Equipment For Fusion Of Solids

The thermal duty here is the opposite of solidification operations. The indirect heat-transfer equipment suitable for one operation is not suitable for the other because of the material-handling rather than the thermal aspects. Whether the temperature of transformation is a definite or a ranging one is of little importance in the selection of equipment for fusion. The burden is much agitated, but the beds are deep.

Only fair overall coefficient values may be expected, although heat-flux values are good.

Horizontal-Tank Type This type (Fig. 11-56a) is used to transfer heat for melting or cooking dry powdered solids, rendering lard from meat-scrap solids, and drying divided solids. Heat-transfer coefficients are 17 to 85 W/(m2 °C) [3 to 15 Btu/(h ft2 °F)] for drying and 28 to 140 W/(m2 °C) [5 to 25 Btu/(hft2 °F)] for vacuum and/or solvent recovery.

Vertical Agitated-Kettle Type Shown in Fig. 11-56b this type is used to cook, melt to the liquid state, and provide or remove reaction heat for solids that vary greatly in "body" during the process so that material handling is a real problem. The virtues are simplicity and 100 percent cleanability. These often outweigh the poor heat-transfer aspect. These devices are available from the small jacketed type illustrated to huge cast-iron direct-underfired bowls for calcining gypsum. Temperature limits vary with construction; the simpler jackets allow temperatures to 371° C (700° F) (as with Dowtherm), which is not true of all jacketed equipment.

Mill Type Figure 11-56c shows one model of roll construction used. Note the ruggedness, as it is a power device as well as one for indirect heat transfer, employed to knead and heat a mixture of dry powdered-solid ingredients with the objective of reacting and reforming via fusion to a consolidated product. In this compounding operation, frictional heat generated by the kneading may require heat-flow reversal (by cooling). Heat-flow control and temperature-level considerations often predominate over heat-transfer performance. Power and mixing considerations, rather than heat transfer, govern. The two-roll mill shown is employed in compounding raw plastic, rubber, and rubberlike elastomer stocks. Multiple-roll mills less knives (termed calenders) are used for continuous sheet or film production in widths up to 2.3 m (7.7 ft). Similar equipment is employed in the chemical compounding of inks, dyes, paint pigments, and the like.

Steam Equipments Connection

Liquid or steam connection Liquid or steam jacket Mixing kettie wall

Liquid or condensate connection

Liquid or steam connection Liquid or steam jacket Mixing kettie wall

Liquid or condensate connection

Dry-powdered solids hopper

Steam or liquid chamber

Dry-powdered solids hopper

Steam or liquid chamber

Wall

Siphon Peeling knives intermittently operated

Siphon Peeling knives intermittently operated

Wall

Siphon

FIG. 11-56 Heat-transfer equipment for fusion of solids. (a) Horizontal-tank type. (Courtesy of Struthers Wells Corp.) (b) Agitated kettle. (Courtesy of Read-Standard Division, Capital Products Co. ) (c) Double-drum mill. (Courtesy of Farrel-Birmingham Co. )

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