Screen classifying cutter plays key role in leading-edge alternative energy projects

Since 1983, the University of Maine’s Process Development Center (PDC) in Orono has served the paper industry, providing leading-edge, collaborative pulp and paper research for companies throughout the U.S. Recently, the PDC expanded its scope into bioplastics, solid and liquid biofuels, nanomaterials and other technologies.

The process lab―originally part of the university’s forest and paper industry program - houses a virtual “mini” paper mill with a broad range of processing equipment. The PDC employs 12 and is self-sustaining by virtue of its contract work with multiple clients. While the lab’s primary work is still focused on the paper industry, new projects target alternative energy and recycling involving paper, wood, carpet, plastics, and other materials.

“Most of our work is by word-of-mouth from paper and chemical companies who have a problem and need to address their process,” said Mark Paradis, the PDC’s group leader of engineering. “Our equipment is flexible and can be adapted in order to provide these companies with a proof of concept.”

Size Reduction Plays Key Role
The PDC is well equipped to work with a range of raw materials including wood, bark, herbaceous crops, and agricultural residuals. Available processes include extraction, pulping, bleaching, papermaking, coating, and finishing. To facilitate its process work, the lab requires efficient size reduction capabilities to downsize materials into uniform particles. At the outset, the lab used a hammer mill―a conventional size-reduction method employed for decades―which was inefficient and failed to produce consistently sized particles due to its crushing and pulverising action. The PDC replaced it with a Screen Classifying Cutter model "SCC-10" from Munson Machinery, introduced by Munson’s New England representative Armac Inc., Lynnfield, Massachusetts. “We specified that unit because it efficiently reduces materials into uniform particle sizes with a lower energy requirement than the hammer mill,” said Mr. Paradis.

The PDC leased the Screen Classifying Cutter for two years before purchasing it. The unit proved effective at cutting hard, soft, and fibrous materials into controlled particle sizes with minimal fines at high rates for post-usage. It features a proprietary helical rotor design with dozens of cutter tips attached to a helical array of staggered holders called “interconnected parallelograms” to continuously shear oversize materials against twin, stationary bed knives.
Unlike conventional granulators containing a small number of angled rotor blades that slice materials into strips in scissor-like fashion, the SCC cutter is configured with cutter tips along the entire shaft, with no gaps between tips, making total contact with the product. As a result, the material is cut into uniform particles with minimal fines or imperfections, and with little to no heat generation.

The rotor design is said to generate six times greater force per centimetre with each cut than conventional knife-type cutters of equivalent power, contributing to uniform size reduction and reduced energy use.

Alternative Energy is Primary Target
In a 1.19 million Euro alternative energy project, perennial grasses and hay are being pelletised to make compressed biofuel pellets. Grass pellets are said to have the potential to establish a new bioenergy industry in Maine, creating a valuable crop for Maine farmers and reduced energy costs for residents. Several companies have expressed interest in operating biofuel production facilities and licencing the technology.

The SCC cutter plays a key role in the initiative funded by the Maine Technology Asset Fund. The cutter takes one-quarter of the hay or grass bale and reduces the material to 3.2 mm particles.
Similar biofuel projects are underway in the Northeast and Midwest involving pelletising of corn stalks and converting of hay bales into fire logs.

In another project, a University of Maine chemical engineering professor is developing a biodegradable golf ball partially composed of lobster shells. Here, the SCC-10 cutter reduces the shells to powder form.

The PDC is also working to develop cellulose insulation as a replacement for fibreglass in residential construction. Here, the Center has developed unique systems to clean and process recycled newspaper and cardboard before it is reduced. Both Munson’s SCC cutters and its Attrition Mills are being considered as size reduction solutions. The Attrition Mill granulates by means of a disk rotating against a circular grinding plate, producing particles within a relatively narrow size spectrum down to 200 mesh (75 microns). It is employed primarily for reduction of fibrous materials, but is also suitable for friable products. Mr. Paradis said the PDC is leaning toward the Attrition Mill because it can produce a fibrous, fluffy, “cotton candy” type product with an excellent R-value.

The SCC cutter requires minimal maintenance, according to Mr. Paradis.