Environmental efficiency among corn ethanol plants

Efficiency in Midwest US corn ethanol plants: A plant survey

Understanding the revised CARB estimates of the land use changes and greenhouse gas emissions induced by biofuels

Crude oil price speculation during 2000s could have increased installed capacity in corn ethanol plants beyond what was warranted by the market factors. We use Muth’s commodity pricing model and Flood and Garber’s tests to test for speculative investment in US corn ethanol industry. The ethanol price expectations are derived using a system of supply-demand-inventory describing US ethanol markets under rational expectations (perfect foresight). These price expectations can help differentiate the installed capacity into two: capacity supported by the market fundamentals and the probable capacity that is installed based on speculation. Econometric estimation procedures and functional form approximations are discussed.

Explaining the reductions in US corn ethanol processing costs: Testing competing hypotheses

Since 2000, corn ethanol production in the USA has increased significantly – from 1.6 to 15 billion gallons (6.1 to 57 billion liters) – due to supportive biofuel policies. In this study, we conduct a retrospective analysis of the changes in US corn ethanol greenhouse gas emission intensity, sometimes known as carbon intensity (CI), over the 15 years from 2005 to 2019. Our analysis shows a significant decrease in CI: from 58 to 45 gCO2e/MJ of corn ethanol (a 23% reduction). This is due to several factors. Corn grain yield has increased continuously, reaching 168 bushels/acre (10.5 metric tons/ha, a 15% increase) while fertilizer inputs per acre have remained constant, resulting in decreased intensities of fertilizer inputs (e.g., 7% and 18% reduction in nitrogen and potash use per bushel of corn grain harvested, respectively). A 6.5% increase in ethanol yield, from 2.70 to 2.86 gal/bushel corn (0.402 to 0.427 L kg−1 corn), and a 24% reduction in ethanol plant energy use, from 32 000 to 25 000 Btu/gal ethanol (9.0 to 6.9 MJ L−1 ethanol) also helped reduce the CI. The total GHG emission reduction benefits through the reduction in the CI and increased ethanol production volume are estimated at 140 million metric tons (MMT) from 2005 to 2019 in the ethanol industry. Displacement of petroleum gasoline by corn ethanol in the transportation fuel market resulted in a total GHG emission reduction benefit of 544 MMT CO2e during the period 2005 to 2019. © 2021 Argonne National Laboratory. Biofuels, Bioproducts and Biorefining published by Society of Industrial Chemistry and John Wiley & Sons Ltd

Reducing life cycle greenhouse gas emissions of corn ethanol by integrating biomass to produce heat and power at ethanol plants

A life-cycle assessment (LCA) of corn ethanol was conducted to determine the reduction in the life-cycle greenhouse gas (GHG) emissions of corn ethanol compared to gasoline by integrating biomass fuels in a 190 million liter (50 million gallon) per year dry-grind corn ethanol plant to replace fossil fuels (natural gas and grid electricity). The biomass fuels studied are corn stover and ethanol co-products [dried distillers grains with solubles (DDGS), and syrup (solubles portion of DDGS)]. The biomass conversion technologies/systems considered are process heat (PH) only systems, combined heat and power (CHP) systems, and biomass integrated gasification combined cycle (BIGCC) systems. The key inventory components of the LCA are corn production, stover production, ethanol production, fertilizer inputs, truck transport, co-product credits, ethanol transport to blending, biomass fuel conversion systems, and combustion of anhydrous ethanol (E100). The life-cycle GHG emission reduction for corn ethanol compared to gasoline (97.7 g CO2e/MJ gasoline) is 42.5% for PH with natural gas, 61.3% for PH with corn stover, 82.2% for CHP with corn stover, 81.6% for IGCC with natural gas, 127.7% for BIGCC with corn stover, and 119.1% for BIGCC with syrup and stover. These GHG emission estimates do not include indirect land use change effects. GHG emission reductions for CHP, IGCC, and BIGCC include power sent to the grid which replaces electricity from coal. BIGCC results in greater reductions in GHG emissions than IGCC with natural gas because biomass is substituted for fossil fuels. In addition, underground sequestration of CO2 gas from the ethanol plant’s fermentation tank could further reduce the life-cycle GHG emission of corn ethanol by 31.5% compared to gasoline.

The life cycle greenhouse gas (GHG) emissions induced by increased biofuel consumption are highly uncertain: individual estimates vary from each other and each has a wide intrinsic error band. Using a reduced-form model, we estimated that the bounding range for emissions from indirect land-use change (ILUC) from US corn ethanol expansion was 10 to 340 g CO(2) MJ(-1). Considering various probability distributions to model parameters, the broadest 95% central interval, i.e., between the 2.5 and 97.5%ile values, ranged from 21 to 142 g CO(2)e MJ(-1). ILUC emissions from US corn ethanol expansion thus range from small, but not negligible, to several times greater than the life cycle emissions of gasoline. The ILUC emissions estimates of 30 g CO(2) MJ(-1) for the California Air Resources Board and 34 g CO(2)e MJ(-1) by USEPA (for 2022) are at the low end of the plausible range. The lack of data and understanding (epistemic uncertainty) prevents convergence of judgment on a central value for ILUC emissions. The complexity of the global system being modeled suggests that this range is unlikely to narrow substantially in the near future. Fuel policies that require narrow bounds around point estimates of life cycle GHG emissions are thus incompatible with current and anticipated modeling capabilities. Alternative policies that address the risks associated with uncertainty are more likely to achieve GHG reductions.

Corn ethanol plants generate high‐purity carbon dioxide (CO2) while producing ethanol. If that CO2 could be converted into ethanol by carbon capture and utilization technologies it would be possible to increase ethanol production more than 37% without additional corn grain inputs. Gas fermentation processes use microbes to convert carbon‐containing gases into ethanol and so have the potential to be used with the CO2 from biorefineries for this purpose. However, as CO2 utilization technologies for converting thermodynamically stable CO2 are typically energy intensive, it is necessary to evaluate the related life‐cycle greenhouse gas (GHG) emissions (carbon intensities or CIs) to see whether there are actual emission reduction benefits. In this study, we evaluate the CIs of ethanol produced from high‐purity CO2 in corn ethanol plants by gas fermentation plus electrochemical reduction. Our analysis shows that the sources of electricity and hydrogen are key drivers of CO2‐based ethanol's GHG emissions. With wind electricity, the design cases show the potential of near‐zero CI ethanol (1.1 g CO2e/MJ), but that can increase to up to 331–531 g CO2e/MJ when today's U.S. Midwest electricity mix is used. To avoid the renewable electricity intermittency issue, we considered a power purchase agreement option using wind electricity 40% of the time and using the regional mix for the rest, which provides a 42% GHG emission reduction from the CI of gasoline. © 2020 The Authors and UChicago Argonne, LLC, Operator of Argonne National Laboratory. Biofuels, Bioproducts and Biorefining published by Society of Chemical Industry and John Wiley & Sons, Ltd.

Abstract. A life cycle assessment (LCA) study was conducted to understand and assess potential greenhouse gas (GHG) emissions reduction benefits of a biomass torrefaction business integrated with other industrial businesses for the use of the excess heat from the torrefaction off-gas volatiles and biocoal. A torrefaction plant processing 30.3 t/h (33.4 ton/h) of corn stover at 17% wet basis (w.b.) moisture content was modeled. The torrefaction plant produced 136,078 t/year (150,000 ton/year) of torrefied material (i.e., biocoal) at 1.1% (w.b.) moisture content and 28.1 MW th (96 million Btu/h) of excess heat energy in the torrefaction off-gas volatiles. At the torrefaction plant gate, the life-cycle GHG emission for the production of biocoal from corn stover (including corn stover logistics GHG emissions) is 11.35 g CO 2 e/MJ biocoal dry matter (229.5 kg CO 2 e/t biocoal at 1.1% w.b. moisture content). The excess heat from the torrefaction plant met about 42.8% of the process steam needs (excluding the co-products dryer heat demand) of a 379 million liter per year (100 million gallon per year) natural gas-fueled dry-grind corn ethanol plant, which results in about 40% reduction in life-cycle GHG emissions for corn ethanol compared to gasoline. Co-firing 10%, 20%, and 30% (energy basis) of biocoal at a coal-fired power plant reduced the life-cycle GHG emissions of electricity generated by 8.5%, 17.0%, and 25.6%, respectively, compared to 100% coal-fired electricity. A sensitivity analysis showed that adding a combined heat and power (CHP) system at the torrefaction plant to meet 100% electricity demand of the torrefaction plant (i.e., 2.5 MW e ) would result in lower GHG emissions for biocoal, corn ethanol, and co-fired electricity than for the case where the torrefaction plant purchased electricity from the grid.

Agriculture is an important and vital sector in Iran’s economy. This sector provides basic needs along with undesirable outputs such as greenhouse gases. Greenhouse gas (GHG) emissions are main causes of environmental pollution. By considering the pollution in production process, economic performance can be evaluated precisely. We can modify the efficiency model using the desirable and undesirable outputs to improve the quality of the environment, and to achieve sustainable development. In this regard, environmental efficiency of agriculture is an appropriate guide to produce crops using low inputs and environmental pollution. This study aims to estimate the agricultural environmental efficiency in Iran’s different provinces using data envelopment analysis (DEA) method. The results show that for each billion Rial of agriculture gross value added, 11.39 tons of carbon dioxide are produced. Subsequently, regarding the greenhouse gas emissions caused by proportional agricultural activity, the provinces are divided into three clusters. Mean carbon dioxide emission for each cluster is 536,663.7, 804,315.7, and 186,311.8 tons, respectively. Mean environmental efficiency for clusters is 0.294, 0.243, and 0.836, respectively. This indicates that provinces with more greenhouse gas emissions have lower environmental efficiency. In this regard, the politicians should make the less efficient clusters to reduce the use of undesirable inputs to decrease the pollutant emissions. Besides, by proper allocation of capital, the more efficient cluster can improve environmental technologies.

The US corn ethanol industry has grown from virtually nothing in the early 1980s to over 14 billion gallons in 2011. Subsidies have been an important impetus for the industry, and they have existed in one form or another throughout the life of the industry. This paper provides (1) a brief look at the history of the linkages between energy and agriculture and how they have changed with biofuels; (2) a review of some of the major impacts of the US corn ethanol program; and (3) analysis of prospective impacts of cellulosic biofuels. There is no doubt that biofuels have brought about a new era for global agriculture. Historically, the prices of agricultural and energy products moved in response to supply and demand factors relevant to each market, but moved largely independent of one another. Corn ethanol has changed that, and today there is a link between crude oil and corn that is driven by the demand side. Since agricultural commodity prices are linked both on the demand and supply sides, the corn–crude oil link spills over to other agricultural commodities as well. Development of cellulosic biofuels has been much slower than hoped. The feedstocks are more expensive than initially believed. Conversion technologies remain uncertain and expensive. There are many uncertainties through the cellulosic supply chain, and government policy remains uncertain as well. Thus, the future of the cellulosic biofuels industry is, at this point, an open question.

Few of the numerous published studies of the emissions from biofuels-induced "indirect" land use change (ILUC) attempt to propagate and quantify uncertainty, and those that have done so have restricted their analysis to a portion of the modeling systems used. In this study, we pair a global, computable general equilibrium model with a model of greenhouse gas emissions from land-use change to quantify the parametric uncertainty in the paired modeling system's estimates of greenhouse gas emissions from ILUC induced by expanded production of three biofuels. We find that for the three fuel systems examined--US corn ethanol, Brazilian sugar cane ethanol, and US soybean biodiesel--95% of the results occurred within ±20 g CO2e MJ(-1) of the mean (coefficient of variation of 20-45%), with economic model parameters related to crop yield and the productivity of newly converted cropland (from forestry and pasture) contributing most of the variance in estimated ILUC emissions intensity. Although the experiments performed here allow us to characterize parametric uncertainty, changes to the model structure have the potential to shift the mean by tens of grams of CO2e per megajoule and further broaden distributions for ILUC emission intensities.

In the corn ethanol industry, the ability of plants to obtain favorable prices through marketing decisions is considered important for their overall economic performance. Based on a panel of surveyed of ethanol plants we extend data envelopment analysis (DEA) to decompose the economic efficiency of plants into conventional sources (technical and allocative efficiency) and a new component we call marketing efficiency. The latter measure allows us to evaluate plants’ ability to contract favorable prices of corn and ethanol relative to spot market prices and its implications for their overall economic performance. Results show that plants are very efficient from a technical point of view. Dispersion in overall economic performance observed across units is mainly explained by differences in allocative and marketing sources. Our results are consistent with the view that plants with higher production volumes may perform better, in part, because they can secure more favorable prices through improved marketing performance. Plants also seem to achieve significant improvements in marketing performance through experience and learning-by-doing. These results are consistent with two facts; 1) economies of scale may not be the only reason behind the increase in the average size of plants in the ethanol industry and; 2) there might be incentives for horizontal consolidation across plants.

Life cycle assessment of a corn stover torrefaction plant integrated with a corn ethanol plant and a coal fired power plant