The economic feasibility of sugar beet biofuel production in central North Dakota

This study examines the financial feasibility of producing ethanol biofuel from sugar beets in central North Dakota. Under the Energy Independence and Security Act (EISA) of 2007, biofuel from sugar beets uniquely qualifies as an “advanced biofuel”. EISA mandates production of 21 billion gallons of advanced biofuels annually by 2022. A stochastic simulation financial model was calibrated with irrigated sugar beet data from central North Dakota to determine economic feasibility and risks of production for 0.038 hm³y⁻¹ (or 10 MGY (Million Gallon per Year) and 0.076 hm³y⁻¹ (or 20 MGY) ethanol plants. Study results indicate that feedstock costs, which include sugar beets and beet molasses, account for more than 70 percent of total production expenses. The estimated breakeven ethanol price for the 0.076 hm³y⁻¹ plant is $400 m⁻³ ($1.52 per gallon) and $450 m⁻³ ($1.71 per gallon) for the 0.038 hm³y⁻¹ plant. Breakeven prices for feedstocks are also estimated and show that the 0.076 hm³y⁻¹ plant can tolerate greater ethanol and feedstock price risks than the 0.038 hm³y⁻¹ plant. Our results also show that one of the most important factors that affect investment success is the price of ethanol. At an ethanol price of $484.21 m⁻³ ($1.84 per gallon), and assuming other factors remain unchanged, the estimated net present value (NPV) for the 0.076 hm³y⁻¹ plant is $41.54 million. By comparison, the estimated NPV for the 0.038 hm³y⁻¹ plant is only $8.30 million. Other factors such as changes in prices of co-products and utilities have a relatively minor effect on investment viability.     

Marginal cost of delivering switchgrass feedstock and producing cellulosic ethanol at multiple biorefineries

Limited information is available regarding the change in cost to deliver dedicated energy crop feedstock as the quantity of required feedstock increases. The objective is to determine the marginal cost to produce and deliver switchgrass feedstock to biorefineries. A mathematical programming model that includes 77 production regions (Oklahoma counties), monthly feedstock requirements, integer activities for harvest machines and integer activities for each of 16 potential biorefinery locations was constructed. The model was initially solved for a single biorefinery. The number of plants was incremented by one and the model resolved until nearly 10% of the cropland and improved pasture land was converted to switchgrass. The estimated cost to deliver 1.0 Mg of feedstock to a single 189 dam³ y⁻¹ capacity biorefinery is 55 $. The cost to deliver feedstock increases as additional biorefineries are constructed and the cost for the ninth biorefinery of 87 $ Mg⁻¹ is 58% greater than the cost to deliver to the first biorefinery. The cost difference is primarily due to differences in transportation cost. Initial cellulosic biorefineries will have an opportunity for establishing a feedstock cost advantage by carefully selecting land for conversion to switchgrass and by negotiating long term leases.     

Processing and sorting forest residues: Cost,productivity and managerial impacts

Feedstocks generated from processing forest residues have traditionally been considered as a low value product. The economic potential of these materials can be enhanced by emerging biomass conversion technologies, such as torrefaction, briquetting, and gasification; however, these systems require higher quality feedstock. The objective of this study was to determine the cost of processing and sorting forest residues to produce feedstock, so that the best comminution machines (i.e. chipper vs. grinder) could be used to better control feedstock size distribution. The tree tops left from sawlog processing and small-diameter trees were delimbed and separated from the slash pile. Three harvest units were selected and each unit was divided into three sub-treatment units (no-, moderate, and intensive sorting). Results showed that the cost of operations were higher for the sorted sub-units when compared to the non-sorted. The total cost of operation (felling to loading) for sawlogs was lowest at 40.81 $ m⁻³ in the nosorting treatment unit, followed by moderate (42.25 $ m⁻³) and intensive treatment unit (44.75 $ m⁻³). For biomass harvesting, the cost of operation (felling to delimbing and sorting) ranged from 27 to 29 $ oven dry metric ton⁻¹. The most expensive operational phase was primary transportation; therefore, cost of treating the forest residues had less impact on the overall cost. The cost increase (1150 $ ha⁻¹) of sorting forest residues could offset cost savings from avoided site preparation expenses (1100 $ ha⁻¹), provided that the forest residues were utilized.     

Beet tissue ensiling: An alternative for long-term storage of sugars in industrial beets for nonfood use

Industrial beets have significant potential to compete against corn grain as an important source of sugars for nonfood industrial processes including microbial bioconversions. However, dependable, long-term storage techniques are necessary to extend processing campaigns and meet increasingly-important industry requirements such as carbon footprint reductions. This work evaluated the potential of industrial-beet tissue ensiling as an alternative for long-term sugar storage. Ground industrial-beet tissue was ensiled for 8 wk at 23 °C and various combinations of pH, moisture content (MC), and sugar:solids (SSR). The pH, MC, and SSR values ranged from 2.0 to 6.8, 50%–85%, and 38%–76%, respectively, according to a central composite rotatable design. Response surface methodology was used to model and illustrate effects of parameter combinations on beet sugar retention. MC and pH had statistically significant effects on sugar retention in beet tissue silage, whereas SSR had no significant effect. Only some combinations of pH ≤ 4.0 and MC ≤ 67.5% enabled the highest sugar retentions in ensiled tissue (≥ 90%). Moreover, tissue ensiled at pH ≤ 3.0 and MC ≤ 67.5% showed increases of ≤ 7% over initial sugars after 3 d of ensiling, suggesting that highly acidic conditions may partially hydrolyze beet tissue cellulose and/or hemicellulose during storage. In contrast, tissue ensiled at some combinations of pH < 6.5 and MC > 67.5% only achieved sugar retentions of < 30% at 8 wk. Sulfuric acid cost estimates (on a dry-sugar basis) to achieve effective pH (2.0–4.0) for sugar retentions ≥ 90% range from $4.9 Mg⁻¹ to $18.6 Mg⁻¹.     

Evaluation of alternatives for the evolution of palm oil mills into biorefineries

Six alternatives for the conversion of an average Colombian palm oil mill (30 t h⁻¹ of fresh fruit bunches (FFB) into biorefineries were evaluated. The alternatives studied were: (C1) Production of biogas from the Palm Oil Mill Effluents (POME), (C2) Composting of empty fruit bunches (EFB) and fiber, (C3) Biomass combustion for high pressure steam combined heat and power, (C4) Pellets production, (C5) Biochar production and, (C6) Biochar and bio-oil production. The available biomass could result in up to 125 kWh of electricity, 207 kg of compost, 125 kg of pellet, 44 kg of biochar and 63 kg of bio-oil per metric ton of FFB. The global warming potential (GWP), eutrophication potential (EP), net energy ratio (NER), capital expenditures (CAPEX), operational costs (OPEX), net present value (NPV) and internal rate of return (IRR) were calculated for all the alternatives. GHG reductions of more than 33% could be achieved. Anaerobic digestion and composting contributed to 30% reduction of the EP. The CAPEX for all of the biorefinery alternatives studied varies between 0.7 $ t⁻¹ and 2.8 $ t⁻¹ of FFB. The OPEX varies between 1.6 $ t⁻¹ and 7.3 $ t⁻¹ of FFB. The NPV for viable scenarios ranged between 2.5 million and 13.9 million US dollars. The IRR calculated varied between 3% and 56% and the payback periods were between 3 and 8 years. The total extra incomes reached values up to 15.2 $ t⁻¹ of FFB. Overall the pellets production biorefinery was the preferred alternative.     

Economics of small-scale on-farm use of canola and soybean for biodiesel and straight vegetable oil biofuels

While the cost competitiveness of vegetable oil-based biofuels (VOBB) has impeded extensive commercialization on a large-scale, the economic viability of small-scale on-farm production of VOBB is unclear. This study assessed the cost competitiveness of small-scale on-farm production of canola- [Brassica napus (L.)] and soybean-based [Glycine max (L.)] biodiesel and straight vegetable oil (SVO) biofuels in the upper Midwest at 2007 price levels. The effects of feedstock type, feedstock valuation (cost of production or market price), biofuel type, and capitalization level on the cost L⁻¹ of biofuel were examined. Valuing feedstock at the cost of production, the cost of canola-based biodiesel ranged from 0.94 to 1.13 $ L⁻¹ and SVO from 0.64 to 0.83 $ L⁻¹ depending on capitalization level. Comparatively, the cost of soybean-based biodiesel and SVO ranged from 0.40 to 0.60 $ L⁻¹ and from 0.14 to 0.33 $ L⁻¹, respectively, depending on capitalization level. Valuing feedstock at the cost of production, soybean biofuels were cost competitive whereas canola biofuels were not. Valuing feedstock at its market price, canola biofuels were more cost competitive than soybean-based biofuels, though neither were cost competitive with petroleum diesel. Feedstock type proved important in terms of the meal co-product credit, which decreased the cost of biodiesel by 1.39 $ L⁻¹ for soybean and 0.44 $ L⁻¹ for canola. SVO was less costly to produce than biodiesel due to reduced input costs. At a small scale, capital expenditures have a substantial impact on the cost of biofuel, ranging from 0.03 to 0.25 $ L⁻¹.     

Cob biomass supply for combined heat and power and biofuel in the north central USA

Corn (Zea mays L.) cobs are being evaluated as a potential bioenergy feedstock for combined heat and power generation (CHP) and conversion into a biofuel. The objective of this study was to determine corn cob availability in north central United States (Minnesota, North Dakota, and South Dakota) using existing corn grain ethanol plants as a proxy for possible future co-located cellulosic ethanol plants. Cob production estimates averaged 6.04 Tg and 8.87 Tg using a 40 km radius area and 80 km radius area, respectively, from existing corn grain ethanol plants. The use of CHP from cobs reduces overall GHG emissions by 60%–65% from existing dry mill ethanol plants. An integrated biorefinery further reduces corn grain ethanol GHG emissions with estimated ranges from 13.9 g CO₂ equiv MJ⁻¹ to 17.4 g CO₂ equiv MJ⁻¹. Significant radius area overlap (53% overlap for 40 km radius and 86% overlap for 80 km radius) exists for cob availability between current corn grain ethanol plants in this region suggesting possible cob supply constraints for a mature biofuel industry. A multi-feedstock approach will likely be required to meet multiple end user renewable energy requirements for the north central United States. Economic and feedstock logistics models need to account for possible supply constraints under a mature biofuel industry.     

Techno-economic assessment of pellets produced from steam pretreated biomass feedstock

Minimum production cost and optimum plant size are determined for pellet plants for three types of biomass feedstock – forest residue, agricultural residue, and energy crops. The life cycle cost from harvesting to the delivery of the pellets to the co-firing facility is evaluated. The cost varies from 95 to 105 $ t⁻¹ for regular pellets and 146–156 $ t⁻¹ for steam pretreated pellets. The difference in the cost of producing regular and steam pretreated pellets per unit energy is in the range of 2–3 $ GJ⁻¹. The economic optimum plant size (i.e., the size at which pellet production cost is minimum) is found to be 190 kt for regular pellet production and 250 kt for steam pretreated pellet. Sensitivity and uncertainty analyses were carried out to identify sensitivity parameters and effects of model error.     

Analysing the effect of five operational factors on forest residue supply chain costs: A case study in Western Australia

In Australia the use of forest biomass has been developing in recent years and initial efforts are built on adopting and trialling imported European technology. Using a linear programming-based tool, BIOPLAN, this study investigated the impact of five operational factors: energy demand, moisture mass fraction, interest rate, transport distance, and truck payload on total forest residues supply chain cost in Western Australia. The supply chain consisted four phases: extraction of residues from the clear felled area to roadside by forwarders, storage at roadside, chipping of materials by mobile chippers, and transport of chips to an energy plant. For an average monthly energy demand of 5 GWh, the minimum wood supply chain cost was about 29.4 $ t⁻¹, which is lower than the maximum target supply cost of 30–40 $ t⁻¹, reported by many industry stakeholders as the breakeven point for economically viable bioenergy production in Australia. The suggested volume available for chipping in the second year was larger than in the first year indicating that the optimisation model proposed storing more materials in the first year to be chipped in the second year. The sensitivity analysis showed no strong correlation between energy demand and supply chain cost per m³. For higher interest rates, the total storage cost increased which resulted in larger operational cost per m³. Longer transport distances and lower truck payloads resulted in higher transport cost per unit of delivered chips. In addition, the highest supply chain costs occurred when moisture mass fraction ranged between 20% and 30%.     

Lignocellulosic ethanol production from woody biomass: The impact of facility siting on competitiveness

Just as temperate region pulp and paper companies need to compete with Brazilian eucalyptus pulp producers, lignocellulosic biofuel producers in North America and Europe, in the absence of protectionist trade policies, will need to be competitive with tropical and sub-tropical biofuel producers. This work sought to determine the impact of lignocellulosic ethanol biorefinery siting on economic performance and minimum ethanol selling price (MESP) for both east and west coast North American fuel markets. Facility sites included the pine-dominated Pacific Northwest Interior, the mixed deciduous forest of Ontario and New York, and the Brazilian state of Espírito Santo. Feedstock scenarios included both plantation (poplar, willow, and eucalyptus, respectively) and managed forest harvest. Site specific variables in the techno-economic model included delivered feedstock cost, ethanol delivery cost, cost of capital, construction cost, labour cost, electricity revenues (and co-product credits), and taxes, insurance, and permits. Despite the long shipping distance from Brazil to North American east and west coast markets, the MESP for Brazilian-produced eucalyptus lignocellulosic ethanol, modelled at $0.74 L⁻¹, was notably lower than that of all North American-produced cases at $0.83–1.02 L⁻¹.     

Technoeconomic analysis of camelina oil extraction as feedstock for biojet fuel in the Canadian Prairies

This study presents a technoeconomic analysis of commercial extraction of camelina oil as an aviation fuel feedstock. An engineering economic model was designed in Superpro Designer^® to quantify capital investment, scale, production cost, and profitability for a 120,000–1,500,000 tonnes annum⁻¹ solvent extraction plant. The corresponding estimated capital investment was $24.7 - $155 million. Feedstock cost ($0.29–0.40 kg⁻¹), seed yield (1400–2100 kg ha⁻¹), oil content (38–47%), scale, and camelina meal revenue are key factors in the break-even selling price (BESP) and competitiveness of camelina oil as a feedstock. Feedstock represented 81–90% of operating cost. The BESP ranges from $0.43 -$1.22 L^-1. Larger plants have lower BESP compared to smaller plants which require higher breakeven prices. This suggests better economies of scale associated with higher plant scale. Camelina can be introduced into underutilized summerfallow land of semiarid Canadian Prairies of Saskatchewan. Swift Current is an ideal extraction plant location. These results can guide R&D and investment decisions for advancing camelina as an industrial feedstock within the innovation value chain.     

A techno-economic evaluation of the effects of centralized cellulosic ethanol and co-products refinery options with sugarcane mill clustering

This work compares the calculated techno-economic performance for thermochemical and biochemical conversion of sugarcane residues, considering future conversion plants adjacent to sugarcane mills in Brazil. Process models developed by the National Renewable Energy Laboratory were adapted to reflect the Brazilian feedstock composition and used to estimate the cost and performance of these two conversion technologies. Models assumed that surplus bagasse from the mill would be used as the feedstock for conversion, while cane trash collected from the field would be used as supplementary fuel at the mill. The integration of the conversion technology to the mill enabled an additional ethanol production of 0.033 m³ per tonne of cane for the biochemical process and 0.025 m³ t^?1 of cane plus 0.004 m³ t^?1 of cane of higher alcohols for the thermochemical process. For both cases, electricity is an important co-product for the biorefinery, but especially for biochemical conversion, with surpluses of about 50 kWh t^?1 of cane. The economic performance of the two technologies is quite similar in terms of the minimum ethanol selling price (MESP), at 318 $ m^?3 (United States 2007 dollars) for biochemical conversion and 329 $ m^?3 for thermochemical conversion.     

The impact of sugar beet varieties and cultivation conditions on ethanol productivity

The 49 hybrids of sugar beet and semi-forage beet used in this research were characterized by a variable concentration of saccharose (14.58% ± 1.28), Na (5.51 ± 3.07 mmol kg⁻¹), K (57.44 ± 9.71 mmol kg⁻¹), N (21.68 ± 4.75 mmol kg⁻¹), yield (68.36 ± 10.29 t ha⁻¹) and differentiated fermentation efficiency (5.14 ± 1.22 m³ ha⁻¹).It was found that the effectiveness of fermentation depends not only on the saccharose content in the sugar beet, but also its relationships with other components of the dry matter. High sugar beet yield have significant effect on ethanol yield. The impurities such as K, N and Na have a negative effect on efficiency of the fermentation process. It also specifies varietal differences on ethanol yield. It has been found that high ethanol yield is correlated with diploid hybrids which are sugar hybrids.     

Potential for rice straw ethanol production in the Mekong Delta,Vietnam

This study is to evaluate the potential for development of a cellulosic ethanol facility in Vietnam. Rice straw is abundant in Vietnam and highly concentrated in the Mekong Delta, where about 26 Mt year⁻¹ of rice straw has been yearly produced. To minimize the overall production cost (PC) of ethanol from rice straw, it is crucial to choose the optimal facility size. The delivered cost of rice straw varied from 20.5 to 65.4 $ dry t⁻¹ depending on transportation distance. The Mekong Delta has much lower rice straw prices compared with other regions in Vietnam because of high density and quantity of rice straw supply. Thus, this region has been considered as the most suitable location for deploying ethanol production in Vietnam. The optimal plant size of ethanol production in the region was estimated up to 200 ML year⁻¹. The improvement in solid concentration of material in the hydrothermal pre-treatment step and using residues for power generation could substantially reduce the PC in Vietnam, where energy costs account for the second largest contribution to the PC, following only enzyme costs. The potential for building larger ethanol plants with low rice straw costs can reduce ethanol production costs in Vietnam. The current estimated production cost for an optimal plant size of 200 ML year⁻¹ was 1.19 $ L⁻¹. For the future scenario, considering improvements in pre-treatment, enzyme hydrolysis steps, specific enzyme activity, and applying residues for energy generation, the ethanol production cost could reduce to 0.45 $ L⁻¹ for a plant size of 200 ML year⁻¹ in Vietnam. These data indicated that the cost-competitiveness of ethanol production could be realized in Vietnam with future improvements in production technologies.     

Environmental aspects of ethanol derived from no-tilled corn grain: nonrenewable energy consumption and greenhouse gas emissions

Nonrenewable energy consumption and greenhouse gas (GHG) emissions associated with ethanol (a liquid fuel) derived from corn grain produced in selected counties in Illinois, Indiana, Iowa, Michigan, Minnesota, Ohio, and Wisconsin are presented. Corn is cultivated under no-tillage practice (without plowing). The system boundaries include corn production, ethanol production, and the end use of ethanol as a fuel in a midsize passenger car. The environmental burdens in multi-output biorefinery processes (e.g., corn dry milling and wet milling) are allocated to the ethanol product and its various coproducts by the system expansion allocation approach.The nonrenewable energy requirement for producing 1 kg of ethanol is approximately 13.4–21.5 MJ (based on lower heating value), depending on corn milling technologies employed. Thus, the net energy value of ethanol is positive; the energy consumed in ethanol production is less than the energy content of the ethanol (26.8 MJ kg⁻¹).In the GHG emissions analysis, nitrous oxide (N₂O) emissions from soil and soil organic carbon levels under corn cultivation in each county are estimated by the DAYCENT model. Carbon sequestration rates range from 377 to 681 kg C ha⁻¹ year⁻¹ and N₂O emissions from soil are 0.5–2.8 kg N ha⁻¹ year⁻¹ under no-till conditions. The GHG emissions assigned to 1 kg of ethanol are 260–922 g CO₂ eq. under no-tillage. Using ethanol (E85) fuel in a midsize passenger vehicle can reduce GHG emissions by 41–61% km⁻¹ driven, compared to gasoline-fueled vehicles. Using ethanol as a vehicle fuel, therefore, has the potential to reduce nonrenewable energy consumption and GHG emissions.     

Optimization of ethanol production from high dry matter liquefied dry sweet sorghum stalks

The ability of sweet sorghum to be utilized as feedstock for ethanol production at high initial dry material concentration was investigated. Sweet sorghum, after being dried, was liquefacted employing commercial cellulase solution Celluclast^® 1.5L, in order submerged fermentation to be permitted under high-solids concentrations. The presence of a separate enzymatic liquefaction step at 350 kg m⁻³ initial DM enhanced both ethanol production and productivity by 29.76% and 250%, respectively. Response surface methodology, based on the central composite design was applied to explore the combined effect of liquefaction duration and enzyme loading in order liquefaction conditions to be optimized. When the optimum conditions were tested using an enzyme load of 8.32 FPU g⁻¹ of dry material for 8.6 h at 50 °C, high productivity (3.0 kg m⁻³ h⁻¹) and final ethanol production (62.5 kg m⁻³) were achieved.     

Optimizing biofuel production: An economic analysis for selected biofuel feedstock production in Hawaii

Hawaii’s agricultural sector has an immense supply of natural resources that can be further developed and utilized to produce biofuel. Transformation of the renewable and abundant biomass resources into a cost competitive, high performance biofuel could reduce Hawaii’s dependence on fossil fuel importation and enhance energy security. The objectives of the study are to evaluate the economic feasibility of selected bioenergy crops for Hawaii and compare their cost competitiveness. The selected feedstock consists of both ethanol and biodiesel producing crops. Ethanol feedstock includes sugar feedstock (sugarcane) and lignocellulosic feedstock (banagrass, Eucalyptus, and Leucaena). Biodiesel feedstock consists of Jatropha and oil palm.The economic analysis is divided into two parts. First, a financial analysis was used to select feasible feedstock for biofuel production. For each feedstock, net return, feedstock cost per Btu, feedstock cost per gallon of ethanol/biodiesel, breakeven price of feedstock and breakeven price of ethanol/biodiesel were calculated. Leucaena shows the lowest feedstock cost per Btu while banagrass has the highest positive net returns in terms of both feedstock price and energy price.The second approach assumes an objective of maximizing net returns. Given this assumption, biofuel producers will produce only banagrass. As an example, the production of bioenergy on the island of Hawaii is illustrated where 74,793 acres of non-prime land having a “warm and moist” soil temperature and moisture regime are available. Using average yields (static optimization), banagrass production on this acreage can yield 8.24 trillion Btus of energy (ethanol). This satisfies the State’s 10% self-sufficiency energy goal of 3.9 trillion Btus by 2010. Incorporating risk through variability in crop yields and biofuel prices separately shows banagrass as having the highest probability for receiving a positive net return. Banagrass is the leading candidate crop for biofuel production in Hawaii and the State of Hawaii ethanol goal can be achieved by allocating non-prime lands for banagrass production without compromising prime lands currently allocated for agricultural food production in Hawaii. Physical, environmental and socio-economic impacts should be accounted for in evaluating future biofuel projects.     

Environmental and economic assessment of producing hydroprocessed jet and diesel fuel from waste oils and tallow

Animal fats and waste oils are potential feedstocks for producing hydroprocessed esters and fatty acids (HEFA) jet and diesel fuels. This paper calculates the lifecycle greenhouse gas (GHG) emissions and production costs associated with HEFA jet and diesel fuels from tallow, and from yellow grease (YG) derived from used cooking oil. For YG, total CO₂ equivalent (CO₂ eq.) GHG emissions of jet and diesel were found to range between 16.8–21.4 g MJ⁻¹ and 12.2–16.9 g MJ⁻¹ respectively. This corresponds to lifecycle GHG emission reductions of 76–81% and 81–86% respectively, compared to their conventional counterparts. Two different system boundaries were considered for tallow-derived HEFA fuels. In System 1 (S1), tallow was treated as a by-product of the rendering industry, and emissions from rendering and fuel production were included. In System 2 (S2), tallow was considered as a by-product of the meat production industry, and in addition to the S1 emissions, cattle husbandry and slaughtering were also included. The lifecycle emissions (CO₂ eq.) from HEFA jet fuel for S1 and S2 were estimated to be 25.7–37.5 g MJ⁻¹ and 67.1–83.9 g MJ⁻¹ respectively. HEFA diesel lifecycle emissions were found to be 21.3–33.3 g MJ⁻¹ for S1 and 63.4–80.5 g MJ⁻¹ for S2. Production costs for these fuels were calculated using a discounted cash flow rate of return model. The minimum selling price was estimated to be 880 $ m⁻³–1060 $ m⁻³ for YG-derived HEFA, and 1050–1250 $ m⁻³ for tallow-derived HEFA fuels.     

Switchgrass procurement strategies for managing yield variability: Estimating the cost-efficient D (downtime cost) L (land to lease) frontier

Lignocellulosic biorefineries that plan to use switchgrass (Panicum virgatum L.) biomass exclusively will encounter both temporal (across years) and spatial (across locations within a given year) variability in feedstock production. Long term land leases could be employed to facilitate feedstock availability for the expected life of the biorefinery. If the quantity of land leased is based on average yields, in some years more biomass will be produced than can be processed. In other years feedstock production on the leased land may be insufficient to prevent biorefinery downtime. An optimal strategy for identifying which land to lease and seed to switchgrass, while considering yield variability and the opportunity cost of biorefinery downtime, is the focus of the research. The objective is to determine for a given biorefinery location the least-cost quantity, quality, and location of land to lease for alternative estimates of biorefinery downtime cost due to variable switchgrass yields. Fifty years of weather data are used to simulate switchgrass yield distributions for a case study region. An innovative mathematical programming model is developed and used to reveal the cost-efficient D (Downtime Cost) L (Land to Lease) frontier for a 2 Gg d⁻¹ biomass capacity biorefinery. If interyear storage is not permitted, 60,492 ha would be required to insure that the biorefinery run at full capacity every year given the estimated yield distributions. However, for some circumstances, it would be optimal to produce switchgrass on only 49,464 ha and idle the biorefinery for some days in low biomass production years.     

Techno-economic analysis of using corn stover to supply heat and power to a corn ethanol plant – Part 2: Cost of heat and power generation systems

This paper presents a techno-economic analysis of corn stover fired process heating (PH) and the combined heat and power (CHP) generation systems for a typical corn ethanol plant (ethanol production capacity of 170 dam³). Discounted cash flow method was used to estimate both the capital and operating costs of each system and compared with the existing natural gas fired heating system. Environmental impact assessment of using corn stover, coal and natural gas in the heat and/or power generation systems was also evaluated. Coal fired process heating (PH) system had the lowest annual operating cost due to the low fuel cost, but had the highest environmental and human toxicity impacts. The proposed combined heat and power (CHP) generation system required about 137 Gg of corn stover to generate 9.5 MW of electricity and 52.3 MW of process heat with an overall CHP efficiency of 83.3%. Stover fired CHP system would generate an annual savings of 3.6 M$ with an payback period of 6 y. Economics of the coal fired CHP system was very attractive compared to the stover fired CHP system due to lower fuel cost. But the greenhouse gas emissions per Mg of fuel for the coal fired CHP system was 32 times higher than that of stover fired CHP system. Corn stover fired heat and power generation system for a corn ethanol plant can improve the net energy balance and add environmental benefits to the corn to ethanol biorefinery.