Swenson’s multiple-effect evaporators are cost effective when inexpensive, high-pressure steam is available to heat the system.
Optimize energy usage by leveraging vapors generated from one effect to drive another (steam economy)
Reduce overall energy requirements
Increase thermal efficiency
Multiple-effect configurations combine two or more evaporator bodies to conserve steam, which is condensed in the first-effect heat exchanger only. Water evaporated in the first-effect vapor body is condensed in the second-effect heat exchanger, which provides energy for evaporation in the second-effect vapor body—and so on for additional effects.
Vapor from the last effect flows to a condenser. The last-effect vapor body is maintained at a high vacuum with a steam-jet air ejector or mechanical vacuum pump.
For the same overall process conditions, the evaporator with more effects will require less steam. The evaporation in each effect will be approximately 0.7 to 0.9 pounds for each pound of steam condensed in the first-effect heat exchanger. In actual practice, the steam economy can vary widely because of differences in feed temperature and other energy requirements such as heats of dilution and crystallization.
The number of effects is limited by the total available temperature difference between the plant steam and the cooling water temperature. Process liquors with high boiling point elevations typically operate with fewer effects.