Energy Systems Improvement based on Endogenous and Exogenous Exergy Destruction

Abstract

One of the roles of Exergoeconomics is to provide energy system designers and operators with the information, necessary for the improvement of energy systems. It employs both economic principles and exergy concepts particularly taking into account the values of individual components’ exergy destruction: the thermodynamic loss due to irreversibilities within a system’s component. The total exergy destruction occurring in a component is not only due exclusively to the component (endogenous exergy destruction) but is also caused by the inefficiencies of the remaining system components (exogenous exergy destruction). Hence care must be taken in using the total exergy destruction of a component when making decisions to optimize the overall energy system. The understanding of Exogenous and Endogenous Exergy Destruction for any given component can further assist the engineer in deciding whether a subsystem or a structural adjustment is required in the optimization of the entire energy system. With emphasis placed on process performance (i.e. the mutual interdependencies of the components within the system) as oppose to the final output, exogenous and endogenous exergy destruction analysis guarantees that the quality of the output is improved without compromising the performance of individual components. Additionally, only a part of the exergy destruction in a component can be avoided (avoidable exergy destruction) since a system component is also imposed by a number of constraints including physical, technological and economical. Knowledge of the Exogenous and Endogenous exergy destruction together with an understanding of the (unavoidable and avoidable exergy destruction) can provide a realistic measure of the potential for optimising any energy system. The thesis deals with the development of a concept for splitting the exergy destruction and the costs associated with the system components. This concept is then applied to improve three energy conversion plants: a simple gas turbine process, a cogeneration and an externally-fired combined cycle power system and the results compared to the improvement of these said plants using a conventional exergoeconomic analysis.