Multiple-Effect Evaporation Plants

In case of multiple-effect evaporation plants, the exhaust vapors from the product are used to heat the downstream-arranged evaporation effect so that the steam consumption will be reduced accordingly

Considering the heat balance of a single-effect evaporator the heat content (enthalpy) of the evaporated vapor is approximately equal to the heat input on the heating side.

In the common case of water evaporation, about 1 kg/h of vapor will be produced by 1 kg/h of live steam, as the specific evaporation heat values on the heating and product sides are about the same.

If the amount of vapor produced by primary energy is used as heating steam in a second effect, the energy consumption of the overall system is reduced by about 50%. This principle can be continued over further effects to save even more energy.

	Live steam	vapor	Specif. steam consumption
1-effect plant	1 kg/hr	1 kg/h	100 %
3-effect plant	1 kg/hr	3 kg/h	33 %