Evaporation forward-feed multiple-effect

Forward-feed multiple-effect evaporators. A single-effect evaporator as shown in Fig. 8.2-2 is wasteful of energy since the latent heat of the vapor leaving is not used but is discarded. However, much of this latent heat can be recovered and reused by employing multiple-effect evaporators. A simplified diagram of a forward-feed triple-effect evaporation system is shown in Fig. 8.2-3. 

Figure 17. Patterns ofliquid flow in multiple-effect evaporators Forward feed, Backward feed, fcj Mixed Feed.

Multiple-effect evaporator with forward feed. 

As a second example, consider the classic multiple effect evaporator with forward feed, illustrated in Fig. 20. The problem is as follows ... 

Patterns of liquor flow in multiple..effect evaporators (rz) forward feed b) backward feed (c) mixed feed d) parallel feed, (omn) Liquor streams. (-) Steam and vapor condensate streams. 

Scale problems can be minimized by operating a multiple-effect evaporator with forward feed, so that the temperatures drop as the concentrations increase. 

In multiple effect evaporation nnits the steam consumption ) and the liquid flow rates between the various effects can be calculated by means of energy and material balances of the first effect or any other effect. The steam consumption b (here only the heat of condensation r is utihzed) of a forward-feed operation unit according to Fig. 7.2-2 is given by... 

FIGURE 7.9. Allocation of temperature potential in multiple-effect evaporation. (Evapwation of NaO brine forward feed.)... 

I. Temperature drops in multiple-effect evaporators. The amount of heat transferred per hour in the first effect of a triple-effect evaporator with forward feed as in Fig. 8.2-3 will be... 

The feed to a multiple-effect evaporator is usually transferred from one effect to another in series so that the final product concentration is achieved in only one effect. In forward feed operation, raw feed is introduced in the first effect and passed from effect to effect parallel to the steam flow. The concentration of the liquid increases from the first effect to the last and product is withdrawn from the last effect. Forward feed operation is advantageous when... 

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