Design Considerations for Supercritical Carbon Dioxide Brayton Cycles With Recompression

Abstract

Supercritical carbon dioxide (SCO2) Brayton cycles have the potential to offer improved thermal-to-electric conversion efficiency for utility scale electricity production. These cycles have generated considerable interest in recent years because of this potential and are being considered for a range of applications, including nuclear and concentrating solar power (CSP). Two promising SCO2 power cycle variations are the simple Brayton cycle with recuperation and the recompression cycle. The models described in this paper are appropriate for the analysis and optimization of both cycle configurations under a range of design conditions. The recuperators in the cycle are modeled assuming a con stant heat exchanger conductance value, which allows for computationally efficient opti mization o f the cycle's design parameters while accounting for the rapidly varying fluid properties of carbon dioxide near its critical point. Representing the recuperators using conductance, rather than effectiveness, allows for a more appropriate comparison among design-point conditions because a larger conductance typically corresponds more directly to a physically larger and higher capital cost heat exchanger. The model is used to explore the relationship between recuperator size and heat rejection temperature of the cycle, specifically in regard to maximizing thermal efficiency. The results presented in this paper are normalized by net power output and may be applied to cycles of any size. Under the design conditions considered for this analysis, results indicate that increasing the design high-side (compressor outlet) pressure does not always correspond to higher cycle thermal efficiency. Rather, there is an optimal compressor outlet pressure that is dependent on the recuperator size and operating temperatures of the cycle and is typi cally in the range o f30-35 MPa. Model results also indicate that the efficiency degrada tion associated with warmer heat rejection temperatures (e.g., in dry-cooled applications) are reduced by increasing the compressor inlet pressure. Because the opti mal design of a cycle depends upon a number of application-specific variables, the model presented in this paper is available online and is envisioned as a building block for more complex and specific simulations.

Dual Loop line-focusing solar power plants with supercritical Brayton power cycles

“…The energy balances were modeled and simulated with Thermoflow software [19]. The optimal performance parameters in the s-CO 2 Brayton cycles were obtained via the Subplex algorithm from an adapted version of the software provided in Dyreby [20]. Regarding the s-CO 2 thermodynamic properties, were calculated with REFPROP software, developed by National Institute of Standards and Technology (NIST) and integrated in Thermoflow.…”

“…Also for the PCHE detail design we considering the Gnielinsky heat transfer coefficient correlation for calculating the heat transferred inside the semicircular channels. Finally the turbomachines detail designed were achieved also with the adapted software provided in Dyreby [20] obtaining the turbines and compressors rotor diameters, nozzle area and shaft speed for the radial turbomachines configurations. In the Thermoflow simulations we considered the s-CO2 behaves in compressor and turbines as a real gas, and deviation between real and ideal gas conditions were assessed by means of compressibility factor (z) and turbo-machines isentropic efficiencies (η).…”

“…The s-CO 2 Simple Brayton power cycle with ReHeating analysed in this paper for line-focusing solar power plants was previously characterized following the same methodology as stablished by Dyreby [20]. Obtaining the optimized performance parameters via Subplex algorithm, and fixing the recuperator conductance (UA) for different Turbine Inlet Temperatures.…”

Optimization of a recompression supercritical carbon dioxide cycle for an innovative central receiver solar power plant

“…Despite the fact that several research works have been already focused into the use of closed loop Brayton cycles working with sCO 2 [5,12,13] and its optimization have been already addressed [14], this paper is proposing an optimization methodology for the split fraction and recuperators efficiency of sCO 2 power block coupled to a solar central receiver application. In addition, difficulties on sCO 2 Brayton cycle components design, originated from very strong non-ideal fluid characteristics, will be addressed along this paper paying special attention to recuperators design.…”

Supercritical CO2 Brayton power cycles for DEMO (demonstration power plant) fusion reactor based on dual coolant lithium lead blanket

“…Regarding the turbomachinery design, the main problem is found in the compressor design due to, again, its closeness to the critical point, where the use of typical correlations for ideal gases [17] can entail to wrong solutions. Dyreby [18] overcame this issue by adjusting the non-dimensionless coefficients of turbomachinery to experimental data performed at SNL. Finally, the low performance obtained with scale prototypes is a common problem in all laboratories, due to limitations in maintaining the similarity parameters [19].…”