LCA of poplar bioenergy system compared with Brassica carinata energy crop and natural gas in regional scenario
Introduction
The replacement of fossil fuels with biomass in the generation of energy is an important strategy promoted by the European Union (EU) to mitigate the effects of climatic change and enhance the security of the supply and diversification of energy sources [1]. For this purpose, bioenergy is being promoted through several EU Directives, as well as national policies [2], [3]. Biomass-based electricity is being promoted by the Renewable Electricity Directive, which aims to increase the use of renewable energy sources (RES) to 22% by 2010 [2], [3]. Biomass, and in particular energy crops, have attracted attention as a promising, renewable and local energy source [4], [5], [6] which could help the EU reduce its dependency on external energy sources, i.e., the main oil-exporting and gas-exporting countries. Spain is a significant example of an energy-dependent European country as around 75% of its total energy demand is imported [7].
Due to the expectancy that this aroused and the fact that most EU governments recognised that an increase in the use of energy crops should be accompanied by detailed analysis [4], [5], [8], several studies were made that focused on the energy and environmental performance of biomass energy crops [9], [10], [11], [12], [13]. North-western and central European countries put the most effort into the research and use of several biomass sources, mainly forest residue biomass, energy crops and biomass wastes destined for electricity and heat generation in recent decades, while in southern Europe the introduction of biomass, and specifically energy crops, is proving slower and more difficult [5], [8], [9], [14]. For example, only in Spain, it is foreseen that by 2010 one million hectares will be destined for the production of 3.35 Mtep by energy crops, but the fact is that the current energy produced by energy crops is inexistent [5]. The state of the art of energy production by biomass from energy crops in southern European countries justifies the study of energy crops destined for producing biomass as a local RES in order to reduce the dependency on external sources and the environmental impacts produced by the current mix of forms of energy production in the several southern European countries.
The study has selected Populus sp. as a realistic case study of the implementation of energy crops in southern European countries. Populus sp. commonly known as poplar is one of the most widely considered forest species of energy crop in North-western and central Europe [15], [16]. In different areas all over southern Europe the poplar is important in traditional wood use; in 2002 in Spain alone, 2482 ha was cultivated for this purpose [17]. The fact that poplar is not an unknown crop could facilitate its growth for energy application in high density and short rotation conditions [16]. The advantages of the agricultural production of poplar as a short rotation energy crop include the fact that it is a crop with a known tradition in the area analysed [17], high yields, high ecological interest in terms of biodiversity and low fertilizer doses required and comparatively low biomass production costs [11], [16], [18], [19], [20]. On the other hand, the disadvantages of the poplar crop include the high requirement for water, which restricts the natural distribution of the poplar [21]. The amount of water applied during irrigation of these crops in southern Europe should be low or eliminated, especially in an area where water is a limited resource. However, the poplar could be an alternative energy crop worthy of consideration by the agricultural sector from an economic point of view and in terms of its compatibility with other crops [16].
In this paper, we study the environmental and energy behaviour of cultivation of poplar for producing lignocelluloses biomass destined for the generation of heat and electricity in southern Europe using current agricultural techniques. Furthermore, this bioenergy system is compared with other systems as Brassica carinata energy crop commonly known as Ethiopian Mustard, which could be a realistic option for implementation in Spain and also with an equivalent quantity of a non-renewable fuel such as natural gas in order to present the advantages and barriers of the production of biomass by means of the cultivation of poplar.
Section snippets
Methodology
To evaluate the environmental and energetic performance of the production and distribution of poplar as far as a plant, a hectare of experimental plot cultivated in Soria (northern Spain) is analysed using the life cycle assessment (LCA) methodology. This environmental tool follows ISO14040 guidelines [22], [23], according to which, LCA is divided into four steps: (1) goal and scope definition, (2) inventory analysis, (3) impact assessment and (4) interpretation. The environmental analyses were
Goal and scope definition
The main aim of the study is to determine the benefits and barriers of poplar cultivation in a Continental-Mediterranean area (Spain) destined for the production and distribution of solid biomass fuel as far as the thermoelectric plant. Additionally, the study had two significant and specific goals; the hotspots of the agricultural and transport phases of the system were identified and measures were suggested for environmental improvement. The second specific goal was to compare the poplar
Energy analysis of the poplar cropping bioenergy system
The total primary energy consumption of the poplar cropping system (agricultural subsystem and transport subsystem) result is similar to other short rotation energy crops studies (98.30 GJ ha−1) [28], is higher in scenario 2 than in scenario 1, see Table 4. The main reason for the primary energy input increase of 2.39 GJ ha−1 is the lower chip density in comparison with stems, for which there is an increase of 2.18 GJ ha−1 in the transport of the biomass. The second reason is the added primary energy
Conclusions
According to our calculations, the poplar bioenergy system cultivated in southern Europe is energetically efficient. In order to achieve 1 MJ of renewable energy in biomass only a total of 0.20 kJ of primary energy is required. The poplar bioenergy system is particularly energy efficient when compared with other systems such as Ethiopian mustard energy crop and non-renewable fuels such as natural gas, in which cases the primary energy invested to produce 1 MJ up to 120 and 180 kJ, respectively [6].
Acknowledgements
The authors would like to thank to Spanish Ministry of Education and Science for financing the “Evaluation of the Environmental Sustainability of Energetic Crops (CTM2004-06800-C03-01)” project within which this study was carried out and for awarding a research scholarship (AP2005-2518) to junior researcher Carles Martínez Gasol.
Carles Martínez Gasol received a B.Sc. degree in Environmental Science (2003) in Universitat de Girona (UdG, Spain) and an M.Sc. degree in Environmental Science (2005) in Universitat Autònoma de Barcelona (UAB, Spain). In 2005, Martínez Gasol spent 1 month in the South Caroline & Clemson Universities, Colombia (USA) when he did a summer course in environmental management systems. Currently, he is a research junior member of the Institute of the Environmental Science and Technology (ICTA) and
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Carles Martínez Gasol received a B.Sc. degree in Environmental Science (2003) in Universitat de Girona (UdG, Spain) and an M.Sc. degree in Environmental Science (2005) in Universitat Autònoma de Barcelona (UAB, Spain). In 2005, Martínez Gasol spent 1 month in the South Caroline & Clemson Universities, Colombia (USA) when he did a summer course in environmental management systems. Currently, he is a research junior member of the Institute of the Environmental Science and Technology (ICTA) and the SosteniPrA research group (Sustainability and Environmental Prevention) of the Universitat Autónoma de Barcelona (UAB, Spain). Furthermore, he has a research fellowship (AP2005-2518) of the Spanish Ministry. His research topics are life cycle assessment methodology, biomass and environmental indicators.
Xavier Gabarrell Durany has a B.A. in Chemical Engineering, M.A. in Biotechnology, and a Ph.D. in Biotechnology (UAB, Spain). Currently, he is a member of the Chemical Engineering Department of the Universitat Autònoma de Barcelona and he was a Director of the Institute of Environmental Science and Technology (ICTA) of the same university. He teaches courses on a variety of environmental topics in the Chemical Engineering degree and in the Environmental Science degree as well as in the master programmes of the Biotechnology and Environmental Sciences. His research work on the Chemical Engineering Department and the ICTA UAB has been focusing on the field of Environmental Engineering and Biochemical Environmental Engineering during the last 15 years. He is expert in industrial ecology, environmental audits, waste management and industrial water treatment by fungi. His research has been funded by the European Union; Spanish CICYT, the Catalan DURSI and different companies. He is the head of the research group SosteniPrA (Sustainability and Environmental Prevention) and a member of International Society of Industrial Ecology (ISIE).
Joan Rieradevall Pons has a B.A. in Chemical (UAB, Spain), Ph.D. in Chemical Engineering (UAB, Spain) and a M.A. degree in Business and Management (EADA, Spain). Currently, he is a member of the Chemical Engineering Department of the Universistat Autònoma de Barcelona, the Institute of Environmental Science and Technology (ICTA) and the SosteniPrA (Sustainability and Environmental Prevention) research group of the same university. He teaches courses in the Environmental Science degree as well as in the master programmes of the Environmental Sciences. His research work on the Chemical Engineering Department and the ICTA Institute of the Environmental Science and Technology (UAB) has been focusing on the field of Environmental Engineering and the Environmental Prevention. He is expert in life cycle assessment and other environmental prevention tools and waste management. In his commendable scientific work emphasises over 140 articles in scientific and technical journals, 20 books and book chapters and the organisation of the last Life Cycle Management convention celebrated in 2004 (Barcelona, Spain).