December 16, 2004 | General

Transforming Lumber Scraps Into Compost, Mulch And Fuel

BioCycle December 2004, Vol. 45, No. 12, p. 36
Gigantic piles of discarded wood – 500,000 tons – from a Maine paper mill are turned into mulch for soil products and boiler fuel for cogeneration.
Dan Emerson

NEARLY 30 years ago, when the paper mill now owned by South African-based Sappi Fine Paper began operating in Skowhegan, Maine, there wasn’t much of a market for the scraps of wood and tree bark left behind in the papermaking process. Rocks, dirt and pieces of scrap metal mixed in with the wood made it impractical to use as boiler fuel.
As a result, the pile of discarded organic material in Sappi’s mill yard grew to gigantic proportions – covering a 16-acre area, stacked as high as 40 to 50 feet. At its peak, the pile held an estimated 700,000 yards of reject wood, bark and dirt, weighing about 500,000 tons.
Needing more space for lumber storage, in 1994 Sappi hired a contractor to begin removing and screening the pile. This work was stopped after the 1996 season to allow Sappi to sell the accumulated “inventory” of mulch, according to Thomas Griffin, Sappi’s environmental manager. When the project was resumed a few years later, a contractor from New Hampshire was hired but didn’t work out. In 2002, Sappi hired a new contractor to handle the massive project – Ashland, Maine-based Maine Wood Recyclers, which began working on it in October of that year.
The mill, which began operation in late 1976, has a “slasher deck” which cuts full-length logs into 8-foot sections. The 8-foot sections are then conveyed to barking drums which remove the bark. The bark and purchased biomass are used to fuel two power boilers, providing roughly 60 to 75 percent of the fuel. “We burn all the bark we generate,” Griffin says, noting that the boilers also burn dried sludge which remains from the paper-pulp operation.
Sappi started the slasher-refuse pile “with every intention of reclaiming the bark and wood as fuel,” Griffin explains. “Maine Wood Recyclers has a good system for separating the rocks, wood and bark, grinding the wood and bark and giving us the material we can burn in the boilers,” along with the decaying organic material that is sold to Jolly Gardener, Inc. to make its mulch products. “About 25 to 30 percent of the bark is bark we can burn,” Griffin adds. Sappi also buys wood pellets from Canadian lumber mills and biomass as supplemental boiler fuel. Sappi uses the rocks and dirt reclaimed from the pile as fill at its site.
After two years (late October, 2004), Maine Wood Recycler’s Randy Shaw and his crew had removed and processed about two-thirds of the pile that he started reclaiming in 2002. Shaw estimated it would take another 18 months to finish the job. At the depth the crews have reached into the original pile, the wood and bark is about 30 to 40 percent composted material, Shaw estimates, with another 30 to 40 percent still-whole wood material, and around 15 percent oversized rocks.
A Kamatsu 220 excavator, a Kamatsu 380 loader and a John Deere 544 loader are used to dig into the pile and move material. The debris-filled material is fed into a CBI prescreener with a 3-inch scalping screen; 3 inch-minus material is removed as fines. A 6 by16 Construction Equipment Co. (CEC) Roadrunner double-deck screener is also used. CEC uses a ball deck cleaning system, which facilitates screening material that is wet and sticky. Larger pieces are conveyed to a hand-picking station, where rocks are removed. The remaining wood material is fed directly into a CBI 6000 grinder. Shaw also has a 4800 mobile grinder he brings in when necessary to catch up to the material flow. Six people are employed by Maine Wood Recyclers on the Sappi project.
Shaw says the main challenge posed by the Sappi project is “getting the wood from the pile ‘clean’ enough so it meets specs either as mulch or boiler fuel. Over the years, metal and other stuff got mixed in with the wood waste material, like machinery parts from the slashing and wood handling operations. There’s not a lot of it in there, but enough to do some damage.”
It’s not difficult for the crews manning the grinder to spot the metal debris so it can be removed to prevent equipment damage. “You can hear it coming,” Shaw comments.”It makes a racket” on the conveyor. Along the way, Shaw’s workers have found saw blades, pieces of pipe and a sledge hammer mixed in with the bark and wood. One unusual, unanticipated problem is that in cold weather, the steam rising from the warm, decaying pile obscures the crew’s vision; at times, “they can hardly see,” Shaw notes.
Maine Wood Recyclers uses two semi trucks with trailers that each hold 130 yards of material and one “chip truck.” Maine Wood Recyclers is hauling about 10 truckloads a day, with 30 to 35 tons of material in each load, Shaw reports.
When Sappi first contacted him about taking on the reclamation project, “the first thing we did was make sure we had markets for the material.” Some of the wood reclaimed by Maine Wood Recyclers is sold to local cogeneration facilities that produce electricity.
The fines and dirt removed from the pile are sold to Jolly Gardener. The Poland Springs, Maine-based company sells premium composted soils and soil amendments, including potting soil, topsoil, peat humus, organic humus, composted cow manure, dehydrated cow manure, and shrub and tree-planting mix.
Jolly Gardener has had a long-standing relationship with Sappi, having used the paper company’s discarded wood and tree bark for about a decade, according to Jolly Gardener vice-president Richard Morrison. The company buys the fines collected in the screening process by Maine Wood Recyclers and uses it in several bagged soil products with high organic content the company has been selling since the late 1980s.
In recent years, Jolly Gardener has been experiencing 5 to 10 percent annual growth in sales of its bagged soil products, according to Morrison. Most of it is sold to big-box retailers in New England. He has had a mutually beneficial relationship with Sappi, Morrison says. “It’s worked for everyone, using mill waste to recycle as a lawn and garden product. It makes a good product.” The wholesaler uses a third party to truck the material from Sappi’s plant to its facility. Sappi’s Griffin agrees saying, “We had a large pile of what seemed to be unusable material that with the help of Maine Wood Recyclers is being converted into very valuable products: wood fuel, garden mulch and compost.”

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