Kason classifier transforms waste into profit

Kason Corporation has reported how classifying equipment is helping a glass-recycling operation transform waste bottles and jars into profitable products and reduce landfill costs.

The plant is situated on the Isle of Lewis in Scotland's Outer Hebrides, and is run by the Western Isles Council.

The plant employs two basic processes: a glass-breaking and grinding system made by Glass Aggregate Systems, and classifying equipment from Kason Corporation that separates the glass into the desired sizes.

The classifier is the key element because it allows the plant to make relatively valuable products for the local market.

Incoming bottles are loaded into a hopper, from which they drop onto a vibrating tray that controls the flow of bottles onto a conveyor belt.

Although the system is designed for processing bottles that have been separated from other municipal waste, it can also remove metal cans, plastics and other material accidentally mixed with the feed.

First, ferrous metal is picked off the belt by a magnetic drum and sent to a dumpster.

The bottles and extraneous material are conveyed to a popper unit, which uses rotating hammers to shatter the glass into pieces no larger than 2-3in in diameter.

Next, a shearing unit (a rotating drum with a fixed blade) liberates the glass from paper labels and foil, after which the material flows onto a revolving cylindrical screen called a trommel.

The glass particles drop through the screen into a sanding unit and the rest of the waste continues across the screen and is ejected into a bin.

In the sander, the glass is ground into particles that have no sharp edges and range in size from about 0.75in to dust that is less than 0.12in.

Finally, the Kason classifier does the critical job of separating the glass particles into the necessary size fractions for the desired applications.

This is no easy task, since the material is abrasive and may blind screens, particularly if it is wet or contains residue.

The Vibroscreen classifier, as it is called, is a vibratory screener that consists of up to five circular, horizontal screens located one above the other in a vertical, cylindrical housing.

Mounted to the bottom of the unit is a high-torque, 1-HP gyratory motor with a double-extension shaft at both the top and bottom ends of the motor.

Eccentric weights are fitted to each extension to give the motor an imbalanced-weight gyratory motion.

The entire unit is supported on a circular base by rugged springs that allow the screen assembly to vibrate freely without transmitting vibration to the plant floor.

Material to be separated is fed onto the centre of the top screen, whose mesh is the largest.

Oversize particles are moved to the screen periphery in a spiral pathway, and discharged through an outlet, while undersize particles drop through to the next screen.

The mesh sizes become progressively smaller toward the bottom of the unit.

Separation is enhanced by the 3D motion generated by the unit's gyratory motor.

The motor's top eccentric weight generates a horizontal flow to the screen assembly, while the bottom weight creates a high-frequency tilt on the screens.

The combination of the horizontal and vertical movements creates a tangential action that moves oversize material laterally across a screen and encourages undersized particles to flow through the screen.

The machine can be optimised for a particular application by varying the mass of either eccentric weight.

In the Lewis installation, the Vibroscreen classifier is a 48in diameter unit with four screens that can process up to 3 tonnes/h of glass aggregate.

The top screen scalps pieces of glass >=0.51in, along with residual rubbish, and the other screens sequentially separate out glass particles >=0.39in, >=0.24in and >=0.12in.

Dust is collected at the bottom.

Material >=0.51in is used for decorative glass; >=0.24in glass for water filtration or road aggregate; and >=0.12in for weather protection in the cement walls of houses.

In the latter application, called 'rough casting', the glass particles are thrown against a wet cement wall and become embedded.

Particles >=0.12in can also be used for shot-blasting, as can the dust, which produces a smoother finish.

The Vibroscreen classifier uses screens made of a special stainless steel that resists abrasion.

Screen-blinding is precluded by means of a Kason 'Ball Tray Anti-Blinding Device' that utilises the multiplane inertial vibration of the screener to bounce elastomeric balls between the upper 'operating' screen and a lower coarse-mesh 'ball screen', thereby dislodging near-size particles from apertures of the upper screen.

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