Efficiency enhancement in a Rankine cycle power plant: Combined cycle approach

Abstract

Efficiency enhancement in a Rankine cycle power plant operating on a condensing mode is one of the challenging tasks for researchers. In a modern fossil-fired steam power plant even a fraction of percentage difference in efficiency can mean very large savings in annual fuel costs. In this study, effort was put into improving the cycle efficiency by reducing energy loss and irreversibility in the major portion of the cycle such as heat input part, work output part, and heat rejection part. In this study, a new combined cycle concept is proposed to reduce: energy loss in the condenser; power output and efficiency loss in the low pressure turbine due to expansion of low grade or low temperature steam; and irreversibility in the boiler due to higher degree of enthalpy of evaporation. The proposed combined cycle plant uses water as a working fluid in the topping cycle and an ammonia—water mixture in the bottoming cycle and it is 4 per cent more efficient than the standalone Rankine cycle operating on a condensing mode.

Keywords

Rankine cycle condensing mode vacuum pressure combined cycle

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