Publicação
Life cycle assessment of energy production from forest residues
| Resumo: | The production of bioenergy from forest biomass residues has been increasing in the last years in Portugal, mainly as a consequence of concerns related to climate change and forest fires. However, the potential environmental impacts associated with its production should be quantified to support decision-making. This quantification can be performed by using life cycle assessment (LCA), a methodology that evaluates the entire life cycle of a product or process (from the extraction of the raw materials until its end-of-life), allowing to identify the most significant stages and processes along the life cycle. Currently, there is a limited number of LCA studies concerning the production of bioenergy from forest biomass residues. In addition, those studies usually exclude the end-of-life stage (ash management) or only consider ash disposal in landfill, disregarding the valorisation alternatives. Furthermore, given the constraints on forest residues availability, it is important to assess the best use for these residues from an environmental perspective. Therefore, this thesis aims to contribute to increase the knowledge of the environmental performance of the bioenergy sector in Portugal. The two most representative combustion technologies for electricity production from forest biomass residues (grate furnace and fluidised bed) are assessed and compared using LCA throughout all stages of the value chain, namely, forest management, collection, processing, transportation, energy conversion and end-of-life. Moreover, LCA is applied to the end-of-life stage of the ash generated during the combustion of forest biomass residues to evaluate two valorisation alternatives (construction materials and soil amelioration) and compare with ash landfilling. Various scenarios are included in order to identify the most efficient option from an environmental point of view. Additionally, a consequential LCA is used to evaluate the best valorisation option for the forest biomass residues, namely, electricity, heat or bioethanol, in comparison with a baseline that entails leaving the residues in the forest soil and energy is produced from fossil fuels. The results show that fluidised bed presents smaller environmental impacts than grate furnace for all impact categories analysed. Regarding ash valorisation in construction materials, all scenarios assessed had a lower environmental impact than landfilling in all the impact categories. However, the valorisation of ash for soil amelioration presents higher environmental impacts than landfilling for some impact categories, indicating that it can potentially increase the amount of pollutants in the soil. Finally, the results of the consequential LCA indicate that the best use of the forest biomass residues is cogeneration of electricity and heat, but for some impact categories it would only perform environmentally better than the baseline under particular conditions. |
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| Autores principais: | Costa, Tamíris Pacheco da |
| Assunto: | Bioenergy production Environmental impact Forest biomass residues Life cycle assessment Woody biomass ash valorisation |
| Ano: | 2019 |
| País: | Portugal |
| Tipo de documento: | tese de doutoramento |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade de Aveiro |
| Idioma: | inglês |
| Origem: | RIA - Repositório Institucional da Universidade de Aveiro |
| Resumo: | The production of bioenergy from forest biomass residues has been increasing in the last years in Portugal, mainly as a consequence of concerns related to climate change and forest fires. However, the potential environmental impacts associated with its production should be quantified to support decision-making. This quantification can be performed by using life cycle assessment (LCA), a methodology that evaluates the entire life cycle of a product or process (from the extraction of the raw materials until its end-of-life), allowing to identify the most significant stages and processes along the life cycle. Currently, there is a limited number of LCA studies concerning the production of bioenergy from forest biomass residues. In addition, those studies usually exclude the end-of-life stage (ash management) or only consider ash disposal in landfill, disregarding the valorisation alternatives. Furthermore, given the constraints on forest residues availability, it is important to assess the best use for these residues from an environmental perspective. Therefore, this thesis aims to contribute to increase the knowledge of the environmental performance of the bioenergy sector in Portugal. The two most representative combustion technologies for electricity production from forest biomass residues (grate furnace and fluidised bed) are assessed and compared using LCA throughout all stages of the value chain, namely, forest management, collection, processing, transportation, energy conversion and end-of-life. Moreover, LCA is applied to the end-of-life stage of the ash generated during the combustion of forest biomass residues to evaluate two valorisation alternatives (construction materials and soil amelioration) and compare with ash landfilling. Various scenarios are included in order to identify the most efficient option from an environmental point of view. Additionally, a consequential LCA is used to evaluate the best valorisation option for the forest biomass residues, namely, electricity, heat or bioethanol, in comparison with a baseline that entails leaving the residues in the forest soil and energy is produced from fossil fuels. The results show that fluidised bed presents smaller environmental impacts than grate furnace for all impact categories analysed. Regarding ash valorisation in construction materials, all scenarios assessed had a lower environmental impact than landfilling in all the impact categories. However, the valorisation of ash for soil amelioration presents higher environmental impacts than landfilling for some impact categories, indicating that it can potentially increase the amount of pollutants in the soil. Finally, the results of the consequential LCA indicate that the best use of the forest biomass residues is cogeneration of electricity and heat, but for some impact categories it would only perform environmentally better than the baseline under particular conditions. |
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