Abstract
This study presents a novel approach for Rankine cycle (RC) analysis, introducing a generic counter current heat exchanger (HX) model to enable basic fluid thermal and flow behaviour in HXs to be considered in a cycle optimisation process. The generic HX model does not represent a certain HX-type or even a manufacturable design, but applies fluid properties and a minimum amount of generic geometry parameters to estimate local heat transfer coefficients and pressure gradients. The proposed methodology thus permits simultaneous optimization of process state points and the trade-off between overall heat transfer coefficient and pressure drop without relying on a specific HX-geometry concept. The proposed methodology is demonstrated for evaluation of single-stage recuperated RC's of different HX size and working fluids, and compared with more conventional thermodynamic analyses. The comparison showed that the novel analysis resulted in lower net power output than the thermodynamic analyses due to working fluid-depending pressure drop in heat exchangers, and a quantitative HX size estimate in terms of total HX area based on working-fluid depended heat transfer coefficients. We therefore suggest the novel analysis as a low effort and more informative alternative to pure thermodynamic approaches for initial RC analyses.
Highlights
The Rankine cycle (RC), conventionally referred to as ORC when it employs an organic working fluid, is a mature technology
This study presents a novel approach for Rankine cycle (RC) analysis, introducing a generic counter current heat exchanger (HX) model to enable basic fluid thermal and flow behaviour in HXs to be considered in a cycle optimisation process
The comparison showed that the novel analysis resulted in lower net power output than the thermodynamic analyses due to working fluid-depending pressure drop in heat exchangers, and a quantitative HX size estimate in terms of total HX area based on working-fluid depended heat transfer coefficients
Summary
The Rankine cycle (RC), conventionally referred to as ORC when it employs an organic working fluid, is a mature technology. The full potential of RCs is far from reached as the power production potential from the above-mentioned energy sources alone could meet the worlds power demand [2]. One step towards increasing the utilization of RCs, and facilitate reduction of greenhouse gas emissions from fossil fuel power plants, is to optimise the RC for each application. This is a challenging task and research efforts on RCs typically focus on certain aspects such as application, expander technology, dynamics, working fluid, cycle architecture or optimization [3]. This paper focuses on the underlying methodology of the three last aspects, hereafter referred to as RC analysis
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