Optimization Multiple-effect evaporators

Steady-state mathematical models of single- and multiple-effect evaporators involving material and energy balances can be found in McCabe et al. (1993), Yannio-tis and Pilavachi (1996), and Esplugas and Mata (1983). The classical simplified optimization problem for evaporators (Schweyer, 1955) is to determine the most suitable number of effects given (1) an analytical expression for the fixed costs in terms of the number of effects n, and (2) the steam (variable) costs also in terms of n. Analytic differentiation yields an analytical solution for the optimal n, as shown here. 

Other Synthesis Problems. One recent synthesis publication by Nishitani and Kunugita (1979) is difficult to classify under the above headings, it deals with selecting the optimal vapor/ liquid flow patterns to use for a multiple effect evaporator system. The two obvious patterns are cocurrent (the liquid and vapor proceed through the system together) and countercurrent. Other patterns are possible and often significantly improve the economics. 

Nishitani, H. and Kunugita, E., "The Optimal Flow-Pattern of Multiple Effect Evaporator Systems," CACE 79, Montreux, Switzerland, April 8-11, 1979. 

Fig. 7-11. Optimal number of stages of a multiple effect evaporation unit.

The authors pose the problem as a multiple objective function problem, and, in their example, consider the two competing objectives of total evaporator heat exchanger area and steam usage. The paper is really a clever way of eliminating a number of flow patterns as never being candidates for the optimal solution regardless of the relative importance of the cost for area versus steam costs. For a particular triple effect example problem, they show that, depending on the liquid feed temperature, 3,... 

In the other procedure, Rojas et al. [215] optimized the encapsulation of BLG within PLGA microparticles prepared by the multiple emulsion solvent evaporation method. The role of the pH of the external phase and the introduction of the surfactant tween 20, in the modulation of the entrapment and release of BLG from microparticles were studied. Better encapsulation of BLG was noticed on decreasing the pH of the external phase. Addition of tween 20 increased the encapsulation efficiency of BLG and considerably reduced the burst release effect. 

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