Supercritical carbon dioxide (sCO2) power cycles could be a more efficient alternative to steam Rankine cycles for power generation from coal. Using existing labyrinth seal technology, shaft-end-seal leakage can result in a 0.55–0.65% points efficiency loss for a nominally 500 MWe sCO2 power cycle plant. Low-leakage hydrodynamic face seals are capable of reducing this leakage loss and are considered a key enabling component technology for achieving 50–52% thermodynamic cycle efficiencies with indirect coal-fired sCO2 power cycles. In this paper, a hydrodynamic face seal concept is presented for utility-scale sCO2 turbines. A 3D computational fluid dynamics (CFD) model with real gas CO2 properties is developed for studying the thin-film physics. These CFD results are also compared with the predictions of a Reynolds-equation-based solver. The 3D CFD model results show large viscous shear and the associated windage heating challenge in sCO2 face seals. Following the CFD model, an axisymmetric finite-element analysis (FEA) model is developed for parametric optimization of the face seal cross section with the goal of minimizing the coning of the stationary ring. A preliminary thermal analysis of the seal is also presented. The fluid, structural, and thermal results show that large-diameter (about 24 in.) face seals with small coning (of the order of 0.0005 in.) are possible. The fluid, structural, and thermal results are used to highlight the design challenges in developing face seals for utility-scale sCO2 turbines.

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Supercritical carbon dioxide (sCO2) power cycles could be a more efficient alternative to steam Rankine cycles for power generation from coal. In this paper, the end seal layout for a nominally 500 MWe sCO2 turbine is presented and the shaft end sealing requirements for such utility-scale sCO2 turbines are discussed. Shaft end leakage from a closed-loop sCO2 cycle and the associated recompression load can result in net cycle efficiency loss of about 0.55% points to 0.65% points for a nominally 500 MWe sCO2 power cycle plant. Low-leakage hydrodynamic face seals are capable of reducing this leakage loss (and net cycle efficiency loss), and are considered a key enabling component technology for achieving 50–52% or greater thermodynamic cycle efficiencies with indirect coal-fired sCO2 power cycles. In this paper, a hydrodynamic face seal concept is presented for end seals on utility-scale sCO2 turbines. A 3D computational fluid dynamics (CFD) model with real gas CO2 properties is developed for studying the physics of the thin fluid film separating the seal stationary ring and the rotor. The results of the 3D CFD model are also compared with the predictions of a Reynolds-equation-based solver. The 3D CFD model results show large viscous shear and the associated windage heating challenge in sCO2 face seals. Following the CFD model, an axisymmetric finite-element analysis (FEA) model is developed for parametric optimization of the face seal cross-section with the goal of minimizing the coning of the stationary ring. A preliminary thermal analysis of the seal is also presented. The fluid, structural and thermal results show that large-diameter (about 24 inch) face seals with small coning or out-of-plane deformations (of the order of 0.0005 inch) are possible. The fluid, structural and thermal results are used to highlight the design challenges in developing large-diameter and high-differential-pressure face seals for the operating conditions of utility-scale sCO2 turbines.

In order to maintain viability as a future power-generating technology, concentrating solar power (CSP) must reduce its levelized cost of electricity (LCOE). The cost of CSP is assessed with the System Advisor Model (SAM) from the National Renewable Energy Laboratory (NREL). The performance of an integrally geared compressor-expander recuperated recompression cycle with supercritical carbon dioxide (sCO2) as the working fluid is modeled. A comparison of the cycle model to the integrated SAM cycle performance is made. The cycle model incorporates innovative cycle control methods to improve the range of efficiency, including inventory control. The SAM model is modified to accommodate the predicted cycle performance. The ultimate goal of minimizing the LCOE is targeted through multiple approaches, including the cost of the power block, the impact of system scale, the sizing of the thermal system relative to the power block system, the operating approach for changes in ambient temperature and availability of sunlight. Through reduced power block cost and a detailed cycle model, the LCOE is modeled to be 5.98 ȼ/kWh, achieving targeted techno-economic performance. The LCOE of the CSP system is compared to the cost of hybrid solar and fossil-fired systems. An analysis is made on the efficacy of a fossil backup system with CSP and how that relates to potential future costs of carbon dioxide emissions.

In order to reduce the amount of carbon dioxide (CO2) released into the atmosphere, significant progress has been made into capturing and storing CO2 from power plants and other major producers of greenhouse gas emissions. The compression of the captured carbon dioxide stream requires significant amounts of power and can impact plant availability, and increase operational costs. Preliminary analysis has estimated that the CO2 compression process reduces plant efficiency by 8% to 12% for a typical power plant. This project supports the U.S. Department of Energy (DOE) National Energy Technology Laboratory (NETL) objective of reducing energy requirements for carbon capture and storage in electrical power production. The primary objective of this study is to boost the pressure of CO2 to pipeline pressures with the minimal amount of energy required. Previous thermodynamic analysis identified optimum processes for pressure rise in both liquid and gaseous states. Isothermal compression is well known to reduce the power requirements by minimizing the temperature of the gas entering subsequent stages. Intercooling is typically accomplished using external gas coolers and integrally geared compressors. For large scale compression, use of straight through centrifugal compressors, similar to those used in oil and gas applications including LNG production, is preferred due to the robustness of the design. However, intercooling between each stage is not feasible. The current research develops an internally cooled compressor diaphragm that removes heat internal to the compressor. Results documenting the design process are presented including 3D conjugate heat transfer CFD studies. Experimental demonstration of the design is performed on a sub scale centrifugal compressor closed loop test facility for a range of suction pressures.