Multi-effect evaporation process

The flow of solution and steam is the same, from the first effect to the last effect. The raw material liquid is pumped to the first effect, depending on the pressure difference between the effects, from the inflow (in the process of concentration, if there is solid production or the solution viscosity is large, it needs to add the feed pump) to the next effect for processing, to complete the liquid from the final effect pump.

The pressure of the latter effect is low, and the boiling point of the solution is relatively low, so the solution from the former effect into the latter effect will be overheated and self-evaporation, called flash evaporation. Therefore, the latter effect may produce more secondary steam than the former effect, but because the concentration of the latter effect is higher than the former effect, and the operating temperature is lower, the heat transfer coefficient of the latter effect is lower than the former effect, and the heat transfer coefficient of the first effect is often much higher than the final effect. Parallel flow process is suitable for processing heat sensitive materials at high concentrations.

However, when the solution is transported from the second effect to the previous effect, the temperature of the feed liquid is lower than the boiling point of the feed effect, and sometimes additional heating is needed, otherwise the amount of secondary steam produced will gradually decrease. In general, countercurrent feeding process is suitable for handling materials whose viscosity varies greatly with temperature and concentration, rather than heat-sensitive materials.