气淬粒化熔渣液膜破碎过程研究

Study on liquid film breaking process of gas quenched granulated slag

采用计算流体力学的方法研究气淬粒化工艺中熔渣的粒化环节及其破碎机理,利用VOF模型追踪自由界面以及RNG K-epsilon模型描述湍流流动,对气淬作用下的熔渣粒化过程进行数值模拟,得到气淬熔渣粒化的液膜变化过程和气体流场分布,并分析局部动量比对熔渣破碎过程的影响。研究结果表明:熔渣射流在气淬作用下存在球孔状破碎和扁平状破碎2种破碎过程,气液界面间的速度梯度使K-H不稳定性产生,从而生成K-H表面波,这是发生扁平状液膜破碎的主要原因;气液界面间的压力梯度使R-T不稳定性产生,从而生成R-T表面波,这是发生球孔状液膜破碎的主要原因。当局部动量比较小时,K-H不稳定性的影响更大,增大局部动量比,K-H不稳定性的影响随之降低,R-T不稳定性的影响增强,球孔状液膜形成所需时间更短,熔渣破碎逐渐由R-T不稳定性占主导地位;增大局部动量比使R-T和K-H表面波波长均增大,使熔渣颗粒从液膜表面剥离和撕裂的难度增大,颗粒形成的频率降低,增加熔渣粒化的难度;增大局部动量比会让熔渣液膜破碎长度增大,使熔渣发生破碎的时间更晚,熔渣颗粒的飞行距离和换热时间变长。

The process and mechanism of slag granulation during gas quenching was simulated by using computational fluid dynamics(CFD) method. VOF model was used to track the free interface and RNG K-Epsilon model was used to deal with turbulent flow. The liquid film change process and gas flow field distribution of gas quenching slag granulation were obtained by numerical simulation.Then the influence of local momentum ratio on slag crushing process was analyzed. The results show that there are two kinds of slag jet crushing process under the effect of gas quenching: spherical crushing and flat crushing. The velocity gradient between gas and liquid interface causes K-H instability which leads to K-H surface wave, which is the main cause of flat liquid film breakage.The pressure gradient between gas and liquid interface causes R-T instability, which leads to R-T surface wave, which is the main cause of spherical liquid film breakage.The influence of K-H instability decreases with the increase of the local momentum ratio, and the influence of R-T instability increases with the increase of the local momentum ratio, the formation time of the spherical liquid film is shorter, and the slag breakage is gradually dominated by R-T instability. Increasing the local momentum ratio will increase the surface wave lengths of R-T and K-H, and increase the difficulty of the slag particles peeling and tearing from the liquid film surface, which will reduce the frequency of particle formation and increase the difficulty of slag granulation. With the increase of local momentum ratio, the fragmentation length of liquid film of slag increases, the fragmentation time of slag occurs later, and the flight distance and heat transfer time of slag particles become longer.