Conveyors power

Determine the materialfactor for the conveyor. A material factor is used in the screw conveyor power input computation to allow for the character of the substance handled. Table 6.40 lists the material factor for dry ashes as F = 4.0. Standard references show that the average weight of dry coal ashes is 35 to 40 lb/ft3 (640.4 kg/m3). 

The total conveyor power requirement is then 15.6 + 3.7 = 19.3 kW. A 25-kW drive might be appropriate if it meets the requirements of the next subsection. 

Minimize the need to push or pull. Use gravity to move material whenever possible. (Use conveyors, power trucks, lift tables, turn tables, or gravity slides/chutes whenever possible). 

Powered Conveyors. These are designed for continuous control of products on level surfaces, through inclines and dechnes, and around curves. Many powered conveyors are equipped with a computerized control system to provide tracking and diagnostics. Basic considerations for powered conveyors are the same as for gravity conveyors. Powered roller and belt conveyors are the major powered types used to move unit loads. 

Belts (conveyor, power Strength, stiffness, hydrolytic... 

Fig. 4. Top and front views of typical high power conveyor-type industrial microwave equipment.

Harvested and defivered whole, the trees are dried ia an air-supported fiber glass dome stmcture over a 30-d period by usiag waste heat from the combustioa process ia the adjaceat plant (Pig. 5). Trees leave the dome on the conveyor and, at the boiler wall, batches ate cut iato sectioas to fit the boiler. These sectioas are about 8.5 mloag for the 100-MW facility studied by EPRI and the Mianesota Power Light Company. 

Power for each Hquid and the soHd phase must be added to get Pp. P, the soHds process power, = T -AN for scroU decanters, where = conveyor torque and AN = differential speed between bowl and conveyor. Pp is the friction power, ie, loss in bearings, seals, gears, belts, and fluid couplings. P, the windage power, = K and fi = viscosity of surrounding gas p = density of gas D = rotor outside diameter N = rpm and K = shape... 

Manually adjusted screw or ratchet take-ups that adjust the position of the tail pulley to control belt tension can be used on relatively short, light duty conveyors. Automatic take-ups are used on conveyors over about 25 to 30 m long. The most common is the weighted automatic gravity take-up (see Fig. la). Other types of automatic take-ups have hydrauHc or pneumatic powered devices to adjust a snub pulley position and maintain a constant belt tension. The requited take-up movement varies according to the characteristics of the belt constmction and the belt length. Typically, take-up movements for pHed belts are 2% to 3% of the center distance between head and tail pulley, and about 0.5% for steel cable belts. The take-up movements requited for soHd woven belts are usually shorter because of the lower elastic stretch. Take-up requirements for a particular situation should be confirmed by the belt manufacturer. 

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. 

Power to Operate a Screw Conveyor. The power required to operate a screw conveyor is dependent, to a large extent, on the handling characteristics of the material to be transported. Formulas for calculating power use empirically derived factors to account for the conveying characteristics of specific materials, the configuration of the screw, and the beating friction. These formulas have been developed by CEMA and can be found ia the hterature (24,25) and ia engineering handbooks. It is assumed that the total power is equal to the sum of the power required to overcome friction and the power required to transport the material. 

The weight of material in the buckets on the loaded side of an elevator chain causes the elevator to momentarily mn backwards if, during operation, the power is intermpted or there is a failure in the driving system. Because this could be a ha2ard to operating personnel, as well as damage to the elevator, a backstop, similar to that described for a belt conveyor, should be used. 

Excitation can also be suppHed by an electromagnetic exciter that uses a rectified, pulsed a-c power supply, or a-c supply to an apposed electromagnet/permanent magnet drive. These units operate at very short strokes and frequencies of 50 to 60 Hz. Although designed primarily as feeders, they are occasionally used as short conveyors. 

These devices are replacing the older tank and spiral-conveyor devices. Better provisions for speed and ease of fill and discharge (without powered rotation) minimize downtime to make this batch-operated device attractive. Heat-transfer coefficients ranging from 28 to 200 W/(m °C) [5 to 35 Btu/(h fF °F)] are obtained. However, if caking on the heat-transfer walls is serious, then values may drop to 5.5 or 11 W/(m °C) [1 or 2 Btu/(h fH °F)], constituting a misapplication. The double cone is available in a fairly wide range of sizes and construction materials. The users are the fine-chemical, pharmaceutical, and biological-preparation industries. 

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