Process Simulation And Operation Optimization Of Complex Multi-effect Evaporation

In order to improve the utilization efficiency of energy and equipment, a general steady simulation model of complex cross-feed multi-effect evaporation was established for the purpose of in-depth research on rule of multi-effect evaporation. In this model, the energy-saving measures, including extra steam being led off to preheat material liquid, the condensation water flash and solution flash, were adopted, and the solid separation was also considered in the process of evaporation. Material balance and energy balance equations of complex multi-effect evaporation system were expressed in matrix equation, which has the advantages 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 forward-feed, back-feed and cross-reed multi-evaporation system with or without solid separation, extra steam being led off to preheat material liquid, condensation water flash, or solution flash.The models include design and operation. The effective heat-transfer temperature difference (Δt_i) of every effect of multi-effect evaporation subsystem and the preheat temperature rise (Δt_p,j) of every level of multi-level preheat subsystem of the design model were distributed by equal heating area, equal heat-transfer temperature difference, and free proration methods. The simulation of design has been conducted by matrix method combined with iterative method. The free proration method transformed the decision variables fromΔt_i andΔt_p,j with complex restriction intoÏ„_i,Ï„_p,jwith the value range of 0～1, and provided a simple and convenient method for optimum design. An optimum design model of complex multi-effect evaporation system was established on the basis of conventional design simulation. The model aimed at minimum annual cost of whole evaporation system. The temperature of flesh vapor, the temperature of condenser, proration coefficient of temperature difference, and proration coefficient of preheat temperature rise were decision variables. The model was solved by genetic algorithm combined with matrix method. The different control variables of the temperature of flesh vapor(T₀), the temperature of condenser(T_K), the feed rate(F₀) and outlet concentration( x_AZ) were the unknown variables of the operation model. The simulation of the operation has been conducted by matrix method combined with iterative method. An optimum operation model of complex multi-effect evaporation system was established on the basis of simulation of the operation. The model aimed at minimum cost of concentration and the...