Heat-coupled distillation
The heat coupled distillation is a procedural method , the energy consumption in the removal of a solvent by distillation to reduce.
principle
The solvent is increasingly concentrated in a series of evaporators . Each evaporator stage is operated at a different pressure. Changing the pressure changes the boiling temperature. Because the condensation temperature on the condenser of the first stage is higher than the boiling temperature of the next stage due to the higher pressure, the heat generated during condensation can be used for evaporation in the next stage.
In the example shown, the first stage is operated at an absolute pressure of 10 bar. This stage is heated with high pressure steam . At this pressure, water boils at 181 ° C. Due to the heating, part of the water in the feed solution evaporates. The evaporated water is condensed at a temperature of 180 ° C. at the condenser W121 of the first stage. Since the heat of condensation occurs at a high temperature, it can be transferred through the heat exchanger to the next stage, which is operated at a lower pressure of 5.5 bar and at which the boiling temperature in the sump is 157 ° C. The heat is used twice. By coupling further evaporator stages with decreasing pressure, the heat consumption can be reduced even further.
The heat consumption of the heat-coupled distillation can be reduced even further by cooling the hot condensate from the condensers, whereby this heat is used to warm up the solution before it enters the first evaporator stage (heat exchangers W114, W124 etc.).
In the example shown, 4 stages are implemented. The energy consumption is 11.5 MW. If the same amount of water were to be distilled off in a single evaporator stage without thermal coupling, the energy consumption would rise to over 25 MW.