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PERSPECTIVEChallenges in Scaling UpBiofuels InfrastructureTom L. RichardRapid growth in demand for lignocellulosic bioenergy will require major changes in supply chaininfrastructure. Even with densification and preprocessing, transport volumes by mid-century arelikely to exceed the combined capacity of current agricultural and energy supply chains, includinggrain, petroleum, and coal. Efficient supply chains can be achieved through decentralizedconversion processes that facilitate local sourcing, satellite preprocessing and densification forlong-distance transport, and business models that reward biomass growers both nearby and afar.Integrated systems that are cost-effective and energy-efficient will require new ways of thinkingabout agriculture, energy infrastructure, and rural economic development. Implementing theseintegrated systems will require innovation and investment in novel technologies, efficient valuechains, and socioeconomic and policy frameworks; all are needed to support an expanded biofuelsinfrastructure that can meet the challenges of scale.The next few decades will require massivegrowth of the bioenergy industry to ad-dress societal demands to reduce net car-bon emis sions. This is particularly true for liquidtransportation fuels, where other renewable alter -natives t o biofuels appear decades away , especiallyfor truck, marine, and aviation fue ls. But even forelectricity and power, the growth potential of otherrenewables and nuclear power appears limited byhigh cost, technolog y barriers, and/or resource con-straints. W ith estimates of bioenergy potentialranging from just under 10% to more than 60%of w or l d prim a r y ene r g y (1–4), biomass seemspoised to provid e a major alternative to fossil fuels.As a point of reference for considering future bio-mass infr astruc ture needs, the International EnergyAgency (IEA) (4)estimatesthata50%reductionin greenhouse gas emissions by 2050 will requireafactorof4increaseinbioenergyproduction,to150 EJ/year (1 EJ = 1018J), providing more than20% of world primary energy.With both agronomic and societal concernsabout further increases in the use of grains andoilseeds for biofuels, almost all of this increasedbioenergy will likely come from lignocellulosicfeedstocks: dedicated energy crops, crop residues,forests and organic wastes. These materials haveconsiderably lower bulk densities than grains, re-sulting in significant logistical challenges. Thetransportation fraction of the energy required togrow and deliver energy crops to a biorefinery isonly 3 to 5% for grains and oilseeds, but increasesto 7 to 26% for lignocellulosic crops such asswitchgrass, miscanthus, and other forages andcrop residues (5–7). These transportation costs rep-resent a diseconomy of scale for lignocellulosicbiofuels that contrasts with, and at large scales canoverwhelm, the economies of scale associatedwith advanced conversion technologies.To reach the IEA 2050 target of 150 EJ/year,primary energy from biomass would require 15billion metric tonnes [i.e., megagrams (Mg)] ofbiomass annually, assuming 60% conversion effi-ciency (4, 7)andabiomassenergycontentof17MJ/kg dry matter (8). A typical dry bulk density ofgrasses and crop residues is about 70 kg/m3whenharvested, so without compaction the shippingvolume of these 15 billion Mg would requiremore than 200 billion cubic meters (bcm). Atbaled grass and woodchip densities of 150 and225 kg/m3(8–10), this transport volume wouldbe 100 or 60 bcm, respectively (Fig. 1). Usingreported energy densities of pellets, pyrolysis oil,and torrefied pellets (6), these densified productswould require 28, 17, and 15 bcm of transportcapacity, respectively.To gain some perspective on the quantitiesinvolved, consider the volumes of related com-modities currently being managed. For agricultur-al commodities, the sum of rice, wheat, soybeans,maize, and other coarse grains and oilseeds willapproach 2 billion tons in 2010, with a total vol-ume of 2.75 bcm (11). Current global volumes ofenergy commodities are somewhat larger, with6.2 bcm of coal and 5.7 bcm of oil transported in2008 (12). Thus, the combination of expectedgrowth in energy demand and the lower densityof biomass imply that by 2050, biomass transportvolumes will be greater than the current capacityof the entire energy and agricultural commodityinfrastructure.These volumes imply a major growth oppor-tunity for manufacturers of biomass-handling andtransport equipment, but also a major stress on thetransportation infrastructure, especially in ruralregions around the world. If managed poorly, thisadditional traffic could degrade rural roadwaysand increase safety concerns. Butincreased demand for biomasscould also provide a strong incen-tive to improve rural transportationinfrastructure, facilitating agricul-tural and economic developmentin concert with renewable energy.The size and efficiency of bio-energy conversion facilities willdetermine how far these hugevolumes of biomass and biofuelwill need to travel, and thus trans-portation’s contribution to theenergy, economic, and environ-mental impacts of biomass use.At a community scale, biomassenergy can be converted in com-bined heat and power (CHP)systems producing 1 to 30 MWat efficiencies of 80% or more(4). At 80% efficiency, 30 MWof useful energy would require150 Mg/day of biomass, or rough-ly five semi-trailer truckloads per day. Thesedecentralized systems have the potential to sourcefeedstock locally with minimum infrastructurecosts. In contrast, cellulosic biofuel refineries areexpected to achieve economies of scale at 200 to1000 megaliters (ML) per year (7, 13, 14).Above this size range, the marginal cost ofbiomass transport can become greater than themarginal savings of larger biorefinery equipmenton a per -unit basis (13). At the lower end of thisrange, feedstock needs would be equivalent tothose of a 300-MW power plant, and a singlebiorefinery would require 50 trucks to deliver the1600 Mg of biomass consumed each day . At thehigh end of this range, with 250 trucks per day,one truck would be unload ing every 5 minaround the clock.These larger biorefineries and their expectedvolumes of flow will require a shift to a large-scaleDepartment of Agricultural and Biological Engineering,Pennsylvania State University, University Park, PA 16802,USA. E-mail: [email protected] re fied pellets020406080100120Billions of cubic meters2010 world grain volumeFig. 1. Global biomass


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