The moving bed washing process–an alternative to conventional purification steps?

摘要

The moving bed washing process is based on a saturated moving bed that passes a vertical wash chamber continuously. It is penetrated by the wash liquid in horizontal direction displacing the initial solution to a great extent. In the case of several chambers arranged vertically in series a cross-countercurrent flow of solids and wash liquid can be realized. rnThe moving bed exhibits structural properties that are favorable for a washing process: Within the moving bed there is a slight vertical relative movement and rearrangement of the particles. This leads to a continuous change of the particle-particle and particle-boundary contacts while the wash liquid penetrates the moving bed. Thus, stagnant inter-particulate regions within the moving bed and near adjacent boundaries are accessible to the wash liquid. At the same time an undesired mixing of mother and wash liquid that penetrate the porous system horizontally can be avoided to a large extent due to the vertical solids velocity profile. Additionally, the wash chamber is filled evenly with the moving bed reducing a local maldistribution of the wash liquid flow. These properties lead to an excellent washing performance both with respect to the remaining fraction of impurity and the specific wash liquid demand. The washing behavior is demonstrated experimentally with two quartz sand fractions. The application of the uni-axial dispersion model reveals a favorable dispersion behavior. The experimental results show that the dispersion behavior is comparable to extended randomly packed beds. Additionally, a comparison to cake washing (fixed bed structure) and dilution washing processes (dispersed particles) is drawn. Also the dispersion of the wash and initial liquid is determined as one essential aspect of the hydrodynamic behavior of a moving bed.