Paper Recycle Mills

April 23, 1996

Paper recycling is not new: Vincent presses have been installed at two mills that are over fifty years old. At the same time there has been a large construction boom of paper recycling mills in the 1990's. The mills are scattered across the country, generally being located close to population centers. There are seventeen in Los Angeles alone.

Each of these mills specializes in recycling a specific kind of waste paper. The most common is OCC (old corrugated container). Most OCC mills avoid waxed corrugated or corrugated from the far east (because of its weaker fiber make-up). Other mills handle these sub-grades.

The other recycle mills are called deinking plants. They specialize in categories such as ONP (old newspaper), telephone directories, MOW (mixed office waste), magazines and MWP (mixed waste paper).

Each of these categories of waste paper presents special challenges and requires specific technology. Much of the chemistry has to do with ink. Ink manufacturers continuously improve their ink for better adherence to paper fibers, while the recyclers are focused on separating the ink from the fiber. Equally important to the paper recycler is the technology to separate the ink not only from the pulp fibers but also from the stream of usable fiber. The waste rejects frequently end up in a Vincent screw press.

Recycling high quality, glossy magazines presents special challenges. These magazines are generally made of one third kraft fiber for strength, one third ground wood fiber for economy, and one third clay coating for printing quality. The high proportion of clay in the waste stream can make it all but impossible for a Vincent press to operate correctly.

MOW is one of the least desirable forms of waste paper to recycle. The wide variety of contaminants, especially plastics, cause problems for the paper maker. Laser printer inks affect quality because they are thermally (opposed to chemically) bound to the paper fibers.

The common characteristic of recycle paper mills is that they generate a considerable load that most frequently goes to landfill. For example a 300 TPD OCC recycle mill will generate 10%, or 30 TPD (solids) of reject material. This waste is rejected by screens that sort out the cellulose fibers that can be used to produce acceptable pulp. Reject streams containing 1% to 2% solids can be fed directly into a Vincent press to reduce the solids to press cake.

Reducing the solids to press cake reduces the tonnage that must be hauled to landfill. Many landfills require at least 30% solids before they will accept loads of waste. An additional bonus is that pressing eliminates liquid drainage on the highway when the material is being hauled.

Some paper mills press the reject material in order to dewater it to the point where it becomes a suitable boiler fuel.

Issue 42