In today's do-more-with-less economy, turning trash into fuel makes both environmental and economic sense. That's just what Lincoln Paper and Tissue is doing at its manufacturing mill in Lincoln, Maine. Every year, the company produces approximately 70,000 tons of commodity towels, napkins, and specialty napkin-grade tissue, along with another 75,000 tons of uncoated printing paper.
As part of its manufacturing process, all of the mill's liquid waste is pumped to its water treatment plant. The final step in the treatment process incorporates a dewatering screw press, which separates water from paper waste, chips, ash, bark, and other solids. The goal is to remove as much water as possible; Lincoln then uses these solids to mix with other fuel and power its boiler. The drier the solids, the higher the BTUs.
Lincoln generates about half of its electricity by burning the sludge along with wood, bark, and chips, fueling a biomass boiler that supplies steam to the pulp and papermaking process, as well as a backpressure steam turbine. The alternative to burning the sludge is trucking it to a local landfill, an option that is both expensive and contrary to the mill's environmental policy.
“The screw press is a vital part of our water treatment process,” says John Sutherland, Lincoln's utilities maintenance superintendent. “Reliability of the gearbox on this press is crucial for the mill. Downtime is very expensive, not only in terms of gearbox cost, but in man-hours and lost production. If the 60,000 pounds of sludge being dewatered each day is interrupted, costs could reach into thousands of dollars.”
The mill's screw press originally used a cycloidal-type gearbox, from which Sutherland recalls they “were lucky to get 12 months of operation.” He continues, “I was getting tired of replacing an expensive gearbox that underperforms and isn't repairable. Whenever we disassembled the cycloidal unit, in hope of repair, we'd find nearly a pound of metal sitting in the bottom of the gearbox and rollers broken in half. It was a total loss, as fixing it cost more than a new one. That's when I started looking at different solutions.”
Randy Bryant of Lane Conveyors and Drives, Brewer, Maine, Lincoln's local supplier for power transmission equipment, recommended the 300 Series Planetary reducer from Bonfiglioli Inc., Hebron, Ky. The recommendation was based on Lane's experience with these units on various skid steers used in the forest products industry. Bryant explains, “The ductile iron housings, tapered roller bearings, and internal splines give this reducer the shock load capability that make it the right box for the screw press application.”
Lane fabricated special feet for the gearbox as well as a “drop-in” base plate, modifications that allowed Lincoln to make a quick and painless transition from the cycloidal unit to the planetary model. By converting biomass solids and wood waste to steam and electricity, Lincoln saves more than nine million gallons of fuel oil, while also reducing annual greenhouse gas emissions.