硝酸鉀之共熔冷卻批式結晶程序模擬

Abstract

共熔冷卻式結晶能分離鹽水溶液並且同時得到鹽和冰的結晶，利用整個程序結晶在系統的共熔點。相較於其他傳統常見的結晶程序，共熔冷卻式結晶是一個相對新興且極具開發潛力的程序，此程序有著許多優點諸如高分離效率、低成本、乾淨安全等等。 這個研究是使用Matlab程式來進行模擬。硝酸鉀溶液被選為此共熔冷卻批式結晶的分離目標，並且在一開始就有加入硝酸鉀跟冰的晶種。各個結晶其晶種比例的關係是先被研究的來了解更多這兩種結晶的特性，並且試著以此結果來應用預判在共熔冷卻式結晶系統上。接者，結晶的成長速度、成長速度等等其他特性都有被計算出來，並且繪製了最終的結晶個數分布圖與結晶體積分布圖。 進一步的此研究分別更改了此程序的一些參數，包含晶種比例、晶種量、晶種平均粒徑與冷卻速率來分析這些參數對結果的影響。在這當中可以看到成核與晶種成長兩種結晶的比例平衡是如何被改變的。而共熔冷卻式結晶的最大特色，也就是有複數結晶同時產出，可以在某些結果看見在整個程序中這些物質其實是深深互相影響著彼此的結晶成長。

Eutectic freeze crystallization (EFC) separates aqueous solution into ice and salt crystals simultaneously by operating the process at the system’s eutectic point. It is a novel crystallization process which is an effective, low cost, safe and clean process. In this research, simulation is performed using code written in Matlab. A batch crystallization is set up to separate ice and potassium nitrate from a potassium nitrate solution into crystalline form. Seeds of both species are added. A critical seed loading chart is produced for both species to understand more about the kinetics of both crystallization processes and make predictions for the EFC process. The moments, nucleation rate and growth rate during the batch is calculated, and the final crystal size distributions based on number and volume are plotted. In addition, the seed loading, seed mean size, seed mass and heat removal strategy of the process are adjusted to study the effects on the simulation results. The effects on nucleated mass ratio and seed-grown mass ratio is investigated. The feature of EFC is that two or more crystal species form at the same time, and these species will affect each other significantly on the crystals’ properties, and this could be observed in some of the results.