Elevators, bucket

Bucket elevators (a) centrifugal-discharge-spaced buckets, (b) positive-discharge-spaced buckets, (c) continuous bucket, and (d) super capacity continuous bucket. 

Bucket elevator horsepower for spaced buckets and digging boots can be calculated using the following equation  

For continuous buckets with loading leg, the horsepower can be calculated by 

In Equations 3.24 and 3.25, T is the bucket capacity in tons/h and H is lift in meters. Both equations include normal drive losses, as well as loading pickup losses, and are applicable for vertical or slightly inclined lifts. For estimating purposes, tables and design graphs can be consulted in reference books, such as Green and Perry (2008). 

Elevator buckets are bolted to one or two strands of endless earrying chain. Material is loaded into the buckets via a hopper and loading leg at the boot in a eontinuous elevator, or is scooped up by the buckets as they round the lower sproeket in a eentrifugal disehaige elevator. The material is discharged by centrifugal foree or gravity as the buekets overturn at the head sprocket 

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Cmshed stone is conveyed by a mbber-belt conveyor and bucket elevator. Fine stone and dust are conveyed by enclosed screw conveyors, air slides, or pneumatic air systems into storage bins and tank tmcks for shipment. For screening, changeable vibratory screens predominate for all sizes from 23 cm to 0.074 mm (200 mesh). Most stone is stored uncovered on the ground in conical stockpiles, suppHed by radial belt conveyors. Such a conveyor can maintain four stockpiles of different sized stone. Large commercial plants typically stockpile stone in 10 sizes ... 

Fig. 13. Schematic of precipitated sihca production (54), where H =, eg, reactor, washer, filter, and dryer Q = pump or transfer device, eg, bucket elevator...

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. 6. Bucket elevators (a) centrifugal (b) continuous (c) positive (d) internal discharge (e) super capacity and (f) cement mill.

Bucket elevators, skip hoists, and cranes are used for top feeding of the furnace. Retention and downward flow are controlled by timing of the bottom discharge. Gases are propelled by a blower or by induced draft from a stack or discharge fan. In normal operation, the downward flow of sohds and upward flow of gas are constant with time, maintaining ideal steady-state conditions. 

Continuous Percolators Coarse sohds are also leached by percolation in moving-bed equipment, including single-deck and nmlti-deck rake classifiers, bucket-elevator contactors, and horizontal-belt conveyors. 

The Bollman-type extractor shown in Fig. 18-76 is a bucket-elevator unit designed to handle about 2000 to 20,000 kg/h (50 to 500 U.S. tons/day) of flaky solids (e.g., soybeans). Buckets with perforated... 

Lift can usually be handled most economically by vertical or inclined bucket elevators, but when lift and horizontal travel are combined, other conveyors should be considered. Conveyors that combine several directions of travel in a single unit are generally more expensive, but since they require only a single drive, this feature often compensates for the added base cost. 

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. 

Continuous-Bucket Elevators These elevators (Fig. 21-5c) are generally used for larger-lump materials or for materials too difficult... 

The most common chain conveyor is the bucket elevator already discussed, but there are a wide variety of special chain conveyors which are used so infrequently that they shoiild be selected only on the specific recommendation of a quahfied materials-handhng engineer. 

TABLE 21 8 Bucket Elevator Specifications for CentrifugakDischarge Buckets on Belt, Malleable lron/ or Steel Buckets ... 

TABLE 21-9 Bucket-Elevator Specifications for Continuous Buckets on Chain ... 

Track hoppers are needed for some boxcar and bottom-dump-car shipments. Since boxcars discharge to one side, fairly light construction can be used for the hoppers, which are located to one side of the tracks. However, for bottom-dump cars, the hoppers must be located on the centerline of the tracks. This requires heavy track girders over a hopper and feeder conveyor pit, but hopper depth must be set to give sufficient angle for material to flow well. Belts or reciprocating-plate feeders commonly carry the material to the bucket elevator. 

Bulk alum can be stored in mild steel or concrete bins with dust collector vents located in, above, or adjacent to the equipment room. Recommended storage capacity is about 30 days. Dry alum in bulk form can be transferred or metered by means of screw conveyors, pneumatic conveyors, or bucket elevators made of mild steel. Pneumatic conveyor elbows should have a reinforced backing as the alum can contain abrasive impurities. 

Bins may be located inside or outside and the material transferred by bucket elevator, screw, or air conveyors. Ferric sulfate stored in bins usually absorbs some moisture and forms a thin protective crust which retards further absorption until the crust is broken. 

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. 

Bucket elevators are suited to vertical transport of sticky and abrasive materials. With buckets 20 x 20 in. capacity can reach 1000 cuft/hr at a speed of 100 ft/min, but speeds to 300 ft/min are used. 

Part 2 1975 Rubber and plastics belting of textile construction for use on bucket elevators. BS 1796 1989 Method for test sieving. 

Vessel (internal coils Bucket elevator and agitation)... 

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