Sustainable production

Manufacturing paper is an industrial process that involves the use of water and energy and that results in emissions and (generally unwanted) residual materials.

Papermakers, however, have financial as well as community and customer relations reasons to seek out sustainable production methods that conserve resources and minimize waste. Energy-from-waste technologies are foremost among the options available.

In the selection of energy feedstock, during the papermaking production process and in the handling of residuals and byproducts, the paper industry has found several ways to tie into energy-from-waste technologies.
 

Closing loops

When the American Forest & Paper Association (AF&PA), Washington, produces an annual sustainability report, it can point to the industry’s widespread and long-established practice of recycling (repulping) discarded paper and converting it into new paper as an accomplishment.

Increasingly, paper mill operators also are incorporating different waste-to-energy systems as a way to further their sustainability goals, reduce emissions and decrease their reliance on fossil fuels.

In its 2012 Sustainability Report, the AF&PA wrote, “According to the U.S. Department of Energy (DOE) Energy Information Agency (EIA), the forest products industry produced 33.7 percent of CHP (combined heat-and-power system) power generated by [all] manufacturing facilities.”

The feedstock powering the paper industry’s turbines also has changed dramatically in the past quarter century. “Over time, the industry has shifted away from reliance on fossil fuels toward [the] use of biomass manufacturing residuals,” the AF&PA states on its website. “At pulp and paper mills, fossil fuel and purchased energy use per ton of product decreased by 25.4 percent between 1990 and 2012,” the association says.

Subsequently, forest and paper products facilities accounted for 62 percent of the renewable biomass energy consumed by all manufacturing industries in all sectors in 2012, according to the AF&PA.

“On average, about 66 percent of the energy used at AF&PA member pulp and paper mills is generated from carbon-neutral biomass, which is made from manufacturing residuals that do not end up in finished products, including spent pulping liquors, bark, wood, wood scraps, wood byproducts and process residuals,” according to the association.

Among the paper manufacturers enacting this strategy has been Montreal-based Domtar Corp., which says 77 percent of its power is derived from biomass, including wood residuals such as bark, biofuels and black liquors (a thick liquid byproduct from the kraft papermaking process).

The AF&PA cited the company’s mill in Rothschild, Wisconsin, for its partnership with a public utility that “resulted in replacement of several old boilers with a new biomass-fueled cogeneration system that created 150 jobs to provide fuel, 450 jobs at the mill, a 30 percent reduction in boiler air emissions and direct payments to the community and county.”

The ability of the paper industry to use its residuals and byproducts as an energy source has been made possible by the willingness of equipment makers to research and develop new technology to make the process feasible and cost effective.
 

Investing to sustain

A 2015 technical article authored by Michael Waupotitsch and Regina Puschnig of Austria-based Andritz AG provides an overview of how existing (but in many cases relatively recent) technologies have been designed to help the paper industry convert byproducts into energy.

Waupotitsch, who is a vice president of sludge, reject and recycling for Andritz, and Puschnig, who is the marketing manager of the Andritz Pulping and Fiber Division, say technology adopted by the paper manufacturing industry “collects, treats and converts waste into energy or saleable byproducts,” helping paper mills reduce their dependency on purchased power and eliminating landfill costs, thus improving a mill’s profitability.

Among the residuals at paper mills that pulp recycled paper are plastics, metals and other contaminants that can be found in the scrap paper bales that are shipped to these mills. “In recycled paper mills, depending on the grade of the recovered paper, rejects can account for more than 10 percent of the raw material,” the Andritz duo writes.

While these materials are unwelcome as paper ingredients, some of them have stored energy value. “Rejects can contain burnable material with a considerable calorific value, such as plastics and textiles,” according to Waupotitsch and Puschnig.

“The opportunity is that it becomes economically attractive to recycle the mill waste,” they continue. “In this way, an internal fuel source is created, disposal costs are avoided, landfill volume is reduced and so is the burden on the environment.”

Andritz offers what it describes as “innovative pyrolysis technology for full recycling of plastic rejects and laminates (plastic-aluminum compounds)” at scrap-paper-fed mills.

Waupotitsch and Puschnig describe pyrolysis as “a chemical process—a technology for high-temperature heating of organic material in the absence of oxygen.”

In the traditional combustion boiler sector, Andritz provides boiler technologies that it says are “well-suited for biomass and alternative fuels, with high combustion efficiency.”

Using both pyrolysis and combustion processes, “complex waste products can be converted,” according to the company’s Waupotitsch and Puschnig.

Regarding mill rejects screened from recycled paper mill pulpers, Andritz says, “With few exceptions, practically all recycled paper rejects can be used as a fuel source.” The company says it has helped its customers do this by developing systems that “separate out contaminants that cannot be readily converted into energy.”

The metallic portion of a mill’s reject stream, however, can be prepared for conventional recycling.

Equipment provided by Andritz as well as by other manufacturers addresses how paper manufacturers should prepare these and other byproducts for use as boiler and power system feedstock because the density, size and shape of the feedstock can be critical factors affecting whether an energy-from-waste system operates efficiently and cost effectively.

Residual materials and byproducts that can be used in paper mill boilers include:

• pulper rags, pulping rejects and coarse screening rejects;
• sludge from deinking systems, paper machine loops, make-up water treatment and sedimentation;
• sludge from biological waste water treatment;
• raw sludge and sludge from fresh water treatment;
• bark and waste wood;
• forest waste and residuals; and
• other biomass, such as sawmill residuals, furniture industry scrap and demolition wood.

Equipment manufacturers around the world continue to work with paper mill operators on energy feedstock preparation systems for sludges and other byproducts of the paper manufacturing process that must be dried before being turned into pellets to fuel their boilers.

While the paper industry is a basic materials sector with a history that goes back centuries, it has proven to be both willing and adept at embracing renewable energy-from-waste technology.

The author is editor of Recycling Today and can be emailed at btaylor@gie.net. A version of this article ran in the November/December 2015 issue of Recycling Today Media Group’s Renewable Energy from Waste.