solid waste management (tka 4201) lecture notes 8

SOLID WASTE MANAGEMENT

UNIVERSITI MALAYSIA TERENGGANU

TKA 4201 SOLID WASTE MANAGEMENT

LECTURE BY: NAZAITULSHILA RASIT

Eng. Science Dept, Faculty Science & Technology

CHAPTER 8Processing Techniques

Necessary for the recovery of reusable and recyclable of waste.Waste management depend on:1. Reuse & recycling opportunities2. Available option for separation

Unit operation designed:1. To modify the physical characteristics of the

waste.2. To remove specific components and

contaminants from the waste stream.





Size reduction.Shredder.

Size separation.Vibrating, trommel, disc.

Separation.Density.Magnetic.

Densification.Balers.Can crusher.





Waste are mechanically reduced in size.Other terms: grinding and milling.Objective: to obtain a final product that is reasonably uniform and reduced in size in comparison with its original form.Common types are:1. Shredder2. Glass crusher3. Wood grinders





Most common types:1. Hammer mill2. Flail mill @ shredder3. Shear shredder

Other types of shredding devices:1. Cutters2. Cage disintegrators3. Drum pulverizers4. Wet pulpers









Hammermill

Very effective with brittle material.

Involve hammer which attached to a rotating elements and strike the waste as its enters.

The cutting action continues until the material is of the size required and falls out of the bottom of the mill.

Can be designed in either horizontal or vertical shaft configurations.





Hammermill





Flail mill

Similar to hammer mill but provides only coarse shredding, as the hammer are space apart.

Single pass devices, whereas material remains in a hammer mill until it will pass through the openings in the bottom grate.

Often used as bag breakers.





Flail mills





Shear shredder

Composed of two parallel counter rotating shaft with a series of discs mounted perpendicularly that serve as a cutters.

The waste material to be shredded is directed to the center of the counter rotating shaft.

The size of the waste material is reduced by the shearing or tearing action of the cutter discs.

The shredded material drop or is pulled through the unit.





Shear shredder





Glass crusher

Used to crush glass containers and other glass products.

Often crushed after it has been separated to reduce storage and shipping costs.

Can also separated optically by color but not commonly used at present because of high cost and unreliability of equipment.





Glass crusher





Wood grinders

Used to shred large pieces of wood into chips, which can be used as fuel and can be composed.

Tub grinders: large tub having a revolving upper section, and a stationary lower section containing a hammer mill.

The continuous stream of shredded material is carried away from the grinder by a conveyor.

The wood that has been ground in tub grinder is usually sorted by size.

Larger material used as biomass fuel or as a bulking agent in composting operations. Fine material is usually composted.





Tub Grinders





Also known as screening.Involves the separation of a mixture of materials into two or more size fractions.Can be accomplished dry or wet.Involve:1. Removal of oversize and undersize materials.2. Separation of light & heavy noncombustible.3. Recovery of paper & plastics from glass & metal.4. Separation of glass, grit and sand (combustible).5. Separation of rock & debris (construction site).6. Removal of oversized materials from combustion

ash.





Common types:1. Vibrating screens2. Rotary screens3. Disc Screens4. Density separation5. Magnetic separation





Vibrating screens

Used to remove undersized material from commingled SW and to process construction and demolition wastes.

Vibration motion (side to side, vertically or lengthwise).

Used to separate relatively dry materials such as glass or metals and for the removal of broken pieces of concrete from construction debris.





Vibrating screens





Rotary screens

Trommel screen: most common type

Used to separate waste into several size fraction

The material to be separated is introduced at the front end of inclined rotating trommel.

Small particles will fall through the holes in the screen (undersize).

Material retained by the screen is known as oversize.

Equipped with metal blades or teeth that protrude into the drum.





Trommel





Disc screens

Set of parallel horizontal shaft with spaced between each shaft.

The undersized materials to be separated fall between the spaces in the discs.The oversized material ride over the top of the discs as in a conveyor belt.

Spacing can be adjusted for various size.

Advantages of self cleaning and adjustability with respect to the spacing of the discs on the drive shaft.





Disc Screens





Density separation: Air classification

Widely used to separate light materials (paper, plastic) from heavier materials (ferrous metals) based on the weight difference of the material in air stream.

By introducing air stream with sufficient velocity into a system comprised of air classifier and cyclone separator.

Light materials will be carried away with the air while heavier materials will fall in the counter current direction.





Magnetic

Separation of ferrous metals from nonferrous by utilizing magnetic properties.Used to recover ferrous materials from source separated, commingled and shredded MSW.

Also to separate aluminum cans from tin cans or ferrous materials from combustion residue.

Can be used before or after shredding and before density separation.





Also known as compaction.Increase density of waste materials so that they can be more efficiently stored and transported.Several techniques:

BalingCan crusher

Performed for:1.Reduction in storage requirements2.Reduction volume for shipping3.Preparation of densified refuse derived fuels

(dRDF)





The end

solid waste management (tka 4201) lecture notes 8

Documents

science dept

solid waste management

waste material

nazaitulshila rasit

solid waste management

waste stream

recyclable of waste

size separation