A new drum dryer safety initiative led by the Wood Pellet Association of Canada breaks down silos among industries and sectors, bringing together key insight to develop best practices
By Lisa Gibson
BIOGAS/RNG Accelerating a Cleaner Future
An RNG producer and distributor is helping decarbonize heavy-duty engines with low-carbon-intensity fuel.
By Katie Schroeder
Biofuels in the Twin Cities
The International Fuel Ethanol Workshop and Expo drew nearly 2,500 attendees with stakes in the ethanol, biobased diesel, sustainable aviation fuel and carbon capture industries to Minneapolis in mid-June.
By Anna Simet
ADVERTISER
BIOGAS/RNG Advancements and Opportunities in Codigestion for RNG Projects
The U.S. EPA’s new set rule unlocks potential for higher revenue streams through renewable identification number generation under the federal Renewable Fuel Standard.
By David Lindenmuth
32 FEEDSTOCK
Enhancing Pellet Quality: Advanced Preprocessing Techniques for Corn Stover
Corn stover’s potential as a biofuel feedstock is limited by considerable compositional variability, but advanced preprocessing techniques can significantly improve pellet performance and consistency.
By Zachary P. Smith
ANNA SIMET EDITOR asimet@bbiinternational.com
RNG a Biomass Bright Spot
Last week, Bioenergy Europe released its annual Statistical Report on Pellets, which analyzes the development of the world pellet market, with a main focus on Europe. One of the core findings was that the production and consumption of pellets has “stagnated worldwide, breaking a two-decadelong trend of uninterrupted growth.”
This is attributed to numerous factors, including higher input prices—for example, electricity costs for producers, which inflates the cost of pellets—falling industrial demand, and a record warm winter with “shockingly fewer” heating degree days than average.
As for positives, the report highlighted the residential market as remaining strong. Data indicates that in 2023, the share of residential and commercial consumption of pellets reached 59%, the highest in a decade.
Speaking of residential markets, in just a few days, I will be traveling to the Pellet Fuels Institute’s Annual Conference, where they will be one of the main discussion topics. The opening panel, “A Statistical Review of Domestic and Global Wood Pellet Markets,” features Connor Murphy of the U.S. EIA, Tim Portz of the PFI and Gilles Gauthier of Hawkins Wright, and I suspect I’ll hear more about the challenges discussed in the report. Be sure to watch Biomass Magazine online for future coverage of the panel and event.
As for content in this issue, as we do every year, we’ve highlighted the topic of safety and fire and explosion protection. Our page-14 feature, “Working Toward a Common Goal,” by contributing writer Lisa Gibson, discusses at length an ongoing campaign, largely driven by the Wood Pellet Association of Canada, to improve drum dryer safety and reduce incidents associated with their operation. Drum dryers are a critical component of many biomass operations, and it’s gratifying to see so many rally behind this effort to share information, educate operators and determine if there are any design improvements that can be made to enhance their overall safety record.
Moving to renewable natural gas (RNG), our page-20 feature, “Accelerating a Cleaner Future” by associate editor Katie Schroeder, takes a dive into the role Clean Energy Fuels has made in expanding the availability of RNG as a transportation fuel in the United States. This has involved a great deal of strategy, which began with purchasing a landfill gas-to-RNG facility in Texas, and then navigating the process of transporting the fuel across state lines to participate in California’s Low Carbon Fuel Standard. The company was patient and waited for the market to develop, and when it did, it began to accelerate its efforts to form strong partnerships and increase project investments, ultimately resulting in the sale of 225 million gallons of RNG sold to customers last year.
The RNG market has been an exciting one to watch over the past several years, and there is plenty more in this edition that is focused on just that, from increasing profitability through codigestion to a column from the RNG Coalition discussing growth in and outside of California.
We’ll soon be updating our rapidly growing North American Renewable Natural Gas Map, which includes operating and under construction RNG plants in the U.S. and Canada. Be sure to reach out to our new map data & content coordinator, Chloe Piekkola, at chloe.piekkola@bbiinternational.com if your facility isn’t on the map or on our radar, or to provide an update on progress.
The North American SAF Conference & Expo, produced by SAF Magazine in collaboration with the Commercial Aviation Alternative Fuels Initiative (CAAFI), will showcase the latest strategies for aviation fuel decarbonization, solutions for key industry challenges, and highlight the current opportunities for airlines, corporations and fuel producers. The North American SAF Conference & Expo is designed to promote the development and adoption of practical solutions to produce SAF and decarbonize the aviation sector. Exhibitors will connect with attendees and showcase the latest technologies and services currently offered within the industry. During two days of live sessions, attendees will learn from industry experts and gain knowledge to become better informed to guide business decisions as the SAF industry continues to expand.
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2025 Int’l Biomass Conference & Expo
MARCH 18-20, 2025
Cobb Galleria Centre, Atlanta, Georgia
Now in its 18th year, the International Biomass Conference & Expo is expected to bring together more than 900 attendees, 160 exhibitors and 65 speakers from more than 25 countries. It is the largest gathering of biomass professionals and academics in the world. The conference provides relevant content and unparalleled networking opportunities in a dynamic business-to-business environment. In addition to abundant networking opportunities, the largest biomass conference in the world is renowned for its outstanding programming—powered by Biomass Magazine–that maintains a strong focus on commercial-scale biomass production, new technology, and near-term research and development. Join us at the International Biomass Conference & Expo as we enter this new and exciting era in biomass energy.
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2025 Int’l Fuel Ethanol Workshop & Expo JUNE 9-11, 2025
CHI Health Center, Omaha, Nebraska
Now in its 41st year, the FEW provides the ethanol industry with cutting-edge content and unparalleled networking opportunities in a dynamic business-to-business environment. As the largest, longest-running ethanol conference in the world, the FEW is renowned for its superb programming—powered by Ethanol Producer Magazine—that maintains a strong focus on commercial-scale ethanol production, new technology, and near-term research and development. The event draws more than 2,400 people from over 31 countries and from nearly every ethanol plant in the United States and Canada.
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Subscriptions Biomass Magazine is free of charge to everyone with the exception of a shipping and handling charge for anyone outside the United States. To subscribe, visit www.BiomassMagazine.com or you can send your mailing address and payment (checks made out to BBI International) to Biomass Magazine Subscriptions, 308 Second Ave. N., Suite 304, Grand Forks, ND 58203. You can also fax a subscription form to 701-746-5367. Back Issues & Reprints Select back issues are available for $3.95 each, plus shipping. Article reprints are also available for a fee. For more information, contact us at 701-746-8385 or service@ bbiinternational.com. Advertising Biomass Magazine provides a specific topic delivered to a highly targeted audience. We are committed to editorial excellence and high-quality print production. To find out more about Biomass Magazine advertising opportunities, please contact us at 701-746-8385 or service@bbiinternational.com. Letters to the Editor We welcome letters to the editor. Send to Biomass Magazine Letters to the Editor, 308 2nd Ave. N., Suite 304, Grand Forks, ND 58203 or email to asimet@bbiinternational.com. Please include your name, address and phone number. Letters may be edited for clarity and/or space.
Beyond the Golden State: Expanding California’s RNG Progress Across North America
BY SAM WADE
As North America strides toward greater energy independence and sustainability, California’s success with renewable natural gas (RNG) presents a clear and successful roadmap for other jurisdictions to emulate. Driven by climate-smart policies such as California’s Low Carbon Fuel Standard and supported by federal programs like the Renewable Fuel Standard, RNG’s recent growth illustrates that great things happen when policymakers support technologies that can reduce greenhouse gas emissions today.
Our journey at RNG Coalition began over a decade ago, inspired by the early legislative efforts in California. In 2012, California enacted AB 1900, a landmark bill promulgated by RNG Coalition that allowed integration of RNG into state natural gas pipelines. This was a transformational moment for RNG in California, setting the stage for integration into the state’s renewable portfolio standard and LCFS transportation programs.
Nationwide, California’s policies have been complemented by the RFS, which has been pivotal in legitimizing and expanding the use of RNG across the nation. By mandating increased use of renewable fuels like RNG, the RFS has helped reduce reliance on fossil fuels while promoting clean fuels as a sustainable alternative.
State and federal endorsement from programs like these have improved the visibility and economic potential of RNG projects, helping explain rising RNG consumption in California and nationwide. In 2023, RNG accounted for 97% of all onroad fuel used in natural gas vehicles (NGVs) in California, and 79% of all fuel used in NGVs nationwide. These numbers both represent record highs and speak to growing demand.
The Road Forward
Despite these strides, we still have important work to do to improve public understanding of RNG’s environmental credentials among certain audiences. A recent survey conducted by the RNG Coalition at the Society of Environmental Journalists conference in Philadelphia yielded surprising results: Roughly 70% of climate journalists formally surveyed at the event declared no knowledge or little knowledge of RNG. Despite the industry’s rousing success since the RNG Coalition
was founded in 2011, these results outline the work yet to be done in educating the public on the merits of our sustainable, flexible replacement for fossil gas.
Success in California will be central to that educational effort. Strides taken in the Golden State will continue to serve as a case study on how RNG can successfully offer a “dual emissions reduction benefit,” meaning the capture of methane emissions at waste sites, plus the displacement of fossil fuels in our energy system.
Fortunately, our California case study continues to bear fruit. Aside from our success in maximizing opportunities in transportation markets supported by the state’s LCFS, RNG has started to penetrate new markets. State utilities, prompted by the SB 1440 legislation originally supported by the RNG Coalition in California, have begun to deepen their commitment to RNG. RNG Coalition member SoCalGas earlier this summer became the first California utility to publish detailed plans to purchase RNG under SB 1440 legislation, in a May 31 request to state regulators. This marks an encouraging step.
Will other states follow California’s lead? Earlier this year, New Mexico became the fourth state in the U.S. to pass a clean fuel standard like California’s LCFS, making the Enchanted State the first U.S. jurisdiction beyond the West Coast to implement such a program. On the utility front, in recent years, Colorado and Vermont have enacted Clean Heat Standards that will foster further RNG capture, with RNG Coalition closely involved with the latter rulemaking process as a member of Vermont’s CHS technical advisory committee.
The story of RNG in California is more than a success; it’s a clarion call for action across the United States. As California pioneers new RNG markets, its progress offers a compelling template for clean energy policy. With growing interest and legislative momentum nationwide, now is the time for other states to take notes on California’s success as we pursue a sustainable and thriving energy future for present and future generations.
Author: Sam Wade Director of Public Policy, RNG Coalition
The Nonenergy Benefits of the Biomass Industry
BY JULEE MALINOWSKI-BALL
Too often, politicians and energy leaders do not take into account the social and nonenergy benefits when making recommendations to achieve clean energy goals. However, it is important to recognize the positive impact of the biomass industry in various areas such as land use, public health and air quality, economic effects and resilience. Considering all available data, it becomes clear that the biomass industry has numerous ancillary benefits contributing to California’s overall wellbeing.
Regarding land use, the biomass industry in California does not seek to expand the number of facilities, but aims to maintain the existing ones and reopen shuttered facilities. This means that there is no additional impact on land use. Furthermore, the biomass industry is crucial to improving land usage by annually reusing over 6.5 million tons of wood and agriculture waste as fuel. Instead of allowing these materials to clog landfills, decay in forests or be disposed of with open burn piles, biomass facilities convert them into energy. The amount of waste biomass used each year would fill the Rose Bowl over 25 times, providing a sustainable alternative to disposing of wood waste.
When it comes to public health and air quality, biomass plants produce clean and renewable electricity by utilizing organic materials. By converting biomass into energy, the industry minimizes emissions through advanced technologies. A joint report by the California Natural Resources Agency and the California Air Resources Board states that converting forest or agricultural residue to energy reduces the most harmful climate pollutants by 98% compared to controlled burns or wildfires. The San Joaquin Valley Air Pollution Control District estimates that the open burning of agricultural waste has increased 400% over the past five years, leading to serious health impacts on disadvantaged communities. Biomass facilities help address this issue by removing black carbon from the air and transforming it into a renewable energy source.
The biomass industry also has positive economic effects, employing over 2,000 Californians and serving as a significant employer in rural communities. Additionally, thousands of in-
direct family wage jobs such as forestry and truck transportation jobs are supported by the biomass industry. These economic benefits contribute to the overall stability and wellbeing of local economies.
In terms of resilience, biomass offers a reliable power source that helps stabilize the grid. This becomes particularly important during peak demand or when renewable sources like solar and wind can’t meet the energy needs. Biomass serves as a tool for ensuring power stability and reliability, especially during events such as wildfire-related power shutoffs. Its ability to convert waste into clean, renewable power offers an additional measure of grid stability.
Finally, in fire-prone areas, sustainable forest management results in the generation of a significant amount of organic material that requires proper disposal. In California, the majority of this material is either burned or chipped to reduce the risk of fires. However, due to limited available disposal facilities, there is often no choice but to leave the remaining residue in forests. This is where biomass plants play a crucial role in repurposing wood waste and become an integral part of the solution.
Biomass energy represents a vital tool to address waste management, stabilize the grid, reduce pollution and facilitate sustainable forest management. While many of its ancillary benefits often go unnoticed, they are invaluable to California’s clean energy goals. As the Senate Utilities and Energy committee chair once said, “Biomass and biowaste are clean, reliable and renewable. And as long as you have humans on this planet, you will have waste.” It is crucial to acknowledge the value that biomass energy brings to the state, and to consider its contributions when formulating clean energy strategies.
Author: Julee Malinowski-Ball, Executive Director, California Biomass Energy Alliance www.calbiomass.org
Biomass News Roundup
The USDA Foreign Agricultural Service on June 11 published a report discussing how the recent boom in United States renewable diesel production has caused market-altering shifts to both foreign and domestic feedstock trade. U.S. renewable diesel consumption has increased substantially in recent years, from approximately 250 million gallons in 2013 to just under 3 billion gallons in 2023. That growth has been driven largely by California’s Low Carbon Fuel Standard, with the report noting that biomass-based diesel accounts for approximately 60% of the California diesel pool while the rest of the U.S. remains in the low single digits.
The USDA report cites several market factors that have aided in the rapid expansion of U.S. renewable diesel production in recent years, including the ability to repurpose oil refineries to produce the fuel. Production of renewable diesel has expanded at the expense of biodiesel production, as the two fuels are made from the same feedstocks. The report notes that biodiesel production has gradually trended downward since its peak in 2018, with renewable diesel capacity surpassing that of biodiesel in 2022 and renewable diesel production exceeding biodiesel production the following year.
The increase in renewable diesel capacity and production has bolstered demand for feedstocks, driving explosive growth in U.S. imports of vegetable oils and animal fats, according to the report. The USDA offers several examples, such as the U.S. EPA’s 2022 Renewable Fuel Standard pathway approval that allowed canola oil to become an eligible feedstock for renewable diesel production, which supported record high imports of canola oil. While much of the canola oil imported into the U.S. was used to produce fuel,
the USDA notes increased canola oil imports also helped backfill displaced soybean oil in other markets, such as food production, which had been impacted by increased demand for soybean oil for use as biofuel feedstock. According to the USDA, the spike in canola oil demand is unlikely to be short-term, as U.S. canola oil imports, food use consumption and industrial consumption are all expected to set records for the third consecutive year in 2024-’25. Much of that canola oil comes from Canada. Approximately 91% of Canada’s canola oil exports were destined for the U.S. last year, up from 50%-60% in previous years. The USDA notes that canola oil supplies should remain robust, as Canada has announced plans to expand crush capacities over the next several years.
The imports of several other renewable diesel feedstocks have also spiked in recent years. According to the USDA, the import values of all animal fats and vegetable oils more than doubled between 2022 and 2023, with used cooking oil (UCO) imports more than tripling in 2023 on account of increasing imports from China.
A changing tax credit structure in the U.S. starting in January 2025 is expected to drive additional growth in renewable diesel feedstock imports, as the current blender’s tax credit for biobased diesel expires and will be replaced with a clean fuels production tax credit. The change from a blender’s credit to a producer’s credit means that the tax incentive will apply only to biobased diesel produced in the U.S. As a result, demand for biofuel imports is expected to drop substantially. Increased demand for U.S.-produced fuels is expected to drive even higher imports of fats and oils for use as biofuel feedstock, particularly lower carbon-intensity feedstocks such as tallow, UCO and corn oil.
The USDA points out that the boom in renewable diesel production has not only impacted import markets, but U.S. export markets also have also experienced changes. U.S. soybean exports have trended down in recent years, and the U.S. share of global soybean trade is expected to remain below the five-year average in 2024-’25.
Domestic soybean crush, however, is expected to set a record for the fourth consecutive year in 2024-’25 as a direct result of expanding U.S. renewable diesel production.
The U.S. EPA has approved a Renewable Fuel Standard pathway for BP Products North America’s Cherry Point refinery in Blaine, Washington. The approval will allow the facility to generate D5 advanced biofuel renewable identification numbers (RINs) for renewable diesel produced via a hydrotreating process that coprocesses carinata oil and petroleum.
In May, BP released a statement discussing renewable fuel production at the Cherry Point facility, indicating that refinery, which has the capacity to process approximately 250,000 barrels of crude oil per day, began producing renewable fuels via coprocessing in 2018. The facility has coprocessed beef tallow, used cooking oil, canola oil, soybean oil and corn oil, among other materials.
Sevana Bioenergy has acquired the Rialto Bioenergy Facility, a renewable natural gas (RNG) plant located in Rialto, California, the company announced in June. The facility, previously owned by a subsidiary of Anaergia Inc., was purchased via a bankruptcy auction.
In May, Anaergia reported that its subsidiary, Rialto Bioenergy Facility LLC, had initiated voluntary Chapter 11 restructuring proceedings in the U.S. Bankruptcy Court for the Southern District of California. During an earnings call in late 2023, the company indicated it was exploring the possibility of selling the Rialto plant. Sevana Bioenergy successfully bid $20 million for the facility in May.
Waste Management has opened a new renewable natural gas (RNG) facility in Lewisville, Texas, outside of Dallas. The nearly $55 million WM DFW RNG facility is expected to generate approximately 1.2 million MMBtu per year of RNG, which serves the equivalent of almost 55,000 households annually, or the ability to fuel up to 1,100 heavy-duty vehicles per day. The DFW RNG facility processes landfill gas captured from the WM DFW Landfill. Including the new facility, WM now owns or hosts 22 RNG facilities at its landfills.
CPM announced the acquisition of Innovative Pelleting Solutions GmbH and its high-capacity, direct-drive pellet mill technology invented by Graf Equipment GmbH. The new technology is capable of processing various biomass feedstocks and is beneficial for several reasons, according to CPM. The force from the pellet mill motor is directly driven to the machine, which reduces the need for other mechanical components, thus offering a smaller footprint and simplified maintenance. In addition, higher torque produces denser pellets, and the technology is more sustainable as it lowers the use of grease due to its low vibration and low die speed, also preserving the longevity of machine parts.
Stantec announced it has been selected by the Onimiskiw Opitciwan Limited Partnership to design the future biomass cogeneration plant for the Atikamekw community of Opitciwan in the Mauricie region of Quebec. The new cogeneration plant will supply electricity to the Opitciwan community, located on the north shore of the Gouin Reservoir, 220 kilometers northwest of La Tuque. The plant will be built near Opitciwan’s existing saw-
mill, utilizing cutting-edge technologies to convert biomass generated by the sawmill—such as bark, wood chips, and other organic waste—into electricity and heat. The 4.8-megawatt plant will be connected to Hydro-Québec’s power grid and generate electricity for the community. The plant will also supply power to the sawmill through 4.16 kilovolt (kV) and 25 kV feeders.
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Verbio has broken ground on a conversion project at its ethanol plant in South Bend, Indiana, that will allow the facility to produce both ethanol and renewable natural gas (RNG) using an innovative production approach. A similar project is already underway at the company’s biorefinery in Nevada, Iowa.
The company received approval for the South Bend expansion project from the city of South Bend in April. Once the project is complete, the facility is expected to have the capacity to produce at least 85 MMgy of corn ethanol and 2.8 billion cubic feet of RNG annually. During the first phase of the upgrade, which is scheduled to last six months, Verbio will build the foundations for eight new anaerobic digester tanks. During the second phase of construction, the company will construct the eight digesters, along with related piping and wiring, several new buildings, and miscellaneous process equipment.
The facility will produce RNG from corn stillage, a coproduct of corn ethanol production. RNG produced at the South Bend plant will be fed into the regional natural gas grid and support the needs of industrial and commercial uses. Commercial-scale RNG production is expected to begin in 2026.
In its latest quarterly report, released May 14, Verbio announced commercial production at the Nevada biorefinery was expected to commence in the “near term.” According to the company, the biomethane portion of the Nevada plant was commis-
On April 29, the U.S. EPA issued a Renewable Fuel Standard pathway approval that will allow the Nevada facility to generate D6 renewable fuel renewable identification numbers (RINs) for the corn ethanol it produces. According to the EPA, corn ethanol produced at the Nevada facility is expected to achieve a 34% greenhouse gas (GHG) emission reduction when compared to a fossil baseline. Ethanol must achieve at least a 20% GHG reduction in order to qualify for the generation of D6 RINs.
CHAR Technologies Ltd. has commenced a production run of 500 metric tons of pelletized biocarbon. The pelletized biocarbon is destined for use at various heavy industrial facilities, including ArcelorMittal sites, to fulfill a portion of the company’s previously announced biocarbon offtake agreement. The production run is an important milestone in the ongoing commercial upgrades at CHAR Tech’s state-of-the-art Thorold facility. CEO Andrew White said the company is looking forward to getting its pelletized biocarbon into the hands of clients, including ArcelorMittal, over the coming months.
India’s Ministry of Power on May 14 issued a revised policy on biomass cofiring, announcing it will now require certain coal-based thermal power plants to begin cofiring 5% biomass within one year. The new requirements update regula-
Combustible Dust Explosion Protection: Compromise Has Consequences
Many industrial processes pose combustible dust explosion risks that require critical efforts to identify and manage hazards effectively and reliably. At the core of these initiatives are dust hazard analyses (DHAs), which serve as the foundation for identifying dust hazards, documenting existing protection and prevention strategies, and recommending additional hazard management solutions.
The effectivity and reliability of explosion protection systems is only as good as the weakest link, so a reliable protection strategy must inclusively consider the dynamics of an initial dust cloud ignition, the function and reliability of the protection system, and the residual effects of the event. If corners are cut or something is overlooked, it can result in a hazardous situation and create a false sense of security under the perception of complete, reliable protection.
Dust explosions are highly chaotic events with many influencing variables. Their predictability does not necessarily follow a simple mathematical scale factor; protection systems must be designed and tested for the range of
expected conditions and application parameters of each specific operation. Outside the range of tested conditions and parameters, there is reduced confidence that the protection system will perform as required.
NFPA standards for explosion protection systems require testing and certification for most explosion protection equipment. Some examples include flameless explosion venting devices, explosion isolation valves and active protection systems. To ensure an unbiased reliability of the equipment to perform under the range of tested conditions, these devices must be independently tested by a credible organization according to a published set of testing procedures.
Some influencing factors for certified flameless vents include dust type and characteristics, protected volume, design pressures and device efficiencies. Certification parameters for explosion isolation devices include the above-mentioned influential factors, but also include connection pipe parameters such as installation distances, elbows and fittings, dust concentration, conveying air velocity and pressures.
Vent panels must be installed so that they can freely open, with the effects of venting discharge taken into account. The release of a pressure wave and a fireball must be considered so that residual damage or harm is avoided. Compromised vents reduce the system’s venting efficiency and reliability. Vent ducts, directional venting and flameless venting can be used to help manage the safety zone of a vent discharge.
Publications such as the NFPA standards serve to guide the industry on the fundamentals of explosion safety. A DHA and associated explosion protection solutions led by competent, qualified experts will not only apply the fundamental intentions of the NFPA standards, but also evaluate the risk based on the relevance, severity and probability of actual hazards while considering the consequences to personnel, property and process integrity. Where industrial safety is concerned, any compromise can increase the risk and severity of hazard consequences, meaning the difference between cleanup and maintenance activities or injury and extended downtime.
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WORKING TOWARD A COMMON GOAL
A new drum dryer safety initiative led by the Wood Pellet Association of Canada breaks down silos among industries and sectors, bringing together key insight to develop best practices.
BY LISA GIBSON
On the heels of a successful safety campaign focused on belt dryers, the Wood Pellet Association of Canada kicked off its drum dryer safety initiative in early April with its virtual Drum Dryer Symposium. It was just the first step of a process that will culminate in a set of safety best practices guiding drum dryer use in all relevant industries, globally. “The main objective of this symposium was to try to spray everybody with tons of information and raise awareness,” says Gordon Murray, executive director of WPAC. “Now, we are putting together our subcommittee and then we’ll just be digging into
drum dryers for the next year or so, getting into every aspect of operation.”
The new subcommittee dedicated to drum dryer safety has representation from dryer manufacturers, pellet producers and safety equipment suppliers, Murray says. And it’s preparing for its first meeting. “The overarching goal is to have fewer near misses and incidents around drum dryers, to protect people and protect operations,” says Kayleigh Rayner Brown, lead engineer in Industrial Process Safety for Jenson Hughes and process safety services adjunct for FutureMetrics. “Inherently, there’s just a lot of risk in wood pellet plants. There
The most recent campaign for the Wood Pellet Association of Canada aims to reduce drum dryer safety incidents through broad research inclusive of input from several industry sectors. Dryer manufacturers like Uzelac Industries keep safety top of mind in design, engineering, installation and maintenance.
is just the inherent nature of the material being handled—there’s risk with that.”
Safety is a critical component of WPAC’s ongoing work, Murray says, adding that the organization has a large safety committee that meets once per month. “We’ve got a really strong safety culture in the industry, and we’re always trying to get better and dig into new initiatives. This is just a campaign for our industry to get better,” Murray adds. “We’ve always got something like this on the go that we work through until it’s done. So, this is not a unique, novel or new idea coming about because of an incident; it’s just part of our routine of trying to get better.”
Routine Risks
During the April symposium, Rayner Brown, then a process safety specialist with Obex Risk Ltd., talked through the most significant safety risks inherent in drum dryer operation. It is vital to kick off the safety campaign with awareness around
those risks, she says. “I think there are still people who are learning about the major risks associated with drum dryers. When
people understand how you can have explosions in your dryers, they understand why the safety controls and the barriers that are
The dust explosion pentagon outlines the key factors that lead to safety incidents with dryers.
in place are, in fact, in place. People can better understand the role they have in helping to protect the facility and their colleagues.”
Certainly, one of the two main risks in pellet production is wood dust, as it is highly combustible. “The risk varies, and certain factors affect how explosive the material is, but in general, you need five factors for a dust explosion: oxygen, an ignition source and fuel—in this case, combustible dust— and then also dispersion and confinement,” she explains.
The other main risk is the formation of gas from the combustible dust, even in the drum itself. Those gases include methane, carbon monoxide and hydrogen, which are all highly explosive and highly combustible. Those two main risks become a hazard to upstream and downstream equipment as well, Rayner Brown says. “Because everything is connected, if you have an explosion in your burner or drum dryer, one of the biggest issues is that it will propagate through the process—it’s going to propa-
gate to the upstream equipment, it’s going to propagate to the downstream equipment.”
During the April symposium, participants identified startup and shutdown as the highest-risk process components, as well as outfeed and infeed failure and induced draft fan failure.
The Work Ahead
With a full understanding of the risks, the WPAC subcommittee will assess every aspect of drum dryers, Murray says, including fuel, heat source, backup electricity, friction reduction, etc. The research will include lab work that will sample feedstock, contaminants, air and more. Murray says the research is expected to last about a year, but no firm timeline has been set. Lab work will be conducted at the University of British Columbia, accessible through a joint appointment of WPAC’s director of research and technical development, Fahimeh Yazdan Panah.
Undoubtedly, one area of study will be inherently safer design. “There are things that can be changed with pellet plants with respect to design,” Rayner Brown says. “We’ve done a lot of work on inherently safer design.”
For instance, Rayner Brown cites, perhaps the dust collector can be built to withstand an explosion, or equipment could be relocated away from personnel and critical infrastructure. Control room design can be optimized with computer screen locations. “Is the control room set up in a way so that operators can clearly understand what’s actually happening in the process? Are there a lot of nuisance alarms that are overwhelming them? Have alarms and notifications been minimized? Is everything laid out in an intuitive way?”
Operation, inputs and process controls are also key. “If you heat up too fast or cool down too fast, or shut down the induced draft fan too quickly, you can get that accumulation of combustible gas,” Rayner
Brown says. “If you can simplify any processes, if you can automate any processes, that’s inherently safer design implementation. So, yes, there are a lot of inherent risks to pellet plant operation, but there are design changes that can be made that can reduce the risk.”
Mia Ivetić, corporate vice president and service manager with dryer manufacturer Uzelac Industries, says safety is top of mind in engineering and design at Uzelac. “The technology has been around a very long time, but being we have engineering in house—we are constantly making tweaks,” she says. The company has a safety checklist it recommends be performed biweekly by maintenance or operators, as well as an annual inspection so Uzalec can conduct the safety check itself. The list includes thorough checks of the following areas: high-temperature control unit; high gas-pressure switch; low gas-pressure switch; combustion fan pressure switch; combustion blower and main fan auxiliary contacts; drum motion switch; UV flame scanner; and product outfeeding system. Fire suppression systems are standard in all Uzelac dryers, designed to shut down everything except the drum, as sudden shutdown could cause warpage and mechanical issues, according to Justin Poja, Uzelac service technician. Poja recommends all checklist items be done together, but emphasizes two main ones. “Make sure that high gas-pressure switch is working, because that can be catastrophic if something goes wrong, as well as testing the hi-limit (in the high temperature control unit) and that the fire suppression would come on in the event of an upset issue.”
Training operators is also important, as those roles tend to see high turnover rates, Ivetić says. “When our service technicians start up a dryer, we do go through training, and we do that during our annual visits when there are new operators.”
She is fully supportive of WPAC’s safety campaign. “I think that it sounds great—it’s something we really stress: maintenance and safety.”
A rotary dryer installation by Uzelac Industries, a manufacturer based in Greendale, Wisconsin, that has drying systems in operation worldwide.
IMAGE:UZELAC INDUSTRIES LTD.
‘These safety initiatives take time and resources, but everyone has the same issues and is doing great work on their own. So, it’s important to bring folks together as one instead of working in silos.’
—Kayleigh Rayner Brown, Industrial Process Safety Lead Engineer, Jenson Hughes
The Results
Much like the belt dryer safety initiative, the drum dryer campaign will result in safety guidelines accessible not just to WPAC members, but all industries that utilize dryers globally. “The Canadian commitment to safety is we are completely open, and we freely share everything,” Murray says. “If we found a way to be safer than the next guy, we share that. We do not compete on safety.”
WorkSafeBC will be brought into the process as well. Murray says WPAC has cultivated a positive relationship with the regulator, dispelling its reputation of enforcement agency or cop. “We tried to turn that on its head and say, we want to be safe and we want them to support us. We want to always have them working with us to try to make us better. We meet twice a year, and we share our work plan—it’s just a measure we’ve adopted. We are just completely open with them, and it’s worked out beyond our expectations.”
Each time WPAC begins a new initiative, including the belt dryer safety campaign, WorkSafeBC becomes a fast partner. Such safety initiatives have significant impact on the betterment of entire industries, Rayner Brown says. Beyond raising awareness of inherent risks, she hopes the drum dryer safety campaign improves sharing of information across the whole pellet sector and allied industries, with input from consultants, experiences from other industries, input from manufacturers and explosion protection equipment providers.
Ultimately, these well-balanced subcommittees help improve dryer operation in all relevant industries, she says. “I think it’s important to highlight that the belt dryer workgroup was successful. Everyone came together and took a lot of effort. These safety initiatives take time and resources, but everyone has the same issues and is doing great work on their own. So, it’s important to bring folks together as one instead of working in silos.
“Overall, I think a lot of the progress that’s been made in the pellet sector really just demonstrates the power of people coming together and working toward a common goal.”
Contact: Anna Simet asimet@bbiinterational.com
INTERNATIONAL TRADE F AIR FOR INNO VATIVE ENER GY SUPPLY
ACCELERATING A CLEANER FUTURE
An RNG producer and distributor is helping decarbonize heavy-duty engines with low-carbon-intensity fuel
BY KATIE SCHROEDER
Clean Energy Fuels Corp. has played a substantial role in pioneering the use of renewable natural gas (RNG) as a transportation fuel in the United States. To keep growing and moving forward, the company forges strong partnerships and maintains a flexible outlook.
As a distributor of RNG, Clean Energy helps fleets reach their sustainability goals and decarbonize their operations, working closely with engine manufacturers to help
fleet customers—including UPS and Amazon—make the switch to RNG trucks, explains Clay Corbus, head of renewable fuels and senior vice president of strategic development with Clean Energy Fuels. “Our whole business has really been working with heavy-duty fleets that burn a lot of fuel and transitioning them from using diesel to using renewable natural gas,” he says.
Replacing diesel with RNG sourced from a landfill has a carbon intensity (CI) score of 45.9, according to data from the
California Air Resources Board’s Low Carbon Fuel Standard pathway. The carbon reduction benefits are even more drastic when using manure-based RNG, dropping down to negative 330 CI points on average.
A Brief History
At the start, Clean Energy was primarily a distributor of fossil-based natural gas. As stated on the company’s website, T. Boone Pickens, one of the company’s cofounders, was a champion of natural gas as a cleaner
alternative for heavy-duty trucks that burn substantial amounts of gasoline and diesel. “Boone was involved in natural gas, and he always thought that a higher value for natural gas was to vehicles, rather than going into electric power generation,” Corbus explains. “His whole idea was, ‘Let’s take the natural gas, it’s really clean relative to diesel, it’s cheap on a commodity basis, it’s much cheaper than diesel or gasoline, and it’s all-American—you don’t have to import it.’”
In his former job as an investment banker, Corbus played a role in bringing the company public in 2007. Recognizing the available opportunities, he joined the Clean Energy team shortly after. He explains that RNG started to become a focus in 2008, when exploring the fuel was included in the company’s strategic plan. Several things happened after 2008 that further increased Clean Energy’s interest. In 2011, California’s LCFS was put into place, followed by the
Renewable Fuel Standard’s renewable identification number (RIN) program amendments in 2014 that allowed landfill gas and other RNG to generate a D3 RIN. “Those two factors are what really started to accelerate the transition from what we call blue gas or fossil natural gas, to renewable natural gas,” Corbus says.
Clean Energy first entered the RNG production space through the purchase of a project at one of the country’s largest landfills, the McCommas Bluff Landfill, near Dallas. Corbus explains that it is common for landfills to burn the methane collected from the landfill to generate electricity, then sell it to the grid. However, because the McCommas Bluff Landfill was so big, it made more sense to clean the gas and put it in a pipeline to be sent to a cogeneration facility. “It costs a lot of money to put that cleanup equipment in, but once you have it [installed], you can upgrade the gas to a
higher quality, making the process more efficient and making more money off of it,” Corbus says. But rather than sending it to a local cogeneration facility, Clean Energy successfully navigated the process of transporting the RNG across state lines to California, which was appealing because of the renewable energy requirements in place there. Prior to the maturation of the LCFS credits market, the California utilities were the primary buyer, with any extra RNG being sold into the vehicle market. “The LCFS credit market matured over time, and then when the RIN market developed, we [put] all that gas directly into the vehicle fuel market,” Corbus says. “Because you could just get a lot more money for the gas taking it to the vehicle fuel market with those credits than you could in ... the voluntary market, taking it to utilities.”
Clean Energy opened state-of-the-art RNG fueling stations in San Bernadino (pictured) and Perris, California, in early June.
IMAGE: CLEAN ENERGY FUELS CORP.
Market Dynamics
Clean Energy utilizes offtake agreements to supply RNG demand at its stations and make money doing so. Corbus outlines an example of how these offtake agreements work. “Say there’s a landfill in Tennessee, and it can sell its renewable natural gas to the local utility for $20 per thousand cubic feet. If you put it into a vehicle in California you can get double that, $40. But how do they get it into a vehicle in California? That’s where we show up,” he says.
The company could offer to take the RNG to California for 20% of the fuel’s value, which would be $8 in this scenario. After the fuel is sold into the Californian fuel market, the producer gets $32 per thousand cubic feet, rather than the $20 they would have received selling it locally, and Clean Energy gets the remaining $8. “We get a commission basically, we get a cut of the profits for bringing it [to the market], and that’s important because we have to pay for the station— we need to make money, too,” he says.
In 2010, when oil prices were high and the cost benefits of natural gas versus diesel were very significant, Clean Energy seized the opportunity to increase the number of fueling stations across the country. Most of the landfill gas assets were sold to companies such as BP during the “lean years” after oil prices dropped, according to Corbus. However, the company continued to distribute the landfill gas produced at the various sites by arranging offtake agreements with the buyers.
Fueling Logistics
Currently, 90% of Clean Energy’s natural gas volume sold into the transportation fuel market is RNG, explains Corbus. Nearly all of that RNG is purchased through offtake agreements with third parties and not produced by the company itself; however, Corbus hopes that dynamic will soon shift as more of the RNG facilities developed by the company come online. Clean Energy sold 14 million gallons of RNG to fleet vehicles in 2013 when the company was the first to introduce it as a transportation fuel, compared to 225 million gallons in 2023.
Corbus explains that RNG-powered vehicles are useful in a wide range of sectors, including trash removal, shipping, metropolitan buses and airport shuttles. Companies with large fleets of vehicles, such as transit agencies in Los Angeles and New York, waste companies like WM and Repub-
lic Services, and companies that move goods like FritoLay and PepsiCo, use Clean Energy’s 600 stations across the country to operate. The engines for these vehicles are made for the buyer at the OEM’s factory and have same power and torque as their diesel counterpart, and are covered by the same warranty as a diesel-powered engine.
Although these engines are more expensive than standard heavy-duty diesel engines, the fuel cost savings are worth it for fleets in the long run, according to Corbus. “If a fleet like UPS ... is saving $40,000 a year on fuel, but the engine cost $60,000 more, you’ve got a year and a half where you’re paying it back. If you keep that vehicle for 10 years, you’ve got eight and a half years of savings,” he says.
The hundreds of fueling stations scattered across the U.S. and Canada offer a similar fueling experience to diesel, with some key differences. The nozzle used for fueling is clamped on when filling the tank because the fuel is gaseous. There are also different ways to fuel—for example, a truck driver or fleet could choose to refuel slowly overnight to save on the electricity costs of refueling in the middle of the day.
Developing Partnerships and Production
Clean Energy is the touchpoint for many companies as they pursue sustainability goals and look to access the opportunities provided by RNG. Corbus explains that though Clean Energy is not a huge company, it is a significant and well-known player in the RNG space, with its hundreds stations fueling 50% to 60% of the natural gas fueled vehicles on the road.
Clay Corbus, Clean Energy Fuels
In January, Clean Energy completed a new RNG production facility at Drumgoon Dairy in Lake Norden, South Dakota. The 6,500-cow dairy farm is expected to supply 1.66 million gallons of negative-carbon-intensity RNG annually to the transportation market when at full capacity.
IMAGE: CLEAN ENERGY FUELS CORP.
As Low Carbon Fuel Standard credit values climbed, Clean Energy began getting phone calls from RNG production project developers seeking assistance in getting their RNG into the California market. These developers would sometimes inquire about investors who would like to be involved in making an RNG project a reality. “We were getting all this inbound interest in [entering] into the California fuel market, and meanwhile, our stock price had recovered, we had raised money, and we were fiscally healthy,” Corbus says. “So, we thought this might be a good opportunity for us to get back into the production business—what we call the upstream side—where we’re generating the RNG as well.”
Clean Energy has joint ventures in place with BP and TotalEnergies to invest in RNG projects. These partnerships help the company access more capital and benefit from their partners’ technical expertise in the global energy market. “It also helps us from a due diligence standpoint, where sometimes we might be more aggressive and
more risk tolerant, and they’re usually more careful, so it helps keep everybody on a level playing field,” Corbus says.
Over the past three years, Clean Energy has invested in several dairy-based RNG projects. Six of them are online, with the seventh planned to begin operations soon and several other projects in the pipeline. These projects require lot of time, Corbus says. “There are a lot of engineering and
design that goes into a project, because you should be near a natural gas pipeline, and if you’re not, you have to figure out how you’re going to get it to the pipeline. These projects are complicated.”
Generally, the size of the dairy needed is 5,000 cows, or a combination of multiple smaller dairies that have their manure collected together. However, this number is only an estimate. “There are many variables
In October, Clean Energy and TotalEnergies announced that RNG from Del Rio Dairy in Friona, Texas, had begun generating D3 renewable identification numbers credits under the Renewable Fuel Standard, as well as credits through Oregon’s low carbon fuel standard program.
that go into what the minimum size dairy is,” Corbus says. “It’s the manure collection techniques, it’s the distance from a pipeline. It’s the type of digester you’re using, whether it’s a covered lagoon or a big tank digester.” And, he adds, the timeline can stretch longer due the delay associated with getting verified in the state, a window stretching from 15 to 24 months.
Right now, RNG is the only practical solution for heavy-duty vehicles on the road, Corbus explains. However—true to its name—the company is interested in pursuing any clean energy solution that will fulfill its customers’ needs. “As we look further down the road, hydrogen certainly might be something that’s viable, and when it is, we’ll be there,” he says. Clean Energy has built and is operating a few hydrogen stations, which
operate similarly to RNG stations. Hydrogen is not quite ready for “prime time” due to the high barrier-to-entry cost around the vehicles, he says. RNG also provides an opportunity to adapt, should the market move toward electric heavy-duty vehicles, since that RNG could also be used to make electricity. “I think ... in the immediate-term, RNG going directly into an RNG truck—a natural gas truck—is the most immediate opportunity and the one that we see growing the fastest,” Corbus says.
Throughout the history of Clean Energy, the company’s goals have remained focused on providing a cleaner and more affordable option for customers, targeting both environmental and economic sustainability. This adaptive approach that leverages partnerships and innovation to move forward has enabled Clean Energy to become a key player in the RNG fuel space, realizing Pickens’ dream of a cheaper, cleaner, American-made transportation fuel.
RNG is flowing at the Del Rio Dairy. Clean Energy broke ground on the biogas digester in November 2021, completed construction in February 2023, and stored the RNG produced until regulatory approval in June. Del Rio Dairy is the first low-carbon-intensity RNG project completed by the company.
BIOFUELS IN THE Twin Cities
The International Fuel Ethanol Workshop & Expo drew nearly 2,500 attendees with stakes in the ethanol, biobased diesel, sustainable aviation fuel and carbon capture industries to Minneapolis in mid-June.
BY ANNA SIMET
Photos by Sarah Morreim Photography
Opportunities within the sustainable aviation fuel (SAF) market was a hot topic of discussion at the 40th annual International Fuel Ethanol Workshop & Expo, which was held simultaneous to the Biodiesel, Renewable Diesel & Sustainable Aviation Fuel Summit Minneapolis, June 10-12. Also held on-site were the Carbon Capture & Storage Summit and Ethanol 101.
Nearly 2,500 attendees from 47 states, seven Canadian provinces and 30 countries registered for the events, which welcomed 380 exhibiting companies. Nearly a quarter of attendees were biofuel producers.
Topics discussed at the Biodiesel, Renewable Diesel & SAF Summit included project economics and available funding pathways; renewable diesel and SAF pretreatment strategies; project economics, market demand and federal policy require-
ments; SAF production technologies; as well as Minnesota’s Sustainable Aviation Fuel Hub—the first of its kind in the country— which was announced last August. Julia Silvas of GREATER MSP, one of the major hub partners, discussed progress to date, which includes securing state SAF tax credits and a construction incentive, as well as recruiting potential SAF producers. Silvas went into detail on what the hub is focused on now, a series of next steps that include
devising blending solutions, determining site feasibility for alcohol-to-jet, securing producer agreements and formulating environmental guardrails.
Also speaking on the panel was Brian Werner, executive director of the Minnesota Bio-Fuels Association, who provided a history and overview of the state’s biofuel industry. Currently, he said, Minnesota ranks fifth in the nation for ethanol capacity. In 2003, the state became the first to mandate
a 10% ethanol blend in gasoline, and today, approximately 500 retail stations across the state offer E15. Werner also discussed corn production and ethanol supply and demand on a national scale, and opportunities and key barriers for ethanol to jet. One of the main challenges, he said, is the ability of ethanol producers to measurably reduce their emissions to qualify for Renewable Fuel Standard renewable identification numbers and SAF tax credits under the Inflation
Reduction Act. Additional barriers Werner discussed included policy and regulatory uncertainty and environmental permitting.
David Winsness, president of Comstock Fuels, and Nick Jordan, professor of agronomy and plant genetics at the University of Minnesota, also presented on the panel.
The 41st International Fuel Ethanol Workshop & Expo will be held in Omaha, Nebraska, June 9-11.
Tim Portz, program developer for BBI International (left), moderated the FEW general session, which featured Brian Jennings, CEO at the American Coalition for Ethanol; John Fuher, vice president of government affairs at Growth Energy; and Troy Bredenkamp, senior vice president of government and public affairs at the Renewable Fuels Association.
Brian Werner, Minnesota Bio-Fuels Association (at podium), discussed the state’s biofuel industry. Also speaking on the panel were (from left) Nick Jordan, University of Minnesota; Julia Silvas, GREATER MSP; David Winsness, Comstock Fuels; and moderator Steve Csonka, Commercial Aviation Alternative Fuels Initiative.
Ethanol breakout panelists present to a full room.
The Whitefox Technologies crew poses for a photo on the trade show floor.
CTE Global’s exhibit included a virtual reality experience.
Visitors of Veloia’s booth could register to win a YETI Roadie cooler.
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ADVANCEMENTS AND OPPORTUNITIES IN CODIGESTION FOR RNG PROJECTS
The U.S. EPA’s new set rule unlocks potential for higher revenue streams through renewable identification number generation under the federal Renewable Fuel Standard.
The arena of renewable natural gas (RNG) has experienced a pivotal evolution due to the recent regulatory advancements by the United States Environmental Protection Agency. A notable development is the expansion of the practical implementation of the regulation to allow codigestion with improved economic outcomes. The introduction of the new set rule signifies a strategic shift in the EPA’s approach to codigested feedstocks for RNG production, particularly impacting the
BY DAVID LINDENMUTH
financial justification and operational design of these types of RNG projects.
Codigestion and the New Set Rule
Codigestion refers to the process in which multiple organic feedstocks, such as dairy manure (classified as a D3 feedstock under the Renewable Fuel Standard) and food waste (classified as a D5 feedstock), are processed together in a single anaerobic digester to produce biogas. The EPA’s revised regulations have introduced methodologies
that now enable the differentiation of biogas output derived from each feedstock type, thereby allowing the generation of both D3 and D5 renewable identification numbers (RINs).
Under the prior regulations, codigestion of D3 and D5 feedstocks resulted exclusively in the generation of D5 RINs. This limitation often negatively impacted the economic feasibility of projects due to the lower value of D5 RINs compared to D3 RINs. The revised rule, however, allows for the allocation of D3
CONTRIBUTION: The claims and statements made in this article belong exclusively to the author(s) and do not necessarily reflect the views of Biomass Magazine or its advertisers. All questions pertaining to this article should be directed to the author(s).
and D5 RINs based on the “converted fraction,” a calculated measure of the amount of biogas produced from a D3 feedstock. This fraction is critical, as it determines how much of the generated gas can be attributed to each feedstock type, thereby unlocking the potential for higher revenue streams through D3 RIN generation.
Determining the Converted Fraction
Project operators now have the following two options for establishing the converted fraction when registering their facility with the EPA.
User-defined approach: This method requires operators to conduct precise measurements of their digester’s operating conditions, including temperature, pressure and residence time. The resulting converted fraction is applicable only if the digester operates within these measured parameters.
EPA predetermined values: The EPA has established four preset converted fractions for common feedstocks such as swine, bovine, chicken manure and municipal biosolids. These values are linked to specific operational conditions, such as a minimum temperature of 95 degrees Fahrenheit and hydraulic and solids retention time exceeding 20 days.
Project Considerations and Financial Implications
With the updated regulations, the op erational setup and sizing of RNG facilities take on heightened importance. Facilities may want to be equipped to handle additional or ganic waste streams and ensure that their bio gas upgrading systems can accommodate the increased biogas production. Furthermore, compliance with the new rule necessitates meticulous data gathering and management to satisfy the EPA’s requirements for both the user-defined and predetermined converted fraction methodologies.
The economic landscape for some RNG projects has been transformed by the new rule. Projects that were once limited to the D5 RIN market can now leverage the higher value of D3 RINs, potentially dou bling annual revenue without an increase in biogas production. This financial uplift could drive the expansion of existing projects and
the development of new ones. Additionally, the inclusion of D5 feedstocks, which often come with a tipping fee, presents a new revenue avenue for project operators.
Quality Assurance and Compliance
Ensuring compliance with the RFS’s RNG program requirements is critical to accessing the financial benefits of RIN credits. This involves a comprehensive quality assurance program that includes biannual site visits, ongoing data review and adherence to mass and energy balance standards. For mixed digesters, additional verification layers are required, especially for the biogas energy calculation that establishes the D3 to D5 RIN generation ratio.
Future Outlook
The EPA’s registration timeline indicates that new project applications could be submitted starting April 1, 2024, with approvals
commencing on July 1. All projects must align with the biogas reform rule by January 1, 2025, with a deadline of October 1, 2024, for updating existing pathways.
The revised EPA regulations herald a new era for mixed-waste digester RNG projects, particularly in the realm of codigestion. By offering a more nuanced approach to RIN generation and enabling more accurate financial modeling, these regulations have created fertile ground for innovation and investment in the RNG sector. As the industry continues to adapt to these changes, the focus remains on compliance, technical proficiency and leveraging the newfound opportunities to drive sustainable energy solutions forward.
Author: David Lindenmuth Managing Director, RNG Services EcoEngineers dlindenmuth@ecoengineers.us
ENHANCING PELLET QUALITY: ADVANCED PREPROCESSING TECHNIQUES FOR CORN STOVER
The utility of corn stover as a biofuel feedstock is limited by considerable compositional variability, but advanced preprocessing techniques can significantly improve pellet performance and consistency.
BY ZACHARY P. SMITH
Corn stover, which is comprised of the stalks, leaves, cobs and husks left behind after corn is harvested, is an abundant agricultural byproduct in the United States, with approximately 144 million dry tons produced annually. Despite its vast potential as a biofuel feedstock, the utility of corn stover is limited by considerable compositional variability, influenced by regional agricultural practices, annual rainfall, crop variety and harvesting methods. To address these issues, advanced preprocessing techniques such as fractionation, grinding and reblending are crucial, significantly improving both pellet performance and consistency.
Understanding Corn Stover Variability
Corn stover’s variability can be observed through detailed compositional data maintained by the Biomass Feedstock National User Facility at the Idaho National Laboratory, which includes thousands of samples of various feedstock types, harvest locations, methods and years. A dataset of corn stover samples was pulled from the library to highlight the significant variations, with samples having the leaf fraction ranging from 6% to 36% of the total biomass, and cob content fluctuating between 9% and 34%. Additionally, the lignin content—a key component affecting biofuel yield—varies from 11.5% to 24%, according to a published study performed by the National Renewable Energy Laboratory. These fluctuations underline the necessity for sophisticated preprocessing strategies to ensure a more standardized quality of feedstock for biofuel production.
Preprocessing Steps: From Fractionation to Pelleting
Initial Processing and Screening. The preprocessing of corn stover begins with a
The processing steps of baled corn stover, from bale deconstruction to pelletization. IMAGE: OAKRIDGE NATIONAL LABORATORY
IMAGE: STOCK
low-speed bale deconstructor. This machine carefully dismantles bales to preserve material integrity, which is crucial for effective mechanical separation in subsequent stages. The stover then passes through a series of disc and oscillating screens designed to segregate materials based on size and fragility. This step effectively isolates the leaf fraction, which is more susceptible to crumbling under mechanical stress from handling.
During this screening process, a significant reduction in ash content is also achieved. Fines from this process were shown to concentrate ash at levels nearing 60%, compared to substantially lower levels in the other fractions. The ash that is removed during this step consists entirely of extrinsic ash (i.e., dirt) that had been collected during harvest and collection of the corn stover.
Density Separation. The screened material then undergoes density separation using a Spudnik Airsep, a device typically used in the potato industry to separate the rocks and vines from the potatoes. This equipment, optimized for corn stover, sorts the material into three main fractions— stalk, husk and cob, based on their density. This step is critical for reducing overall material variability, which is essential to achieving uniformity in the final pellets. This step is optimized using a variable frequency drive to control fan speed, accommodating different moisture contents and operational conditions.
Milling and Particle Size Optimization. Each fraction is milled to a consistent particle size of 2 millimeters. Various mills are tested for efficiency, including a rotary shear crumbler, knife mill, hammer mill, and shredder. As expected, the hammer mill has the widest particle size distribution while the rotary shear crumbler has the tightest particle size distribution. The knife mill is found to be the most effective for corn stover, providing the best combination of material meeting size specification and low energy consumption.
Blending and Pelleting. Post-milling, the fractions are blended in predetermined ratios to optimize characteristics like ash content and carbohydrate levels using compositional data for each fraction. For example, a blend of 40% cob, 30% leaf, 15% stalk
FEEDSTOCK ¦
and 15% husk is used to maximize carbohydrate content and minimize total ash, which is critical for enhancing biofuel production efficiency. This blend not only boosts the total carbohydrate content by 8%, but also reduces the total ash content by 66%.
The processed feedstock is then conditioned and pelleted, resulting in pellets with a bulk density of nearly 500 kilogram per cubic meter and an impressive durability of 98.5%. These pellets are well suited for use in both thermochemical and biochemical conversion processes, meeting specific feedstock requirements.
Environmental and Economic Implications. The development of advanced preprocessing techniques for corn stover not only addresses technical challenges, but also has significant environmental and economic implications. By improving the efficiency of biofuel production, these methods can help reduce dependency on fossil fuels, lower greenhouse gas emissions and provide a sustainable income source for farmers. However, the scaling of these technologies must consider potential impacts on soil health, biodiversity and the long-term sustainability of agricultural practices.
Future Directions and Conclusion
Continued research is necessary to further optimize preprocessing techniques and expand their application. Future studies could explore the integration of enzymatic treatments to enhance digestibility, or the development of more efficient pelleting technologies to improve energy consumption and output quality. Ultimately, the advanced preprocessing of corn stover represents a critical step toward making biofuel production more viable and sustainable.
By addressing the variability and enhancing the quality of corn stover pellets, these techniques not only make the biomass a more reliable source for bioenergy, but also contribute to broader renewable energy solutions. As these preprocessing methods evolve, they promise to unlock greater efficiencies and support the sustainability of the biofuel industry.
Author: Zachary P. Smith Research Engineer
Biomass Feedstock National User Facility Idaho National Laboratory Zachary.Smith@INL.gov
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