falling film evaporatorIt is to add the material liquid from the upper tube box of the heating chamber, distribute it evenly into each heat exchange tube through the liquid distribution and film forming device, and flow down along the inner wall of the heat exchange tube in a uniform film shape. During the downflow process, the steam generated by the shell side heating medium vaporizes and enters the separation chamber of the evaporator together with the liquid phase. The steam and liquid are fully separated, and the steam enters the condenser for condensation (single effect operation) or enters the next effect evaporator as the heating medium, thus achieving multi effect operation. The liquid phase is discharged from the separation chamber.
The process flow of falling film evaporator includes four forms: co current (parallel flow), mixed flow (cross flow), advection, and countercurrent, as shown below:
Parallel flow:The solution and vapor flow in the same direction, from the first effect to the final effect. The raw material liquid is pumped into the first effect and automatically flows into the next effect based on the pressure difference between each effect. The liquid is then pumped out from the final effect (usually operated under negative pressure). Due to the low pressure of the latter effect and the low boiling point of the solution, when the solution enters the latter effect from the former effect, it will flash off some water and produce more secondary vapor. As the concentration of the latter effect is higher than that of the former effect and the operating temperature is lower, the heat transfer coefficient of the former effect is often much higher than that of the latter effect. The downstream process is generally suitable for handling materials that are thermally sensitive at high concentrations.
Mixed flow:It combines the advantages and disadvantages of both forward and reverse flow processes, but the operation is complex and requires a high degree of self-control.
advection:Each effect has added materials and produced a complete liquid, and each effect has crystal precipitation, which can be separated in a timely manner. It is generally used for evaporation of saturated solutions.
Against the Current:The raw materials are pumped from the final effect to the front effect, and the finished liquid is discharged from the first effect. The liquid and steam flow in the opposite direction. It is generally suitable for handling solutions with large viscosity changes with temperature and concentration, and is not easy to handle heat sensitive materials.