Turning wood into a new product could boost a flagging lumber industry in northern Minnesota, and investigators at the Natural Resources Research Institute – University of Minnesota Duluth – are leading the way in perfecting the technology.
Using a process called torrefaction at their site in Coleraine, NRRI is converting biomass, primarily wood waste, into a direct replacement for fossil coal. Torrefaction can take virtually any kind of plant, dry it out, roast it and then form it into a shape to meet any furnace requirement – pellets, briquettes or bricks – so that power plants do not have to make costly modifications.
Torrefied biomass has much the same characteristics as coal with much lower levels of pollutants, and can be used as a co-feed with coal to allow power plants to reduce coal use and meet air quality standards. Rolf Weberg, NRRI’s executive director, said that NRRI’s focus is to help area industries evolve in a sustainable way while reducing business risk.
“We want businesses to invest in our region to create jobs for tomorrow and protect the environment,” Weberg said.
Kicking off in 2015 with a $1.9 million Xcel Energy grant, the project has met some roadblocks.
Delays, including a small fire in the fuel collector, have caused the NRRI to backtrack and revamp parts of the process.
“We can make torrefied material at any time, but we want to densify it and plan to get back to running that facility in the next two months,” said Don Fosnacht, NRRI associate director and the project’s principal investigator. Calling the setbacks part of the learning process, Fosnacht said that taking measured careful steps is critical to making their goal of large quantities of fuel for testing.
The idea started with the problem of woody biomass waste, like sawdust from lumber mills, but soon expanded to include switchgrass, substandard wood species and cattails as potential sources of fuel. Taking a comprehensive view, NRRI researchers say that in addition to supporting forest resource management, agricultural resources could play a role in the biofuel project.
Prompted by downturns in paper and strand board manufacturing, Fosnacht said the question of how to manage Minnesota’s forests, maintaining them for the logging industry and forest management, became pressing.
“Right now, we are underutilizing the available sustainable harvest. There is room to take a significant amount of new material that is not being used, and that directly supports the logging industry,” Fosnacht said, noting that just 50 percent of available forest materials that can be harvested is being cut. While pine, aspen, popple, hemlock are all potential material to convert to biofuel, NRRI researchers believe lower-quality species and wood waste give the best economic boost.
Using low-value wood to avoid competing with timber fit for lumber mills, torrefaction drives out the moisture and leaves behind a more carbon-rich material with an energy content similar to low-sulfur coal, or at darker levels of torrefaction, even sub-bituminous coal.
Without many of the polluting elements that plague coal (heavy metals, sulfur and phosphorus), developers call the feedstock carbon neutral as long as the forests are sustainably managed
Starting at a lab bench scale, Coleraine’s NRRI facility has now stepped up the game and is working to make biofuel at an industrial scale.
“The torrefaction system we have right now has the potential to produce about six tons of fuel per day, enough over a 10-day period to send out for testing at an industrial plant,” Fosnacht said.
Creating relationships with industrial partners is a key part of NRRI’s development plan, and when they are able to increase production, NRRI intends to send biofuel to Minnesota Power for testing.
“They are a collaborator and are interested in testing the material in their units,” Weberg said.
Another pathway that NRRI has been investigating is hydrothermal carbonization. Pairing nicely with the torrefied material, they take very wet biomass like invasive cattail plants and cook them into what the scientists are calling “energy mud.” Combustible and energy rich, the energy mud works well as an organic binder for the torrefied briquettes, making them better stand up to transportation.
The Coalition for Sustainable Rail has a formal relationship with NRRI in its quest for advanced biofuels and modern boiler-based electricity generators. An experiment with 500 pounds of biofuel sent to the Milwaukee Zoo this fall showed how much cleaner biofuel is, even to the naked eye. Used in the children’s steam-powered train ride, the coal-fired ride belched black smoke, while the biofuel exhaust could not be seen.
Fosnacht said Sustainable Rail’s original concept was to compete with diesel electric rail power. “The advanced boiler-generator system will accelerate faster and sustain speed longer than diesel electric,” said Fosnacht, who explained that the use of biofuel in a modern boiler generator could actually be a viable competitor with diesel electric power. He said the boiler-generation system currently in the works could also be used in third world countries to generate power and heat using readily available plant materials.
NRRI is getting ready to take biofuel to the next level: syngas, or synthesis gas. Working with SynGas Technology of Elk River, the torrefied material can be used in the process of fuel conversion that uses synthesis gas.
The process starts with a pile of wood waste, turns that into coal-like biofuel, then treats it to create syngas that can be used in the process to make higher value chemicals like diesel fuel, jet fuel, polymers and plastics.
An Xcel Energy grant of $2.3 million is funding the startup of a new pilot project that will bring a torrefaction reactor to be tested in Coleraine. Standing four stories tall, the new system will have biomass material fed in the top.
“We’ll be comparing the two technologies for ease of construction and efficiency,” Fosnacht said.
Torrefaction and hydrothermal carbonization are very efficient processes, requiring just 10 percent of the biomass’s available energy to make it into biofuel.
“That means we can still have 90 percent of the original energy after taking out water and light hydrocarbons,” said Fosnacht, who explained that biofuel’s energy efficiency, flexibility and low ash content are all characteristics that should make it attractive for coal plants that across the country are looking to change over to greater renewable energy sources.
Gaining national attention, as well as in Canada, Weberg believes the technology has a global relevance that makes it a good investment for Minnesota.