in which the heating steam is used multiple times is called multi-effect evaporation.
(3) Intermittent evaporation and continuous evaporation
According to the evaporation process mode, it can be divided into intermittent evaporation and continuous evaporation. Intermittent evaporation refers to the evaporation operation of batch feeding or discharging. The characteristics of intermittent operation are: Throughout the process, the concentration and boiling point of the solution in the evaporator change with time, so intermittent evaporation is an unsteady operation. Generally, batch evaporation is suitable for small-scale and multi-variety occasions, while continuous evaporation is suitable for large-scale production processes.