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过程工程学报 ›› 2021, Vol. 21 ›› Issue (2): 174-182.DOI: 10.12034/j.issn.1009-606X.220002

• 过程与工艺 • 上一篇    下一篇

NaOH–烟道气法卤水净化中成垢离子的沉降行为

罗兴国1， 彭建波2， 郑三强1， 张明宇3*， 李兴彬1， 魏 昶1， 邓志敢1   

  1. 1. 昆明理工大学冶金与能源工程学院，云南 昆明 650093 2. 云南省盐业有限公司，云南 安宁 650021 3. 云南省能源研究院有限公司，云南 安宁 650021
  • 收稿日期:2020-01-02 修回日期:2020-04-10 出版日期:2021-02-22 发布日期:2021-03-01
  • 通讯作者: 张明宇 631722997@qq.com
  • 基金资助:
    云南省科技计划科技入滇专项;昆明市科技计划重点项目

The settling behavior of scaling ions in brine purification process by NaOH–flue gas method

Xingguo LUO1, Jianbo PENG2, Sanqiang ZHENG1, Mingyu ZHANG3*, Xingbin LI1, Chang WEI1, Zhigan DENG1   

  1. 1. Faculty of Metallurgical and Energy Engineering, Kunming University of Science and Technology, Kunming, Yunnan 650093, China 2. Yunnan Salt Industry Co., Ltd., Anning, Yunnan 650021, China 3. Yunnan Energy Research Institute Co., Ltd., Anning, Yunnan 650021, China
  • Received:2020-01-02 Revised:2020-04-10 Online:2021-02-22 Published:2021-03-01

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摘要： 卤水中的成垢离子(Ca2+, Mg2+和CO32–等)在真空蒸发浓缩过程中易形成低热力学活性和强吸附性的碳酸钙和硫酸钙垢层，降低换热管传热效率。NaOH–烟道气法卤水净化可利用电厂废气–烟道气以及氯碱厂低浓度的废碱，在节能环保方面具有绝对的优势和广阔的前景。为研究NaOH–烟道气法卤水净化过程中成垢离子的沉降行为规律，采用CO2替代烟道气开展卤水净化实验研究。采用Factsage热力学软件、XRD和SEM–EDS等分析手段探究了不同CO2通入时间和pH值对Ca2+, Mg2+和CO32–沉降行为的影响及所得沉淀物的矿物学特征。结果表明，当控制pH=11.5，CO2通入时间60 min时，可将卤水中的Ca2+浓度降低至6.0~8.0 mg/L，延长沉降时间至80 min，Mg2+浓度可降低至0.65 mg/L。此外，该pH值条件下沉淀反应的平衡常数最大，钙、镁的净化效果较其他pH条件下更佳。控制过程pH=9.5时，所得沉淀物为球霰石(Vaterite)型碳酸钙晶体；当pH升至10，碳酸钙的晶型由球霰石转化为霰石型(Aragonite)晶体，其形貌由规则的球形转变为椭圆形；当pH=11和11.5时，沉淀物为钙和镁的共晶体，碳酸钙的晶型由球霰石转换为热力学更加稳定的方解石型(Calcite)晶体。

关键词: 卤水净化, CO2, 钙离子, 镁离子, 碳酸根

Abstract: The scaling ions (Ca2+, Mg2+ and CO32–) in raw brine are easy to form calcium carbonate and calcium sulfate deposit in the process of vacuum evaporation. Because of their poor thermal conductivity and their good adherence to the walls, these mineral compounds decrease the heat transfer ratio and even shorten equipment life by corrosion. The brine purification method of NaOH–flue gas can utilize the flue gas from a power plant and low concentration waste alkali from chlor-alkali enterprises, which has absolute advantages and broad application prospects in energy conservation and environmental protection. In order to analyze the behavior of scaling ions in the process of brine purification by NaOH–flue gas method, the experiment of brine purification by CO2 instead of flue gas was carried out. The effects of CO2 feeding time and pH value on the behaviors of Ca2+, Mg2+ and CO32– in brine were investigated. The behavior of scaling ions and the mineralogical characteristics of precipitates were studied by thermodynamic calculation (Factsage), XRD and SEM–EDS. The thermodynamic and experimental results showed that when pH=11.5 and CO2 introduction time was 60 min, Ca2+ in raw brine was reduced to 6.0~8.0 mg/L, and Mg2+ concentration was reduced to 0.65 mg/L when the time was extended to 80 min. There was a linear relationship between the concentration of CO32– and CO2 entry time. Besides, the dissolution amount and ratio of CO2 in brine were the largest, and the equilibrium constant (K) was the largest at the pH=11.5. Then, the results of XRD and SEM showed that the precipitated vaterite type of calcium carbonate crystals was obtained when the pH of the process was controlled at 9.5. When the pH value increased to 10, the crystal form of calcium carbonate transformed from vaterite to aragonite crystals, and its morphology changed from a regular spherical shape to an oval shape. When the pH was 11 or 11.5, the precipitation was a eutectic of calcium and magnesium, and the crystal form of calcium carbonate was converted from vaterite to calcite crystals, which was more thermodynamically stable.

Key words: brine purification, CO2, calcium ion, magnesium ion, carbonate ion