翼形桨在气液固三相搅拌反应釜中的混合性能

MIXING CHARACTERISTICS IN GAS - LIQUID - SOLID THREE-PHASE STIRRED REACTOR WITH A NEW TYPE AXIAL IMPELLER

机械搅拌槽中高速旋转的叶轮产生的排出流中,径向速度主要用于气体的剪切分散,而其轴向速度是固体悬浮和液相轴向混合的主要动力。三相体系的混合不仅要求叶轮具有较强的径向剪切分散能力,而且要有一定的轴向混合能力,以此达到对气体和固体的同时分散。理想的混合水平不仅要求达到二者在宏观上的均匀,而且在微观混合上也要达到一定的均匀度,为此对搅拌桨的设计提出了较高的要求。在气液二相的混合操作中比较多的采用了盘式涡轮桨,而在液固二相的混合操作中比较多的使用螺旋桨,这都是为了利用各自不同的混合优势。涉及到气液固三相混合,由于气体和固体的分散是一个相互制约的问题。

This paper presents the characteristics of three - phase mixing in terms of the critical impeller speed of complete suspension of solid, gas and solid dispersion state, stirred power, gas - liquid mass transfer coefficient for different suspension concentration and gas volume in liquid by using a new type axial impeller(K4) in mechanically stirred vessels. It is revealed that the critical impeller speed Njsg and stirred power per unit volume Pjsg/ V for incipient complete suspension state increase with increasing gas volume. The aeration coefficent k and aeration factor K represent the intensities of these effects, and usually k= 0.124 ~ 0.580, K = 0.72. The total dispersion process in three - phase system can be defined as two dispersion regions. In the first dispersion region, the gas dispersion ia from flooding to complete dispersion while the solid dispersion is from the state of lift - off to complete suspension, In the second dispersion region the gas and solid concentrations are well distributed in the stirred vessels, which is regarded as pseudo - homogeneous dispersion. The impeller speed index m in the equation of power consumption is close to the index for homogeneous system, usually, the mean speed index m = 2.67. The volumetric mass transfer coefficient KLa increases with incresing gas volume as a result of gas holdup increaing with the increasing of the gas volume. The power index β accounts for the effect of the stirred power on the volumetric mass transfer coefficient KLa and usually β= 0.71 ~0.93.