Multi-effect vacuum evaporators are best suited for the treatment of high flow rates, especially when a low-cost heat source (e.g. hot water or steam) is available.
Vacuum evaporators can treat an aqueous waste stream efficiently and simply without using reagents. They are highly effective even when conventional technologies are not viable. Using a vacuum evaporator, waste effluent is transformed into two streams: one, highly concentrated (perhaps even dry) and the other high quality water. Evaporators work under vacuum conditions to reduce the boiling temperature of the liquid effluent and lower energy consumption.
We have multi-stage concentrator evaporators that use hot water or steam from an external circuit as a source of energy, which allows residual heat flows to be utilized.
They are units composed of 1 (single effect evaporator), 2 (double effect evaporator) or 3 (triple effect evaporator) effects, where the heat transferred to the evaporated product is completely recycled in the following stages, producing a cascade effect. Finally, the distillate is condensed by a cooling tower, with little water consumption.
The range of multi-effect vacuum evaporators covers a wide range of capacities. The Envidest DPM1, Envidest DPM2 and Envidest DPM3 units, with one, two and three effects respectively, have a horizontal boiler and internal heat exchanger and are designed to handle flow rates up to 30 m3/day.
The Envidest MFE1, Envidest MFE2 and Envidest MFE3 evaporators, with one, two and three effects respectively, have a vertical boiler and forced circulation external heat exchanger designed to handle higher flows up to 180 m3/day.
A multi-effect vacuum evaporator consists of a set of interconnected evaporators where the first effect is the first evaporator, and so on. The operation is based on the steam produced in one effect being used as the heat source for the following effect. As the temperature decreases from one effect to the next, the vacuum is increased so that the boiling point is lower and evaporation is maintained. Thus, there is a working pressure and temperature gradient in which both parameters decrease from one effect to the next.
This configuration considerably increases the energy efficiency of the process. In practice, a 3-effect evaporator consumes the same energy as a single-effect evaporator but produces 3 times more distillate. Although the investment cost is higher, the energy consumption is much lower, so multi-effect vacuum evaporators are the most suitable for the treatment of high flows. When residual waste heat is available, the multi-effect vacuum evaporators can take advantage of it and are highly competitive.
These multi-effect vacuum evaporators are designed to be extended from 1 to 2 or 3 stages, and therefore to double or triple production without increasing the energy supply.