Belt lift

FIG. 19-41 Types of lifting magnets, (a) In-line lifting magnet, (b) Cross-belt lifting magnet. Courtesy ofEriez Magnetics.)... 

Service to large structures may require an elevator or traveling belt lift. 

Exhibit 12-4 shows a traveling belt lift. This device consists of an electric drive belt with steps and hand grips. It is constantly in motion at a slow rate. The lift provides rapid access to a large structure without the need for a standard elevator. 

The same idea has been described except it does not lift the top half of the pressure compartment but opens and closes Htde gates for the belt to pass through (20). This filter is proposed for dewatering of fine coal in particular. 

Fig. 3. Suspended magnets, where A = conveyor belt width B = suspension height C = overall height D = distance to magnet centerline and E = location of lift point, (a) Manually cleaned over conveyor mn system, (b) manually cleaned over head pulley, and (c) self-cleaning separator over head...

Hydrauhc transport is used in mines and for lifting coals to the surface in Russia, Poland, and France. Pneumatic transport of coal is used over short distances in power plants and steel mills. The longest (14.5 km) single flight conveyer belt in the world near Uniontown, Kentucky, has a capacity of 1360 t/h. 

Power. The power requited to drive a belt conveyor is derived from the tensile forces requited to propel or restrain the belt at the design speed. These include the tensile forces produced by the frictional resistance of the drive, conveyor components, and material the acceleration of the material and the gravitational forces requited to lift or lower the material. Detailed information and methods of calculation can be found in belt conveyor design handbooks and in Reference 9. 

Bucket Elevators. In a bucket elevator, a series of buckets attached to an endless belt or chain are filled with material and lifted vertically to a head pulley or sprocket, where the material is dumped. The buckets are then returned back down to a tail pulley or sprocket at the bottom. Bucket elevators are not self-feeding. They must be fed at a controlled rate to avoid overfilling the buckets and damagiag the machinery. In the usual arrangement of a bucket elevator, the chain or belt path is vertical or steeply inclined ia a single plane. Special chain supported bucket systems that can travel ia two and three planes have been developed. 

Fig. 7. Plant for spray-drying of detergents and soaps. 1, Burner 2, air combustion 3, cold air fan 4, hot air generator 5, spray-drying tower 6, cleaning ring 7, no22les circuit 8, tower suction cyclones group 9, tower suction fan 10, double-flap dischargers 11, recovery powder cyclone 12, recovery powder fan 13, belt conveyor 14, air lift 15, air lift suction cyclones 16, air lift suction fan 17, double-flip dischargers 18, vibrating sieve.

Conveyor-belt speeds above approximately 300 ft per minute (1.5 meters per second) impart sufficient momentum to material discharging at its head pulley to cause lifting of material streams in a trajectory from the head pulley. A trajectory is illustrated in Fig. 19-7. Blades of the sample cutter are positioned to intersect the trajectoiy. See Fig. 19-7 for an example of a linear-traversing bottom-dump cutter installation. Calculation of trajectory profiles are described in the Conveyor Equipment Manufacturers Association publications and similar references. 

Cross-belt magnetic separators are based on the same principle as lifting magnets. Although these units have relatively low capacities, the same unit can produce selective separations with different products by using different pole gaps and field strengths. (See Fig. 19-42.)... 

Bucket elevators are the simplest and most dependable units for making vertical lifts. They are available in a wide range of capacities and may operate entirely in the open or be totally enclosed. TFe trend is toward highly standardized units, but for special materials and high capacities it is wise to use specially engineered equipment. Main variations in quality are in casing thickness, bucket thickness, belt or chain quahty, and drive equipment. 

A second type of control required is that of the package or pallet itself as it is handled by conveyors and other equipment. This handling may consist of right-angle transfers in a vertical lift or of a set of restrainers on the sides of a belt conveyor. 

Exceptions to the preceding requirements would apply where explosionproof equipment is needed building ceiling heights are such that the standard 3.7-m (12-ft) lift is all that wih ever be needed and loads will never exceed 1 to 1.5 tons. Safety requirements for lift trucks are mandated by OSHA, by NIOSH (National Institute of Occupational Safety and Health), by State Depts. of Labor, and often by individual company standards. Among these requirements are backup-movement signals, seat belts, overhead framework for pro-... 

Flat-Belt Conveyors These powered conveyors can lift containers up inchnes. With the aid of special belt surfacing, grades may be quite steep. Belts also keep containers spaced out in exactly the way in which they are placed on the conveyor. However, because of the relatively high fric tion containers cannot be slid off belts by pushing devices. 

Reciprocating compressors are available with a large variety of other drivers, which include the piston engine, steam turbine, or, in rare cases, a gas turbine. Next in popularity to the electric motor is the piston engine. The arrangement lends itself to skid mounting, particularly with the semi-portable units found in the oilfield. The unit is also popular as a lease unit, which may be lifted onto a flat bed trailer and moved from one location to another as needed. The engine is either direct-coupled or. as with smaller compressors, it may be belt-connected. 

Where a vertical lift is required, the most widely used equipment is the bucket elevator, consisting of buckets fitted to a chain or belt which passes over a driven roller or sprocket at the top end. Bucket elevators can handle a wide range of solids from heavy lumps to fine powders and are suitable for use with wet solids and slurries. 

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. 

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