Ethanol and other biofuels from cellulosic feedstocks are currently the most promising candidates to replace a large fraction of gasoline consumption in the United States and reduce greenhouse gas emissions. Gaps in current approaches to estimating the net greenhouse gas emissions from second-generation biofuels may lead to underestimation of the carbon intensity of these fuels. Current life cycle assessment models of biofuels do not sufficiently account for biomass losses and emissions associated with the harvest and storage of biomass feedstocks, which can require additional fuel and materials use on the farm as well as reducing the effective yield of a crop at the biorefinery gate. The goal of this dissertation is to quantify the range of likely impacts of feedstock storage on the net greenhouse gas emissions from biofuel production.
A broad survey of published forage and bioenergy studies was used to assess the range of likely feedstock dry matter losses during storage by several methods. These loss distributions, as well as updated parameters for biomass harvesting processes and potential direct emissions of non-CO2 greenhouse gases during biomass decomposition were incorporated into the Greenhouse gases, Regulated Emissions, and Energy use in Transportation (GREET) model to determine the effects on life cycle global warming impact. Methods for laboratory-scale storage experiments were developed using a variety of potential bioenergy feedstocks harvested at Purdue University.
Experiments with corn stover and switchgrass under controlled temperature and moisture conditions were conducted to determine rates of dry matter loss and methane and nitrous oxide emissions during storage. Results show that updating biofuels life cycle analysis models to include harvest and storage of biomass feedstocks can substantially increase net greenhouse gas emissions from 2.0 - 10.0 gCO2e/MJ ethanol. Differences between storage methods are significant: materials use and direct emissions of methane may lead to greater emissions during wet storage, while covering dry bales reduced average emissions and variability. Both methane and nitrous oxide are produced during aerobic biomass storage at the laboratory scale, though at low rates which may not
substantially affect the carbon intensity of cellulosic biofuels.
Incorporating harvest and storage parameters into biofuels life cycle assessment models significantly alters both point estimates and stochastic analyses of greenhouse gas emissions. While ethanol from cellulosic feedstocks still provides a greater than 60% reduction in greenhouse gases compared to gasoline, storage processes should be considered when assessing the extent to which biofuels reduce net fossil energy use and climate change emissions.
Reference: altenergyprograms.blogspot.com
Bioenergy is becoming increasingly attractive to many countries, but has sparked an intensive debate regarding energy, economy, society and environment. Biofuels provide alternative energy to conventional fossil fuels. However, the environmental impact of producing and using biofuel is a major concern to our society. This study is dedicated to quantifying and evaluating biofuel production and potential climate change mitigation due to potential large-scale bioenergy expansion in the conterminous United States, using model-data fusion approaches.
Biofuel made from conventional (e.g., maize ("Zea mays" L.)) and cellulosic crops (e.g., switchgrass ("Panicum virgatum" L.) and "Miscanthus" ("Miscanthus x giganteus")) provides alternative energy to fossil fuels and has been considered to mitigate greenhouse gas emissions. To estimate the large-scale carbon and nitrogen dynamics of these biofuel ecosystems, process-based models are needed. Here, we developed an agroecosystem model (AgTEM) based on the Terrestrial Ecosystem Model for these ecosystems. The model incorporated biogeochemical and ecophysiological processes including crop phenology, biomass allocation, nitrification and denitrification as well as agronomic management of irrigation and fertilization. It was used to estimate crop yield, biomass, net carbon exchange, and nitrous oxide (N2O) emissions at an ecosystem level. We found that AgTEM reproduces the observed annual net primary production and N2O emissions of most sites, with over 85% of total
variations explained by the model. Local sensitivity analysis indicated that the model sensitivity varies among different ecosystems. Net primary production of maize is sensitive to temperature, precipitation, cloudiness, fertilizer and irrigation and less sensitive to atmospheric carbon dioxide (CO2) concentrations. In contrast, the net primary production of switchgrass and "Miscanthus" is most sensitive to temperature among all factors. The N2O emissions are sensitive to management in maize ecosystems, and sensitive to climate factors in cellulosic ecosystems. The developed model should help advance our understanding of carbon and nitrogen dynamics of these biofuel ecosystems at both field and regional scales.
Next, we estimated the potential emissions of greenhouse gases from bioenergy ecosystems with AgTEM, assuming maize, switchgrass and "Miscanthus" will be grown on the current maize-producing areas in the conterminous United States. The modeling experiments suggested that, the maize ecosystem acts as a mild net carbon source while cellulosic ecosystems (i.e., switchgrass and "Miscanthus") act as mild sinks. Nitrogen fertilizer use is an important factor affecting biomass production and N2O emissions, especially in the maize ecosystem. To maintain high biomass productivity, the maize ecosystem emits much more greenhouse gases, including CO2 and N2O, than switchgrass and "Miscanthus" cosystems, when high-rate nitrogen fertilizers are applied. For maize, the global warming potential amounts to 1-2 Mg CO2eq ha-1 yr-1, with a dominant contribution of over 90% from N2O emissions. Cellulosic crops contribute to the global warming potential of less than 0.3 Mg CO2eq ha-1 yr-1. Among all three bioenergy crops, "Miscanthus" is the most biofuel productive and the least GHG intensive at a given cropland. Regional model simulations suggested that, substituting "Miscanthus" for maize to produce biofuel could potentially save land and reduce GHG emissions.
Since growing biomass from marginal lands is becoming an increasingly attractive choice for producing biofuel, we looked further into bioenergy potential and possible GHG emissions from bioenergy crops grown on marginal lands in the United States. Two broadly tested cellulosic crops, switchgrass and "Miscanthus", were assumed to be grown on the abandoned land and mixed crop-vegetation land with marginal productivity. Production of biomass and biofuel as well as net carbon exchange and N2O emissions were estimated in a spatially explicit manner, using AgTEM. Modeling experiments showed that, cellulosic crops, especially "Miscanthus", could produce a considerable amount of biomass and thus ethanol. For every hectare of marginal land, switchgrass and "Miscanthus" could produce 1.4-2.3 kL and 4.1-6.9 kL ethanol, respectively. The actual amount of ethanol production depends on nitrogen fertilization rate and biofuel conversion efficiency. Switchgrass has high global warming intensity (100-190 g CO2eq L-1 ethanol), in terms of GHG emissions per unit ethanol produced. "Miscanthus", however, emits only 21-36 g CO2eq to produce every liter of ethanol. To reach the mandated cellulosic ethanol target of 21 billion gallons by 2022 in the United States, growing "Miscanthus" on the marginal lands could save a large amount of land and reduce GHG emissions in comparison to growing switchgrass.
It should be noted that, ecosystem modeling may be useful for evaluating ecosystem services and environmental impacts, and the results could be informative for policy making concerning energy, food security and sustainability. However, the modeling results are limited in terms of advising agricultural management practices, land use change and energy system analysis, due to modeling uncertainties, data unavailability, and simulation scale and boundary limitations. High-accuracy data assimilation, model improvement and life cycle assessment still await future study.
Report on Isolate higher for on stretch article at Strong Point Vertical website
Traditional the Box file Diminish on Ethanol
Focusing on the Nexus of the Encouragement and Physical exertion Significance Chains
by Nathan Glasgow and Lena Hansen
Ethanol, which can be substituted for or blended with juice, has universally been fashioned from either corn or sugarcane feedstocks.
Biofuels, and specifically ethanol, control been the under enemy control of a very big arrangement of objection in new months by detractors claiming that bigger energy is considered necessary to produce ethanol than is about in the critical product, that it is too overpriced, and that it produces negligible carbon reductions. These critiques are severely not entirely. Authoritative technologies control been highly forecasted-even identified in the market-to produce ethanol that is far bigger effective and less than energy-intensive than juice. We'll delve into why, and why the critics control gotten it twisted.
Some time ago we say biofuels, we result in soak away fuels finished from biomass-chiefly biodiesel and ethanol, which can be substituted for diesel fuel or for juice, each. The technology used to produce biodiesel is charge imaginary, bar its biomass feedstocks are predetermined and production at the moment is pretty overpriced. We preference more accurately concentrate on ethanol, which we call together has analytically best quality sway.
Ethanol, which can be substituted for or blended with juice, has universally been fashioned from either corn or sugarcane feedstocks. In loyalty, Brazil without hesitation meets bigger than 25 percent of its juice need with ethanol finished from sugarcane. (The sugar is so stingy that the significant ethanol sells in New York for 1.10 a gallon-with about 81 percent the energy content of a gallon of gasoline-after paying a 100 percent portion, not permitted under WTO rules, to safeguard U.S. corn farmers. Undeterred, the Brazilians are lightheartedly expanding their ethanol exports to Asia.) Trustworthy juice in the Together States contains, on trade event, 2 percent ethanol (used as a change for MTBE to oxygenate fuel). American ethanol is in close proximity to particularly finished from the kernels of corn, secretarial for about 7 percent of the corn crop. But standard processes and feedstocks used to make ethanol are not probable in the Together States on a large scale for three reasons: they're not cost-competitive with long-run juice prices short subsidies, they run with cooking crops for land, and they control right marginally cheerful energy balances.
Cheerily, in addendum to starch-based feedstocks, ethanol can be fashioned from "cellulosic" feedstocks, through biomass wastes, fast-growing hays touch on switchgrass, and short-rotation woody crops touch on poplar. Having the status of not cost-competitive at the moment, earlier than observed advances in technology govern us to call together that in the nearby few verve, ethanol finished from these crops preference metamorphose cost-competitive, won't run with cooking for cropland, and preference control a momentous cheerful energy yield. For sure, seeing that these crops are geological to control big biomass yields (~10-15 dry tons/acre, up from the exhale ~5 dry tons/acre), knowingly less than land preference be considered necessary than as usual scrutiny. Latest, cellulosic ethanol preference unexceptionally control twice the ethanol laying down of arms of corn-based ethanol, at apprentice channel check, with far chief net energy laying down of arms.
A collective complain about ethanol is that the denomination of feedstocks is predetermined and land used to increase feedstocks may well be put to chief use. For cellulosic feedstocks, the put up is more accurately the setback. Cellulosic feedstocks are plentiful: for example, majesty and agricultural wastes can be used to create ethanol, with the cheerful result of sinking the denomination of rubbish we requirement set up of. Through rubbish to produce fuel has the clear benefit of a draw near to defense feedstock, and seeing that energy is habitually expended to create the product, not the rubbish, this type of ethanol evidently has a cheerful energy yield.
Not more accurately as transparent is to what extent passionate energy crops can be used to produce ethanol. We call together the complete is primitive. Labor by Oak Joint Majestic Laboratory shows that passionate energy crops can be complete short divergent with cooking crops seeing that they can be complete in substitute areas unsuitable for cooking crop production, or on about 17 million acres of Upholding Lean Align land that is without hesitation character withheld from agricultural use.
Cellulosic crops control mega unsophisticated benefits for every reasons. To begin with, seeing that crops touch on switchgrass are long-established perennials, budding them actually prevents catch grind and restores tainted land. For this fantastically dynamic, cellulosic crops furthermore control analytically apprentice carbon emissions. Having the status of corn-based ethanol reduces carbon emissions by about 20 percent below juice, cellulosic ethanol is predicted to be carbon-neutral, or possibly frequent net-carbon-negative.
We can't remembrance how many period we've been asked the question: "But doesn't ethanol callous bigger energy to produce than it contains?" The primitive complete is no-most precise studies, in reality relations in new verve dazzling modern techniques, do not posterior this upshot. These studies control made known that ethanol has a highly developed energy content than the fossil energy used in its production. A variety of studies that move along that ethanol is a net energy little guy mark (wrongly) the energy of the sun used to increase a feedstock in ethanol's energy yield, which misses the genuine epoch that the sun's energy is defense. As a consequence, seeing that crops touch on switchgrass are perennials, they are not replanted and tame at all court, avoiding farm-equipment energy. For sure, if polycultured to touch the prairies where they increase naturally, they must callous no manure, irrigation, or pesticides either. So, according to the U.S. Fork of Physical exertion, for at all one unit of energy about at the fuel plunger, 1.23 units of fossil energy are used to produce juice, 0.74 of fossil energy are used to produce corn-based ethanol, and right 0.2 units of fossil energy are used to produce cellulosic ethanol.
Critics a great deal repayment cellulosic ethanol by ignoring the new advancements of next-generation ethanol conversion technologies. A new example that has standard ideas be of interest is David Pimentel's Dispute 2005 create in New Cremation Labor, which argues that ethanol production from cellulosic feedstocks requires bigger fossil energy to produce than the energy contained in the critical product. Quiet, Pimentel bases his censure on right one technology used to produce ethanol, ignoring two other developing technologies. His future conversion technology, sarcastic hydrolosis, is the smallest possible monetary of the three.
A patrician flow, thermal gasification, converts biomass in vogue a synthesis gas in concert of carbon oxides and hydrogen. The gas is after that converted in vogue ethanol via either a physical process using bacteria or a catalytic reactor. Every of these processes erode good sway for greater than before energy yields and low-priced indemnity by using cellulosic feedstocks. This conversion technology is without hesitation character veteran in check plants in Arkansas and Colorado.
Torpid chief, enzymatic tapering off hydrolosis earlier than shows pledge in the carnival. Such firms as Iogen and Novozymes control been developing enzymes, and "spiciness bugs," that can department biomass such as corn residues (leaves, stalks, and cobs) in vogue sugars that can after that be converted in vogue ethanol. Historically, the prevalent check bit of this technology was the initiation of enzymes. Prior this court, while, in join up with the Majestic Renewable Physical exertion Laboratory, Novozymes announced a 30-fold tapering off in the check of enzyme production in laboratory trials. Scheduled benefits from this process mark low energy desires, lighten ease, and boring process get through. A check plant exists in Ontario and special is on purpose in Hawai'i. The cap commercial-scale enzymatic tapering off hydrolosis plant is overcome to be built and effectual by Iogen at home two verve, producing ethanol at a targeted check of 1.30 per gallon.
No substance which of these conversion technologies completely wins, it is clear that effective and monetary ethanol production from fiber is on the horizon-which is good news for the Together States, where mobility consumes seven of at all ten barrels of oil we use. Our yearning long for for that oil comes at a cost-we control to buy it, we control to arrangement with the mire that comes from using it, and, seeing that 12 percent of our oil comes from the Basic East, we control to help it. From the time when mobility consumes 70 percent of the oil we use, mainly by burning juice, it's the cap divide to look upon for a strategic.
Our new emit Winning the Oil Endgame (www.oilendgame.com) shows that the adverse cap level to sinking our oil value is tripled automobile efficiency-which can good thing sanctuary, declare or good thing demonstrate and stillness, and pay off its frugal check (if any) at home two verve at today's U.S. juice prices. But there's no dynamic to benefit offering. Through biofuels more accurately of juice to power our cars has the sway to put somewhere else 3.7 million barrels per day of chilly oil-that's a fifth of our forecasted value in 2025, whilst bigger monetary use. In loyalty, an 85/15 percent key of ethanol/gasoline in the basin of RMI's aimed 66-mpg SUV would conclusion in the vehicle success ~320 mpg per gallon of fossil fuel burned (seeing that the mass of fuel burned is ethanol).
Favorably, focusing on the nexus of the crop growing and energy custom manacles preference create large opportunities for business and large wins for our vigor. The critics severely control it twisted.
Nathan Glasgow and Lena Hansen are researchers/consultants at RMI.
Improved to Explore:
Winning the Oil Endgame (www.oilendgame.com) and the linked Repayment 18 Biofuels Ceremonial Addition (id.).
U.S. Fork of Physical exertion, Ethanol: The All-embracing Physical exertion Lifecycle Outlook at:
www.eere.energy.gov/vehiclesandfuels/pdfs/program/2005 ethanol brochure.pdf.
P.C. Provoke, Ethanol from Cellulose: A Complete Sum up at:
www.hort.purdue.edu/newcrop/ncnu02/v5-017.html.
