IMPROVEMENT OF THE PERFORMANCE OF THERMAL POWER SYSTEMS THROUGH ENERGY AND EXERGY ANALYSIS

ABSTRACT

This research work is aimed at using the energy and exergy analysis with thermodynamic data to suggest improvements in the performance of steam and gas turbine power plants. In this regard, specific data from Egbin steam power plant and Geregu I gas turbine power plant were used for the analysis.  In the analysis, scientific tools such as Engineering Equation Solver (EES) programme with built-in functions for most thermodynamic and transport properties was used to calculate the enthalpy and entropy at various nodal points, while EXCEL spreadsheet and SCILAB software code were used to analyze both the energetic and exergetic efficiencies of the individual components, thermal efficiencies, gross station heat rate etc. These software were also used to calculate   the exegetic performance coefficient and exegetic sustainability indicators of the power plants. The results of the analysis at both design and operating conditions show that exergy destruction occur more in the boiler/steam generator of Egbin steam power plant and combustion chamber of Geregu I  gas turbine power plant than in other major components of each plant. The normal operating conditions of the steam boiler exit pressure and temperature are 125.70/540.72 and condenser pressure and temperature are 0.0872bar and 42.950Crespectively for Egbin steam power plant in the year 2009. From the study, the maximurm exergy loss was found in the boiler/steam generator with a value of 55.32% in the year. Changing the boiler exit pressure and temperature from the normal operating conditions to 165.70/560.72 (ie, in step of 10 bar and 50C), the exergy loss reduced to 53.99%.The cycle thermal energy and exergy efficiencies at the normal operating conditions were 41.03% and 39.94 % respectively.  Improvement in the cycle thermal energy and exergy efficiencies with the same steps from normal operating conditions to 165.70/560.72 were 41.23% and 40.12% respectively.  The improvement increased the power output from 197593.8KW to 199358.57kW showing power increase of 1764.77kW or 1.765MW. The gross station heat rate decreased from 8775kJ/kWh to 8732kJ/kWh which is good for the life of the plant. Also, the improvement increased the exergetic performance coefficient from 0.6133 to 0.6188.  The exergy sustainability indicators such as environmental effect factor decreased from the value 1.0412 to 1.0230 showing about 1.75% reduction in hazardous gaseous emissions to the environment. Another exergy indicator, the sustainability index factor increased from the value 0.9604 to 0.9775 indicating 1.78% resource utilization and sustainability. For Geregu I gas turbine plant, the operating condition of the combustion chamber are pressure of 11 bar and 10600C Turbine Inlet Temperature (TIT). The study showed that maximum exergy loss was found in the combustion chamber at a value of 26.30%. It is higher than any other major component at the operating conditions in the year 2009.Adjusting the normal operating pressure and temperature to 15 bar and 10800C reduced the exergy destruction ratio to 26.06%. The gas turbine   cycle energy and exergy efficiencies   increased from 32.77% to 34.85% and30.44% to 32.34% respectively.  The power output in the year was increased from 133456.01kW to 145013.13kW showing power increase of 11557.12kW or 11.56 MW due to the improvement. For exergetic sustainability indicators, the environmental effect factor decreased from the value 0.7132 to 0.6522 indicating 8.55% reduction in greenhouse gas emission to the environment and ecology. The sustainability index factor was increased from the value of 1.4022 to1.5332 showing 9.34% energy resource utilization for societal development.  In conclusion, any increase in exergy efficiency has effect on the environmental effect factor and sustainability index factor for both power plants. Therefore, increase in exergy efficiency improves the exergetic sustainability index. However, any increase in environmental effect factor decreases the sustainability index factor. These parameters are expected to quantify how thermal power plants become more environmentally benign and sustainable.