Life Cycle Assessment and Energy Potential of Residual Biomass

Taiwan is a country with an energy shortage. Ninety-nine percent of Taiwanese energy is imported, and the energy self-sufficiency rate in 2010 was merely 0.7%. Therefore, when the government develops new energy policies, the development of biomass energy should be a crucial project to increase the proportion of domestic renewable energy.While the first generation biomass may threatening food supplies, this study only explores the issues of residual biomass, including straw, corn stover, kitchen waste, pig manure. The amount of waste mentioned above in 2010 is calculated to estimate its energy potential. Furthermore, a life cycle assessment (LCA) approach is used to evaluate the impacts and benefits of five biomass cases on the environment and to calculate the energy return on investment rate (r_E). ((1) generating electricity by torrified biocoal (2) enzymatic hydrolysis of corn stover cellulosic ethanol (3) biogas production from kitchen waste mix pig manure (4) biogas production from corn stover mix pig manure (5) generating electricity by biogas.) Environmental benefits were also evaluated by comparing with 3 fossil reference system: generating electricity by imported hardcoal, unleaded 95 petrol supply chain, and natural gas supply chain for domestic heating. Inventories came from Ecoinvent database and literature review. Environmental analyses were carried out using a SimaPro 7.2 LCA software and adopting the IMPACT 2002+ methodology for evaluation of potential environmental impact. Results showed that, the case of terrified biocoal had the highest environmental impact in categories of global warming, the case of cellulosic ethanol had the highest environmental impact in categories of non-renewable energy, other three cases of biogas related had the highest environmental impact in categories of respiratory inorganics. Comparing to reference system about greenhouse gas emission reduction, all biogas cases, firing stage in biocoal case and car-use stage included in cellulosic ethanol case were beneficial to reduction. Regarding to energy return on investment, r_E value for all cases are > 1, that means they at least capture some renewable energy value with our nonrenewable investment. Although bioenergy system had less environmental impact than fossil energy system, especially on non-renewable energy consumption; however causes higher impact on other impact categories. Besides, there were many uncertain factors in the data acquired by this study and evaluative methodology. Policy makers should consider the appropriate weights for the different types of environmental impacts to evaluate the net environmental benefit of biomass energy.