Feed systems properties

Useful for selecting the material of construction of the feed system. Properties affecting potential corrosiveness are pH and moisture content. 

Fig. 13. Spray-dryer system designed for production of agglomerated food powders with instant properties (82) A, Hquid-feed system B, spray-dryer chamber C, drying air heater D, cyclones for fines recovery E, vibrofluidizer as afterdryer F, vibrofluidizer as aftercooler and G, fines return to drying...

Several features of the hypothetical system in Eigure 2 can be used to illustrate proper selection of crystallizer operating conditions and limitations placed on the operation by system properties. Suppose a saturated solution at temperature is fed to a crystallizer operating at temperature T. Because the feed is saturated, the weight fraction of in the feed is given as shown in Eigure 2. The maximum crystal production rate from such a process depends on the value of and is given by... 

Artificial control of the monomer concentrations is possible by changing the monomer feed methods, which includes multishot, stage feed (19), and continuous feed. A multishot emulsion polymerization is expected to form multilayered particles if the monomers are chosen properly. When the layers are sufficiently thin, the particles exhibit unique thermal and mechanical properties. The stage feed system is shown in Figure 11.1.6. It makes it possible to produce particles having gradient composition of different monomer units. 

Flow ratio control is essential in processes such as fuel-air mixing, blending, and reactor feed systems. In a two-stream process, for example, each stream will have its own controller, but the signal from the primary controller will go to a ratio control device which adjusts the set point of the other controller. Figure 3.17(a) is an example. Construction of the ratioing device may be an adjustable mechanical linkage or may be entirely pneumatic or electronic. In other two-stream operations, the flow rate of the secondary stream may be controlled by some property of the combined stream, temperature in the case of fuel-air systems or composition or some physical property indicative of the proportions of the two streams. 

In the case of flash degassing, the polymer solution is first heated under pressure to above the boiling point of the volatile components and decompressed directly into the ZSK. The polymer and solvent (monomer) spontaneously separate from each other inside the ZSK and the majority of the volatile components are released via the back venting system. Depending on the pressure and the temperature, up to 90% of the solvent can be removed in this way. Efficiency depends on the temperature of the polymer solution at the feed intake, the pressure drop in the back vent, and the material properties of the feeding system. The back vent is located upstream from the polymer or polymer solution feeding port (see Fig. 10.2). In this case, there is no melt in the screw channel so that the entire screw cross-section is available for the removal of gas or vapors. 

Fig. 7.6. Spray dryer for production of coarse food powders with instant properties [29]. (1) Liquid feed system. (2) Spray dryer chamber. (3) Drying air heater. (4) Cyclones for fines recovery. (5) Vibrofluidizer as after-dryer. (6) Vibrofluidizer as after-cooler. (7) Fines return to drying chamber.

Dried product is collected in either cyclones or bag filters depending upon the product-particle properties. When primary collection is carried out in cyclones, secondary collection in a bag filter or scrubber is usually necessary to comply with environmental regulations. A rotary valve is used to provide an air lock at the discharge point. Screws are utilized to combine product from multiple cyclones or large bag filters. If required, a portion of the dried product is separated from the main stream and returned to the feed system for use as backmix. 

In the design of extraction equipment with complex flows, mass-transfer coefficients are determined by experiment and then correlated as a function of molecular diffusivity and system properties. The available theories provide an approximate framework for the data. The correlation constants vary depending upon the type of equipment and operating conditions. In most cases, the dominant mass-transfer resistance resides in the feed (raffinate) phase, since... 

In an attempt to overcome the limitation that only surface feeding chewing insects can be controlled by the known antifeedant compounds, Jermy and coworkers (Jermy and Matolcsy, 1967 Matolcsy et al. 1968) investigated the antifeedant activity of some substituted phenoxyethanols and phenoxyacetic acids which do not affect plant growth and which are known to possess systemic properties. 2,4,6-Trichlorophenoxyethanol (6) and 2,4,6-trichlorophenoxyacetic acid (7) have shown the highest antifeeding activity both under laboratory and field conditions. 

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