Thermodynamic modeling of calcium sulfate hemihydrate formed from seawater and concentrated brine at elevated temperature

Q1 Environmental Science

Case Studies in Chemical and Environmental Engineering Pub Date : 2024-12-31 DOI:10.1016/j.cscee.2024.101088

Ali Al-Hamzah , Caillan J. Fellows , Christopher M. Fellows

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Abstract

Formation of hard scale, predominantly calcium sulfate, is the limiting factor in the operation of multi-stage flash (MSF) thermal desalination of seawater, restricting the top temperature and top brine concentration that can be achieved. More accurate prediction of the solubility product of calcium sulfate hemihydrate, the scaling species formed initially above 100 °C, under conditions found in MSF plants, would allow better control of MSF operations. In this report literature data for calcium sulfate solubility is analysed and the Pitzer model applied to determine solubility product values at temperatures up to 148 °C and total dissolved solids concentration up to 99 g/L (equivalent to a concentration factor for Arabian Gulf seawater of 2.2). From these an analytical expression is determined for predicting the supersaturation index (SI) under these conditions to simplify the task of MSF plant operators, SI = 61.5891–0.4783 ln(TDS) + 0.3223 (ln(TDS))²–31.7890 ln(T) + 3.7977 (ln(T))²

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由海水和浓盐水在高温下形成的半水合硫酸钙的热力学模拟

以硫酸钙为主的硬垢的形成是海水多级闪蒸（MSF）热脱盐运行的限制因素，限制了海水能达到的最高温度和最高卤水浓度。更准确地预测半水合硫酸钙的溶解度产物，在MSF工厂中发现的条件下，最初在100°C以上形成的结垢物质，将有助于更好地控制MSF操作。在本报告中，对硫酸钙溶解度的文献数据进行了分析，并应用Pitzer模型来确定温度高达148°C和总溶解固体浓度高达99 g/L（相当于阿拉伯湾海水的浓度系数为2.2）时的溶解度积值。由此确定了在这些条件下预测过饱和指数（SI）的解析表达式，SI = 61.5891-0.4783 ln(TDS) + 0.3223 (ln(TDS))2 - 31.7890 ln(T) + 3.7977 (ln(T))2，以简化MSF工厂操作员的任务

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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