【作者】 王燕；

【导师】 李军；

【作者基本信息】 四川大学 ， 化学工艺， 2002， 硕士

【摘要】 在用钾、钠含量高的湖北磷矿生产湿法磷酸时，真空过滤系统存在严重的结垢堵塞问题。垢物质地坚硬、清洗困难，堵塞管道，严重影响了生产的正常进行。许多生产厂家已经从工艺、设备、管线材质等方面提出了一些改进措施，但这些措施只能缓解垢物的析出，仍然不能从根本上解决问题。因此，深入系统地研究过滤管线上垢物的形成过程及规律，以便找出合适的解决方案具有重要的现实意义。 本文首先采用人工冷却系统模拟湿法磷酸生产的真空过滤系统冷却过程，研究垢物的析出规律，实验结果得知：垢物的主要成分为氟硅酸钠和氟硅酸钾，氟硅酸钠首先析出，结构致密，其次是氟硅酸钾，最后是二水硫酸钙，氟硅酸钠对氟硅酸钾有很强的结晶诱导作用；然后在三种生产中常用的不同的材质钼二钛、聚氯乙烯和聚四氟乙烯表面进行结垢试验，发现聚四氟乙烯表面最不易结垢，而在钼二钛表面最易结垢。其次，尝试将界面能与结晶理论结合起来应用于本试验系统，具体方法是应用Van Oss et.al界面能方法得到上述三种垢物与不同板材表面之间的界面能，并结合结晶理论判定垢物的析出机理，理论分析与模拟实验结果相符合，这说明界面能这种研究方法是可行的。因此，如果选择合适的表面活性剂作为添加剂改变器壁与结垢物间的界面性质，从而缓解垢物结晶析出并在管壁生长，就可找出有效阻垢的方法。为此我们接着研究 摘要了五种添加剂对垢物在磷酸介质中的界面能的影响以及对介稳区宽度的影响。结果表明：表面活性剂使界面能增加，这样使得垢物组分成核位垒提高，不易结晶析出，同时使介稳区宽度增大，这样意味着氟硅酸钠和氟硅酸钾的极限过饱和度增大，溶液稳定性增强，也不易析出晶体。将这五种表面活性剂应用于动态模拟实验，阻垢率均达到50％以上。因此我们可以在上述两种实验方法及其原理的基础上挑选工业上合适的添加剂。更多还原

【Abstract】 In the wet-process phosphoric acid production from the Hubei phosphate ore, one of the bothersome problems is that potassium fluosilicate and sodium fluosilicate scales are liable to form on the filtration system owing to its high potassium and sodium content, which greatly restrains the application of Hubei phosphate ore. Some factories have thought out many methods to solve this problem through changing the process, equipments, pipe material and so on,but they didn’ t work very well. Therefore, it is very important to study the scale formation mechanism systematically in order to solve the scale problem.Firstly, we studied the crystallization mechanism of the scales formation by means of simulating the cooling process of the vacuum filtration in the wet-process phosphoric acid production in laboratory, the experiment results show that: the main components of scales are sodium fluosilicate and potassium fluosilicate, the former is segregated out earlier than the latter, and has an inducing effect on the latter, the third main component of the scales is gypsum which is the lastest to precipitate; we made scale-segregating experiment on the surface of the three common pipe materials PVC, PTFE and Mo2Ti, then found that the scales is most easily crystallized on Mo2Ti and not easily on PTFE.Secondly, the interface energy principle and the crystallization principle were integrated and applied to this system, the interfaceparameters between the above three scales and pipe materials were got by means of Van Oss et al’s interface energy principle (that is LWAB principle), according to the scale formation mechanism integrated with crystallization principle, it is found that the mechanism is accordant with the simulation experiment results satisfactorily. All these show that the used method is feasible.We have found several additives to change surface characters in the system and try to inhibit the scale crystal on the pipe. Their effects on the interfacial energy and metastable zone width of the three scales in phosphoric acid were studied, the results show that the additives increase the interfacial energy , therefore decrease the rate of nucleation and make crystal process harder, at the same time the additives increase metastable zone width , consequently makes the critical super saturation larger and the solution system more stsLle, so the scales is more difficult to crystal. The experiments’ results also verified these analyses. Based on the above two methods, we can choose appropriate additives in industry.更多还原