| Summary: | 碩士 === 國立成功大學 === 環境工程學系碩博士班 === 96 === The objective of construction of an inventory database in a company would be 1) to identify hot-spot for improvement of a product lifecycle, 2) environmental product declaration, and to provide their suppliers and downstream customers with a database for conducting Life-Cycle Assessment (LCA) of their product. Manufacturing procedure is usually complex and tends to have more than one product, therefore, it is not simple to construct an inventory database for LCA. Especially, methodological choices in allocation of environmental loads into multiple products are crucially important because it could affect the final decisions.
In this thesis, first, to what extent and how the flow model in LCA can be simplified, without influencing the result is discussed. There are two major known allocation approaches, namely partitioning and system expansion approaches in life cycle inventory analysis. Three aggregation patterns, namely “branch”, “straight”, and “complete” aggregation patterns were identified in this thesis, and the criteria to allow such aggregation is discussed in conjunction with the two allocation patterns.
Integrated steel manufacturing is taken as a case study to discuss in what cases data aggregation and partitioning could affect the reusability and comparability of LCA studies. And the result shows that it can reflect varied avoided impact by using system expansion for allocation. LCA result shows that emission factor of producing one ton steel is 0.7330 ton-CO2 equivalent and One-at-a-time (OAT) method is used for sensitivity analysis for all parameters in LCA model.
Usually, when the consequences of changes in used amount of steel in a product is evaluated using the amount calculated above. However, above value merely explains how much emission occurred in retrospect to production of one ton of steel, and does not explain how much change will be induced by reduction of or increase in one ton of steel consumption in prospect. To elucidate such difference, four scenarios are set up for a hypothetical integrated steelmaking process, discussing how much change in CO2 emission occurs by decreasing one ton of hot-rolled steel. Interestingly, the result shows that in some scenarios, reduction of use of hot-rolled steel could result in increase of CO2 emission. The case study clearly points out that:
1)Objectives of LCA must be clearly distinguished: whether it is supposed to be a study for identifying the alternatives via hot-spot identification, or it is a change-oriented study that actually evaluate the consequences of applying different alternatives
2)Database for downstream producers should provide both stand-alone LCA results, and change-oriented LCA results, to allow both stand-alone and comparative types of LCA.
Above two points are especially important for products such as steel (lots of co-products, relationships with other industries) and electric power (same product is produced from different production methods), because its application is extremely wide.
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