Powders and Pastes

HP and pm Requirements of an Aerated y ted Tank A tank contains 5000 gal of liquid with sp gr = 1.0 and viscosity 100 cP that is aerated and agitated. The ratio of impeller to tank diameters is dA) = 0.4. Two sets of conditions are to be examined. 

From Table 10.2, a liquid velocity of 0.6-0.7 ft/sec wUl give moderate to high dispersion. Table 10.5 gives possible HP/rpm combination of 30/125, somewhat less than the value foimd here. 

The closest reading from Table 10.5 is HP/rpm = 25/100 which is a good check. 

Industries such as foods, cosmetics, pharmaceuticals, plastics, rubbers, and also some others have to do with mixing of high viscosity liquids or pastes, of powders together and of powders with pastes. Much of this kind of work is in batch mode. The processes are so diverse and the criteria for uniformity of the final product are so imprecise that the nonspecialist can do little in the way of equipment design, or in checking on the recommendations of equipment manufacturers. Direct experience is the main guide to selection of the best kind of equipment, predicting how well and quickly it will perform, and what power consumption will be. For 

282-300) and a similar one for powder mixers (loc. cit., pp. 301-311). Since this equipment industry has been quite stable. 

Figare 10.15. Some mixers and blenders for powders and pastes, (a) Ribbon blender for powders, (b) Flow pattern in a double cone blender rotating on a horizontal axis, (c) Twin shell (Vee-type) agglomerate breaking and liquid injection are shown on the broken line, (d) Twin rotor available with jacket and hollow screws for heat transfer, (e) Batch muller. (f) Twin mullers operated continuously, (g) Double-arm mixer and kneader (Baker-Perkins Inc.), (h) Some types of blades for the double-arm kneader (Baker-Perkins Inc.). 

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Valentin, Mixing of Powders and Pastes Basic Concepts, Chem. Eng. (London), 45, CE99-CE106 (1967). 

Jenike, A. W. and Johnson, J. R. (1970) Chem. Eng. Prog. 66 (June) 31. Solids flow in bins and moving beds. Jones, R. L. (1985) Chem. Engr., London No 419 (Nov.) 41. Mixing equipment for powders and pastes. Jones, A. G. (2002) Crystallisation Process Systems (Butterworth-Heinemann). 

Schofield, C., Scale-up of powder and paste mixers, Chem. Ind., February (1977) 105-108. 

Three electrode types are used. The first is a partly smooth surface to allow minimum contact with the test atmosphere. The second is corrugated to enhance the contact and facilitate HC1 escape. The third is hollow on the bottom for placing powdered materials and has a corresponding projection on the upper part (Figure 5). PVC materials in the shape of powder and paste foils can be evaluated in the apparatus... 

Expansion joints Powder and paste High load, heat... 

Mixers. See also Agitation blend time, 290 dimensionless groups, 290 gas dispersion, 296-301 in line type, 300,301 liquids, power and speed need, 293,295 powders and pastes, 301,303,304 power number, 290-292 quality characterization, 290-292 suspension of solids, 295-299 tank desien. 287.288 Moisture c tent, critical, 237 Molecular distillation, 425-427 equipment sketches, 427 Hickman still, 427 operating conditions, rate of evaporation. 

Yeast extracts are concentrates of soluble material derived from yeast following hydrolysis of the cell material, particularly the proteins, carbohydrates and nucleic acids. Hydrolysis is carried out by use of the yeast s own hydrolytic enzymes (autolysis) or by other methods (hydrolysis or plasmolysis). Yeast extracts are commercially available as powders and pastes. 

B. Atkinson, Compaction of powders and pastes in double roll presses, NCB/CRE/Solid Products Department Report No. 108, Feb. 1964. 

H. R. A. Lane, B. Atkinson, and S. Harvey A theory for the compaction of powders and pastes in double roll presses, NCB/R D Department (CPC), Coal Research Establishment, Solid Products Department, Report No. SP 116, Dec. 1965. 

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