lca biomasa

8/13/2019 LCA Biomasa

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1.0 IntroductionThe potential environmental benefits from biomass power arenumerous. In addition to a dramatic decrease in the amount ofcarbon dioxide produced per kWh, implementation of biomass

power systems will reduce fossil fuel consumption andsignificantly mitigate sulfur and nitrogen oxide emissions. Additionally, compared toconventional crops, biomass plantations may increase biodiversity and soil carbon, andreduce soil erosion. owever, biomass power may also have some negative effects on theenvironment. Although the environmental benefits and drawbacks of biomass power have

been debated for some time, the total significance has not been assessed. This studyserves to answer some of the !uestions most often raised in regard to biomass power"What are the net #$ % emissions& What is the energy balance of the integrated system&Which substances are emitted at the highest rates& What parts of the system areresponsible for these emissions&To provide answers to these !uestions, a life cycle assessment '(#A) of a hypothetical

biomass power plant located in the *idwest +nited tates was performed. (#A is ananalytical tool for !uantifying the emissions, resource consumption, and energy use,collectively known as environmental stressors, that are associated with converting a rawmaterial to a final product. -erformed in con unction with a technoeconomic feasibilitystudy, the total economic and environmental benefits and drawbacks of a process can be!uantified. This study complements a technoeconomic analysis of the same process,reported in #raig and *ann '1//0) and updated here.The process studied is based on the concept of power generation in a biomass integratedgasification combined cycle ' I2##) plant. roadly speaking, the overall systemconsists of biomass production, its transportation to the power plant, electricitygeneration, and any upstream processes re!uired for system operation 'see 3igure 1). The

biomass is assumed to be supplied to the plant as wood chips from a biomass plantation,which would produce energy crops in a manner similar to the way food and fiber cropsare produced today. Transportation of the biomass and other materials is by both rail andtruck. The I2## plant is si4ed at 115 *W, and integrates an indirectly6heated gasifierwith an industrial gas turbine and steam cycle.


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Although a significant amount of work has been performed on many parts of this system orsimilar systems, very little has been done from a life cycle viewpoint. 3or example, earlierstudies have assessed the energy used at the biomass plantation, but did not include upstreamoperations such as raw material extraction or e!uipment manufacture 'see section 11.$).*oreover, processes re!uired for biomass production have not formerly been integrated withtransportation and electricity production for the purpose of identifying ma or emissions beyond#$ %. +nlike previous efforts, this study serves to pull together all ma or operations involved in

producing electricity from biomass, while identifying a large number of possible stressors on theenvironment.2enerally, a life cycle assessment is conducted on two competing processes. uch a comparativeanalysis highlights the environmental benefits and drawbacks of one process over the other. Inkeeping with the primary purpose of this study, to better define the environmental aspects of this

process irrespective of any competing process, a comparative analysis was not performed. 3uturework, however, will seek to answer the !uestion of how this process measures upenvironmentally against other renewable and fossil6based systems.3re!uently, others perform life cycle assessments in order to respond to criticism about theenvironmental effects of a product or to address a limited number of possible conse!uences. Indoing so, only data that are re!uired to address the goals of the pro ect while keeping the scopeof the assessment reasonable are included. In conducting this life cycle assessment, every effortwas made to include all correct and best available data. ince the primary goal of this work is toidentify sources of environmental concern and to discover possible design improvements tomitigate these concerns, it is our intention to report all possible environmental impacts of the

process. +nfortunately, because no biomass6based I2## plants are currently operating, it will bedifficult to validate some of the assumptions used in this study for some time. The system beingassessed is conceptual, and represents only what an integrated power facility using biomass

grown as a dedicated feedstock might look like. owever, emissions from the power plant itselfmay be verifiable from tests on the demonstration facility now being constructed in urlington,7ermont. Additionally, biomass test plots will continue to provide more accurate information onre!uired feedstock production operations and what environmental effects are likely. This studywill be regularly updated as real operating data become available.2.0 MethodologyIn the +nited tates, the ociety of 8nvironmental Toxicology and #hemistry ' 8TA#) has beenactively working to advance the methodology of life cycle assessment through workshops and


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publications. 3rom their work, a three6component model for life cycle assessment has beendeveloped ' 8TA#, 1//1), and is considered to be the best overarching guide for conductingsuch analyses. The three components are inventory, impact analysis, and improvement. Theinventory stage involves !uantifying the energy and material re!uirements, air and wateremissions, and solid waste from all stages in the life of a product or process. The second element,

impact assessment, examines the environmental and human health effects associated with theloadings !uantified in the inventory stage. The final component is an improvement assessment inwhich means to reduce the environmental burden of a process are proposed andimplemented. It should be emphasi4ed that life cycle assessments are not necessarily

performed step6wise and that they are dynamic rather than static. 3or example, processimprovements may become obvious during the inventory assessment phase, and alteringthe process design will necessitate a reevaluation of the inventory. Additionally,depending on the purpose of the (#A, an impact assessment may not be necessary. *ostimportantly, a life cycle assessment needs to be evaluated periodically to take intoaccount new data and experiences gained. To date, most work in life cycle assessment has

focused on inventory, although efforts to advance impact assessment and improvementare significant. The International 9rgani4ation for tandardi4ation 'I 9) is also involvedin life cycle assessment development under the new I 9 1:$$$ environmentalmanagement standards. pecifically, the ub6Technical Advisory 2roup working on thistask has made progress in constructing inventory assessment guidelines, but muchdisagreement remains on the impact and improvement elements.A detailed inventory was conducted for this study, and is the sub ect of most of the results

presented in this report. Additionally, some very simple design changes were made to the power plant, and recommendations for further process improvements are made.*ethodology development for performing impact assessments is in its infancy and felt tohave limited value for achieving the goals of this work. Therefore, only a cursoryexamination of the environmental effects was performed. This consisted of placing eachstressor 'e.g., #$ %, coal consumption) into an impact category 'e.g., greenhouse gas,resource depletion, etc.). It is important to note that even without a full impact analysis,recommendations for process improvements can be made by identifying ma or sources ofenvironmental stressors.2.1 System Boundaries and Data AvailabilityThe system boundaries for any life cycle assessment should be drawn as broadly as

possible. In addition to counting the material and energy flows of the primary process ofinterest, those processes involved in the extraction of raw materials and production of

intermediate feedstocks must be included. Intermediate feedstocks are sometimes referredto as ancillary materials because they are used indirecdy in the manufacture of the final product 'e.g., the fertili4er needed to grow biomass). The means of disposing products, by6products, wastes, and process materials are also included within the life cycle boundary. The system concept diagram shown in 3igure % serves to better describe themeaning of terms such as boundary, process, intermediate feedstock, and materials.


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The !uestion of where to stop tracking the energy and material uses of upstream processes is animportant one since the analysis is infinite if boundaries are not drawn to encompass the mostimportant impacts to the environment. 2enerally speaking, the impacts of upstream processes

become less significant the further you get from the process of interest, and a situation ofdiminishing returns becomes apparent past the third level of upstream processes. #onducting a

life cycle assessment can be extremely time consuming, and as part of the scoping process,decisions should be made to determine at which point the results will have limited use. 7eryoften, the determination of system boundaries is made based on data availability, and to a largeextent, this is how the present analysis was conducted. ;ata exist on the extraction of naturalresources, processing, manufacture, and delivery to the point of use for most process feedstocks,such as diesel fuel and ammonium nitrate fertili4er. Thus, the assessment included nearly all ofthe ma or processes necessary to produce electricity from biomass. 8xamples of operations that


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