Thermoeconomic analysis and design evaluation of a Waste to Energy power plant: an Input–Output approach

The growing concern about the limited reserves of fossil fuels has led research efforts in the energy field on increasing thermodynamic efficiency of energy conversion systems. Although the operation of renewable power plants avoids direct depletion of fossil fuels, literature points out that both direct and indirect contributions to primary fossil fuel depletion occur in every phase of the system life cycle (LC). In this perspective, a fair and meaningful thermodynamic performance evaluation and optimization process should take into account such primary fossil fuel depletion. Boundaries of traditional methods such as Thermoeconomic Input Output analysis (TIOA) are limited to the considered system, neglecting the additional consumptions due to non-energy related goods and services. Therefore, design improvements proposed through TIOA should be verified in the perspective of primary resources consumption: indeed, not necessarily a reduction of irreversibilities within the considered system are accompanied by a reduction of primary resources requirements. The present work aims at improving the standard Thermoeconomic Input Output analysis (TIOA) in order to account for the primary exergy cost of energy system products: the novel method of Exergy-based Input–Output Analysis (ExIO) is then proposed, which models all the supply chains that feed the Life Cycle of the analyzed system through the national Monetary Input Output Tables (MIOTs). Beside traditional thermoeconomic indicators, such as the exergy cost of products and the exergy cost of exergy destructions, appropriate indicators based on ExIO method are here defined: primary exergy cost of products and Exergy Return on (Exergy) Investment (ExROI). Standard TIOA and the novel ExIO method are then applied for the analysis and design evaluation of a Waste-to-Energy (WtE) power plant operating in the Italian context. Exergy cost and primary exergy cost of electricity are computed, together with the related thermoeconomic indexes, revealing that that the indirect fossil-fuel consumption related to the Life-Cycle of a WtE facility is not negligible; nonetheless, the plant is able to produce a net amount of useful exergy to completely pay back its primary fossil fuels consumption more than 100 times.