Solids mixing continuous equipment

A standard testing procedure for solids-mixing equipment is available (Ref. 1). This contains details and references pertaining to sampling from solids mixtures for both batch and continuous mixing. 

Multi-phase mixing is often seen in industries. In general, the distribution of not only the dispersed phase but also the continuous phase depends on the local position in the equipment in the case of a multi-phase operation such as gas-liquid mixing system, liquid-liquid mixing system, solid-liquid mixing system, and gas-liquid-solid mixing system. In order to evaluate the mixing state in such systems, both the dispersed phase and continuous phase should be considered. 

An important mixing operation involves bringing different molecular species together to obtain a chemical reaction. The components may be miscible liquids, immiscible liquids, solid particles and a liquid, a gas and a liquid, a gas and solid particles, or two gases. In some cases, temperature differences exist between an equipment surface and the bulk fluid, or between the suspended particles and the continuous phase fluid. The same mechanisms that enhance mass transfer by reducing the film thickness are used to promote heat transfer by increasing the temperature gradient in the film. These mechanisms are bulk flow, eddy diffusion, and molecular diffusion. The performance of equipment in which heat transfer occurs is expressed in terms of forced convective heat transfer coefficients. 

To 450 cc. of concentrated hydrochloric acid (sp. gr. 1.19) and 500 cc. of water in a 4-I. (i-gal.) earthenware crock equipped with an efficient stirrer is added 143 g. (1 mole) of /3-naphthyla-mine. The suspension of the amine hydrochloride is cooled by the addition of 500 g. of cracked ice. When the temperature reaches 5° solid sodium nitrite (about 69 g.) is added until starch-iodide paper shows an excess. During the diazotization about 600 g. of cracked ice is introduced at such a rate as to keep the temperature at 50. The cold solution of the diazonium salt is filtered to remove a small amount of precipitate and returned to the crock. A solution of 271 g. (1 mole) of mercuric chloride in 300 cc. of concentrated hydrochloric acid is mixed with 300 g. of ice and added slowly to the rapidly stirred solution. A heavy yellow solid separates. Stirring is continued for one-half hour to secure complete reaction. The yellow addition compound of /3-naphthalene diazonium chloride and mercuric chloride is collected on a 20-cm. Buchner funnel, sucked as dry as possible, and then washed with two 400-cc. portions of water and two 150-cc. portions of acetone (Note 1). The... 

Fig. 10.6 The single-stage FCM. (a) Size 15 FCM with chamber opened and rotated hydraulically (b) top view of staged apex twin rotors and the axial zones for carrying out the solids feed handling and the melting and mixing elementary steps (c) cross-sectional view of two rotor orientations, tip-to-tip (cx) and tip-to-flat (c2). [Reprinted by permission from E. L. Canedo and L. N. Valsamis, Farrel Continuous Mixer Systems for Plastics Compounding, in Plastics Compounding—Equipment and Processing, D. B. Todd, Ed., Hanser, Munich, 1998.]...

Many operations treat particle-liquid mixing in chemical industry. The first aim of solid-liquid mixing is to make a solid particle float. However, mixing performance of operations/equipment is not clear. Additionally, when many kinds of particles are involved, it is not known whether there is any difference in the mixedness between the following two cases the case where all particles are treated as a particle (two-phase mixing—particle and continuous liquid phase) and the case where every particle is treated individually (multiple-phase mixing—each particle and continuous liquid phase). Therefore, a solution to this unsolved problem is not imperative. 

---