| complex cross-feed and parallel-feed multi-evaporation systems for conventional design was first established to lucubrate on disciplinarian and influential factors of multi-evaporation. In this model, the energy-saving measures, such as extra steam being led off to preheat material liquid, the condensation water flash and solution flash, were adopted. The solid separation was also considered in the process of evaporation and solution flash. Material balance and energy balance equations of complex cross-feed and parallel-feed multi-evaporation system were expressed in matrix equation that has the advantage of clear structure and high modularization. By holding or omitting correlation block-matrix in matrix equation, matrix equation could be used to describe the difference of cross-feed and parallel-feed multi-evaporation system with and without solid separation, extra steam being led off to preheat material liquid, condensation water flash, or solution flash. The model could also be used to different effect calculation The complex cross-feed multi-evaporation model could also be simplified to forward-feed or backward-feed multi-evaporation model in the same way. The solid-liquid equilibrium data in multi-evaporation system with solid separation was fitted to equation by new intelligent fitting method, which helped to solve this problem by computer for the first time. The parameters of conventional design of complex cross-feed and parallel-feed multi-evaporation conventional design could be obtained by solving material balance, energy balance, solid-liquid equilibrium, vapor-liquid equilibrium and heat transfer velocity equations by iterative method and matrix method. A optimum design model of cross-feed and parallel-feed multi-evaporation systems were established on the basis of conventional design to accomplish the optimum energy-saving effect. The model aims at minimum annual cost (including operating cost and equipment depreciation cost) of whole evaporation system (including two sequential system——multi-evaporation system and multi-level preheating system). The tempreture of flesh vapor, the tempreture of condenser, effective heat-transfer temperature difference of vari-effect, and outlet solution temperature of vari-level preheater were both decision variables. The objective function is a multi-variable, nonlinear and complex one with equality constraints and inequality constraints (including implicit constraints and explicit constraints). So it is more difficult to solve this model. The method to solve this model had not been reported in the literature. Then a new algorithm genetic algorithm combined with Lagrangian multiplier method, iterative method and matrix method was presented and studied in this work. The process of solving objective function was divided into inner and outer layer by this new method. The outer decision variables T0, Tk, tpj were solved by genetic algorithm. The inner decision variables Δti was solved by Lagrangian multiplier method which can deal with equality constraints problem well. The iterative method and matrix method are used to solve other design parameters. New algorithm was realized by Visual Basic 6.0. The result showed that the conventional and optimum design model of complex multi-evaporation had good universality. The new algorithm could be used to solve model more stably and more effectivly. The energy-saving effect was notable when all kinds of energy-saving measure were adopted and T0, Tk, tpj, Δti were optimized. In these conditions, the annual cost of optimum design decreased by 36.44% and 40.76% respectively than conventional design for the complex cross-feed and parallel-feed quadruple-effect evaporation system with solid separation. An optimum design software for multi-evaporation was developed, which had strong function, amity interface and easy maneuverability. This software may be applied to conventional and optimum design of multi-evaporation system under different conditions. |
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