Richard, T. August 23, 2010. Challenges in scaling up biofuels infrastructure. Science. (329)
Below are excerpts from this paper. Look at the impossible scale of biomass required:
- 150 EJ/year = 15 billion metric tons of plant biomass = 200 billion cubic meters of bales, wood chips, pellets, etc
- Agricultural products: Rice, wheat, soy, corn, etc: 2 billion tons, 2.75 billion cubic meters
- Coal: 6.2 billion cubic meters, Oil: 5.7 billion cubic meters
- Therefore, the biofuel biomass required would be much larger than all energy and agricultural commodities now.
Rapid growth in demand for lignocellulosic bioenergy will require major changes in supply chain infrastructure. Even with densification and preprocessing, transport volumes by mid-century are likely to exceed the combined capacity of current agricultural and energy supply chains, including grain, petroleum, and coal.
The next few decades will require massive growth of the bioenergy industry to address societal demands to reduce net carbon emissions. This is particularly true for liquid transportation fuels, where other renewable alternatives to biofuels appear decades away, especially for truck, marine, and aviation fuels. But even for electricity and power, the growth potential of other renewables and nuclear power appears limited by high cost, technology barriers, and/or resource constraints.
With both agronomic and societal concerns about further increases in the use of grains and oilseeds for biofuels, almost all of this increased bioenergy will likely come from lignocellulosic feedstocks: dedicated energy crops, crop residues, forests and organic wastes. These materials have considerably lower bulk densities than grains, resulting in significant logistical challenges.
The transportation fraction of the energy required to grow and deliver energy crops to a biorefinery is only 3 to 5% for grains and oilseeds, but increases to 7 to 26% for lignocellulosic crops such as switchgrass, miscanthus, and other forages and crop residues (5–7).
To reach the IEA 2050 target of 150 EJ/year, primary energy from biomass would require 15 billion metric tonnes [i.e., megagrams (Mg)] of biomass annually, assuming 60% conversion efficiency (4, 7) and a biomass energy content of 17 MJ/kg dry matter (8). A typical dry bulk density of grasses and crop residues is about 70 kg/m3 when harvested, so without compaction the shipping volume of these 15 billion metric tonnes would require more than 200 billion cubic meters (bcm). At baled grass and woodchip densities of 150 and 225 kg/m3 (8–10), this transport volume would be 100 or 60 bcm, respectively (Fig. 1). Using reported energy densities of pellets, pyrolysis oil, and torrefied pellets these densified products would require 28, 17, and 15 bcm of transport capacity, respectively.
For agricultural commodities, the sum of rice, wheat, soybeans, maize, and other coarse grains and oilseeds will approach 2 billion tons in 2010, with a total volume of 2.75 bcm (11).
Current global volumes of energy commodities are somewhat larger, with 6.2 bcm of coal and 5.7 bcm of oil transported in 2008 (12).
The combination of expected growth in energy demand and the lower density of biomass imply that by 2050, biomass transport volumes will be greater than the current capacity of the entire energy and agricultural commodity infrastructure.
a major stress on the transportation infrastructure, especially in rural regions around the world. If managed poorly, this additional traffic could degrade rural roadways and increase safety concerns.
DELIVERY
The transportation and logistics at the back end of a biofuel refinery must also be addressed. Ethanol is incompatible with the current fuel pipeline distribution system due to its corrosivity and its azeotrope with water, which can lead to pipe or tank failure and fuel contamination, respectively. That 200 ML/year biofuel plant would require 16 to 20 tanker trucks or railcars per day to move the fuel to market, increasing both traffic and costs
These fuel distribution challenges are helping drive the interest in “drop-in” fuels that would be compatible with both the existing fuel distribution infrastructure as well as the vehicle fleet. Several such advanced biofuels are nearing commercialization, including butanol, Fischer-Tropsch fuels, and other bio-based gasoline and diesel equivalents. But regardless of the fuel product, massive investments in new pipe, rail, and highway infrastructure are needed to move those fuels from a new biorefinery network dispersed across the landscape.
Economic analysis of both preprocessing and conversion systems highlights the importance of year-round operations, as it is difficult to amortize capital costs for facilities that are only used for a few months of the year (6, 13). However, many biomass feedstocks have optimal harvest periods that may run for only a few weeks. There are likely other seasons during which harvesting should not occur due to weather or various ecosystem constraints. Livestock farmers have been facing a similar problem supplying forages to their 24/7/365 milk- and meat-producing animals for over a thousand years, and have developed effective wet (<70% dry matter) and dry 80% dry matter) storage systems for grasses and crop residues (Fig. 3). Dry biomass is preferred for pellets, torrefaction, and downstream thermochemical processing, where the presence of water would reduce overall energy efficiency
The size and efficiency of bioenergy conversion facilities will determine how far these huge volumes of biomass and biofuel will need to travel, and thus transportation’s contribution to the energy, economic, and environmental impacts of biomass use. At a community scale, biomass energy can be converted in combined heat and power (CHP) systems producing 1 to 30 MW at efficiencies of 80% or more (4). At 80% efficiency, 30 MW of useful energy would require 150 Mg/day of biomass, or rough overwhelm, the economies of scale associated with advanced conversion technologies.
In contrast, cellulosic biofuel refineries are expected to achieve economies of scale at 200 to 1000 megaliters (ML) per year (7, 13, 14). Above this size range, the marginal cost of biomass transport can become greater than the marginal savings of larger biorefinery equipment on a per-unit basis (13). At the lower end of this range, feedstock needs would be equivalent to those of a 300-MW power plant, and a single biorefinery would require 50 trucks to deliver the 1600 Mg of biomass consumed each day. At the high end of this range, with 250 trucks per day, one truck would be unloading every 5 min around the clock.
Both feedstock supply and fuel distribution logistics will influence the optimal size required for these biorefineries to achieve economies of scale
Brazilian sugar cane factories operate as a plantation system, with monocultures of sugar cane surrounding each refinery. Most sugar cane production is within 100 km of Sao Paulo, Brazil’s largest city and industrial base, so the markets for biofuels are relatively close. In the United States, by contrast, midwestern corn ethanol must travel by road and rail more than 1000 km to markets on the east and west coasts.
Although capital costs, oil stability, corrosivity, and deoxygenation remain challenges for pyrolysis (6), downstream conversion possibilities include gasification and blending with petroleum in conventional refineries. Pyrolysis also produces a biochar coproduct that can be used to improve soil quality, serving as a carrier for returning recovered nutrients to the soil. Interestingly, the economies of scale for most of these densification and preprocessing technologies plateau in the range of 20 to 80 MW thermal equivalent (6).
ENDNOTE: other scaling articles
CEC 2015. An assessment of biomass resources in California 2013. California Energy Commission, U.C. Davis. CEC-500-11-020
Total technical energy generation potential of California’s biomass is 34.5 TWh per year, 11.5% of California’s 300 TWh electrical energy demand. Nowhere in this document is the energy return on invested, such as how much diesel fuel energy will be used by heavy-duty trucks to harvest, transport, build the low-efficiency biomass thermal plant (just 20%) or biogas refinery, the gasoline burned by truck drivers to and from work, and all the other fossil energy inputs over the life-cycle of this project. Nor did the document mention how much biomass is already being used by the biofuel industry, for animal feed and bedding, mulch, compost, biochemicals, and other industries.
References and Notes
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J. E. Campbell,,
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- ↵A.E. Farrel. Ethanol can contribute to energy and environmental goals. Science 311, 506 (2006).doi:10.1126/science.1121416
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I thank C. Taylor, K. Ruamsook, E. Thomchick, and C. Hinrichs for providing helpful comments and sources.