摘要
晶种分解过程是复杂的结晶和传质过程,是拜耳法生产氧化铝的关键工序之一,它对氧化铝产品的产量和质量均有重要影响,并对其它的工序也存在间接作用。由于国内铝土矿资源情况与国外的有很大差别,其种分过程与国外种分过程有不同之处,因此,对具有中国特色的种分过程的机理和动力学的研究具有很重要的现实意义。
本文通过对晶种分解过程及主要设备的详细研究,综合利用多相流体力学、计算流体力学及传输过程等理论,构建了晶种分解过程多相流动的多流体模型;以商业软件CFX4.3为平台,研制开发了晶种分解过程多相流动的数值模拟系统。以两种不同结构的空气搅拌式种分槽为研究对象,完成了晶种分解过程气—液两相流动的三维数值模拟。数值模拟结果表明,种分槽内的流场分布对铝酸钠溶液的混合、槽内结疤等现象有着直接的影响;翻料管为喇叭套管的种分槽内溶液循环量大,副风管的的上提强化了种分槽下部溶液的扰动,其流场明显优于翻料管为直套管的种分槽。
建立了晶种分解过程中的标量传输模型,并与气—液两相流动的多流体模型耦合,研制开发了晶种分解过程中铝酸钠溶液扩散及分解时间的数值模拟程序。计算结果表明,翻料管为直套管的种分槽内存在明显的溶液“短路”现象,溶液在槽内的分解时间低于翻料管为喇叭套管的种分槽。
设计并制作了晶种分解水模型实验装置,对晶种分解过程铝酸钠溶液的扩散与分解时间进行了实验研究。实验结果表明,不使用挡板的情况下种分槽内存在溶液“短路”现象;实验结果与数值模拟结果相吻合,证实了数值模拟程序的可靠性。
The seeded precipitation is a complex crystallization and mass transfer process and is one of the key steps in the Bayer process for the production of alumina. It has great influence on alumina product's outputs and quality and also has indirect effect on other procedures. Owing to the difference of the bauxite with foreign one, China has its own precipitation process. The study of the mechanics and dynamics of the precipitation with Chinese character is significant.
In this paper, multi-fluid model of multi-phase flow in the seed precipitation process was built based on the detailed study of the precipitation process, equipment and theories for multi-phase fluid dynamics, computational fluid dynamics and transmission. The numerical simulation system of multi-phase flow in the precipitation process was developed based on the commercial software CFX4.3. The air-liquid two-phase flow of the seed precipitation process in two air-agitated tanks with different structures was numerical simulated in three dimensions. The results showed that the flow field had a direct effect on the solution mixing and sediment in air-agitated tanks, and the flow field in the tank using horn riser tube was better than that of in the tank using straight riser tube since the solution circulation was increased by using horn tube and disturbance was enhanced by lifting the secondary windpipe.
Scalar transport model in the precipitation process was built and coupled with multi-fluid model, the numerical simulation program of solution diffusion and precipitation time was developed in this paper. The results illustrated that there was obviously short-circuiting in the tank using straight riser tube, and precipitation time is less comparing with the tank using horn tube.
Experimental apparatus for water model was design and the solution diffusion and precipitation time experiments were carried out in it. Experimental data showed that there was short-circuiting in the tank without baffle plate. And the experiment results agreed well with simulation situation, which proved that the numerical simulation program was credible.
引文
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