Combined risk and exergy analysis

Energy systems are necessary to satisfy human needs and improve quality of life, but no source of energy is neutral with respect to the environment. Many environmental concerns are caused or related to energy production, transformation and use. 11 major areas of environmental concern are identified in which energy plays a major role such as environmental accidents, water pollution, land use, hazardous air pollutant, ambient air quality and global climate change. Hence, in the energy sector, the evaluation of environmental impact is gaining growing relevance. The relation between energy and environmental impact has been demonstrated. In this dissertation therefore the purpose is to use the risk associated to a plant combined to exergy analysis to provide a complementary assessment of the impact of a plant and accounting in particular for the impact on health and safety. The Combined Risk and Exergy Analysis (CRExA) is an analytical model aiming at finding the correlation between inefficiency sources of an energy system or process and the direct impact that these have on human health and environment and minimizing the associated risk. Exergy analysis is an effective method and tool for: a) combining and applying the conservation of mass and conservation of energy principles together with the Second Law of Thermodynamics for the design and analysis of energy systems, b) improving the efficiency of energy and other resource use, c) revealing whether or not and by how much it is possible to design more efficient systems by reducing the inefficiencies in existing systems, d) addressing the impact on the environment of energy and other resource utilization, and reducing or mitigating their impact. The CRExA model combines exergy and risk analyses for improving efficiency and safety of energy systems by reducing the associated risk once the influence of irreversibility is identified via a thermodynamics analysis. Indeed irreversibility can increase resource consumption in processes and lead to a quantifiable effect on the risk associated to the system. The integration of the two analyses is performed within the Thermoeconomic frame. Thermoeconomics is defined as a technique that combines economic and thermodynamic analysis by applying the concept of cost to exergy, in order to provide the analyst with information not available through conventional energy analysis and economic evaluation. Another relevant definition is “exergy aided cost minimization”. In this sense, the concept of exergy is used in the CRExA model as a measure for accounting the social cost in terms of risk to human health, and the thermoeconomic approach provides the relevant information on the irreversibility influence on cost. Hence, using risk analysis as objective function on the theoretical structure of the Thermoeconomic analysis can lead to the identification and quantification of such contribution. Assuming the risk of the system, evaluated according to risk analysis methodology, as a cost for the society, this approach can produce an information equivalent to what Thermoeconomics does for monetary cost, where the cost is represented by the risk to “accept” in order to benefit from the product of the system (e.g. electricity, gas, heat for energy systems). The model hence is conceived to identifying the elements of highest impacts in terms of damage to human health. In this manner, it can be used to delineate specific indications for the system design and the identification of the safety measures required by regulations. The model has been proposed to scientific community and two papers have been published on it. However, the CRExA model is at its first implementation and needs further development and application. In the doctoral thesis a number of points of strength and weakness and possible development paths have been identified.

L’obiettivo della Tesi è lo sviluppo di un modello integrato di analisi degli impatti dei sistemi energetici. Il modello sviluppato prende il nome di Combined Risk and Exergy Analysis (CRExA) e combina l’analisi di rischio associato a un impianto con la relativa analisi exergetica, utilizzando la struttura dell’analisi Termoeconomica. Il concetto di rischio associato è utilizzato come costo “sociale” dell’impatto del sistema e l’integrazione con l’analisi exergetica permette di valutare il contributo al rischio totale del sistema derivante dalle irreversibilità termodinamiche. La struttura dell’analisi Termoeconomica permette inoltre di trovare la configurazione del sistema a cui è associato il rischio minore a parità di prodotto del sistema. Il modello è stato proposto alla comunità scientifica internazionale e due articoli su casi applicativi sono stati pubblicati. La Tesi contiene infine l’analisi dei punti di forza e di debolezza del modello CRExA e i suoi possibili sviluppi futuri.