Four process flow of falling film evaporator

The falling film evaporator process has four forms: downstream (cocurrent), countercurrent, mixed flow (crossflow) advection:

The first type, downstream:

The solution and the steam flow are the same, and all flow from one effect to the last. The raw material liquid is pumped into one effect, and the pressure difference between the various effects is automatically flowed into the next effect, and the finished liquid is pumped out from the last effect (generally operated under a negative pressure). Since the pressure of the latter effect is low, the boiling point of the solution is also low, and the solution will flash part of the water after the first effect, and the secondary steam generated is also more, because the post-effect concentration is higher than the pre-effect and the operating temperature is low. Often, the heat transfer coefficient of the first effect is much higher than the final effect. The downstream process is generally suitable for processing materials that are heat sensitive at high concentrations.

Second, countercurrent:

The raw materials are sent to the pre-effect by the pump from the final effect, and the finished liquid is discharged by one effect, and the feed liquid and the steam flow in the opposite direction. Generally, it is suitable to treat a solution whose viscosity changes greatly with temperature and concentration, and it is difficult to handle heat sensitive materials.

The third, mixed flow:

It is a combination of the forward flow process and the advantage of the forward flow to avoid its shortcomings, but the operation is complicated and requires a high degree of self-control.

Fourth, advection:

Each effect feeds out the completion liquid, and each effect has crystal precipitation, which can be separated and crystallized in time, and is generally used for evaporation of a saturated solution.