There are four points to note when choosing a multi-effect evaporator:
1, the number of effects:
Mainly consider the size of the treatment volume, the boiling point rise value of the evaporated material, and the amount of equipment.
2. Selection of spent steam condenser:
When the spent steam must be recycled, it is best to use indirect condensers, such as tube-type, spiral plate heat exchangers; when the steam does not need to be recycled, it is best to use a direct condenser, such as direct atmospheric condenser, water jet pump condensation Wait.
When the flow is downstream, the pressure of the after-effect evaporation chamber is lower than that of the pre-effect, and the power of the pump required for the delivery of the solution between the effects is small.
In addition, since the after-effect evaporation temperature is low, after the pre-effect solution enters the after-effect, a part of the steam is flashed off, so the raw steam consumption is relatively small. However, at the time of the downstream process, the post-effect concentration is high, the temperature is low, the viscosity is increased, and the heat transfer rate is small. The reverse operation is opposite to the downstream operation. The pre-existing temperature is high, the concentration is high, the after-effect temperature is low, and the concentration is low, so that the heat transfer rate of each effect is close, but the required efficiency of the over-feed pump is large, and the steam consumption is large. . Not suitable for handling heat sensitive materials, and not suitable for materials with enhanced corrosion and temperature as the temperature and concentration increase. In addition, it can adopt the process of advection and mixed flow according to the specific conditions of the material.
4. Heating area:
Determining the heating area of the evaporator is determined by comprehensive consideration of factors such as material balance, heat balance, heat transfer calculation, and the type of process used.
The multi-effect evaporator can be divided into two types: an ordinary multi-effect evaporation system and a forced circulation multi-effect evaporator. The forced circulation evaporator is based on a plurality of external circulation evaporators, and then an external circulation pump is added. The forced circulation evaporator can be applied to the case where there is crystallization during the evaporation process and it is a non-heat sensitive material.