A Study of Sections Interaction Effects on Thermodynamic Efficiencies of a Thermal Power Plant

Abstract

Aim: A study of energy and exergy analyses was carried out on a thermal power plant in order to investigate the interaction effects of coupling sections of the plant and overall system. Study Design: Simulation, energy and exergy analyses were used. Place and Duration of study: The plant is located at Egbin in Lagos State of Nigeria and the duration of study was between March and May 2010. Methodology: The thermal power plant was simulated using Hyprotech System Simulation (HYSYS) software and Excel spreadsheet was used for the energy and exergy analyses. The sections were grouped into four, namely: turbine-generator, condenser, regenerator and furnace-boiler sections. The energetic and exergetic efficiencies and irreversibilities at different throughputs (50, 75, 100 and 110% power outputs) were evaluated for each section and the sections were coupled into subsections one after the other until the whole sections were coupled. Results: The results showed that the furnace-boiler and the condenser sections have the least exergetic efficiencies of an average of 24.08% and 38.85%, respectively, while the energetic efficiencies of the regenerator and furnace-boiler were the least and were 67.04% and 62.74% on the average, respectively. The overall system energetic and exergetic efficiencies were at an average of 20.21% and 11.17%, respectively. Furthermore, the results showed that the closed loop topology of the thermal plant and the high irreversibilities in the furnace-boiler section made the highest contributions in determining the overall process efficiencies. The overall irreversibilities of the plant increased as the throughput increased, but the overall energetic and exergetic efficiencies were not sensitive to changes in plant throughput. Conclusion: The overall second-law efficiency (exergy efficiency) of the plant was lower than the overall energy efficiency as was expected because of proper accounting of different types of process exergies of material, heat and work in the plant.