Bulk Conveying

Solids may be conveyed mechanically or pneiunaticaUy. Mechanical conveyors are tj ically belt, flight, screw, roller, or en masse transport devices. Solids are also moved by cranes and bucket elevators and by vibratory, star, and rotary plow feeders. 

TABLE 2-9 Guide to Selection of Dust Control Equipment  

Factors Cyclones Wet washers low energy Wet washers high energy Dry electro- static precipi- tators Wet elearo- static precipi- tators Aggre- gate filters Fabric filters Fibrous Filters 

High inlet burden / y care care care y beware 

Sticky beware care y beware beware care 

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Flow Regimes Flow on chutes Filling hoppers Emptying hoppers Bulk conveying Feed off the end of belt conveyors... 

Spray Drying and Agglomeration. Most instant coffee products are spray-dried. Stainless steel towers with a concurrent flow of hot ak and atomized extract droplets are utilized for this purpose. Atomization, through pressure nozzles, is controUed based on selection of the nozzles, properties of the extract, pressures used, bulk density, and capacity requkements. Low inlet ak temperatures (200—280°C) are preferred for best flavor quaHty. The spray towers must be provided with adequate dust coUection systems such as cyclones or bag filters. The dried particles are coUected from the conical bottom of the spray drier through a rotary valve and conveyed to bulk storage bins or packaging lines. Processors may screen the dry product to... 

The bulk soHds conveying industry is interwoven with all aspects of the chemical industry, from mining of raw materials to in-process handling and to final product dehvery. The 1987 value of U.S. product shipments of bulk conveyors and parts was 2.11 biUion according to CEMA. Lists of conveyor manufacturers in the United States (49—51), and worldwide (52) are available. 

Eocus Conveying Belt Technology," Bulk Solids Handling (Nov. 1991). 

H. Cohjn, Mechanical Conveying for Bulk Solids Elsevier, Amsterdam, 1985, pp. 236—328. 

M. V. Arastoopour, M. V. Modi, D. V. Punwani, and A. T. Talwalker,M Keview of Design Equations for Dilute Phase Gas-Solids Hori ntal Conveying Systems for Coal and Belated Material, Powder and Bulk SoHds Conference, Philadelphia, 1979. 

The capacity of a pneumatic-conveying system depends on (1) produc t bulk density (and particle size and shape to some extent), (2) energy content of the conveying air over the entire system, (3) diameter of conveying hne, and (4) eqmvalent length of conveying hue. 

TABLE 21-13 Air Velocities Needed to Convey Solids of Various Bulk Densities ... 

Because of the railroad-car shortage that has persisted for many years, boxcars are often used for bulk materials. Lined with suitable materials to prevent contamination and with special bulkheads at each door, these cars are acceptable substitutes for covered hopper cars even though unloading is more difficult. Vacuum conveying wands are used to pick up the material, as are front-end-loader-type vehicles. 

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