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Gas-steam combined cycle power systems currently are the most advanced power systems operating with fossil fuels since offer the highest efficiency level and lowest pollution. Even so, amount of waste heat released with flue gas into the atmosphere is still significant. A typical way to recover it is heat production but this solution is not viable when there is no heat demand. The interest in this case is for production of additional power. A possible solution is to add an organic Rankine cycle unit downstream the gas-steam combined cycle power plant, which thus is converted into a gas-steam-organic combined cycle power plant. The performance of such a power system, based on Orenda OGT15000 gas turbine with 16.5 MW output in simple cycle, is analyzed in the paper. Besides, the fuel savings and their cost are assessed. Two organic working fluid were considered, namely R134a and R123. The study shows that efficiency of the power plant increases by roughly 1.1 % when the ORC unit is added. Taking into account the current concerns regarding the fossil fuel depletion, the estimated fuel savings could be considered significant.
Bălănescu et al. (Tue,) studied this question.