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Purpose: Napier grass, one of the high yield perennial energy crops can be grown on marginal lands with minimal inputs, but with increased soil carbon sequestration in the southeastern US. The sustainable use of Napier grass for bioenergy applications such as combined heat and power at low cost to mitigate greenhouse gas emissions needs to be investigated. Methods: In this study, an integrated life cycle assessment and techno-economic analysis approach were used to estimate the energy use, environmental emissions, and minimum selling price (MSP) of electricity and thermal heat produced from Napier grass and compared with a coal or natural gas-fired combined heat and power generation plant. Results and discussion: The use of Napier grass as a feedstock decreased the global warming potential (GWP) of the medium-sized CHP (i.e., 13 MWe) plant by 73–92 % compared to that of a coal and natural gas-fired CHP plants. Other environmental impacts were also reduced by 24–100 %. Eutrophication was the only impact comparable to that of the coal-fired CHP plant. The energy return on investment (EROI) was around 5:1. The minimum selling price of electricity generated from the CHP plant was US$0.05–0.4 MJe−1 (US$0.13–0.18 kWh−1) considering the credits for steam production, renewable electricity production tax credit (PTC), and carbon footprint from the fossil fuel-based electricity generation. Conclusions: Although the pelleting of Napier grass for the CHP plant increased the cost and GHG emissions by 38% and 55% over the non-pelleted system, the pelleting process can ensure consistent quality and uninterrupted supply of the feedstock for heat and power generation. [ABSTRACT FROM AUTHOR]

Densification of thermally treated energy crops by torrefaction is required to increase the bulk density and to reduce the handling, transport, and storage cost for bioenergy applications. In this study, we investigated the densification characteristics of thermally treated energy cane and napier grass grown on marginal lands at various applied forces and binder levels. The addition of starch (0, 10, and 15%) and lignosulfonate (0, 5, and 10%) was examined to enhance the strength and durability of raw and torrefied briquettes, respectively. Although the use of starch binder relatively increased the bulk density, it did not improve the hardness and durability of untreated energy crop briquettes. The addition of 10% lignosulfonate binder increased the torrefied briquette density of up to 11% for energy cane and up to 38% for napier grass and decreased the compression energy by up to 35% for both samples. Moreover, the hardness (compressive resistance) was tripled, and the durability was relatively improved for both torrefied briquettes. The increase in applied force not only increased the bulk density but also increased the specific energy required for densification. However, there was no substantial change in hardness and durability when the compression force was increased from 15 to 20 kN for all samples. In overall, densification of thermally treated energy crops is required, and the quality of the briquettes can be improved by the use of appropriate binders for efficient handling, transport, and storage. [ABSTRACT FROM AUTHOR]

Storage of agricultural residues and energy crops is essential for preserving and maintaining its economic value, and year-round continuous delivery to a biorefinery. In this study, a dynamic cost model was developed for three storage methods (Indoor, Outdoor-tarped, and Outdoor-open) with two biomass bale types (rectangular and round) to estimate the storage cost of corn stover and switchgrass. The effects of storage time and multiple-use of a storage facility on the storage cost were also evaluated to develop effective storage strategies. The cost of bale storage systems comprised of capital expenses for infrastructures, bale handling, dry matter loss ( DML) and quality loss costs. Among storage methods, the outdoor-tarped storage with rectangular bales was the least expensive options for corn stover ($14.6 dry Mg−1) and switchgrass ($16 dry Mg−1). Indoor storage of round bales was costly due to the large storage footprint requirement and high infrastructure investment. However, the indoor storage cost could be reduced, if the storage facility could be used more than once a year. The sensitivity analysis study illustrated that the DML, biomass cost, loading/unloading time and bale density were the most sensitive parameters influencing the storage cost. An example storage strategy developed for a typical biorefinery could reduce the average annual storage cost (up to $10 dry Mg−1) along with an annual cost saving ranging from 10 to 100% compared with any single storage option. © 2017 Society of Chemical Industry and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Unprecedented opportunities for biofuel development are occurring as a result of rising fossil fuel prices, the need to reduce greenhouse gases, and growing energy security concerns. An estimated 250 million hectares (ha) of farmland could be utilized globally to develop a bioenergy industry if efficient and economical perennial biomass crops and bioenergy conversion systems are employed. In temperate zones, C 4 or warm-season grass research and development efforts have found switchgrass (Panicum virgatum) and Miscanthus capable of producing biomass yields of 10 to 20 oven dried tonnes (ODT)/ha/yr, while in tropical areas Erianthus and napier grass (Pennisetum purpureum) are producing 25 to 35 ODT/ha/yr. The potential to annually produce 100 barrels of oil energy equivalent/ha with a 25:1 energy output to input ratio appears achievable with high-yielding, N-fixing warm-season grasses grown on marginal lands in the tropics. Commercialization of densified herbaceous plant species has been slow because of the relatively high alkali and chlorine contents of the feedstocks, which leads to clinker formation and the fouling of boilers. This challenge can be overcome by improving biomass quality through advances in plant breeding and cultural management to reduce the chlorine, alkali, and silica content and through the use of new combustion technologies. Warm-season grasses can be readily densified provided suitable grinding and densification equipment and pressure are utilized. The major advantages of producing densified warm-season grasses for BIOHEAT include: it is the most efficient strategy to use marginal farmlands in most temperate and tropical climates to collect solar radiation; it has an excellent energy balance; the feedstocks can be used conveniently in a variety of energy applications; and it is relatively environmentally friendly. Densified warm-season grass biofuels are poised to become a major global fuel source because they can meet some heating requirements at less cost than all other alternatives available today. [ABSTRACT FROM AUTHOR]

Wheat and barley straws, corn stover and switchgrass at two moisture contents were ground using a hammer mill with three different screen sizes (3.2, 1.6 and 0.8 mm). Energy required for grinding these materials was measured. Among the four materials, switchgrass had the highest specific energy consumption (27.6 kW h t-1), and corn stover had the least specific energy consumption (11.0 kW h t-1) at 3.2 mm screen size. Physical properties of grinds such as moisture content, geometric mean diameter of grind particles, particle size distribution, and bulk and particle densities were determined. Second- or third-order polynomial models were developed relating bulk and particle densities of grinds to geometric mean diameter within the range of 0.18–1.43 mm. Switchgrass had the highest calorific value and the lowest ash content among the biomass species tested. [Copyright &y& Elsevier]

Anaerobic Digestion (AD) is a well-developed sustainable technology to convert organic waste streams and energy crops to produce renewable gaseous biofuels, while recycling nutrients and mitigating greenhouse gas emissions. In this study, the environmental and economic impacts of an integrated-state AD technology (i -AD) producing Compressed Natural Gas (noted as BioCNG) were investigated from dairy-manure, food-wastes, and miscanthus biomass feedstocks, and compared with that of stand-alone liquid-state (LS-AD) and solid-state (SS-AD) AD technologies. A coupled life-cycle assessment and techno-economic analysis (LCA‐TEA) approach was used to estimate the Global Warming Potential (GWP) and the Minimum Selling Price (MSP) of BioCNG ‒ a renewable alternative to fossil-CNG. The results illustrated that the Fossil Energy Ratios (FERs) for BioCNG were between 2.3 and 3.3 in the increasing order as LS‐AD < i ‐AD < SS‐AD. The life-cycle GWPs to produce BioCNG via LS‐AD, SS‐AD, and i ‐AD were −5.1, −15.1, and −12.0 kgCO 2 eq/GGE (Gasoline-Gallon-Equivalent) respectively. The MSP of BioCNG (without incentives) via LS‐AD ($2.9/GGE) was lower than that of both SS‐AD ($4.1/GGE) and i ‐AD ($4.9/GGE). When the tipping-fee ($44/Mg), RIN(Renewable Index Number)-credit ($0.46/RIN), and carbon-credit($13.6/MgCO 2 eq) were considered, the MSP of BioCNG dropped by up to 70%, 45%, and 25% for LS‐AD, SS‐AD, and i ‐AD, respectively. Fungal-pretreatment of miscanthus had negligible impacts on the environmental and economic performances of BioCNG. Backhauling of solid-digestate for miscanthus cultivation may reduce the MSP, energy usage, and GWP by up-to 5%, 16%, and 7%, respectively. The commercial production of BioCNG from energy crops can potentially be competitive at a higher BioCNG market price or with favorable energy policies, financial support, and tax-benefits. Image 1 • BioCNG production of an integrated-state AD technology was studied. • The Global Warming Potential of BioCNG ranged from −5 to −15.0 kgCO 2 eq per GGE. • The Minimum Selling Price of BioCNG ranged from $3 to $5 per GGE without any credit. • The solid-state AD technology to produce BioCNG from miscanthus was very promising. • BioCNG through solid-state AD can be economical at a carbon price of $35/MgCO₂eq. [ABSTRACT FROM AUTHOR]

Strip-mined land (SML) disturbed by coal mining is a non-crop land resource that can be utilized to cultivate high-yielding energy crops such as miscanthus for bioenergy applications. However, the biomass yield potential, annual availability, and environmental impacts of growing energy crops in SML are less understood. In this study, we estimated the yield potential of miscanthus (Miscanthus sinensis) in SML and its environmental impacts on local streams using the Soil and Water Assessment Tool (SWAT). After calibration and validation of the SWAT model, the results demonstrated that miscanthus yield potentials were 2.6 (0.8−5.53), 10.0 (1.3−16.0), and 16.0 (1.34−26.0) Mg ha−1 with fertilizer application rates of 0, 100, and 200 kg-N ha−1, respectively. Furthermore, cultivation of miscanthus in SML has the potential to reduce sediment (~20%) and nitrate (2.5−10.0%) loads reaching water streams, with a marginal increase in phosphorus load. The available SML in the United States could produce about 10 to 16 dry Tg of biomass per year without negatively impacting the water quality. In conclusion, SML can provide a unique opportunity to produce biomass for bioenergy applications, while improving stream water quality in a highly dense mining area (the Appalachian region) in the United States. [ABSTRACT FROM AUTHOR]

Energy crops grown on marginal lands offer an alternative supply of renewable resources while avoiding competition with food crops and supporting feed crops. To sustainably grow energy crops, the economic and environmental impacts of various crop management practices such as the adoption of cover crops, fertilization rates, harvesting methods and its end use applications for animal feed or biofuels should be investigated. In this study, we investigated the life cycle analysis (LCA) and economic evaluation of growing two energy crops (energy cane, and napier grass) on the marginal lands with three fertilizer treatments (0, 100, and 200 kg N ha⁻¹), and with a cover crop (clover, Trifolium incarnatum L) in the southeastern United States (US). Energy crop was harvested once a year in the late fall for biofuel applications, while the Napier grass was harvested twice a year: first harvested early in spring for animal feed and later harvested in the fall for biofuel application. Experimental field data such as biomass yield, crop management practices, farm inputs, and carbon stored in the soil, were determined to assess the global warming potential and the delivered cost of each energy crop. Napier grass had lower global warming (GW) impacts and biomass delivery costs, 34–153 kg CO₂ eq. per oven-dry metric ton (ODMT) and $51–$57 perODMT, respectively than that of energy cane. However, both the energy crops provided carbon sequestrations (−17 and −232 kg CO₂ eq. ODMT⁻¹) and thus net GW impact varied between 51 and (−14) kg CO₂ eq. ODMT⁻¹ based on the treatments. When the napier grass was harvested for both biofuel and fodder applications, the overall GW impacts and the delivered costs were reduced. Therefore, energy crops can be grown in marginal lands for increased carbon sequestration while reducing the GW impacts of energy crops for biofuel production. The integrated environmental and economic analyzes further demonstrated that the energy crop delivered costs and GW impacts could be further reduced, if the energy crops can be utilized for both biofuel and feed applications. • Estimated cost and environmental impacts of producing energy crop on marginal land. • Crop management practices, including cover crop and double harvest, were evaluated. • Global warming (GW) impacts and cost of napier grass were lower than energy cane. • Among all, biomass production with cover crop had the lowest GW impacts and cost. • In napier grass, co-production of biomass and fodder reduced GW impacts and costs. [ABSTRACT FROM AUTHOR]

Climate change induced by greenhouse gas emissions from the extraction and use of fossil fuels has raised global concerns and needs to develop alternative and environmentally friendly transportation fuels from biomass and other organic carbon sources. In this study, a cradle to grave attributional life cycle assessment (LCA) was conducted to produce drop-in renewable diesel from biogas (via solid-state anaerobic digestion) derived from energy crop, i.e. miscanthus cultivated in strip-mined lands. The analysis included miscanthus cultivation, harvesting, and transportation to the biorefinery, conversion of the biomass to Fischer-Tropsch diesel, and combustion of the drop-in renewable diesel for a passenger vehicle. Results showed that the miscanthus derived drop-in renewable diesel could reduce greenhouse gas emissions by up to 73% when compared with that of the conventional fossil-derived diesel. Similarly, the proposed design consumes 4.91 MJ/GGE of fossil fuel compared to the conventional diesel with fossil fuel depletion of 18.98 MJ/GGE. Although the respiratory effects, smog formation, acidification, and eutrophication potentials of the miscanthus to drop-in renewable diesel process are relatively higher than the conventional process, the proposed technology still represents a sustainable liquid fuels pathway that is less dependent on fossil fuel, can substantially reduce greenhouse gas emissions, and help attain the renewable transportation fuels standard. Image 1 • Renewable diesel derived from miscanthus by anaerobic digestion and F-T synthesis. • GHG emissions of renewable diesel reduced by 73% when displacing fossil diesel. • Use of digestate as chemical fertilizer further reduced the GHG emissions by 24%. • Renewable diesel qualifies for the U.S. Renewable Fuel Standard credits. • Ten other environmental impacts of renewable diesel compared with fossil diesel. [ABSTRACT FROM AUTHOR]