Pneumatic driers

Figure 12-5. The Lummus Crest Inc. process for producing polystyrene " (1) reactor, (2) holding tank (Polystyrene beads and water), (3) centrifuge, (4) pneumatic drier, (5) conditioning tank, (6) screening of beads, (7,8) lubrication and blending, (9) shipping product.

During World War II pneumatic driers of cellulose were developed in Germany and they are in use in modem industrial practice. They are based on the... 

The advantage of pneumatic driers is that they serve both for drying and transporting the cellulose. Drying is very quick. 

Cellulose material, such as cotton or wood cellulose, is dried until the moisture content is below 1%, or in the pneumatic drier to ca. 2%, and then loaded into sealed sheet metal containers or bags, to cool to room temperature. 

Terminology involves drier outlet dew point at the line pressure or the pneumatic circuit. This is the saturation temperature of the remaining moisture contained in the compressed air or gas. If the compressed gas temperature is never reduced below the outlet dew point beyond the drying equipment, there will be no further condensation. 

Figure 7.2-11. Spray drier with heat recovery system 1. Spray tower and drying system 2. Air heater 3. Air fan 4. Cyclone dust separator 5. Wet dust separator and entrainment separator 6. Exhaust air fan 7. Pneumatic product conveyer 8. Intermediate product storage 9. Product sieving and packing 10. Wet product pumping system (by courtesy of BMA, TAG-Division). 

Figure 9.4. Types of dryers cited in Tables 9.1 and 9.2. (a) Tray or compartment, (b) Vacuum tray, (c) Vertical agitated batch vacuum drier, (d) Continuous agitated tray vertical turbo, (e) Continuous through circulation, (f) Direct rotary, (g) Indirect rotary, (h) Agitated batch rotary (atmos or vacuum), (i) Horizontal agitated batch vacuum drier, (j) Tumble batch dryer, (k) Splash dryer. (I) Single drum, (m) Spray, (n) Fluidized bed dryer, (o) Pneumatic conveying (mostly after Nonhebel and Moss, 1971).

Sodium sulfite is produced by reacting sulfur dioxide-containing gases with sodium hydroxide in a saturated sodium sulfite solution at 60 to 80°C. The salt is. separated by centrifugation and dried in a pneumatic-conveyor drier. It is marketed as its anhydrous salt. 

Thorpe G.R., Pneumatic conveying driers, Chemical Industry Development, Incorporating CP E, pp. 13-19,1975. 

There are many applications which call for the use of clean, dry air, for example pneumatic instruments and air masks. This need is often met by using an oil-free compressor and aftercooler or by fitting an aftercooler and air drier to a conventional compressor. This reduces the need to fit and maintain local dirt eliminators as well as reducing the number of water traps required. In some factories, both systems are in operation. 

Over the years, many failures of plant systems and components have been attributed to solenoid-operated valve (SOV) problems. Several events have occurred in which SOV failures affected redundant safety components, multiple trains of safety systems, or multiple safety systems. SOVs are in wide-spread use in each nuclear power facility. They are used in safety-related systems indirectly as pilot operators working with control system fluid (such as pneumatic or hydraulically operated isolation valves) and directly in fluid systems (such as to vent the reactor vessel head or to supply air to the starting system for emergency diesel generators). Many SOVs are also used in non-safety-related systems that can significantly affect safety systems (such as plant instrument air drier systems). 

The heat required to evaporate moisture may be obtained by convection from the gas stream, by conduction e.g. on heated trays, in pneumatic risers, fluidized beds, spray towers, or by radiation. A typical fluidized bed drier is depicted in Figure 4.28. The hydrodynamic principles of fluidization were summarized in Chapter 2. Within a fluid bed drier, heated air, or other hot... 

Before processing, wool has to be scoured to remove contaminating particles such as dirt, sweat, and wool fat. The wool is dried in perforated cylinder driers and then opened in the breaker card. After these stages the fibers are oiled to alter the frictional properties of the fibers and to prevent electrostatic charging. The fibers are then pneumatically transported to the mixing chamber. Because raw wool scouring systems are very expensive and subject to strict environmental protection laws, most worsted spinning mills purchase scoured wool, card slivers, or combed slivers. 

In this chapter, we focus on our efforts to model dispersed multiphase flows in which a discrete phase (consisting of solid particles, gas bubbles, or liquid droplets) is moving through, or is moved by, a continuous Newtonian fluid phase. Such flows appear frequendy in process equipment in the chemical, metallurgical, pharmaceutical, and food industries. Examples include fluidized bed reactors, spouted bed reactors, pneumatic conveyors, bubble column reactors, slurry reactors, and spray driers. Figure 1 shows a schematic overview of typical dispersed multiphase systems. 

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