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Performance of combined cycle power plants with external combustion

Doğan, Osman Tufan
Externally Fired Combined Cycle (EFCC) is a recent tcehnology which utilizes coal as the primary fuel a gas turbine cycle. EFCC is among the clean coal technologies aiming at improving the coal combustion performance in a cost effective and environmentally friendly manner. Natural gas is used as the supplementary fuel. The ultimate goal of the EFFC concept is coal onyl option, since natural gas can better be utilized in a modern Gas Turbine Combined Cycle (CCGT) plant. In this study, performance of the EFCC plant is evaluated based on 1st and 2nd law analysis. Different levels of supplementary firing are included in the analyses together with the coal onyl option. Effect of certain plant parameters on the performance indicators are analyzed. Exergy distribution throughout the plant is obtained. It is shown that air heater is the most significant component in terms of irreversibilities. It is also desired to evaluate the performance of the plant, in economic terms. Thermoeconomic analyses are performed for this purpose, based on the SPECO method and the results of exergy related analysis. Cost balance e quations are derived, together with the auxiliary equations formed by using F and P rules, and the resulting set of equations are solved. Cost formation processes are investigated and levelized cost values per unit exergy unit are obtained for each material stream in the plant. It is exit stages of compressor and pump. Results of this study indicate that supplementary firing improves the plant performance, whereas cost of products also increase with supplementary firing. Another observation is that EFCC plant offers performance figures comparable to those for advanced power plant technologies such as Integrated Gasification Combined Cycle(IGCC).