Evaporators: Energy Conservation Strategies and Process Control – Chemical
By Alan Gabelman, Gabelman Process Solutions |
Several strategies for improving energy consumption and process control in evaporation processes are presented here
In industrial evaporation, a heat source (usually condensed steam) is used to concentrate a material through the removal of a liquid solvent. There are several types of evaporators and a number of important design principles. This article describes techniques to reduce energy usage in industrial evaporation, and also control methods for evaporators. For more information on evaporation fundamentals and equipment selection, please see Ref. , Evaporators: Design Concepts and Equipment Selection.
To a first approximation, the heat obtained upon condensation of 1 pound (lb) of steam is enough to evaporate 1 lb of water, leading to an expected steam economy of about 1 lb of water evaporated per 1 lb of steam for an ordinary evaporator. However, the evaporated vapor also contains latent heat of vaporization. Rather than releasing this heat to cooling water flowing through the condenser, why not use it to evaporate more water? Such an arrangement is shown in Figure 1 for a double-effect evaporator. Note that in Figure 1, the temperature in the first effect (T1) is greater than that in the second…