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Paper recycling plants require specific equipment to ensure a successful flow of operations and a quality product.
The procedure of transforming discarded residential and corporate waste product into new material begins by transporting the feedstock -- usually via a conveyor belt -- into a pulper where a mixture of water, caustic soda, hydrogen peroxide, sodium silicate, talc, soap and fatty acids is used to disintegrate the dry cellulose fibers and start the initial separation of inks. This is usually accomplished by means of mechanical rotation.
The caustic soda breaks down the fiber, while the soap and fatty acids trap some of the ink. The hydrogen peroxide serves as a bleaching agent. During this stage, some of the larger debris (plastic wrappers, etc.) is also removed.
The resulting mixture is then passed through a series of cleaners, fiberizers, separators and/or screens. These types of paper recycling equipment are known by many brand names, such as Turbo Separator, Combisorter, Cyclone Cleaner and many others.
Often utilizing centrifugal force in combination with a screen barrier, these separators propel heavier elements toward a reject outlet. With some machines, ultra-light rejects rise to the top of the raw pulp where they can be sifted off. Depending on the desired product quality and type, the raw pulp may pass through the sorters multiple times.
Following this primary screening stage, inks are usually still present in the mixture. To achieve their removal, the pre-screened pulp is passed through additional paper recycling equipment, namely flotation and wash cells. Here, more fatty acid and soap are added to react with the talc already present in the mix. A scum-like layer subsequently forms on top of the mixture and, when air is introduced, turns into a bubbly froth. The inky froth can then be skimmed off the top or is simply allowed to overflow off the pulp, which is then rinsed and passed through a secondary screening (using hydrocyclones and pressure screens) to remove the smallest of foreign particles.
A secondary filtration system, often using a rotary vacuum or disc filter, keeps the pulp fiber in constant suspension with a slow rotating motion. During this stage in the process the fiber is separated from its liquid suspension and collected by a filter cloth. The fiber is then air-dried in a vacuum. Mechanical scrapers or high-pressure water jets subsequently peel the fiber layer off the filter cloth.
The next type of paper recycling equipment the fiber must pass through – in an effort to thicken stock consistency -- is a dewatering press. At this time, the product is pumped into a tank where rotating motion presses the fiber against a drum covered with wire cloth. Any leftover liquid is forced through the porous steel contraption into the interior of the drum and subsequently carried away from the fiber, which in turn forms a layer on top of the wire cloth. Mechanical knives then scrape the remaining fiber off the cloth and the product emerges from the tank via a screw conveyor.
The screw feeder transports the fiber mat to its final paper recycling equipment stop – a disperger, where any residual wax or ink particles are finely dispersed with the help of steam. The final product is then bundled and ready for further distribution.
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