氢氧化镁连续生产时高镁垢形成机理初探

Preliminary mechanism research of high-magnesium scaling during continuous production process of magnesium hydroxide

在10万t/a氢氧化镁连续生产过程中,反应釜和一些管道中会生成高镁垢,影响传质传热,定期停车酸洗,既浪费原料增加成本,也影响生产的连续性。为有针对性地解决该问题需要弄清高镁垢形成机理。通过对垢样进行化学分析、XRD、SEM和热分析,确定结垢物的主成分是氢氧化镁,次要成分是碱式氯化镁。通过高镁垢的微观形貌、结晶性和热分解特性,进而分析确定高镁垢形成并逐渐硬化的机理:正常的氢氧化镁产品是团聚粒,但反应体系内会生成少量独立的片状和针柱状异形晶,这些异形晶会沉积挂壁,特别是针柱状碱式氯化镁会贯穿各片层如钉书针样将片状的氢氧化镁订牢,使结垢物更致密。

High-magnesium scale,forms in the reaction tank and tubes during the continuous production process of 1×10^5 t/a magnesium hydroxide,has an impact on the mass and heat transfer.Periodic downtime for acid washing is not only increasing cost,but also affecting the continuity of production.In order to solve these problems,It is necessary to understand the forming mechanism of high-magnesium scale.The result of chemical analysis,XRD,SEM and TA indicated that the scale is composed of major magnesium hydroxide and marginal basic magnesium chlroide.The mechanism of forming and hardening was confirmed by micromorphology,crystallization and thermal decomposition.Apart from normal agglomeration grains of magnesium hydroxide,a trace of paramorph crystal,flaky and acicular respectively,was crystallized in the synthesis system of magnesium hydroxide and easily adhesive to the tank.The acicular basic magnesium chloride embeds in the other flaky crystal just like stapling,which can solid the magnesium hydroxide and densify the scale.