Falling film evaporation is to add the feed liquid from the upper tube box of the heating chamber of the falling film evaporator and evenly distribute it into the heat exchange tube through the liquid preparation and film forming device. Under the action of gravity, vacuum induction and air flow, it becomes a uniform film. Flow from top to bottom. During the flow process, it is heated and vaporized by the heating medium at the shell side, and the generated vapor and liquid phases enter the separation chamber of the falling film evaporator together. After the vapor-liquid separation is complete, the steam enters the condenser for condensation (single-effect operation) or enters the next effect falling film evaporator to heat the medium for multi-effect operation, and the liquid phase is discharged from the separator.
The operation failure of the falling film evaporator is because the low vacuum degree is too low to maintain the boiling point of the concentrated solution, which increases the temperature of the secondary steam, thus reducing the temperature difference between the heating steam and the concentrated solution, thus reducing the heat transfer and slowing down the steam evaporation rate. In addition, the heating temperature of the heating material will affect the preservation of the effective ingredients. Due to the low vacuum, in addition to the influence of mass concentration, the production capacity of falling film evaporator is also reduced. The reasons for low vacuum are as follows:
1. Compress all parts of the equipment into air. Air infiltration will increase the burden of vacuum equipment, and may even cause failure.
2. Insufficient cooling water. In addition to pumping equipment, the main reason for insufficient cooling water is that the pipe of falling film evaporator is blocked, resulting in valve damage. Too much cooling water will hinder the timely condensation of secondary steam and seriously affect the operation of vacuum equipment.
3. The cooling water temperature is too high. If the cooling water temperature is too high, a large amount of secondary steam generated by central heating will not be condensed in time. Therefore, the vacuum of falling film evaporator will decrease rapidly.
4. The steam pressure is too high. If the heating steam pressure is too high, the evaporation rate of the falling film evaporator will increase rapidly. The generation of a large amount of secondary steam increases the load of cooling equipment, and the vacuum degree gradually decreases. Reducing the vacuum degree will also increase the evaporation temperature of the material, affect the product quality, and reduce the production capacity of the falling film evaporator.
