低磷浓度下鸟粪石结晶成粒及反应器流态模拟

Struvite pellet crystallization at low phosphorus concentration and fluidization simulation of the reactor

为扩大鸟粪石(MAP)结晶成粒技术的应用范围,对低磷浓度下MAP成粒最优条件进行了研究.试验得出该技术应用的磷浓度应大于50mg/L,并在此基础上研究得到低磷浓度条件下MAP结晶成粒的最佳条件:pH 9.0,磷氮物质的量比1:8.此时生成的MAP平均粒径为0.56mm,总体积生长率为4.95cm^3/h,纯度可达99.9%.为进一步优化流化床反应器中MAP成粒条件,利用CFD商用软件(Fluent 6.3)对反应器流态进行了模拟.结果表明:MAP流化床反应器的生长区能够形成明显的自下而上的水力分级,截面流速也较为均匀,有利于颗粒的生成,但沉淀区和进水区存在死区、涡流等不利条件.因此,有必要改进生长区和沉淀区的连接方式以及进水管的分布,以获得更为优质的MAP颗粒.

In order to expand the application field of struvite（MAP） pellet crystallization technology, the optimal conditions for struvite pellet formation at low phosphorus concentrations were investigated. Results show that the phosphorus concentration over 50mg/L would be better for application of this technology. The optimal conditions for struvite pellet formation were as follows： pH = 9.0 and phosphorus to nitrogen molar ratio = 1：8. Under the conditions, the average size of harvested struvite particle reached 0.56 mm, the volume growth rate was 4.95cm^3/h and the struvite purity reached 99.9%. In order to further optimize MAP formation in the fluidized bed reactor, CFD software（Fluent 6.3） was used to simulate the flow fed to the reactor. It turned out that the bottom-up hydraulic classification was formed obviously in the growing zone of the crystallizer. Velocity in the cross-section was relatively uniform, which is beneficial to struvite formation. But some adverse conditions such as dead zone, vortexes and circulation loops were also present in the settling and influent zones. Therefore, it is necessary to improve the connection between the growing zone and settling zone as well as the distribution of inlet pipes to obtain high-quality MAP pellets.