Prepared By, GAJERA DEEP ( ) PATEL VIRAJ ( ) VAGHASIYA DHAVAL ( ) S AL C OLLEGE OF E NGINEERING AHMEDABAD Mixers for Cohesive Solids

Mixing is one of the important unit operation widely used from reaction to finishing stages in chemical industry. A production (chemical) engineer has to operate the running and modifications with the installed type for the particular process or recommend one in case of plant erection or process design. The selection or modification with these equipment is highly subject to the set of properties of material being handled. Mixers are meant to shift the non-homogeneity of a batch to a homogenous state Introduction

Cohesive solids employ maximum consideration in terms of mixer selection and operating parameters due to influence of rheology and forces of cohesion. The power consumption for this type of mixers is high due to these factors. Mixing of sticky solids however is supported by shearing, folding, stretching and compressing elements. Different mixers being employed follow three mixing phenomenon: the small-scale random motion (diffusion), the large-scale random motion (convection) and the interchange of particles by virtue of slip zones (shear). Mixers are employed both for solids and liquids phases with varied interests.

4 Types of mixers  Mixing is by slow speed agitation of the mass with an impeller  By tumbling  By Centrifuging smearing and impact  For cohesive solids – powerful and heavier machines  For free flowing solids – light in construction

5  Different types of mixers are: 1. Change-Can mixer 2. Kneading machine 3. Two arm kneaders 4. Disperser 5. Masticator 6. Muller mixer Mixers for Cohesive solids

6 1. Change-Can Mixers  For viscous liquids and light pastes as:  Food processing  Paint manufacturing  5 to 100 gal. in size  Change-Can mixer are: 1. Pony mixer 2. Beater mixer

7 1. Pony mixers  Agitator consist of vertical blades held on rotating head positioned near the wall of the can  Blades are slightly twisted  Agitator is mounted eccentrically  Can rest on a turn table driven in direction opposite to that of agitator  All the material in the can is brought to the blade to be mixed  When mixing is completed –blades are cleaned and can is replaced

Change Can Mixer (Pony Mixer)

9 2. Beater mixers  Can or vessel is stationary  Agitator has a planetary motion  Visits all parts of vessel  Beaters are shaped to pass with close clearance over the side & bottom of mixing vessel

Change Can Mixer (Beater)

11 Kneaders  Kneading – “squashing the mass flat, folding it over on itself and squashing it once more”  Also tear the mass apart and shear it between a moving blade & a stationary surface.  For deformable & plastic solids  Large energy requirements

It is heavier in construction and draws more power than a kneader it works on additives & coloring agent into split material. Disperser

A masticator is still heavier & draw even more power it can distigrate scrap rubber & compound the toughest plastic masses. Masticators are often called intensive mixer. Masticators

14 Design of Blades  Sigma blade:  Used for general purpose kneading  Edges are serrated to give a shredding action  S-type Double-naben (fish-tail blade):  Effective with heavy plastic materials  develop high shear force  Z-type Disperser blade:  Heavier and develop high shearing forces  Disperse powders or liquids into rubbery masses.

Construction & Working It consists of two counter rotating sigma blades(2-shaped) are in coport in the vessel is turned up by one blade and is immedr turned under adjecent one. The blades are turned by bear at either or both ends. The material to be kneaded is chopped into through and mixing for a priod of about 5 to 20 minute or longer. Application: Striding of cotton litters Acetic acid & Acetic acid anhydride to from cellulose acetate. Two Arm Kneader

Kneader (Sigma Blades)

Kneader (Sigma Blades)

Double Naben Blades Z-type Disperser blade

19 Muller mixer  Suitable for heavy solids and pastes, muller mixer applies smearing, rubbing and somewhat skidding action to achieve the desired mixing levels. Its working action is similar to that of mortar and pestle. It has several types, three most common include: Stationary-pan mixer, Rotating-pan mixer and Countercurrent-pan-muller mixer. The roller wheels move in a circular chamber to ride over the material, producing shearing action that causes size reduction as well as intermixing of material.

Muller Mixer