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.
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 Händelöverket CHP plant in Norrköping, 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,” the researchers say.
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 Norrköping 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.”
He continues, “We are now sure that we are able to significantly lower the operational and maintenance costs in most of the thousands of fluidized bed combustor plants that are currently in use internationally.”
The utility firm E.on is making arrangements to use the new ilmenite-based bed material in two boilers in Norrköping later in 2015 and has several other plants in line for consideration.
“This is the biggest improvement I have experienced,” says Bengt-Åke 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.”
“One of the advantage [of ilmenite beds] is that it enables the burning of difficult fuels like coarse waste. This could become crucial in the future, if we are to meet our climate goals,” says Lind. A video with additional details on the new process has been posted to 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,” 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.
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