To make the evaporation system more affordable to all the segments of the industry, the equipment has to be necessarily economical interms of capital cost and sustainable in terms of operation costs.
Evaporation can be carried out in a single effect, at low capital costs, but operational costs make them uneconomical. In a single effect evaporator, the heat content of the evaporated vapour is approximately equal to the heat input on the heating side.
The stream consumption of evaporation plants can be considerably reduced by utilizing the heat content of the evaporated vapour to heat the second effect can be further used to heat the third effect. With every additional effect, the operational cost is reduced substantially and the optimum number of effects is selected on the basis of desired rate of return on investment. In some large installations it is economically feasible to utilize as many as seven effects.