Analysis of Energy Potential of Switchgrass Biomass

CABI Reviews, 2012

The biomass-based energy sector will play an important role in our drive towards renewable energy. Switchgrass has been identified as one of the candidate-dedicated energy crops in the USA because of its various desirable traits. However, many challenges still exist in ensuring a commercially viable switchgrass crop that is sustainable and techno-economically feasible. This article reviews the existing literature to highlight those challenges and potential solutions and recommendations to address those in the future. Various stages in the switchgrass-based biofuel system, namely crop production, provision and logistics, and conversion, are analysed. For each of these stages, the important challenges as reported in the literature are mentioned, and research gaps are identified. The systems-level issues as well as the challenges associated with the practical implementation of switchgrass production are also highlighted. The review illustrates that although switchgrass is a viable biof...

Agronomy

Biomass as a renewable energy source includes energy crops that are not used for food but solely for biomass production with the goal of conversion to various forms of biofuel. Switchgrass, a perennial grass native to North America, has been explored as an energy crop for many years. It is suitable because it does not require much agrotechnical input, is highly resistant to pest infestation and disease development, and can provide very high biomass yields. The aim of this work was to determine the biomass quality of the mentioned plant in relation to the autumn and spring harvest, considering its use in direct combustion processes. Significant differences were found in the percentages of ash, carbon, nitrogen, sulfur, oxygen, and water, as well as in the percentages of micro and macro elements, in the harvest dates studied. Compared to the autumn, the moisture content decreased from 33.88% to 10.95% and ash content from 4.59% to 3.1% in the spring harvest, while the carbon content i...

2016

Energy &Environmental Science, 2010

Over the past two decades, the use of biomass as a resource for biofuels and bioenergy has garnered much interest. The reduction in green house gas emissions of renewable fuels as compared to conventional fossil fuels, coupled with the sustainability of these technological approaches, has fostered increased research into this field. Switchgrass is a perennial grass native to North America, and as a feedstock for biofuels it has garnered much interest because of its high productivity, adaptability and potential ease of integration into existing agricultural operations. In order to maximize the use of switchgrass as an energy crop, the chemical constituents as well as the chemical processes involved in its conversion to biofuels need to be understood. The goal of this paper is to review the published work on the chemistry of switchgrass as it pertains to biofuel production including elemental composition, chemical composition, biopolymer constituents and their structure. In addition, the impacts of these chemical constituents on the biological conversion to ethanol and pyrolysis oils are summarized.

Agronomy Journal, 2012

All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. C ellulosic refineries will require substantial amounts of biomass on a year-round basis and are expected to have higher capital costs than similar sized grain ethanol plants based on first-generation biomass refining technology (Wright and Brown, 2007). A reliable feedstock supply will be essential in maintaining stable operational costs. Further, cellulosic refineries will be required to convert biomass with potentially greater feedstock quality variability than existing corn (Zea mays L.) grain ethanol plants. Switchgrass is being developed as a biomass energy crop for the temperate regions of North America (Vogel and Mitchell, 2008). Temporal and spatial variation information across production years and fields for biomass yield and quality will be needed for establishing reliable feedstock supply areas for a cellulosic biorefinery. Information on field-scale spatial and temporal variation for biomass yield of switchgrass is becoming available (Schmer et al., 2010). Switchgrass biomass composition and theoretical ethanol production at the field-scale have thus far not been reported. Biomass conversion to transportation fuels by biochemical methods will be dependent on efficient cellulose and hemicellulose polymer hydrolysis to simple sugars and then conversion to oxygenated hydrocarbons (Himmel et al., 2007). First generation cellulosic biorefineries, using biochemical methods, will produce primarily ethanol by converting cellulose, hemicellulose, and noncell wall carbohydrates into simple sugars which are then fermented to ethanol by genetically engineered organisms (Lynd et al., 1991; Perlack et al., 2005). Lignin, an abundant phenolic polymer in cell walls, can be used for combined heat and power generation (Demirbas, 2001; Lynd and Wang, 2003; Sheehan et al., 2003). Biochemical methods involve a pretreatment to reduce cell wall recalcitrance and increase cell wall porosity, a saccharification process to hydrolyze complex polysaccharides to monosaccharides, and a fermentation process to convert monosaccharides to a biofuel (Stephanopoulos, 2007). Near-term commercialized efforts to convert lignocellulosic feedstocks to biofuels through biochemical methods will likely involve simultaneous saccharification and fermentation (SSF). Alternative conversion systems such as consolidated bioprocessing which combines the enzymatic production, hydrolysis, and fermentation process into one reactor, thus reducing capital costs and increasing biorefinery efficiency, are expected to be commercially available as well (Lynd et al., 2005). Cellulosic biomass conversion to biofuels via biochemical or thermochemical methods require more complex and ABstrAct Information on temporal and spatial variation in switchgrass (Panicum virgatum L.) biomass composition as it affects ethanol yield (L Mg-1) at a biorefinery and ethanol production (L ha-1) at the field-scale has previously not been available. Switchgrass biomass samples were collected from a regional, on-farm trial and biomass composition was determined using newly developed near-infrared reflectance spectroscopy (NIRS) prediction equations and theoretical ethanol yield (100% conversion efficiency) was calculated. Total hexose (cell wall polysaccharides and soluble sugars) concentration ranged from 342 to 398 g kg-1 while pentose (arabinose and xylose) concentration ranged from 216 to 245 g kg-1 across fields. Theoretical ethanol yield varied significantly by year and field, with 5 yr means ranging from 381 to 430 L Mg-1. Total theoretical ethanol production ranged from 1749 to 3691 L ha-1 across fields. Variability (coefficient of variation) within established switchgrass fields ranged from 1 to 4% for theoretical ethanol yield (L Mg-1) and 14 to 38% for theoretical ethanol production (L ha-1). Most fields showed a lack of spatial consistency across harvest years for theoretical ethanol yield or total theoretical ethanol production. Switchgrass biomass composition from farmer fields can be expected to have significant annual and field-to-field variation in a production region, and this variation will significantly affect ethanol or other liquid fuel yields per ton or hectare. Cellulosic biorefineries will need to consider this potential variation in biofuel yields when developing their business plans.

Agronomy Journal, 2006

Seasonal time of switchgrass (Panicum virgatum L.) harvest affects yield and biofuel quality and balancing these two components may vary depending on conversion system. A field study compared fall and spring harvest measuring biomass yield, element concentration, carbohydrate characterization, and total synthetic gas production as indicators of biofuel quality for direct combustion, ethanol production, and gasification systems for generation of energy. Switchgrass yields decreased almost 40% (from about 7-4.4 Mg ha 21 ) in winters with above average snowfall when harvest was delayed over winter until spring. The moisture concentration also decreased (from about 350-70 g kg 21 ) only reaching low enough levels for safe storage by spring. About 10% of the yield reduction during winter resulted from decreases in tiller mass; however, almost 90% of the yield reduction was due to an increase in biomass left behind by the baler. Mineral element concentrations generally decreased with the delay in harvest until spring. Energy yield from gasification did not decrease on a unit biomass basis, whereas ethanol production was variable depending on the assessment method. When expressed on a unit area basis, energy yield decreased. Biofuel conversion systems may determine harvest timing. For direct combustion, the reduced mineral concentrations in spring-harvested biomass are desirable. For ethanol fermentation and gasification systems, however, lignocellulose yield may be more important. On conservations lands, the wildlife cover provided by switchgrass over the winter may increase the desirability of spring harvest along with the higher biofuel quality.

BioResources, 2016

Production of bioenergy from cellulosic sources is likely to increase due to mandates, tax incentives, and subsidies. However, unchecked growth in the bioenergy industry has the potential to adversely influence land use, biodiversity, greenhouse gas (GHG) emissions, and water resources. It may have unintended environmental and socioeconomic consequences. Against this backdrop, it is important to develop standards and protocols that ensure sustainable bioenergy production, promote the benefits of biofuels, and avoid or minimize potential adverse outcomes. This paper highlights agronomic information on switchgrass, a high-potential bioenergy feedstock, and the role of specialized certification programs. The existing sustainability standards and protocols were reviewed in order to identify key gaps that justify a certification program specifically for switchgrass-based bioenergy. The criteria and indicators that should be considered for such a certification program are outlined.

Biomass and Bioenergy, 2002

Renewable bioenergy could be supplied by high yielding grass crops, such as switchgrass (Panicum virgatum L.). Successful development of a bioenergy industry will depend on identifying cultivars with high yield potential and acceptable biofuel quality. The objective of this study was to evaluate 20 switchgrass populations in a ÿeld study planted in May 1997 in southern Iowa, USA. The populations included released cultivars and experimental germplasm of both upland and lowland ecotypes. Yield, plant height, stand, lodging, leaf:stem ratio, cell wall ÿber, total plant nitrogen, and ash were determined on all entries between 1998 and 2001. Ultimate and proximate analyses together with chlorine and major oxide determinations were made on three cultivars in 2000 and 2001. Biomass yield was determined from a single autumn harvest each year. The lowland cultivars 'Alamo' and 'Kanlow' produced the most biomass, exceeding the production of the widely recommended upland cultivar 'Cave-In-Rock'. Other traits di ered among the cultivars, although the range was less than that for yield. The di erences among years were substantially greater for the ultimate, proximate, and major oxide analyses than di erences among cultivars. The highest yielding cultivars had low ash, slightly lower ÿber concentrations, and moderate levels of important minerals, suggesting that excellent germplasm is available for biofuel production. The persistence of the lowland cultivars in southern Iowa may need more research because the winters during the experiment were mild. ? (E.C. Brummer). through crop diversiÿcation, decreased erosion, and improved water quality compared with a traditional annual row crop system . The perennial nature of these crops makes their cultivation desirable on highly erosive land, particularly if they can produce acceptable yields on poor quality soils. In order to be profitably grown, energy crops need to produce high yields of biomass, low concentrations of water, nitrogen, and ash, and high concentrations of lignin and cellulose . Switchgrass, a warm-season (C 4 ) grass native to 0961-9534/02/$ -see front matter ? 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 1 -9 5 3 4 ( 0 2 ) 0 0 0 7 3 -9

Biomass and Bioenergy, 1998

AbstractÐIncreased atmospheric CO 2 , caused partly by burning fossil fuels, is assumed to elevate the risk of global warming, while nitrate contamination of surface runo and groundwater from fertilizer and agricultural wastes constitutes a serious environmental hazard on a regional scale. Switchgrass (Panicum virgatum L.) grown as an energy crop could reduce atmospheric CO 2 accumulation by replacing fossil fuels and sequestering C. It could also improve soil productivity by C sequestration, and reduce xy À1 3 contamination of water by absorbing N lost from fertilizer and agricultural waste if planted in ®lter strips on adjacent land. The objective of this study was to assess potential impacts of switchgrass on C and N balances by reviewing and synthesizing information from current literature, unpublished data and on-going research. Replacing fossil fuels with switchgrass, or any other biomass, will have a much greater eect on atmospheric CO 2 than C sequestration. This is because replacing fossil fuels provides a cumulative eect, while C sequestration oers only a one-time bene®t. Furthermore, switchgrass will provide net gains in C sequestration only if it replaces annual row crops, but not if it replaces grazed pasture. Nitrogen recovery by switchgrass in an Alabama study was 65.6%, which compares favorably with the 50% recovery frequently quoted as the norm for wheat (Triticum aestivum L.) and corn (Zea mays L). #

Biomass and Bioenergy, 2006

Biomass tensile and shear ultimate failure stresses were measured with the aim of identifying biomass ''weakest mode of failure'' or ''natural fracture point'' as a basis for future grinder designs. Switchgrass (Panicum virgatum L.) ultimate stresses were determined for Alamo and Kanlow varieties over ranges in maturity and moisture content. Alamo had greater ultimate tensile stress than Kanlow (P ¼ 0:0091), with mean values of 97.8 and 89.7 MPa, respectively. Alamo had greater ultimate shear stress than Kanlow (P ¼ 0:0091), with mean values of 20.5 and 17.9 MPa, respectively. Shear was the ''weakest mode of failure''. Grinders that use knives, shear bars, and mechanical pinch points that apply opposed-sliding actions are expected to be more energy efficient. Mean ultimate tensile stress and shear stress were significantly different between switchgrass varieties. A survey of failure stresses for a range of biomass feedstocks is recommended for future study. Ultimate tensile stress increased twofold as elapsed time after harvest increased from 2 to 386 h, with a corresponding (confounded) decrease in moisture content of $60-10% (wet basis (w.b.)). Future study should isolate whether the effect was due primarily to moisture or aging. Tensile-dominant size reduction should be conducted early in the harvest process and at a high moisture content to minimize energy consumption for grinding. Ultimate shear stress was relatively insensitive to switchgrass maturity, elapsed time after harvest, and moisture content.