Life cycle assessment of producing biocoal from rice straw via torrefaction
Date Issued
2011
Date
2011
Author(s)
Syu, Fu-Siang
Abstract
According to the target of increasing proportion of renewable energy and CO2 reduction, Taiwan Environmental Protection Administration draft a promotion plan of the transformations from expired incinerators to bio-energy centers which utilize bio-waste as feedstock. Base on the estimations in this study, crop residue such as rice straw is produced in abundance on Taiwan. However, the high moisture content and low heating value of rice straw affect its biomass utilization efficiency. Furthermore, poor grindability of rice straw decreases rates of co-milling with coal at coal-fired power plants. Torrefaction is a thermal pretreatment technology which improves the properties of biomass in order to deal with the above problems. This study focuses on production chains which utilize torrefied biomass (biocoal) derived from rice straw for co-firing in power plant. The production chains are investigated using a Life Cycle Assessment (LCA) approach, which takes into account all the input and output flows occurring along the production chain. Investigation was carried out using a SimaPro 7.2 LCA software and adopting the IMPACT 2002+ methodology for evaluation of potential environmental impact. Environmental impact reductions were also evaluated by comparing with fossil reference system generating electricity with combustion of imported hardcoal. The comparative results show that the bioelectricity production chain had impact reductions in impact categories of aquatic ecotoxicity, terrestrial ecotoxicity, global warming and non-renewable energy use. Moreover, results indicated that the bioelectricity had higher impact reduction with increasing in biocoal replace ratio. On the other hand, the bioelectricity production chain had higher impact potential than reference system in carcinogens, non-carcinogens, ionizing radiations, ozone layer depletion, respiratory organics, terrestrial acidification, aquatic acidification, aquatic eutrophication, respiratory inorganics, land occupation and mineral extraction. Concerning GHG emission savings, the possible saving of biocoal co-firing increased with increasing in biocoal replace ratio, and had a maximum of 0.61 kg CO2 eq/kWh (100% replace with biocoal). Also, the GHG saving was 0.49 kg CO2-eq per kg of rice straw which was used for generating bioelectricity. Based on the results, the bioelectricity production chain has environmental benefits in GHG savings and non-renewable energy consumption, but cause higher impact in other impact categories than fossil system. Therefore, policy makers should comprehensively consider various impacts in order to determine the feasibility of developing bioenergy in aspect of environment.
Subjects
Rice straw
Torrefaction
Life cycle assessment
Co-firing
Type
thesis
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