Convey solids

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

Screw conveyors, also called worm conveyors, are used for materials that are free flowing. The basic principle of the screw conveyor has been known since the time of Archimedes. The modem conveyor consists of a helical screw rotating in a U-shaped trough. They can be used horizontally or, with some loss of capacity, at an incline to lift materials. Screw conveyors are less efficient than belt conveyors, due to the friction between the solids and the flights of the screw and the trough, but are cheaper and easier to maintain. They are used to convey solids over short distances, and when some elevation (lift) is required. They can also be used for delivering a metered flow of solids. 

Large diameter, melt-fed extruders are commonly used for the final devolatilization and pelletization of LDPE and PE copolymers in resin manufacturing plants. A full description of this type of extruder and process is provided in Section 15.3. Simulation of these processes is complicated by the multiple flights used in the design and the high H/W aspect ratios of the channels. The processes can be simulated from the feed hopper to discharge, however, since they are not required to convey solids and melt resin. This section will show the requirements and difficulties for simulating these processes. 

Figure 17. Continuous mixing of pneumatically conveyed solids and liquid...

As with a plasma-arc furnace, various gases and pneumatically conveyed solids have been added to the various types of a-c open-arc furnaces to decrease alloy loss, to stabilize the arc, and to decrease the noise level, but with mixed commercial success. 

When conveying solids with a low bulk density, high fill rates in the intake zone can cause fluidization, if the air that is drawn in cannot escape from the extruder. This can be avoided by a partially filled downstream plastification zone (e. g., with conveying kneading blocks) and a vent opening installed downstream of the plastification zone. 

Pumping Liquids Compressing Gases Conveying Solids... 

Although waste is considered as a material, in fact it is a mixture of materials, each one having its own handling characteristics, somehmes entirely different than those of the other components. There are several handling systems used to convey solid waste. The most widely used are steel plate, belt and vibrating conveyors, bucket elevators, and pneumatic systems. 

In this section, we consider gas moving equipment for pressure service and then for vacuum liquid moving equipment. Then, two-phase flow is considered in Section 16.11.2.4. Hydraulic conveying of solids is discussed in Section 16.11.2.5. Conveying solids is considered in Section 16.11.2.6, while Sections 16.11.2.7 and 16.11.2.8 address piping and steam. 

Shaft furnaces are usually refractory-lined vertical cylinders, in which gravity conveys solids and liquids to the bottom and by-product gases to the top. Examples are cupolas, blast furnaces, and lime kilns. 

For the flowability, use the Johanson indices to characterize dry particles (see also related topics conveying solids. Section 2.6, storage bins. Section 10.3, mixing. Section 7.4) These indices are ... 

Negative pressure dust control and pneumatic conveying systems usually have the exhaust fan on the clean air side of the dust collector or filter receiver, especially if the dust or conveyed solids are combustible. NFPA 654, Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing and Handling of Combustible Particulate Solids , permits the passing of combustible particulate solids through a fan or blower under certain conditions. See NFPA 654, 2006 Edition,... 

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