Life Cycle Assessment Applied to an ORC System Operating Under Two Modes: Evaluation of Two LCIA Methods

Life Cycle Assessment (LCA) is a remarkable tool that allows decision-makers to reduce the environmental impact, identify possible improvements, and compare the environmental performance of products and services. Thus, considering the increasing interest in the environmental assessment of thermal systems, this work applies the LCA tool in a proposed cogeneration system, previously studied by the authors, comparing different Life Cycle Impact Assessment (LCIA) methods for two distinct operation modes, namely, Organic Rankine Cycle - Simple (ORC-S) and Organic Rankine Cycle - Combined (ORC-C). The LCIA methods considered for this study are Eco-Indicator 99 (Hierarchist, Average weighting - H,A) and ReCiPe Endpoint (Humanitarian, Average weighting - H,A). The considered functional unit is 1 kWh of produced electricity. The cogeneration system comprises mainly an ORC system working with R134a and a piece of equipment operating as the heat sink. The latter is what defines the system operation mode, i.e., a cooling tower (ORC-S) or an Absorption Chiller (ORC-C). The system was designed to partially meet the power and thermal demands of a lab facility, located in the Federal University of Paraíba, Northeast - Brazil, and to be powered by ICE exhaust gases. Simulations have been performed through open-source software openLCA version 1.10.3, running the Life Cycle Inventory (LCI) database Ecoinvent 3.7.1. The results have confirmed the importance of LCA on a trade-off decision once it adds valuable information beyond the thermodynamic and economic ones. Also, the results have shown that the environmental impacts for electricity energy produced from the ORC-C mode are, at least, 6 times higher than those of ORC-S. Among the main reasons for that is the cooling energy from absorption chiller and the high consumption levels of fossil fuels throughout the life cycle of each studied component.