Thermodynamic and economic investigations of transcritical CO2-cycle systems with integrated radial-inflow turbine performance predictions

Abstract

Transcritical CO2 (TCO2) cycle systems have emerged as a promising power-generation technology in certain applications. In conventional TCO2-cycle system analyses reported in the literature, the turbine efficiency, which strongly determines the overall system performance, is generally assumed to be constant. This may lead to suboptimal designs and optimization results. In order to improve the accuracy and reliability of such system analyses and offer insight into how knowledge of these systems from earlier analyses can be interpreted, this paper presents a comprehensive model that couples TCO2-cycle calculations with preliminary turbine design based on the mean-line method. Turbine design parameters are optimized simultaneously to achieve the highest turbine efficiency, which replaces the constant turbine efficiency used in cycle calculations. A case study of heat recovery from an internal combustion engine (ICE) using a TCO2-cycle system with a radial-inflow turbine is then considered, with results revealing that the turbine efficiency is influenced by the system's operating conditions, which in turn has a significant effect on system performance in both thermodynamic and economic terms. A more generalized heat source is then considered to explore more broadly the role of the turbine in determining TCO2-cycle power-system performance. The more detailed turbine-design modelling approach allows errors of the order of up to 10-20% in various predictions to be avoided for steady-state calculations, and potentially of an even greater magnitude at off-design operation. The model allows quick preliminary designs of radial-inflow turbines and reasonable turbine performance predictions under various operating conditions, and can be a useful tool for more accurate and reliable thermo-economic studies of TCO2-cycle systems.

Advanced exergy analysis of a Joule-Brayton pumped thermal electricity storage system with liquid-phase storage

“…In this investigation, the power capacity is fixed to 10 MW and the charge/discharge times are set to 6 h. The thermodynamic parameters of the PTES system are optimised using the optimisation method [71] to achieve the highest roundtrip efficiency considering the limitations of the working temperature of the storage materials and the manufacturing capability of the main components in practical applications. A sequential quadratic programming algorithm [72] has been proven to be the most reliable method for solving the optimisation problem.…”

Energetic and exergetic efficiency comparison of recuperative transcritical organic Rankine cycles under different pure and mixture fluids

“…Recently, operating conditions affecting turbine performance on Brayton cycles and CO 2 transcritical cycles have been investigated. 22,23 Hsieh 24 indicated the pseudocritical temperature of CO 2 in TRC should be increased to approach half the expander inlet temperature. Although CO 2 -based mixtures have been investigated in the literature, the associated system costs were markedly high because the supercritical pressure of CO 2 is higher than that of other organic mixtures.…”

“…Gayer et al 21 found that a pressure level of approximately 13.5 MPa maximized the thermal and exergetic efficiencies in a CO 2 transcritical cycle without a regenerator at a pressure range from 9 to 15 MPa. Recently, operating conditions affecting turbine performance on Brayton cycles and CO 2 transcritical cycles have been investigated 22,23 . Hsieh 24 indicated the pseudocritical temperature of CO 2 in TRC should be increased to approach half the expander inlet temperature.…”

Comparative thermoeconomic analyses and multi-objective particle swarm optimization of geothermal combined cooling and power systems

“…In future work, different geothermal temperature gradients can also be considered for different regions which have not been considered in this study. In addition, optimal designs and system performance with integrated component performance modelling [54] as well operational modelling in the presence of heat-source (or sink) intermittency while accounting for changing component performance are important in making predictions close to expectations in practice [55].…”