Creating paper chains

Waste conversion technology is helping paper mills promote sustainability in several links of the papermaking chain.

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

Papermakers, however, have financial as well as community and customer relations reasons to seek out sustainable methods that conserve resources and minimize waste. Energy-from-waste (EFW) technologies are foremost among the options available. The paper industry has found several ways to tie into EFW technologies.
 

Fully 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 waste-to-energy (WTE) systems as a way to further their sustainability goals, reduce emissions and decrease 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 website states. “At pulp and paper mills, fossil fuel and purchased energy use per ton of product decreased by 25.4 percent between 1990 and 2012.”

Swedish researchers tout CHP technology improvement

Researchers at Chalmers University of Technology in Sweden say they have demonstrated that using an ilmenite-based fluidized bed material improves the combustion efficiency of waste and biomass while decreasing operating and maintenance costs. In collaboration with Germany-based energy supplier E.on, the researchers say they “have proven the concept in today’s commercial boilers.”

The findings make combined heat and power (CHP) technology, often used at paper mills, “highly interesting both from a profit and a climate perspective, and open [the way] for smarter next generation designs,” according to a press release issued by the university.

From November 2014 to May 2015, researchers at Chalmers University and E.on personnel conducted testing with the new bed material at the Handeloverket CHP plant in Norrkoping, Sweden.

Fluid bed material in the form of sand is used to even out heat fluctuations and make the combustion of fuel more efficient. In one of the plant’s five boilers, the silica sand normally used was replaced with an ilmenite-based bed material. The iron-titanium mineral ilmenite and other metal oxides demonstrated that they “have a clear advantage compared to regular sand,” say the researchers.

Ilmenite materials “can transport oxygen inside the combustion chamber from places where there is an abundance of oxygen to places where there is a depletion in oxygen. When oxygen-carrying bed material is circulated inside the chamber, mixing with the fuel, the oxygen is distributed evenly in time and space,” according to the Chalmers researchers.

“This brings forth an array of positive effects, which testing completed in Norrkoping confirms,” says Fredrik Lind of the Department of Energy and Environment at Chalmers University, who also served as the project’s coordinator. “The combustion becomes more uniform and efficient. The boiler’s total efficiency increases. The emission of carbon monoxide is lowered radically, as are problems related to ash fouling.”

The utility firm E.on is making arrangements to use the new ilmenite-based bed material in two boilers in Norrkoping later in 2015, and has several other plants in line for consideration. “This is the biggest improvement I have experienced,” says Bengt-Ake Andersson, adjunct professor in combustion technology and a senior specialist at E.on, who says he has worked with fluidizing bed technology for many years. “[It is] a little like placing a turbo charge to the process.”

A video with additional details on the new process is available at https://vimeo.com/141717645.

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,” AF&PA says.

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 company’s mill in Rothschild, Wisconsin, was cited by AF&PA 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 paper industry’s ability to use its residuals and byproducts as an energy source has been made possible by the willingness of equipment makers to research and develop technology to make the process feasible and cost-effective.
 

Investing to sustain

A 2015 technical article prepared 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 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 the plastic, metal and other contaminants that can be found in the scrap paper bales shipped to 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,” write the Andritz duo.

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 calls “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 it says are “well suited for biomass and alternative fuels, with high combustion efficiency.” With both pyrolysis and combustion processes, “complex waste products can be converted,” write 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.” Andritz 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 this stream, however, can be prepared for conventional recycling.

Equipment provided by Andritz and other manufacturers addresses how to prepare these and other byproducts as boiler and power system feedstock, as the density, size and shape of the feedstock can be critical specifications affecting whether an EFW system is efficient.

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

  • pulper rags, pulping rejects, and coarse screening rejects;
  • sludge from deinking systems, paper machine loops, make-up water treatment and sedimentation;
  • sludge from biological wastewater 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 continue to work with paper mill operators on energy feedstock preparation systems for sludges and other byproducts that must be dried before being turned into pellets.

While the paper industry is a basic materials sector with a history that goes back centuries, it has proven both willing and adept at embracing newer and renewable EFW methods.


 

The author is an editor with the Recycling Today Media Group and can be contacted at btaylor@gie.net.

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