Transport Phenomena

CONVEYORSBySidraJabeen

Department of Chemical Engineering,University of Engineering & Technology Lahore Conveying is a term used to transport, transfer or transmit. Conveyor is a device that transports or transmits somethingConveyors are machines that transport material fed to them at controlled rate to desired location.

2Conveyors

Screw ConveyorBelt ConveyorBucket ElevatorsVibrating or Oscillating ConveyorPneumatic Conveyors

3Types of Conveyors

The screw conveyor is one of the oldest and most versatile conveyor types.It consists of a helicoid flight (helix rolled from flat steel bar) mounted on a pipe or shaft and turning in a trough.Power to convey must be transmitted through the pipe or shaft.Screw-conveyor capacities are generally limited to around 10,000 ft3/h.Screw conveyors can also be adapted to a wide variety of processing operations in addition to their conveying ability

4Screw Conveyors

Contd..Screw conveyor can be used for mixing, heating, cooling, and drying operations.A further advantage is the fact that the casing can be designed with a drop bottom for easy cleaning to avoid contamination when different materials are to be run through the same system.

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The belt conveyor is almost universal in application. It can travel for miles at speeds up to 1000 ft/min and handle up to 5000 tons/h. It can also operate over short distances at speeds slow enough for manual picking, with a capacity of only a few kilograms per hour. Belt-conveyor slopes are limited to a maximum of about 30, with those in the 18 to 20 range more common.Direction changes can occur in the belt path and must be carefully designed as flat bends.

8Belt Conveyors

Contd..Belt conveyors inside the plant may have higher initial cost than some other types.Temperature and chemical activity of the conveyed material play important roles in belt selection.Moisture can cause poor discharge conditions because of material sticking to the belt. 910

Bucket elevators are the simplest and most common 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.

11Bucket Elevator

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Most vibrating conveyors consist of a spring-supported horizontal pan vibrated by a any of the vibrating mechanism.The motion imparted to the material particles may vary, but its purpose is to throw the material upward and forward so that it will travel along the conveyor path in a series of short steps.

13Vibrating or Oscillating Conveyors

14Vibrating / Oscillating Conveyor

One of the most important material-handling techniques in the chemical industry is the movement of material suspended in a stream of air over horizontal and vertical distances ranging from a few to several hundred feet. Material is dropped into an air stream by a rotary air-lock feeder.The velocity of the stream maintains the bulk material in suspension until it reaches the receiving vessel, where it is separated from the air by means of an air filter or cyclone separator.

15Pneumatic Conveyors

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17Conveyor Selection

Selection of the correct conveyor for a specific bulk material in a specific situation is complicated by the large number of interrelated factors:

Capacity requirementLength of travelLiftMaterial characteristics

Capacity requirement is a prime factor in conveyor selection. Belt conveyors, which can be manufactured in relatively large sizes to operate at high speeds, deliver large tonnages economically. On the other hand, screw conveyors become extremely bulky as they get larger and cannot be operated at high speeds without creating serious abrasion problems.18Capacity Requirement

Length of travel is definitely limited for certain types of conveyors.The length limit on belt conveyors can be a matter of miles. Pneumatic conveyors are limited to 305 m (1000 ft); vibrating conveyors, to hundreds of meters or feet, Screw conveyors can travel upto 50 m.19Length of travel

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.20Lift

Material characteristics, both chemical and physical, should be considered, especially flow ability. Abrasiveness and lump size are also important. Chemical effects (e.g., the effect of oil on rubber) must be considered Moisture or oxidation effects from exposure to the atmosphere may be harmful to the material being conveyed and require total enclosure of the conveyor.21Material Characteristics

22Conveyors for bulk materials

Conveyor drives may account for from 10 to 30 percent of the total cost of the conveyor system, depending on specific job requirements.They may be of either fixed-speed oradjustable-speed type. 23

Conveyor Drivers

Fixed-speed drives are used when the initially chosen conveyor speed does not require change during the course of normal operation. In any event, the conveyor must be shut down while the speed change is made.

Adjustable-speed drives are designed for changing speed either manually or automatically while the conveyor is in operation, to meet variations in processing requirements.

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