Afsin Gungor

In view of sustainable future energetic–exergetic and economic analysis of a natural gas cogeneration plant

Thermodynamics plays an important role in performing energy and exergy analyses of industrial processes. The first law is widely used in engineering practice, and is the basis of the heat–balance method of analysis that is commonly used in energy systems performance analysis. However, the second law involves the reversibility or irreversibility of processes, and is a very important aspect of the exergy method of energy systems analysis. For a sustainable future, exergy analysis allows for improvements not necessarily attainable via energy methods, like increased efficiency, reduced fuel use and reduced environmental emissions. From the viewpoints of energy conservation and environmental benefits, cogeneration systems can be considered as systems of sustainable energies. From this point of view, in this study, the energy, exergy and economic analysis of an actual natural gas cogeneration plant with a total capacity of 121.5 MWh electrical powers is carried out. The first and second law efficiency of the cogeneration plant is calculated as 40.8% and 90.2%, respectively. The pay–back period of the cogeneration plant is calculated as three years, which means this plant runs quite efficiency and economically.

Efficiency assessment of a cogeneration system

For the sustainable usage of fossil fuels; thermodynamic analysis allows for improvements not necessarily attainable via energy methods, like increased efficiency, reduced fuel use and reduced environmental emissions. The first law is widely used in engineering practice and is the basis of the heat-balance method of analysis that is commonly used in energy systems performance analysis. However, the second law involves the reversibility or irreversibility of processes and is a very important aspect in the exergy method of energy systems analysis. From this point of view, in this study, thermodynamic analysis of an actual diesel engine based cogeneration plant with a total capacity of 11.52 MW electrical powers, 9 t/h of steam and 140 t/h of hot water is carried out by analyzing the components of the system separately. Both the performance characteristics of the internal combustion engine unit and the supporting components in the plant are evaluated. The present study provides important information regarding exergetic performance of the entire plant and its components through exergy destructions and exergy efficiencies. Identifying the main sites of exergy destruction shows the direction for potential improvements. The exergetic performance results show that the diesel engine is the major component contributing most to the plant’s total inefficiency, due to its inherent nature. The results show that 39.86% of the exergy entering the plant is converted to electrical power. The net steam production of the plant constitutes 8% of the total exergy input and the hot water production of the plant constitutes only 1.26% of the total exergy input. The remaining 50.88% of the exergy input is lost.