Análise comparativa de diferentes metodologias de alocação na ACV por meio de métodos tradicionais e métodos termoeconômicos

Abstract

Life Cycle Assessment (LCA) is a methodology that allows the quantification of potential environmental and social impacts of products, processes or activities by providing the indicators that allow the assessment of sustainability. Studies using Life Cycle Assessment (LCA) are highly effective for assessing many energy conversion systems. However, when analyzing multi-product systems, the allocation of resources and waste presents a difficulty. This adversity can be solved through thermoeconomic approaches. These approaches are well known for their rational allocation of resources and, therefore, can be an ideal combination to carry out LCA studies in this type of complex systems. Thus, the objective of the present work was to carry out a comparative analysis between the traditional methods, recommended by the ISO 14000 standard, and thermoeconomic in the LCA of a cogeneration system composed of a gas microturbine and a lithium Water. First, the total emissions of the system were calculated, and then the allocation of resources was carried out. This allocation was achieved in three ways: traditional allocation, thermoeconomic allocation, and allocation through exergoenvironmental analysis. In order to carry out the last two allocations, exergetic costs were calculated considering the Physical Structure a and the Productive Structure of the production flows (with the two different ways of making the production structure and using four different exergy breakdown models). With the result of exergetic costs, the environmental impacts (environmental costs) were calculated by means of the thermo-economic allocation and ex-environmental analysis. Then the environmental impacts (environmental costs) found through LCA with allocations that use thermoeconomics were compared with those obtained by LCA with traditional allocation (energetic and exergetic). Thus, it was found that there is little precision in the results obtained by the energy allocation and the allocation that uses the thermoeconomics with the E model (which defines input and product using only the exergetic flow), because of the high environmental cost of the cold. This is because these models have simple methodologies that do not cover systems with many dissipative elements. It was also found that there is no difference in using an exergetic allocation or an allocation that uses thermoeconomics if the system does not have many dissipative components, such as the valve, or does not require much precision in the results, since both perform the same calculations with very few modifications. We conclude that it is necessary to allocate resources from a LCA through thermoeconomics with a higher level of disaggregation only in energy systems with many dissipative elements, such as condensers and valves. And for this type of allocation that considers thermoeconomics, it is possible to use both thermoeconomic allocation and exergoenvironmental analysis.