مدل‌سازي ترموديناميكي و شبيه‌سازي عددي يك كريستالايزر گردش اجباري به‌منظور بازيافت آب در فناوري تصفيه‌ي پساب بدون پسماند مايع

In this study, a forced circulation crystallizer was designed an‎d modeled with the aim of developing a comprehensive framework for performance prediction an‎d system design. First, the governing mass an‎d energy balance equations, along with crystallization kinetics, were derived an‎d implemented within a numerical algorithm. The developed algorithm enabled the calculation of the crystallizer volume, mass flow rates (including recirculation, recovered water, an‎d produced solid salt), operating conditions, an‎d the required energy input to the system. Subsequently, the model was coded in MATLAB, an‎d an industrial-scale crystallizer was designed as a case study. The effects of key parameters—such as feed conditions, vapor temperature, heat exchanger outlet temperature, an‎d crystallizer outlet concentration—on system performance were systematically investigated. The results indicated that increasing the feed temperature leads to a slight reduction in the heat exchanger heat load an‎d a marginal increase in pump power. Increasing the feed mass flow rate results in an increase in all major parameters, including crystallizer volume an‎d mass flow rates of the recirculation, recovered water, an‎d produced solid salt. An increase in feed concentration decreases the crystallizer volume, recirculation mass flow rate, an‎d recovered water mass flow rate, while increasing the amount of solid salt produced. Raising the vapor temperature increases the crystallizer temperature an‎d pressure, significantly enlarges the crystallizer volume, substantially increases the recirculation mass flow rate, an‎d notably increases pump power, while slightly decreasing the heat exchanger heat load an‎d reducing the condenser heat load. Increasing the heat exchanger outlet temperature leads to a relatively pronounced reduction in crystallizer volume an‎d recirculation mass flow rate, a considerable decrease in pump power, an‎d a slight increase in heat exchanger heat load. Furthermore, increasing the crystallizer outlet concentration results in increases in crystallizer volume, recirculation mass flow rate, an‎d recovered water mass flow rate, while reducing the amount of produced solid salt. Among the studied parameters, vapor temperature an‎d heat exchanger outlet temperature exhibited the highest sensitivity an‎d therefore play a critical role in crystallizer design. Careful an‎d informed selec‎tion of these two parameters can significantly contribute to achieving an optimal an‎d efficient design. In the final stage, to gain deeper insight into the flow pattern an‎d particle size distribution, a three-dimensional, two-phase CFD simulation of the crystallizer was performed using ANSYS Fluent. The results demonstrated well-developed particle growth behavior: particles entered the crystallizer with a mean diameter of 75.2 µm an‎d a Sauter diameter of 121.1 µm, an‎d exited with a mean diameter of 89.8 µm an‎d a Sauter diameter of 191.3 µm. Overall, the findings of this research indicate that the integration of thermodynamic modeling an‎d CFD simulation provides an effective an‎d reliable tool for the design an‎d optimization of industrial crystallizers.

رامين كوهي كمالي

محسن دوازده امامي , احمد سوهان كار اصفهاني