Daystar - Integrated Cost and Environmental LCA of Biomass

7/27/2019 Daystar - Integrated Cost and Environmental LCA of Biomass

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Integrated Cost and Environmental Life Cycle Analysis of BiomassSupply Systems for Biofuels and Bioenergy

Jesse S. Daystar North Carolina State University, [email protected] W. ReebNorth Carolina State University, [email protected] Gonzalez North Carolina State University, [email protected] A. Venditti North Carolina State University, [email protected]

Abstract. The production of six regionally important cellulosic biomass feedstocks, includingpine, eucalyptus, unmanaged hardwoods, forest residues, switchgrass, and sweet sorghum,was analyzed using consistent life cycle methodologies and system boundaries to identifyfeedstocks with the lowest cost and environmental impacts. Supply chain analysis models werecreated for each feedstock calculating costs and supply chain requirements for the production453,592 dry tonnes of biomass per year. Cradle-to-gate environmental impacts from thesesupply systems were quantified for nine mid-point indicators using SimaPro 7.2 LCA software.

Conversion of grassland to managed forest for bioenergy resulted in large reductions in GHGemissions, due to carbon sequestration associated with direct land use change. However,converting forests to energy cropland resulted in large increases in GHG emissions. Productionof forest-based feedstocks for biofuels resulted in lower delivered cost, lower greenhouse gas(GHG) emissions and lower overall environmental impacts than the studied agriculturalfeedstocks. Forest residues had the lowest environmental impact and delivered cost per drytonne. Using forest-based biomass feedstocks instead of agricultural feedstocks would result inlower cradle-to-gate environmental impacts and delivered biomass costs for biofuel productionin the southern U.S.

Introduction. Production of cellulosic biofuels and other bio-based products are expected toincrease national energy independence, improve rural economies, and reduce greenhouse

gases (GHG) compared to conventional transportation fuels (Demirbas 2008). To ensuregreenhouse gas (GHG) emission reductions and a sustainable bioenergy industry, the EnergyIndependence and Security Act (EISA) established the life cycle greenhouse gas (GHG)thresholds (percent reduction) compared to the 2005 base line, with reductions of 20% forrenewable fuels, 50% for advance fuels, 50% for biomass-based fuels and 60% for cellulosicbiofuels (EPA 2012). The feedstock type used for biofuels conversion can play a central role indetermining the overall GHG emissions as well as the financial and technological feasibility of arenewable biofuel. This study evaluated six potential biomass supply system scenarios forrenewable energy production (liquid and/or solid fuels) in the southern U.S. Supply chain

logistics, delivered cost and environmental burdens of these biomass feedstocks were qualifiedand quantified from cradle-to-gate. Feedstocks analyzed included loblolly pine, eucalyptus,unmanaged hardwood, forest residues, switchgrass and sweet sorghum. Previous studies have

revealed feedstock production and delivery as the single largest contributor to the financialfeasibility of bioenergy

Proceedings of the International Symposium on Sustainable Systems and Technologies(ISSN 2329-9169) is

published annually by the Sustainable Conoscente Network. Melissa Bilec and Jun-ki Choi, co-editors.

[email protected].

Copyright 2013 by Jesse S. Daystar, Carter W. Reeb, Ronalds Gonzalez, Richard A. Venditti.Licensed under

CC-BY 3.0.

Cite As:

Integrated Cost and Environmental Life Cycle Analysis of Biomass Supply Systems for Biofuels and Bioenergy.

Proc. ISSST, Jesse S. Daystar, Carter W. Reeb, Ronalds Gonzalez, Richard A. Venditti. http://dx.doi.org/10.6084/

m9.figshare.810432. v1 (2013)


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Copyright 2013 by the Authors

technologies, accounting for 35 45% of the total production cost (Tao and Aden 2009,Gonzalez et al. 2011b, Gonzalez et al. 2011c, Pirraglia et al. 2012).

Key biomass supply system metrics were used to compare feedstocks, including: delivered costand kg CO2-equivalent GHG emissions per dry metric tonne, per metric tonne of carbohydrates,per million BTU, per hectare over 100 years. These metrics have been identified as key

parameters for measurement of feedstock supply chain efficiency due to industry use of thesemetrics to compare feedstock feasibility for specific conversion pathways (Gonzalez et al. 2011).Due to manuscript length limitations, only the per tonne basis will be discussed here, however,the full analysis can be found in Daystar et al 2013.

Goal. The goal of this study was to explore and define the tradeoffs between delivered cost andenvironmental impacts for each biomass feedstock supply system and to provide insight forindustry, academic, and governmental stakeholders about specific parameters of feedstockproduction for bioenergy in the southern U.S.

Investigative Method. Several key parameters were identified from Gonzalez et al. (2011) asintegral to the selection of feedstocks for bioenergy or biofuel production, including:

1. High biomass productivity (dry tonnes per hectare per year).2. High carbohydrate content, and suitable for biochemical conversion into ethanol.3. Current availability of that biomass in the southern U.S.4. Species studied previously for biofuel or bioenergy use.5. Convertibility of feedstock types for biofuel or bioenergy.

A constant biomass supply of 500,000 dry short tons (equivalent) year -1 (453,592 metrictonnes year -1) was assumed for all biomass scenarios. Collection area and land used,transportation distance, land use change, and many other aspects of each scenario werecalculated from delivery quantity using productivity and yield in the integrated cost, supply chainand life cycle assessment models.

A sensitivity analysis was performed for different biomass productivity levels by using threedifferent multipliers: low (0.75), medium (1.00) and high (1.25), relative to a central assumptionof biomass productivity per hectare per year. Biomass productivity is presented here in metrictonnes (dry tonnes) and in some cases data is also presented as bone dry short ton equivalent.

The delivered cost per dry tonne includes the cost of growing the biomass (IRS 2007), profit forthe farmer (estimated at 8% Internal Rate of Return [IRR]), harvesting cost, and freight cost. Forthis study an 8% IRR was used for all feedstock supply chain models. The discount rate (theopportunity cost of using capital for a specific investment; often called the hurdle rate) used inthe analysis was 8% (Brealey and Myers 1996, Ross et al. 2004). The base year for theanalysis, prices, and costs is first quarter 2012. Table 1 outlines the various productivity values

and other parameters of the supply systems analyzed. Figure 1shows the system boundary forthe analyzed biomass supply systems and the life cycle stages and activities for which impactsand costs were quantified.


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Table 1. Feedstock productivity, management, and moisture content assuming medium productivity and 10%covered area.

Sources: a = Amateis et al. 2001, Gonzalez et al. 2011a; b = Gonzalez et al. 2011a; c = SunGrant-Bio Web2008, USDA 2012, Gonzalez et al. 2011a; d = Gonzalez et al. 2011a; e = McLaughlin; f = Irvin et al. 2001,Gonzalez et al. 2011a

Figure1: BiomassLife Cycle. Stages and system boundary for the production and delivery of biomass feedstocks.

Note, the unmanaged hardwoods and forest residue biomass analysis does not include biomass production.

Agricultural

biomass types require storage before delivery to the biorefinery

During the growth of biomass, carbon in the form of CO2 is absorbed from the atmospherethrough photosynthesis. This carbon can be stored in the above ground biomass, forest litter, orbelow-ground biomass (root system). Only the carbon captured in the harvested above groundbiomass was counted as a negative emission within this study (Rabl et al. 2007).

Previous studies have shown that land use change impacts can represent a substantial share ofthe life cycle burdens for biomass to bioenergy supply chain scenarios (Walsh 2003,Gnansounou et al. 2009, Mathews and Tan 2009, Mala and Freire 2012). The Forest IndustryCarbon Assessment Tool (FICAT) was used to analyze twenty conversion scenarios. This multiscenario approach covers many ways in which land would be changed to grow biomass forbiofuels and bioenergy.

Emissions from forest operations required to establish and maintain the biomass, harvest, andcollect forest based biomass were calculated using U.S. LCI data. Sweet sorghum and

DescriptionLoblollypine

a

Eucalyptusb

Unmanagedhardwoods

c

Forestresidues

d

Switchgrasse

Sweetsorghum

f

Productivity (drytonne ha

-1year

-1)

17.1 17.6 2.2 1.0 17.9 15.7

Rotation length 12 4 50 n/a n/a n/a

Harvesting windowYear-round

Year-round Year-round Year-round Three monthsThree

months

Moisture content 45% 45% 45% 45% 16% 74%

Delivery form Logs Logs Logs Chips Square bales Cane

Trees per ha 2,965 1,400 n/a n/a n/a n/a

Establishment cost($/ha)

638 552 n/a n/a 182 416

Maintenance cost($/ha)

62.41 62.4

1 n/a n/a 85.3

2 n/a

1 = Second year of plantation; 2 = Maintenance cost per year, year 2 through 10

Biorefinery

GatePlantation

Establishment

Maintenance Harvesting Transportation

FertilizerHerbicide

Diesel

CO2

FertilizerHerbicide

Diesel Diesel Diesel

Processing

Biomass Production


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switchgrass, agricultural crops with seasonal growing periods, required storage to ensure aconstant annual supply. Emissions and costs from the storage of 70% of the annual agriculturalbiomass supply were modeled in this study. During this storage period, the biomass releasedGHGs through aerobic and anaerobic decomposition. In this study, decomposition wasassumed to occur only aerobically (Wortmann et al. 2010). Transportation emissions werecalculated using emission factors from the U.S. LCI database.

The primary functional unit was one dry delivered tonne of biomass. A second functional unitwas used for additional analysis purposes incorporating land use efficiency: one managedhectare of each feedstock over 100 years. LCI data from the Excel based supply chain modelswere used as input data for the SimaPro modeling software which calculated direct and indirectemissions due to chemical use, transportation, electrical use, and storage emissions (Glew et al.2012, Gonzlez-Garca et al. 2012, You et al. 2012). The Tool for the Reduction andAssessment of Chemical and Other Environmental Impacts (TRACI) impact assessmentmethod (Bare et al. 2003, Jolliet et al. 2004), Eco-invent database (Neupane et al. 2011) andthe US Life Cycle Inventory database (You et al. 2012) were used to calculate the cradle-to-grave feedstock production and delivery environmental impacts.

Results. It was determined that a feasible supply chain for continuous biomass supply tobioenergy and bioethanol facilities is possible and that woody feedstocks offer advantages overagricultural feedstocks. Biomass supply chains for loblolly pine, eucalyptus, switchgrass andsweet sorghum resulted in lower transportation distance ranging from 20 40 kilometers.Forest residues and unmanaged hardwood production resulted in the highest transportationdistance (101 180 kilometers). Transportation distances did not influence the environmentalimpacts greatly, however, transportation costs associated with lower biomass productivity didincrease the overall delivered cost.

Delivered cost per dry tonne equivalent (biomass is actually delivered green) was calculated foreach of the three productivity levels (low, medium, and high) and are shown in Figure 2. Forestresidues had the lowest delivered cost ranging from $51.2 to $56.7 BD tonne-1, followed by

loblolly pine with values ranging from $51.3 to $61.4 BD tonne-1. Forest residue had a lowerdelivered cost per BD tonne primarily due to no land rent, establishment or maintenance costs.The increased transportation costs due to lower yield did not exceed the savings due to lowerbiomass cost. Delivered cost per tonne of carbohydrate and per MMBTU were examined,however, are not reported in figures due to length limitations. The delivered cost per MMBTUand tonne of carbohydrate produced similar results to the per tonne basis, except the cost pertonne of carbohydrate for sweet sorghum. Sweet sorghum, with carbohydrate contents around80%, can be delivered at a cost of around $87, lower than all other biomass feedstocks otherthan forest residues. In addition to lower carbohydrate cost, sweet sorghum has high levels ofsoluble sugars which are more easily fermented to bioethanol.

The renewable fuels standards are primarily focused on GHG emissions, however, other

emissions and environmental impacts occur due to the production biomass feedstocks.Environmental impacts were calculated on a per dry tonne basis for each feedstock scenarioand reported in Figure 3. Forest based feedstock production resulted in similar environmentalimpacts in most impact categories. Unmanaged hardwoods and forest residues, requiring nofertilizers or herbicides, had lower impacts several impact in several impact categories.Agricultural feedstocks production, switchgrass and sweet sorghum, resulted in higherenvironmental impacts primarily due to yearly harvesting and more intensive biomassmanagement operations.


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Figure2: Annual Delivered Costs. Delivered biomass cost at 500,000 BDT (453,592 metric tonnes) per year andGHG captured per tonne of biomass, assuming medium productivity and 10% covered area. The error bars

represent the range of uncertainty due to feedstock productivity.

Figure3: Environmental Impacts. Environmental and human health impacts from SimaPro using TRACI 2impactassessment method for biomass feedstocks relative to the feedstock scenario with the highest impact for each

impact category. Assumptions: 500,000 BDT (453,592 metric tonnes) delivered per year to a single facility, mediumbiomass productivity, and 10% covered area.

The production of biomass for biofuels and bioenergy may require land conversion to dedicated

energy crops. When such land is converted, land carbon stores are disturbedresulting in eithercarbon sequestration or carbon emissions, Figure 4. The FICATmodel, used in this study,


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showed converting non forest land to forest land resulted in negative emissionsdue to directland use change. Converting forest land to grow agricultural

feedstocks, as switchgrass orsweet sorghum, resulted in significantlyGHG emissions. It is worth noting that only direct land

use change was considered in this study, while in reality,both indirect and direct land use

changemayoccur.

Figure4: Land Use Change Impacts. Direct LUCGHG emissions from converting one hectare of land to biomassfeedstock growth over 100 years. Also shown is the net GHG emissions with no LUC impacts considered as a

comparison, assuming 500,000 BDT/year (453,592 metric tonnes/year), medium productivity and 10% covered area.

Conclusions. Forest based biomass types with lower delivered cost and net GHG emissionsper dry tonne may be more feasible for commercial utilization in the southern U.S. than

agricultural feedstocks. For biochemical conversion processes, sweet sorghum with a lowercost per tonne of carbohydrates and easily fermentable sugars, may produce a higher financialreturn than forest based feedstocks, however, with higher cradle to gate environmental impacts.A cradle to grave analysis would be required to fully understand the overall environmentalimpacts of biofuels and energy from these feedstocks.

The use of the three cost metrics (cost per tonne, cost per tonne of carbohydrate, and cost permillion BTU) was an effective methodology for a cradle-to-gate analysis of biomass supplysystem cost and environmental burden. The incorporation of delivered cost, supply chainlogistics and life cycle environmental impacts into one study was beneficial to create morepoints of comparison between the scenarios and therefore more effectively differentiate theforest-based feedstocks from the agricultural feedstocks. These findings can be combined with

a full cradle-to-grave LCA of biomass-to-biofuel scenarios such as biochemical conversion,thermochemical conversion, and combustion for power to inform stakeholders about theeconomic, social and environmental costs of renewable energy feedstock options forcommercial facilities.

Acknowledgements. The authors would liketo acknowledge the Biofuels Center of NorthCarolina, the Southeast Partnership for Integrated Biomass Supply Systems (IBSS).The IBSS

project is supported by Agriculture and Food Research Initiative Competitive Grant no. 2011-68005-30410 from the USDA National Institute of Food and Agriculture.

-3,200,000

-2,700,000

-2,200,000

-1,700,000

-1,200,000

-700,000

-200,000

300,000

From

Cropland

From

Grassland

From

Deciduous

Natural Forest

From

Coniferous

Natural Forest

FromDeciduous

Managed

Forest

FromConiferous

Managed

Forest

Net GHG/haover 100

years (No

LUC)

tonneCO2eq.

perhaover100years

Pine

Eucalyptus

Unmanaged Hardwoods

Switchgrass

Sweet Sorghum


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Daystar - Integrated Cost and Environmental LCA of Biomass