Conveyors, cost

Cross-belt samplers of minimum size for 24-in (600-mm) conveyors cost approximately 15,000 with controls using an electric drive, and about 12,500 with pneumatic drive. 

Convex set in linear programming, 382 Conveyors, cost of 569-571 Coohng towers, cost of 810 COPE, 128... 

Solids. Increasing use of bulk cars, especially of covered hopper cars, has accompanied the expansion of the tank-car fleet. The principal drawback of bulk cars is the requirement for limited use, specialized cars, which necessitates a large investment. However, if such investment can be justified, the cost of transportation for dry bulk materials ia hopper cars usually is less than those for goods ia shipping containers. In many instances, such cars are used in closed-loop service that is, they shuttle in unit trains between filling and discharge points. Similar equipment is also used in specialized highway vehicles whose tmck bodies can incorporate dump hoppers and built-in conveyors. 

A drag chaia coaveyor coasists of a single strand of endless cast or welded steel chain that pushes or drags material through a trough. It is a simple, low cost conveyor for handling ash, coal, hot clinkers, and scrap waste materials. A variety of cast iron, cast steel, and welded steel chains are used for these conveyors. 

Operating costs will include 5 to 10 percent of one worker s time, plus power and fuel required. Yearly maintenance costs will range From 50 to 10 percent of total installed costs. Total power for fans, dr er drive, and feed and prodirct conveyors will be in the range of 0.5 D to 1.0 D". Thermal efficiency of a high-temperature direc t-heat rotary dryer will range from 55 to 75 percent and, with steam-heated air, from 30 to 55 percent. 

In general, this equipment offers an economical heat-transfer area for first cost as well as operating cost. Capacity is hmited primarily by the air velocity which can be used without excessive dust entrainment. Table 12-32 shows hmiting air velocities suitable for various sohds particles. Usually, the equipment is satisfactory for particles larger than 100 mesh in size. [The use of indirect-heated conveyors eliminates the problem of dust entrainment, but capacity is limited by the heat-transfer coefficients obtainable on the deck (see Sec. 11)]. 

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. 

Initial cost of a conveyor system is usually related to life ejqjectancy as well as to the flow rate chosen. There is a great temptation to overdesign, which should be resisted. The first really longdistance belt conveyor was designed and fabricated to extremely hi standards of quality. After 35 years it was still in operation with almost all its original components. Had this operation been planned for only... 

Comparative costs for conveyor systems can be based only on studies of specific problems. For example, belt-conveyor idlers are available in a range of quahties that may make the best unit cost three times as much as the cheapest. Bearing quahty, steel thickness, and diameter of rolls all affect cost, as does design for easy maintenance and repair. Therefore, it is necessary to make cost comparisons on the basis of a specific study for each conveyor application. 

The silicon-controlled rectifier with a dc motor has become predominant in adjustable-speed drives for almost all commonly used conveyors when speed adjustment to process conditions is necessary. The low cost of this control device has influenced its use when speed synchronization among conveyors is required. This can also be done, of course, by changing sheave or sprocket ratios. 

The closed-belt conveyor is not readily adaptable to the handling of sticky materials, and special designs may be required for materials which are highly susceptible to aeration. Initial cost per foot is relatively high because of belting cost, but power requirements are low and with proper instaUation and maintenance belt life is good. 

Slide Conveyors Simple gravity slides and spiral chutes, while not technically conveyors, are widelv used with conveyor systems or as separate units for lowering materials from one floor to another. They are low in cost and require httle floor space if slopes are held at fairly steep angles. However, they must be used only after a careful study... 

Chain Conveyors These devices for handling containers are available in either roller-chain designs or less costly types. There is a variety of slat conveyors that use both single and double strands of roller chain, as well as a slider type using cheaper chain. In general, slat chain conveyors are used only on loads which are too heavy for economical handling by belt, roller, or wheel units or which have odd shapes not suitable for roller or wheel units. They are particularly adaptable to pallet handhng, as are simple open strands of chain with flat-surfaced attachments. 

On small installations an elevated tank above the furnace would be used (refer to Figure 37). The savings from eliminating the pumps, valving, and slurry lines are offset by the additional cost of a structure to support the tank and a rotary feed valve. The tank is fitted with a screened overflow. A dewatering screw conveyor is used for feeding the furnace. 

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