Thermal Efficiency Optimization for a Natural-Gas Power Plant

Abstract

Energy production from fossil fuels has been regarded as the main source of the climatechange. The reason for that is the oxidation of carbon in fossil fuels to carbon dioxide duringcombustion and the highest percentage of greenhouse gases in atmosphere belongs to carbondioxide. Amongst the fossil fuels natural gas is preferred due to its low emission of greenhousegases and having no particulate matter after combustion. While the other fossil fuels emit mainlycarbon dioxide during the combustion process; natural gas emits mostly water together withcarbon dioxide. Around 22 % of the world’s electricity is produced by natural gas and this shareis expected to increase in near future. The power plants operating with natural gas as a gas cycleconsisting of a compressor, a combustion chamber and gas turbine are combined with a vaporcycle in order to increase the efficiency. A heat recovery steam generator is used to reach this aimin recent years in generating steam by the heat received from the combustion gases leaving the gasturbine. It is very important to design and operate such energy conversion systems fired by naturalgas in optimal conditions. If the efficiency can be increased, it can be said that the energetic,economic, and environmental aspects also improve. The modeling and optimization studies for acombined gas-vapor power plant are studied and the most important parameters which influencethe efficiency are determined. The results indicate that the most effective parameters from theviewpoint of efficiency are air/fuel ratio, gas/steam ratio and the pressure ratios of the compressorand, thus, the gas turbine. The thermal efficiency increases by 18.25 % and, in the meantime,the exergy destroyed decreases by 9.84 % using optimum design parameters determined by theoptimization algorithm proposed.