Depots Could Help Solve Biomass Supply Chain Challenges
Creating biofuels from region-specific biomass could make a huge dent in fossil fuel use for transportation. But moving lightweight, bulky biomass from farms to factories could leave a large carbon footprint, and get expensive quickly.
So quickly, in fact, that in order to be economically viable, plant biomass would need to come from an area no more than 50 miles away from where it will be processed into fuel.
A sustainability research team at the Great Lakes Bioenergy Research Center (GLBRC) is working to solve biofuel supply chain issues by exploring a new intermediate structure for gathering, processing and converting biomass into cellulosic biofuels. The proposed structure, called Regional Biomass Processing Depots (RBPDs), could improve both the economics and the sustainability of the biomass supply chain by keeping a portion of pretreatment and processing closer to the farm.
“By staging part of the processing closer to where biomass is grown, a distributed model like the RBPDs could help create jobs in rural communities while also transforming plant biomass into an energy intermediate that’s easier to transport,” says Pragnya Eranki, a doctoral student in chemical engineering at Michigan State University (MSU).
At the heart of the supply chain challenges is transportation.
“For cellulosic ethanol, we really don't know what will happen between the field and the biorefinery,” says Bryan Bals, an MSU postdoctoral researcher. “Would it be stored on the farm in bales, sent to a storage facility, or sent immediately to the biorefinery? Nobody really has that figured out yet.”
As modeled by the MSU research team, the RBPD concept looks somewhat like a web. Regional depots would be scattered across the state to perform pretreatment, making the biomass more amenable to fuel conversion, and compacting it for easier transport to a central biorefinery.
A recent life cycle assessment study conducted by Eranki and Bruce Dale, an MSU professor of chemical engineering, shows that this form of distributed network generates nearly the same net energy as the centralized biorefinery model, but generates significantly lower greenhouse gas emissions.
Not only could the RBPD concept improve the carbon footprint of the supply chain, it could also generate additional revenue for local communities.
The ammonia fiber expansion (AFEXTM) pretreatment that is being modeled as part of these depots can also be used to create high-value co-products, like animal feed. Once pretreated and compacted into pellets, briquettes or cubes at the local depot, the biomass becomes more of an energy intermediate that can be used for either feed or fuel.
"The AFEX process is essentially a more extreme version of what farmers already do to their forages to improve digestibility," notes Bals. "Once the pretreated, densified biomass comes out of the depot, it can be sent back to the farm for animal feed or sent to the biorefinery for processing into fuel."
If each RBPD was customized to the most suitable local feedstock, biorefineries could plan for diverse materials and reduce the risk associated with relying on one type of biomass.
“If you can create a network of these depots across the country that can densify the biomass, you can ship it across the country without a major increase in cost for transportation,” says Bals.