Pneumatic conveying conveyor types

Suitable feeds to a spray dryer are solutions or pumpable pastes and slurries. Such a material is atomized in a nozzle or spray wheel, contacted with heated air or flue gas and conveyed out of the equipment with a pneumatic or mechanical type of conveyor. Collection of fines with a cyclone separator or filter is a major aspect of spray dryer operation. Typical equipment arrangements and flow patterns are shown in Figure 9.14. 

The cutters in use in mechanical sampling are divided into diverter types and bucket types. Both types are used to cut a stream falling due to gravity off the end of a conveyor belt or from the discharge end of a pneumatic conveying pipe or a chute. 

Dense-phase conveying, also termed "nonsuspension" conveying, is normally used to discharge particulate solids or to move materials over short distances. There are several types of equipment such as plug-phase conveyors, fluidized systems, blow tanks, and, more innovative, long-distance systems. Dilute-phase, or dispersed-phase conveyors, are more versatile in use and can be considered the typical pneumatic conveying systems as described in the literature. The most accepted classification of dilute-phase conveyors comprises pressure, vacuum, combined, and closed-loop systems. 

For proper operation of a dilute-phase, pneumatic conveying system the solids fed into the pipeline must be carefully controlled. Two common types of feeders are the venturi feeder and the rotary valve or star feeder, illustrated in Figure 3.31. The venturi feeder is only suitable for low-pressure systems. The rotary valve feeder, also known as star feeder as described previously in this chapter is widely used for feeding medium-pressure conveyors. This feeder is efficient and simple in principle, but requires careful design in order to minimize air leakage. Excessive air loss from feeders, wastes power, causes dust, and leads to system instability. Rotary feeders work well on free-flowing, nonabrasive powders and special types are available for more difficult materials. 

Pneumatic conveyors may operate under pressure or suction, even within tiie same system (e.g., push/pull conveying). Both types are subject to similar hazards. Flammable materials are of particular concern and should therefore be transported by an inert gas. Inert gases should contain no caibon monoxide and have dew points low enough so that free moisture cannot condense or accumulate in the system. 

Airborne fine particulate matter that originates from its native powders but does not escape beyond the physical boundaries of the equipment in which it is conveyed, stored, hauled or processed. Examples of "non-fugitive" dust are dust particles that are air-suspended or carried in enclosed conveyors, such as bucket and screw type, pneumatic conveying systems silos covered bins and hoppers and tank trucks/railroad cars. It is reasonable to assume that dust clouds contained within an enclosed transfer point is "non-fugitive". Clouds of many combustible non-fugitive dusts present potential explosion hazard in a bulk material handling process. 

Different conveyors such as the belt, chain, and screw types, as well as pneumatic equipment, are used to transport bulk powdered foods. Conveyor belts are used for movement of different types of bulk solids at long distances. The belt and its load are supported on idlers on both conveying and return sections. The material can be discharged over the end of the belt either by using a diagonal scraper, by tilting one or more of the idler pulleys, or by using a tripper. 

Forced elevation (including horizontal paths) mechanism is often associated with pneumatic-type conveying systems and some high-speed specialty mechanical conveyor systems such as flexible screw conveyors. 

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