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Alternative TitleThermodynamics and Scale Inhibition of Calcium Sulfate Crystallization in Treating Ammonia Nitrogen
Thesis Advisor曹宏斌 ; 宁朋歌
Degree Grantor中国科学院研究生院
Degree Discipline环境工程
Keyword硫酸钙   溶解度   电解质nrtl模型   阻垢剂
Abstract水体中过量的氨氮等污染物不仅会引起水华、赤潮等,还会给人类工业生产和生活带来诸多问题。2012年我国已把氨氮作为环境保护“十二五”规划重点控制对象。汽提法是目前国内外公认的处理废水中氨氮的有效方法之一。该工艺中需向高浓度的氨氮废水中加入氢氧化钠提高废水pH值,然后通过精馏回收废水中的氨氮。为降低成本,通常用氢氧化钙替代氢氧化钠作为pH调节剂,因而在实际生产过程中不可避免会产生硫酸钙,该晶体易在管壁结垢沉积,使工艺无法连续的进行。为解决此问题,本文对硫酸钙在铵盐溶液中的结晶热力学以及阻垢剂阻垢性能进行了系统研究。 (1)以全组分化学模拟方法基于电解质NRTL活度系数方程建立了可以准确预测二水硫酸钙在NH4Cl–(NH4)2SO4–H2O体系中溶解化学行为的新模型。实验测定了298.15~343.15K二水硫酸钙在氯化铵、硝酸铵及硫酸铵和氯化铵混合电解质溶液中的溶解度。通过回归测定的实验数据得到新的二元相互作用参数,其计算值与实验值吻合良好。 (2)利用沉淀结晶方法获得了硫酸钙在(NH4)2SO4–CaCl2–H2O体系的反应结晶规律。考察了温度,物料比,pH值对硫酸钙在上述体系中结晶过程的影响。结果表面,nCa(OH)2/n(NH4)2SO4比例越高,溶液中钙离子浓度越大;温度越高,平衡时间越短;pH>10,温度升高溶液中的钙离子浓度减小。 (3)揭示了阻垢剂在铵盐溶液中硫酸钙的阻垢机理。为防止硫酸钙在管壁上的沉积,通过静态法对阻垢剂的阻垢测试进行了系统研究。考察了EDTMPS,PASP,AA/AMPS,PAA,ATMP阻垢剂对硫酸钙的阻垢性能。结果表明,随着阻垢剂用量增大,硫酸钙的溶解度增加,最终达到一个稳定值;以上阻垢剂均能够防止高温时半水硫酸钙转变成二水硫酸钙。
Other AbstractAmmonium from industrial, agricultural and domestic wastewater discharges is one of major contributors to ecological eutrophication and brings a lot of troubles in the industrial production. Ammonia nitrogen has been listed as a major controlling object in the Twelve-Five plan for environmental protection in 2012. Steam stripping process is usually recognized as one of the effective methods to deal with ammonia nitrogen wastewater. Basic compound is usually added into the wastewater to liberate ammonia from wastewater via steam. In order to reduce costs, hydrated lime is often used as the pH adjuster. However, the addition of hydrated line causes the scale formation in the process. The scale adheres on the wall and leading to the cease of the treating process. To solve this problem, this article systematically studied the crystallization thermodynamics and scale inhibitor for calcium sulfate. (1) A new model, based on the electrolyte NRTL activity coefficient equation, was established to describe the solubility and chemistry of calcium sulfate dihydrate in NH4Cl-(NH4)2SO4-H2O system. The solubility of calcium sulfate dihydrate in the temperature range of 298.15K~343.15 K in ammonium chloride, ammonium nitrate, and the mixture of ammonium sulfate and ammonium chloride electrolyte solutions were determined. The new binary interaction parameters were obtained by regression of experimental data. The result shows the calculated data are in good agreement with the experimental values. (2) The factors influencing the crystallization of calcium sulfate in (NH4)2SO4-CaCl2-H2O system has been systematically studied. The factors include the temperature, ratio of Ca(OH)2/(NH4)2SO4 and pH. Results shows a high ratio leads to a high concentration of calcium ions in the solution. At the same time a high temperature shortens equilibrium time. When pH>10, the calcium ion concentration reduced with the rise of the temperature in the solution. (3) To prevent the calcium sulfate depositing on the pipeline, scale inhibitor including EDTMPS, PASP, AA/AMPS, PAA, ATMP was tested for calcium sulfate. The result shows that solubility of calcium sulfate increases with the increase of the scale inhibitor concentration, and finally reaches a stable value. All those inhibitors can make the calcium sulfate hemihydrate stable in the solutions.
Document Type学位论文
Recommended Citation
GB/T 7714
田萍. 氨氮废水汽提处理过程硫酸钙结晶热力学与阻垢研究[D]. 中国科学院研究生院,2013.
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