Realities, Opportunities For Cellulosic Ethanol
BioCycle January 2007, Vol. 48, No. 1, p. 46
Securing feedstock sources in close proximity to potential plant locations and storage of raw biomass are among the challenges in moving toward large-scale production of cellulosic ethanol.
Diane Greer
IN 2004, Iogen Corporation built the first demonstration-scale cellulosic ethanol plant with a capacity of almost one million gallons/year in Ottawa, Ontario, Canada. The company plans on building a commercial-scale plant in either the United States or Canada in the next two years. Goldman Sachs recently invested $30 million for a minority stake in the company. The other major investors are Royal Dutch/Shell group and Petro-Canada.
One of Iogen Corporation's criteria when scouting sites for its first commercial-scale cellulosic ethanol plant was to find a location with abundant supplies of its primary feedstock, agricultural wastes in the form of wheat and barley straw, within a 100-mile radius. Though a final decision is still months away, Iogen is already contracting with farmers at two potential locations to supply the straw. "In Idaho, we have signed up over 300 farmers for 400,000 tons of straw supply," says Jeff Passmore, President of Iogen Corporation. "We have done the same in Canada at a possible plant location in Saskatchewan."
Iogen's efforts to secure feedstock sources in close proximity to potential plant sites highlight an often-overlooked challenge in moving toward large-scale production of cellulosic ethanol. Namely, the industry will need to develop the logistics and infrastructure to collect and ship huge volumes of biomass to biorefineries.
How much biomass will be needed? Replacing 30 percent of the nation's petroleum consumption with biomass – a goal set by the U.S. Departments of Energy and Agriculture – will require production of 1.3 billion dry tons/year of biomass from agricultural and forest lands, according to Oak Ridge National Laboratories (ORNL). This volume represents a six-fold increase over the resources used today. In addition to agricultural wastes, such as corn stover and cereal straws, ORNL biomass estimates include energy crops such as switchgrass and willows along with wood wastes from pulp and paper mills, construction and demolition debris and forest trimming operations.
BIOMASS TO ETHANOL
Cellulosic ethanol is produced from a great diversity of biomass including waste from urban, agricultural, and forestry sources. In terms of agricultural residues – which this article focuses on – this includes the nonfood portion of plants, i.e., the leaves and stem. While chemically identical to ethanol made from food crops, such as corn and soybeans, the production process is more complicated. Preprocessing steps are required to liberate the sugars locked in the complex carbohydrates, called cellulose and hemicellulose, which form the cell walls of plants.
During preprocessing, biomass materials are broken into smaller pieces and then treated with enzymes to accelerate biochemical reactions that break down the complex carbohydrates into fermentable sugars. As with grain-based ethanol, the remainder of the process involves the fermentation and distillation of the sugars into alcohol.
To date, efforts to improve the economic viability of cellulosic ethanol have focused on decreasing enzyme costs and improving efficiency of preprocessing. But economics also depend on the ability of farmers to supply feedstocks profitably and at prices that enable these operations to produce a competitive product. "You have to work on conversion and distribution in parallel," says Kevin Shinners, Professor of Agricultural Engineering at the University of Wisconsin. "This stuff will not magically appear at the biorefineries."
Logistical challenges in collecting and transporting agricultural residuals add costs to otherwise inexpensive feedstocks. "The goal is to develop the machines and processes to harvest, store and transport these materials in the most economic way for the [farm] producers," adds Shinners. "If it can't be done economically for producers, the whole value chain is going to fall apart."
The collection and distribution of corn stover illustrates the challenge. Stover is the most widely available biomass material and viewed as the primary feedstock for initial cellulosic ethanol plants, according to Dave Anton, DuPont's Venture Manager for Biofuels. Current techniques for collecting corn stover rely on multiple passes over the field. Producers first harvest the corn and then collect the stover during a second pass. "We have a saying in this business that every time a wheel hits the field it costs you money," says Shinners.
To reduce harvesting costs, several groups are working on single pass harvesters, a machine that simultaneously collects the grain and the stover. Since the stover never hits the dirt, the method also yields a uniform clean product. Under a grant from the USDA, Jim Hettenhaus, cofounder of CEA Inc., is prototyping one-pass harvesters in Imperial Valley, Nebraska. Equipment manufacturer John Deere, in conjunction with DuPont's Integrated Cellulosic Biorefinery (ICBR) project, is also developing single pass harvesters. Instead of a dedicated machine, Shinners' group is working on equipment fitting onto the front and back ends of existing combines. The strategy leverages the current inventory of harvesters, thereby reducing a producer's capital outlays.
MOISTURE CONTENT MATTERS
Once harvested, some agricultural residues such as corn stover exhibit a relatively high moisture content and low bulk density. These factors complicate handling, transportation and storage. "Anything over 15 percent moisture content cannot be stored for very long without spoiling," notes Wayne Hansen, project director with the Agricultural Utilization Research Institute (AURI) in Waseca, Minnesota. "If it is higher in moisture, it can be stored if ensiled."
The moisture content of residues varies based on location and time of harvest. In the western and southeastern U.S., feedstocks can be dried in the field, resulting in a moisture content of 10 to 15 percent. But dry harvesting is less practical in the Midwest and Northeast, where farmers race to harvest crops before the onset of winter. Drying the feedstock prior to shipping is not viable due to the expense. Farmers in these areas must run wet systems or a mixture of wet and dry, according to Richard Hess, Bioenergy Program Technology Manager at the Idaho National Laboratory.
Both Hess and Hettenhaus are working on wet storage systems, called ensilage, which store the biomass at 35 to 40 percent solids. Hansen explains that ensilage is a solid wet product such as finely chopped biomass high in moisture, typically 60 to 75 percent, that is packed to reduce the amount of oxygen. Fermentation in the ensilage creates lactic acid that acts as a preservative. Sugarcane bagasse and animal fodder are handled this way, according to Hettenhaus. Ensilage also may permit the use of biological methods for pretreatment that are currently done with thermal-chemical techniques at biorefineries, adds Tom Richard, Associate Professor and Director of the Biomass Energy Center at Penn State University.
For dry systems, storing and moving feedstocks in bales also present challenges. While bales are a logical starting point, the packaging does not make sense at higher volumes. "Just as we no longer handle grain in sacks, we do not create packages for biomass feedstocks that do not add value," explains Hess. He is exploring bulk systems, which process or grind the material into a flowable form. "If you go from a unitized process like bales to a bulk flowable form, then you can deal with conveyors and flowable systems, reducing labor and unloading times from 30 minutes to 3 minutes," he notes.
Both wet and dry feedstock systems exhibit a low bulk energy density compared to petroleum or seeds like corn or soybeans. Energy density refers to the amount of energy per unit of volume of material. A low bulk energy density translates into higher transportation costs.
For dry systems, increasing the density of the material by grinding it into smaller components helps. The goal is to optimize the material density for hauling and handling, according to Hess. With wet systems, the water from the ensilage process helps to soften the biomass, allowing it to be compacted more densely, according to Richard.
One idea for increasing the bulk density of wet systems calls for preprocessing the feedstock to extract the sugars at the farm or centralized storage locations near producers. The sugars would be trucked or piped to biorefineries or conventional ethanol facilities, akin to how oil is transported to refineries, explains Hettenhaus. Producers would need to obtain a higher price for the feedstock to offset capital and processing costs.
While first generation biorefineries will rely upon trucks delivering feedstock in bales, serious transportation logistics will arise as volumes increase. "A large 200 tons/day plant could see trucks going in and out their door every couple minutes," says John Sheehan, Senior Strategic Analyst at the National Renewable Energy Laboratory. "That's pretty intense."
Hettenhaus is looking at transportation options, in collaboration with Burlington Northern Santa Fe Railway (BNSF), as part of the Imperial Valley study. Scenarios include using existing short line rail systems near grain elevators. Short line railroads will probably provide a critical role, because they are priced right and need the business, says John Madole, a renewable energy consultant in Minnesota.
Investments are desperately needed in freight, rail and barge systems to not only move existing biofuel products but also to accommodate the growth in biofuels and the raw materials supporting the industry, according to Nathanael Greene, Senior Policy Analyst at the Natural Resources Defense Council. Variations in climate, growing season, crop diversity and transportation infrastructure make it unlikely that one solution will solve all the challenges associated with harvesting, storing and transporting feedstocks. "Every part of the country is going to assemble the pieces slightly differently," says Hess. "It is a Chinese menu of harvest and storage systems, preprocessing, transportation, handling and delivery to the plant."
SYSTEM SUSTAINABILITY
Beyond issues related to harvesting and distribution, another important consideration is sustainability of the entire system. "Developing sustainable energy systems from biomass can only be accomplished if they are built upon sustainable agriculture systems," stresses Richard. In many areas, cropping systems depend upon residues to improve soil fertility and prevent erosion. Removing residues, changing from till to no till practices and adding cover crops or energy crops start to introduce risk, capital investments and a learning curve for producers, according to Hess.
As feedstock volumes increase, the sustainability of the system also will be affected by increased use of fertilizers and pesticides along with the resulting pollution. Preliminary studies have started to address sustainability issues, but there is much work to be done. "It is a desperately under-addressed question," Sheehan recognizes.
In the Imperial Valley, grid samples taken from field trials under different cropping systems are being analyzed by the University of Colorado to model soil fertility. Richard's group at Penn State is developing a decision tool called IFARM, allowing farmers to simulate the impact of changing their cropping system on elements such as livestock feed, energy, labor and the environment.
DuPont's ICBR project is working with Dr. Bruce Dale at Michigan State University to conduct Life Cycle Analysis (LCA) studies to understand how removing residuals impacts soil fertility. "We are transitioning into the next stage, working with the farmers to determine how we are going to move this forward," sums up Anton of Dupont.
Energy crops, such as switchgrass, are seen by many as a means to attain feedstock volumes envisioned in the ORNL study while addressing sustainability issues. "Energy crops have very positive benefits for soil health and erosion control and they can be grown using considerably less water and nitrogen than conventional crops," says Sheehan. But energy crops also face challenges. ORNL volume estimates for energy crops assume an increase in yields. If yields per acre are not increased, the economics will not work.
While research is progressing on energy crops, the industry is concentrating on currently available feedstocks. "Biorefiners are going to start with established resources and as the thing becomes profitable, farmers will adjust their cropping options to maximize returns," says Hess. DuPont's Anton agrees: "Since corn is the largest crop in use and since there is already a collection that goes on for the grain, finding the next step along the way is going to be easier than thinking about a whole new crop system."
Although this article has focused on agricultural residues and crops, another feedstock source for cellulosic ethanol is wood and forestry residues. A biomass inventory and bioenergy assessment was conducted in Washington State through the Department of Ecology (DOE) and Washington State University (WSU). "Washington's biggest opportunity in cellulose isn't straw, it is forestry," says Mark Fuchs of DOE, who worked on the inventory project. "That is really clear from our inventory. WSU is working with the University of Washington forestry department on expanding the analysis of forest-sourced materials. However, there are numerous challenges in tapping forests for cellulosic ethanol production. These include transportation costs, process methods, and Best Management Practices for soil fertility in forests for long term, healthy forest management."
CHICKEN OR EGG?
Feedstock markets need to develop before farmers invest in new equipment and systems to harvest agricultural residuals or grow energy crops. "There is a bit of a chicken or egg problem in that nobody wants to build a big biorefinery if they do not know there is going to be feedstock for it," adds Richard. "And nobody wants to grow feedstock until there is a biorefinery to buy it."
To resolve this situation, companies like Iogen are negotiating feedstock contracts with farmers before beginning construction. First generation plants are also minimizing supply challenges by locating in areas with inexpensive and abundant feedstocks, explains Greene of the Natural Resources Defense Council.
Moving beyond the "low hanging fruit," the real question becomes whether the industry can address the challenges fast enough to grow. Richard believes significantly more funding is needed for research and development. "Energy is a pretty serious issue for our country and we should be investing in it," concludes Richard. "There are a lot of good ideas out there that are not being funded because the resources are not available."
Diane Greer is a free-lance writer and researcher based in New York, specializing in sustainable business, green building and alternative energy. She can be reached at dgreer@greerresearch.com.
REPORTS AND RESOURCES PAGE 50
Achieving Sustainable Production of Agricultural Biomass for Biorefinery Feedstock – http://www.bio.org/ind/biofuel/SustainableBiomassReport.pdf.
Biofuels for Transportation: Global Potential and Implications for Sustainable Agriculture and Energy in the 21st Century – Worldwatch Institute – http://www.worldwatch.org/taxonomy/term/445.
Biomass as Feedstock for a Bioenergy and Bioproducts Industry: The Technical Feasibility of a Billion-Ton Annual Supply. Oak Ridge National Laboratories – http://feedstockreview.ornl.gov/pdf/billion_ton_vision.pdf.
Feedstock Harvesting and Supply Logistics: Research and Development Roadmap – http://www.ceassist.com/pdf/feedstock_roadmap_colloquy.pdf.
Innovative Methods for Corn Stover Collecting, Handling, Storing and Transporting – National Renewable Energy Laboratory – http://www.nrel.gov/docs/fy04osti/33893.pdf.
National Renewable Energy Laboratory Biomass Research – http://www.nrel.gov/biomass/biorefinery.htmlchieving Sustainable Production of Agricultural Biomass for Biorefinery Feedstock – http://www.bio.org/ind/biofuel/SustainableBiomassReport.pdf.