Fundamental optimization of steam Rankine cycle power plants

• Published in: Energy conversion and management Vol. 289; p. 117148
• Main Authors: Porto-Hernandez, L.A., Vargas, J.V.C., Munoz, M.N., Galeano-Cabral, J., Ordonez, J.C., Balmant, W., Mariano, A.B.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.08.2023
• Subjects: administrative management; entropy; Entropy generation; exergy; generators (equipment); geometry; heat recovery; Ideal gas model; Internal structure; mass flow; Mass flow rates ratio; mathematical models; NTU-effectiveness method; power plants; steam; Steam actual properties; streams; system optimization; Mass flow rates ratio; NTU-effectiveness method; Ideal gas model; Entropy generation; Internal structure; Steam actual properties
• ISSN: 0196-8904
• DOI: 10.1016/j.enconman.2023.117148

•Dimensionless model for optimizing steam Rankine cycle plants was proposed.•The model was experimentally validated for a heat recovery driven power plant.•Net power output, and second law efficiency were maximized.•Gas to water mass flow rate ratio and plant heat transfer areas were optimized.•Optimal parameters are robust for several geometric and operating conditions. This paper introduces a mathematical model for the design and fundamental optimization of steam Rankine cycle (SRC) power plants. The model assumes that the plant irreversibilities are predominant in the heat exchangers, thus exergy destruction in the turbine, pump, fittings, tubes and other internal components are neglected. The NTU-effectiveness method was utilized to model the heat exchangers, and water was considered as the working fluid, which changes phase in both heat exchangers. Acknowledging that entropy is generated in any physical system, the fundamental optimization problem selected the dimensionless net power output, and second law efficiency as the objective functions to be maximized, after the identification of plant geometric and operating parameters to be optimized based on the intersection of asymptotes method, subject to a fixed total heat exchangers area realistic physical constraint, i.e., for a finite size plant. As a result, two levels of optimization were identified: i) the working fluid to hot stream mass flow rate ratio, M, and ii) the steam generator, xH, and condenser, xL, area fractions of the plant fixed total heat exchangers area. The model was experimentally validated for a heat recovery driven power plant. Sharp maxima were obtained in both levels, which is illustrated with a base case by ∼ 60 % second law efficiency variation in comparison to the obtained maximum for 0.05 < M < 0.25 in the first optimization level, and ∼ 30 % for 0.2 < xH < 0.7 in the second optimization level, so that (xf,H,xfg,H,xg,H)2wo=(0.14,0.13, 0.23), with (M,xH)2wo=(0.16,0.5), in the base case considered in this study. The two-way optima results sensitivity to several plant geometric and operating parameters were thoroughly investigated. The optimized parameters are shown to be robust with respect to several system’s design and operating conditions. Therefore, the herein reported fundamental optimization results are important for whatever actual SRC power plant.