Cold model experiment on ion-exchange reaction between pearlite particles and HCl aq. was carried out in order to understand the effect of particles dispersion and operating factors on solid/liquid mass transfer rate in a mechanically-stirred vessel. Inner diameter of vessel was varied in conjunction with both bath depth as 400 (base) and 300 mm. Rotation speed and volume ratio of particles to liquid were changed between 0-240 rpm, 0.02-0.24 (-), respectively.When rotating speed increased, solid/liquid mass transfer rate increased moderately both in the regions I and III, whereas it increased in the region II. When impeller depth decreased, it was kept almost constant in the region I, increased in the region II and increased moderately in the region III. Solid/liquid mass transfer rate changed less than liquid/liquid one in the region II when rotation speed and impeller height were changed, whereas both of solid/liquid and liquid/liquid mass transfer rates were kept almost constant in the region I. The dimensionless equation on solid/liquid mass transfer rate of each region was given as a function of Sherwood number, Reynolds number, volume ratio of particles to liquid and bath depth normalized by vessel diameter. Dispersion ratio in the region II was ranged by solid/liquid mass transfer coefficient and rotation speed or impeller height of the transitions I-II and II-III. Solid/liquid mass transfer rate of mechanical stirring was larger than that of gas injection practice for the same supplied rate of energy into bath.

Synopsis : Solid/liquid mixing pattern was investigated and compared with the liquid/liquid one in a mechanically-stirred vessel. The cold model experiment was carried out to make clear the effect of operating factors such as volumetric ratio of solid particles to liquid, rotation speed, impeller position, etc. on the mixing pattern. The solid/liquid mixing pattern was observed visually and the vortex depth of solid/liquid or gas/liquid interface was measured with a ruler. It was categorized into 3 types as well as the liquid/liquid mixing pattern. I: the region where solid particles have no dispersion, II: the region where some of the solid particles disperse into liquid, III: the region where almost all of the solid particles disperse into liquid. The solid/liquid mixing pattern transits from I to II, and from II to III as the impeller depth decreased and the rotation speed increased. The transition of I-II shifted to a higher rotation speed in cases of smaller volumetric ratio of solid to liquid, larger particles diameter, larger density difference between solid-liquid and smaller liquid viscosity. The transition of II-III shifted to the higher rotation speed in cases of smaller impeller diameter and larger liquid viscosity, and showed independency on volumetric ratio of solid to liquid, particles diameter and density difference between solid and liquid. Multi regression analysis on the transition of I-II showed that the calculation agreed with the measurement. Dimensionless correlation equation on the transition of II-III also showed a good agreement between calculation and measurement and it was adaptable to liquid/liquid system.