Bucket elevators costs

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. 

Materials-handling equipment is logically divided into continuous and batch types, and into classes for the handling of liquids, solids, and gases. Liquids and gases are handled by means of pumps and blowers in pipes, flumes, and ducts and in containers such as drums, cylinders, and tank cars. Solids may be handled by conveyors, bucket elevators, chutes, lift trucks, and pneumatic systems. The selection of materials-handling equipment depends upon the cost and the work to be done. Factors that must be considered in selecting such equipment include ... 

Conveying equipment. Cost of apron conveyors and bucket elevators. 

Use of the 18-in. spacing between the concentric rings of holes in the catalyst-flow plates of the commercial TCC units ensures uniform catalyst flow at all points higher than 27 in. above the top plate. Catalyst-flow rate in a given plant is relatively inflexible. Moreover, the design catalyst-circulation rate is limited, principally because of the cost of mechanical bucket elevators, to values of 1.5 to 2.5 times the oil-feed rate (51). These catalyst/oil ratios correspond to catalyst-circulation rates of the order of 100 to 150 tons/hour in a 10,000-barrel/day unit. Typical catalyst velocities are 6 to 12 in. per minute in the reactor and regenerator, and 1 to 2 ft. per second in catalyst-carrier lines (241). 

An innovation introduced on Houdriflow units was a continuous system for transferring fresh catalyst in bulk from ground level to the storage bin by means of a high-velocity air stream (8,31). This system replaced the slower and more costly bucket-elevator system previously employed. Attrition and breakage of the catalyst are said to be negligible. 

To illustrate the method of arriving at the total cost of operating a bucket elevator, the following typical example may be taken. 

Like the swing bucket elevator, the continuous-flow conveyor can therefore move the material vertically as well as horizontally. The swing bucket elevator is expensive in initial cost and takes up a considerable amount of space, but has the advantages of low wear and little maintenance. Also, it can handle coarse lumps of material. On the other hand, the continuous-flow conveyor is used only for pulverized, fine-grained or flaky materials, which are carried along in a totally enclosed duct, so that there is no dust nuisance. It is to be noted that these conveyors are quite unsuitable for dealing with sticky, corrosive or ungraded materials with hard constituents. 

Example.—Required the net operating cost of a 100-ft. double-strand (two chain) elevator handling sand weighing 120 lb. per cubic foot. Elevator to have malleable-iron buckets and combination chains. Power delivered at elevator drive commanding a value of 3 cts. per horsepower. Elevator to be used 1,500 hr. per year. Capacity 25 tons per hour. 

---