Exergy Analysis for Combined Heat and Power (CHP) Plants

Combined heat and power plants are an efficient technology for waste heat recovery applications where both heat and power are demanded. Steam Rankine cycles are normally utilized when high temperature exhaust streams are available. Different heat demands and temperatures might be expected depending on the application. Thus, designing a power system capable of meeting the heat demand and producing the maximum possible power supposes a challenge. This work aims at providing some guidelines to properly select, from a second law perspective, a CHP plant configuration depending on the heat demand and temperature. Two plant configurations are considered and broad ranges of heat demand and temperature are studied. A software developed in MATLAB was utilized for all thermodynamic property calculations. Optimization of the thermodynamic cycle was carried out for each set of conditions and the best possible scenario was always evaluated. An exergy analysis of the components integrating the power plant was then performed, pointing out where irreversibilities were more predominant and where there was more potential for improvements. Results showed that extracting process heat in the condenser was more beneficial than utilizing a supplementary heat exchanger in series with the heat recovery steam generator