A Theoretical Framework for Integrating Exergy-Based Life Cycle Assessment with Thermoeconomic Optimisation of Industrial Energy Systems in Nigeria

The conventional application of life cycle assessment and thermoeconomic optimisation as separate analytical tools in Nigerian industrial energy systems design and evaluation leads to fragmented decision-making that fails to capture the thermodynamic quality destruction and economic cost flows simultaneously across the entire system life cycle, limiting the theoretical coherence and practical utility of sustainability analyses in the energy-intensive industrial sector. This research develops an integrated theoretical framework that unifies exergy-based life cycle assessment, exergoeconomic analysis, and multi-period optimisation into a single formalism applicable to complex industrial energy conversion systems, with application to the refinery and petrochemical complex sector of the Niger Delta. The theoretical framework introduces an exergoenvironmental damage cost function that aggregates exergy destruction costs, environmental burden allocation across life cycle stages, and present-value economic flows into a unified objective functional for system design optimisation. The framework is operationalised through a mixed-integer nonlinear programming formulation and applied to the conceptual redesign of a representative refinery utility system configuration in the South South geopolitical zone. Case study results demonstrate that integrated framework optimisation identifies configurations delivering 18 to 31 percent reductions in cumulative exergy destruction compared to economic-only optimisation, with corresponding reductions in environmental burden allocation. Theoretical extensions to district energy system planning and multi-energy system design are developed as generalisable contributions to the engineering thermodynamics literature. Keywords: exergy, life cycle assessment, thermoeconomic optimisation, refinery, theoretical framework.