A comprehensive evaluation of an integrated waste-to-biogas production facility and power plant using the extended exergy accounting (EEA) methodology

The Extended Exergy Accounting (EEA) method assesses the exergy value of labor as equivalent to the primary exergy required to produce and sustain the workforce essential to the system's long-term operation. The neoclassical economic approach, which incorporates capital flows into the thermodynamic framework, falls short in revealing the environmental impacts of various industrial, agricultural, and financial activities. In contrast, the exergy method provides a robust basis for examining the ecological effects of production activities. It allows us to directly calculate the cost of balancing wastes with environmental conditions. Evaluations of waste disposal processes and waste-to-energy (WtE) studies using the EEA method facilitate the determination of service costs in environmental impact management. In this study, a real gas turbine biopower plant, which generates 32.0 GWh of electricity and 33.5 GWh of heat annually and employs approximately 700 people, was analyzed using the EEA method. First, all sub-processes, from raw material input to electricity and heat production, were assessed using the classical exergy method. The system boundaries were then expanded to include emissions from raw material transportation, the labor and capital required for transportation, and waste management following the completion of the production process. These were evaluated through analysis using the EEA method. The exergy efficiency of the biopower plant was 52%, while the bio-methanization unit, responsible for biogas production, had an exergy efficiency of 39%. By applying the EEA method, the labor, capital, and environmental impact factors within the expanded control volume of the biopower plant were quantified in exergy units. Results showed that the exergy equivalent of the labor factor per working hour was 27.64 MJ/h, and that of the unit capital was 18.30 MJ/USD. The environmental impact assessment examined three interconnected systems responsible for disposing of emissions—CO2, N2O, CH4, and compost—generated within the expanded control volume. The labor and capital inputs for each of these systems were calculated separately.