Life Cycle Assessment and Emergy Analysis in Biomass CHP Environmental Accounting
Open Access
- Author:
- Ma, Li
- Graduate Program:
- Forest Resources
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 04, 2013
- Committee Members:
- Charles David Ray Sr., Dissertation Advisor/Co-Advisor
Charles David Ray Sr., Committee Chair/Co-Chair
Judd Harrison Michael, Committee Member
Michael Gerard Messina, Committee Member
Richard Charles Stehouwer, Committee Member - Keywords:
- Life Cycle Assessment
LCA
Emergy Analysis
Environmental Accounting
Uncertainty Analysis
Sensitivity Analysis
Correlation - Abstract:
- This study discusses the similarities, differences, and incompatibilities between two types of environmental accounting tools: Life Cycle Assessment (LCA) and Emergy Analysis (EMA), both of which are used to provide environmental assessment of products and processes. LCA methodology provides emission-focused environmental accounting by expressing all the resource uses (material and energy) across a product's entire life as categorized environmental impacts. In contrast, EMA methodology presents a single unit measured, energy-focused environmental accounting by expressing all the resource consumption (material, energy and labor) in a solar energy equivalent or solar emjoule (sej). A significant, albeit simplified, case study – that of a wood biomass Combined Heat and Power (CHP) system - is used to compare the results and analytically assess merits of LCA and EMA as well as to consider possible integration of the methods. Woodchips production, transportation, facility construction, industrial conversion to energy and disposal of wastes are included in the analysis. A Monte Carlo simulation model is developed by taking into account factors that have inherent uncertainty in a biomass CHP system. The results obtained from the two methods are compared by means of uncertainty analysis, sensitivity analysis and correlation analysis. This research provides three key contributions. The findings suggest that information provided by the two methods is complementary rather than competing. Each of these two methods displays its own unique "optimal field of application": 1)LCA is a useful assessment method to evaluate local and global environmental impacts of the system. Its usefulness is very limited to the assessment of a specific system. However, LCA may be and is commonly used within clearly-stated assumptions, to compare two similar processes and thereby provides environmental sciences a continuous benchmarking tool. 2)EMA provides a more robust assessment of interconnection between an industrial process, its recognized environmental dynamics and its economic potential. Its capability to account for externalities expands its usefulness over a broader spectrum of cases, but also limits its use for improvement of a specific process. The crucial benefit of EMA is that it provides an approach aimed for maximizing utilization efficiency of local environmental resources in supporting industrial process and economy. Simply speaking, EMA answers the question "What is the most efficient product or process?" while LCA answers "How can we improve environmental efficiency of a specific product or process?" Secondly, LCA and EMA indicators are characterized by different degrees of uncertainty: 1)Uncertainty is inherent in the current LCA approach, and cannot be overcome even if practitioners strictly follow the procedures described in the LCA standards. Therefore, uncertainty and sensitivity analysis should always be reported in the LCA final results. 2)EMA indicators are subject to free environmental service and human labor associated with the system, which are not accounted in LCA. This uncertainty analysis of EMA adds value to the extant literature. Given the large degree of uncertainty of the LCA results, using LCA independently as the sole tool for decision-making in energy policy will, in some cases, cause decisions resulting in more environmental damage and poorer economical performance than expected and understood. Therefore, LCA can be a useful tool for a company's internal decision-making, but should not be solely trusted to guide public policy. EMA can quantify the contribution of natural capital for sustaining economic activity. The results become more accurate as the scale of environmental area gets larger, which makes well-executed EMA a better tool for environmentally and economically conscious policy-making. Finally, correlation analysis reveals no significant correlation between Global Warming Potential (GWP), the most commonly referred-to indicator in LCA, and any EMA indicators. On the other hand, varying correlations are found among EMA indicators, suggesting the number of EMA indicators could be reduced as they lead to similar findings. Surprisingly, biogenic CO2 emission from LCA and Transformity (Tr) in EMA are strongly correlated. This relationship suggests that using some LCA components and methodology could possibly increase the applicability and long-term value of EMA in environmental decision-making as it complements the assessment perspective.