Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “supercritical CO2 (sCO2)”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Thermal-Mechanical Analysis of an Additive Manufacturing Ceramic Heat Exchanger for High-Temperature Recuperator in a sCO2 Power System

Supercritical CO2 (sCO2) Brayton power cycle can be configured in a closed-loop power system and has a potentially high cycle efficiency. Compactness and high efficiency of a sCO2 power block make the sCO2 Brayton cycle a versatile power cycle in broad applications. While many heat sources are of sufficient intensity to produce high temperature working fluids to achieve high cycle efficiency, the thermal-mechanical stability of traditional materials (e.g., steels and nickel-based superalloys) used in construction of heat exchangers and turbine components limits the operating conditions and thus thermodynamic efficiency of the system. This effort seeks to establish the viability of ceramic heat exchanger technologies for the most extreme operating conditions envisioned for power generation and other high temperature processes. Heat exchangers constructed from ultra-high temperature ceramics, a class of extreme environment materials featuring melting points (Tmp.) above 3000 degrees C, is particularly appealing for sCO2 Brayton cycles given their ultra-low creep rates and very high retained strength at low homologous temperatures (i.e., T < 0.5 Tmp., or at least 1500 degrees C). To translate these materials properties to ultra-high temperature heat exchangers, innovations are required in ceramic manufacturing techniques to realize the complex architectures featured in compact heat exchangers with high power density. With appropriate processing, ZrB2-SiC based compositions can be sintered to near full density and shaped into complex topologies via ceramic additive manufacturing methods. This paper analyzes heat exchanger designs and explores thermal-mechanical implications of the operating environment. Thermal flow, heat transfer, and conjugate mechanical analyses provide insights into benefits and risks associated with the design approach.

additive manufacturing↗
DOE OSTI2023

Manufacturing and Hydro Testing of a 10 MWe sCO2 Axial Turbine

Abstract Supercritical CO2 (sCO2) power cycles designed for thermodynamic efficiencies above 50% push component designs into pressure and temperature combinations that approach the limits of American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code and ASME Piping Design Codes with Turbine inlet conditions near 250 bar and 715 °C. These design conditions which limit available materials to high nickel alloys are compounded by the high fluid densities of sCO2 at these conditions which result in very compact machinery at the 10 MWe class which are currently being developed for the DOE supercritical transformational electric power (STEP) program. Design of the STEP Turbine is complete with integrated lessons learned from a previous 1 MWth subscale demonstration of a high temperature 10 MWe Turbine designed under the DOE SunShot Program. Fabrication of the STEP Turbine is nearing completion with all housings and pressure containing components in hand. This paper provides a detailed look at design intentions and limitations for the pressurized sections of the main pressure casing and the fabrication of key turbine components. Additional discussion is provided regarding postfabrication inspection and acceptance of the casing for use after issues with casing welds were identified late in the fabrication process.

Engineering↗
DOE OSTI2025

Computational and Experimental Investigation of Discrete “W” Turbulators for sCO2 Turbine Internal Cooling

Direct-fired supercritical CO2 (sCO2 ) cycles are of particular interest for power generation due to the potential for higher thermal efficiencies with inherent CO2 capture. Direct fired sCO2 turbines must withstand high temperatures and the density of the working fluid is much higher than conventional Brayton cycles. Based on conventional Brayton cycle applications, internal serpentine cooling channels with ribbed turbulator strips are a common approach to achieve the required cooling, while minimizing coolant utilization. Most of the previous studies of coolant channel heat transfer enhancements have focused on serpentine channels using air as the cooling media at Reynold’s numbers typical of Brayton cycles. This paper investigates the Nusselt number augmentation of coolant channels with no features, ribbed turbulators, and discrete “W” turbulators with surface roughness effects included and CO2 as the coolant. The numerical results are compared to experimental results using CO2 as the cooling media at Reynold’s numbers ranging from 100,000 to 300,000. The results show the Nusselt number augmentation plateaus with increasing Reynolds number, in contrast to the decay observed in prior publications with air as the coolant media. Additionally, the CFD results indicate the discrete “W” geometry provides a 10% increase in Nusselt number augmentation relative to the angled ribbed turbulators.

computational fluid dynamics (CFD)↗
DOE OSTI2020

Wet Cooling Tower Cooling System Spreadsheet Model for sCO2

The attached cost and performance spreadsheet model is for a wet cooling tower system, one of four cooling system models developed for use in optimizing indirectly-heated supercritical CO2 (sCO2) power cycles. Running the model requires that the user has REFPROP version 9 or below installed, as well as the Microsoft Excel REFPROP Add-In. Upon opening, use Excel’s Edit Links feature to link to the user’s installed REFPROP.xla or REFPROP.xlam file. For the spreadsheet model compatible with REFPROP version 10 and above, contact Nathan Weiland at nathan.weiland@netl.doe.gov. Technical documentation for the model can be found here: https://www.netl.doe.gov/energy-analysis/details?id=3199.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2020

Indirect Dry Cooling System Spreadsheet Model for sCO2

The attached cost and performance spreadsheet model is for an indirect dry cooling system, one of four cooling system models developed for use in optimizing indirectly-heated supercritical CO2 (sCO2) power cycles. Running the model requires that the user has REFPROP version 9 or below installed, as well as the Microsoft Excel REFPROP Add-In. Upon opening, use Excel’s Edit Links feature to link to the user’s installed REFPROP.xla or REFPROP.xlam file. For the spreadsheet model compatible with REFPROP version 10 and above, contact Nathan Weiland at nathan.weiland@netl.doe.gov. Technical documentation for the model can be found here: https://www.netl.doe.gov/energy-analysis/details?id=3199.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2024

Optimization of a High Pressure Turbine Blade and Sector-Based Annular Rig Design for Supercritical CO2 Power Cycle Representative Testing

Abstract As part of the ongoing research into the design of hardware for zero emission cycles, a first-stage high-pressure turbine (HPT) blade is optimized for a 300 MWe supercritical CO2 (sCO2) power cycle using the surrogate-assisted genetic algorithm optimizer in Numeca FINE/Design three-dimensional with objectives of increasing efficiency and decreasing heat load to the blade. Supercritical CO2 property tables are constructed from NIST REFPROP data for the condensable gas simulation in FINE/Turbo. A detailed mesh sensitivity study is performed for a baseline design to identify the proper-grid refinement and efficiently allocate resources for the optimization. Seventy design variables are selected for the initial population generation. Self-organizing maps are then used to focus the design variables on the most important ones affecting the objective functions. The optimization results in approximately 3000 three-dimensional Reynolds Averaged Navier Stokes simulations of different blade shapes with increases in efficiency of up to 0.85% and decreases in heat load of 14%. Families of blade shapes are identified for experimental testing in an annular rig at the Purdue Experimental Turbine Aerothermal Laboratory. A design to adapt the annular cascade for testing optimized geometries is introduced, which features eccentric radius sectors allowing for scaled-up geometries of sCO2 optimized blade profiles to be tested at design cycle representative conditions at high Reynolds numbers in dry air. Analysis into the effects of Reynolds number, working fluid, and geometric relations are presented to prove the efficacy of the test method.

Engineering↗
DOE OSTI2024

High-Temperature Oxidation Behavior of Wrought and Additive Manufactured Ni-based Alloys in Direct-Fired Supercritical CO2 Power Cycle Environments

Materials selection is a key concern for corrosion resistance in elevated temperature and pressure direct-fired supercritical CO2 (sCO2) power cycles. Herein, the wrought product form of alloy H282, as well as several additional nickel-based commercial alloys (230, 263, 617, 625, 740H), were exposed to direct-fired supercritical CO2 conditions (95CO2 – 4H2O – 1O2) at 750 °C and 20 MPa for over 2,000 h. Additionally, additive manufactured (AM) 282 produced by laser powder bed fusion (LPBF) were also included in the exposures. This paper focuses primarily on the differences observed in the degradation behavior of the wrought and additively manufactured materials. AM samples in the as-printed state were found to form less protective oxide scales resulting in higher oxidation rates compared to wrought samples. However, applying a 600 grit surface finish to the AM samples modified the oxidation behavior to closely resemble that of the wrought material. The AM samples formed Mo-rich carbides in the alloy beneath the oxide following sCO2 exposure, implying potentially higher levels of carbon uptake relative to the wrought material. Conversely, the AM samples seemed to be less affected by water-assisted oxide volatilization compared to the wrought material. The results are discussed in terms of the potential compatibility issues that may arise when using Ni-based alloys in the hot portions of direct-fired sCO2 power cycles, particularly in the case of thin-walled components.

Carney, Casey↗
DOE OSTI2024

High-Temperature Oxidation Behavior of Wrought and Additive Manufactured Alloys in Direct-Fired Supercritical CO2 Power Cycle Environments

Materials selection is a key concern for corrosion resistance in elevated temperature and pressure direct-fired supercritical CO2 (sCO2) power cycles. The effect of elevated pressure on corrosion resistance can be critical, as impurities within the supercritical fluid such as H2O and O2 can have additional corrosion effects than found at ambient pressure conditions. Several wrought nickel-based commercial alloys (230, 263, 282, 617, 625, 740H) were exposed to direct-fired conditions (95CO2 – 4H2O – 1 O2) at 750 °C at both atmospheric pressure (0.1 MPa) and supercritical conditions (20 MPa) for over 2,000 h. Additionally, additive manufactured (AM) 282 produced by laser powder bed fusion (LPBF) were also included in the exposures. Supercritical conditions affected the oxidation behavior of several alloys. Most notably, water-vapor assisted Cr-oxide volatilization was observed at 750 °C supercritical conditions. Many alloys did not form sufficient protective Cr-oxide scales at supercritical conditions, leading to increased oxidation at elevated pressure. Differences in oxidation behavior were also observed for 282 AM samples compared to their wrought counterparts, with the differences also dependent on the LPBF build parameters and post-production treatments (heat treatment and surface finishing procedures). The AM samples formed Mo-rich carbides in the alloy beneath the oxide following sCO2 exposure, implying potentially higher levels of carbon uptake relative to the wrought

Carney, Casey↗
DOE OSTI2024

Blade and Rim Seal Design of a First Stage High Pressure Turbine for a 300 MWe Supercritical CO2 Power Cycle

A first stage high-pressure turbine (HPT) blade is optimized for a 300 MWe supercritical CO2 (sCO2) power cycle using the surrogate-assisted genetic algorithm optimizer in Numeca FINE/Design 3D with objectives of increasing efficiency and decreasing heat load to the blade. The National Institute of Standards and Technology Reference Fluid Thermodynamic and Transport Properties Database (NIST REFPROP) [1] data for supercritical CO2 is formatted into tables of bicubic polynomial coefficients for use in condensable gas simulations in FINE/Turbo. Nearly 3000 unique shapes are evaluated via three-dimensional Reynolds Averaged Navier Stokes simulations, yielding increases in efficiency of up to 0.85 percentage points and decreases in heat load of 14%. A final blade, deemed the advanced blade, is chosen for future experimental analysis. Following this, a squealer tip optimization is performed on both the baseline and advanced blade designs. This optimization resulted in a performance gain of 1.25 points in efficiency and 15% reduction in tip heat load compared to the baseline flat tip design at the same clearance. In tandem, an optimization of the rotor-stator platform rim seal is performed using a parametrized geometry allowing for straight, meandering, and knife seal cavities. This multi-objective optimization focuses on decreasing the cooling mass flow and increasing the heat flux from the rotor and stator disk. The optimization resulted in cooling mass flow decreases of up to 26% while maintaining the average heat flux on the rim seal.

Tuite, Logan↗
DOE OSTI2026

Oxidation of Materials and Coatings at 1000°C and 250 bar for use in Oxy-Combustion Turbine

Combinations of materials and coatings were tested in supercritical CO2 (sCO2) to evaluate their reliability in an oxy-fuel turbine being designed to operate in the 150-300 MWe size range at inlet temperatures of 1,150 °C at 300 bar and exhaust temperatures in the 725-775 °C range. Nickel alloys and stainless steels were exposed to supercritical CO2 at 1,000 °C and 250 bar for a total of over 1,500 hours. The materials were tested bare, with a nanocrystalline MCrAlY bond coat only, or with one of two types of bond coat and a thermal barrier coating. A novel test facility using a localized heat zone generated by an induction heater inside an externally cooled autoclave was developed to perform those tests. The specimens were weighed before and after exposure to determine the oxidation rate. All specimens were inspected visually, and a smaller group of coated specimens were studied using secondary electron microscopy (SEM). The integrity of the coating, and the morphology and composition of the thermally grown oxide were especially of interest for the SEM investigation. This paper presents the up-to-date results of the testing coated and uncoated superalloys in sCO2 at up to 1150 °C and up to 300 bar performed at Southwest Research Institute.

Bocher, Florent [Southwest Research Institute, San↗
DOE OSTI2020

Influence of Equation-of-States on Supercritical CO2 Combustion Mixtures

Abstract Fossil fuel based direct-fired supercritical CO2 (sCO2) cycles are gaining the attention of industry, academia, and government due to their remarkable efficiency and carbon capture at high-source temperatures. Modeling plays an important role in the development of sCO2 combustors because experiments are very expensive at the designed operating conditions of these direct-fired cycles. Inaccurate density estimates are detrimental to the simulation output. Hence, this work focuses on comprehensive evaluation of the influence and applicability of various equation-of-states (EOS) which are being used in the supercritical combustion modeling literature. A state-of-the-art supercritical combustion modeling methodology is used to simulate counter-flow supercritical CO2 flames by using various equation-of-states. The results show that using the corresponding state principle to evaluate compressibility factor is not accurate. Also, van der Waal type EOSs predictions can be as accurate as complex Benedict–Webb–Rubin EOSs; hence van der Waal EOSs are more suitable to simulate sCO2 combustor simulations. Non-ideal effects are significant under the operating conditions considered in this work. The choice of EOS significantly influences the flame structure and heat release rate. Also, assuming the binary interaction parameter as zero is reasonable in sCO2 combustion simulations.

Energy & Fuels↗
DOE OSTI2024

Environmental Compatibility Issues for Ni-Based Alloys in Direct-Fired Supercritical CO2 Power Cycles

Direct-fired supercritical CO2 (sCO2) power cycles offer potential for high-efficiency power generation from natural gas and other fossil fuels with built-in carbon capture. Ni-based superalloys are the leading candidates for the hottest portions of these systems, where they must endure long-term exposure to high-temperature, high-pressure, high-velocity, impure CO2-rich environments. Herein we describe results of various experimental testing campaigns conduced at NETL showing that under such conditions, several simultaneously occurring degradation modes may be active including surface oxidation, alloy carburization, and oxide volatilization. It will be shown that the rates of degradation can be strongly affected by the alloy composition, impurities in the CO2, manufacturing method (wrought vs additive), and other factors. The influence of these factors in controlling alloy degradation are discussed in the context of potential compatibility issues for components in real sCO2 systems, such as compact heat exchangers. Finally, as a potential remedial measure, ongoing work involving protective coatings suitable for complex geometries is presented.

alloy oxidation↗
DOE OSTI2024

Performance and Economic Evaluation of sCO2 Bottoming Cycles for Natural Gas Combined Cycle Plants with Capture

Natural gas combined cycles (NGCCs) with carbon capture are expected to play a significant role in decarbonization of the power generation sector. NGCC plants generally use triple pressure reheat steam Rankine power cycles for the bottoming cycle. Some studies in the literature have investigated the application of recompression and cascade style supercritical CO2 (sCO2) cycles for NGCC bottoming cycle applications but these studies have focused on power plants without carbon capture. However, NGCC plants fitted with post-combustion solvent-based CO2 capture systems will require a significant amount of steam for solvent regeneration and this can have a major impact on the optimal sCO2 bottoming cycle design. This study investigates the performance and economic potential of sCO2 bottoming cycles for H-class gas turbine based NGCC plants with a post-combustion capture system. A portion of the gas turbine exhaust heat is used for generation of steam required for solvent-based capture system while the rest of the waste heat is utilized in an sCO2 bottoming cycle for power generation. Overall, the performance and LCOE of investigated sCO2 bottoming cycles is similar to that of a state-of-the-art triple pressure reheat steam Rankine cycle. As the gas turbine exhaust temperature increases (beyond 630oC), sCO2 bottoming cycles begin to show greater performance and economic benefits compared to a steam Rankine cycle.

Pidaparti, Sandeep↗
DOE OSTI2024

Verification and Validation of Spectral Element Code for Supercritical CO2 Flow in Vertical Heated Tubes

The investigation of heat transfer in supercritical CO2 (sCO2) has garnered considerable attention in recent decades, given sCO2's potential as a promising working fluid for advanced power conversion cycles. Despite previous research efforts, there are still gaps in our understanding of sCO2 heat transfer, particularly in conditions associated with heat transfer deterioration. To delve into sCO2 heat transfer more comprehensively, we propose employing the high-fidelity computational fluid dynamics code NekRS to simulate sCO2 flow using the large eddy simulation technique. Through graphics processing unit acceleration, NekRS achieves a higher computational speed than traditional CPU-based systems. However, before using NekRS in practical applications involving sCO2, it is imperative to perform verification and validation. Here, this paper presents our efforts to verify and validate the NekRS code's capability for simulating sCO2 using heated vertical tubes, where heat transfer deterioration usually happens. To accommodate the unique properties of sCO2, we have modified the NekRS code by integrating third-party property modules, such as REFPROP and PROPATH. Our simulations are compared with experimental and numerical data from the literature, instilling confidence in leveraging NekRS for future engineering applications. Our simulations also reveal that the accuracy of the property module significantly impacts the results, with REFPROP outperforming PROPATH for sCO2 properties. Additionally, we observed that, depending on the flow direction, buoyancy can either enhance or suppress turbulence in sCO2 flow. In upward flow, under certain conditions, the suppressed turbulence leads to heat transfer deterioration, resulting in elevated wall temperatures.

NekRS↗
DOE OSTI2020

Hybrid Fuel Cell—Supercritical CO2 Brayton Cycle for CO2 Sequestration-Ready Combined Heat and Power

The low prices and its relatively low carbon intensity of natural gas have encouraged the coal replacement with natural gas power generation. Such a replacement reduces greenhouse gases and other emissions. To address the significant energy penalty of carbon dioxide (CO2) sequestration in gas turbine systems, a novel high efficiency concept is proposed and analyzed, which integrates a flame-assisted fuel cell (FFC) with a supercritical CO2 (sCO2) Brayton cycle air separation. The air separation enables the exhaust from the system to be CO2 sequestration-ready. The FFC provides the heat required for the sCO2 cycle. Heat rejected from the sCO2 cycle provides the heat required for adsorption-desorption pumping to isolate oxygen via air separation. The maximum electrical efficiency of the FFC sCO2 turbine hybrid (FFCTH) without being CO2 sequestration-ready is 60%, with the maximum penalty being 0.68% at a fuel-rich equivalence ratio (Φ) of 2.8, where Φ is proportional to fuel-air ratio. This electrical efficiency is higher than the standard sCO2 cycle by 6.85%. The maximum power-to-heat ratio of the sequestration-ready FFCTH is 233 at a Φ = 2.8. Even after including the air separation penalty, the electrical efficiency is higher than in previous studies.

10 SYNTHETIC FUELS↗
DOE OSTI2025

ENVIRONMENTAL DEGRADATION OF HARD AND SOFT MAGNETIC MATERIALS IN GASEOUS AND SUPERCRITICAL CO2 ENVIRONMENTS

It may be beneficial to use hermetic designs for supercritical CO2 (sCO2) cycles machinery as they would eliminate CO2 leakage through shaft end seals. This would reduce CO2 emissions and operating costs for makeup of lost process fluid. Those designs may replace traditional oil-lubricated bearings with actively controlled magnetic bearings operating at high temperatures in the process fluid environment (to reduce the need for active cooling). This paper investigates the material degradation of various types of magnets in CO2. Included are several permanent and soft magnetic materials (Alnico 9C, Alnico 5-7C, and 18-T550 grade SmCo, and Hiperco 50) with or without coatings (nickel plating or C5 coating). The materials were exposed to: (1) flowing gaseous CO2 at 1,022 °F (550 °C) and atmospheric pressure in a furnace and (2) sCO2 at 842 °F (450 °C) and 1,500 psi (103 bar) in an autoclave. The preliminary mass change measured after total exposures of 1,000 hours and 2,000 hours are included.

supercritical CO2, magnetic material↗
DOE OSTI2022

Analysis of an Elasto-Hydrodynamic Seal by Using the Reynolds Equation

This paper reports numerical studies of an Elasto-Hydrodynamic (EHD) seal, which is being developed for supercritical CO2 (sCO2) turbomachinery applications. Current sCO2 turbomachinery suffers from high leakage rates, which is creating a major roadblock to the full realization of sCO2 power technology. The high leakage rates not only penalize the efficiencies but also create environmental concerns due to greenhouse effects caused by the increased CO2 discharge to the atmosphere. The proposed EHD seal needs to work at elevated pressures (10–35 MPa) and temperatures (350–700 °C) with low leakage and minimal wear. The unique mechanism of the EHD seal provides a self-regulated constriction effect to restrict the flow without substantial material contact, thereby minimizing leakage and wear. This work utilizes a physics-based modeling approach. The flow through the gradually narrowing seal clearance is modeled by the well-known Reynolds equation in EHD lubrication theory, while the deformation of the seal is modeled by using the governing equations of three-dimensional solid mechanics. As for the solution methodology, COMSOL’s Thin-Film Flow and Solid Mechanics modules were employed with their powerful capabilities. The numerical results were presented and discussed. It was observed that the Reynolds equation fully coupled with the surface deformation was able to successfully capture the constriction effect. The maximum and minimum leakages were calculated to be 2.25 g/s and 0.1 g/s at P = 5.5 MPa and P = 11 MPa for the design seal, respectively. It was interesting to observe that the seal leakage followed a quadratic trend with increasing pressure differential, which can become advantageous for high-pressure applications such as sCO2 power generation technology.

42 ENGINEERING↗
DOE OSTI2023

Compatibility of Wrought Superalloys with Supercritical CO2

Supercritical CO2 (sCO2) power cycles, particularly direct-fired cycles, have the possibility of revolutionizing clean fossil energy with peak temperatures above 700 °C and wrought precipitation strengthened alloys like Haynes 282™ for structural components. At temperatures <650 °C, it would be desirable to use less expensive alloys, however, steels are known to be susceptible to carburization. Laboratory 300 bar sCO2 autoclave results were collected on a range of alloys including less expensive Ni-based alloys like 825 compared to advanced austenitic steels like alloy 709 at 600 °C. Both alloys 825 and 709 formed thin, protective Cr-rich oxides after 1,000 h. Alloy 825 also was exposed for 1,000 h in sCO2 at 800 °C and compared to a range of Ni-based alloys. Comparing alloys 625, 825, and 282, the mass gain increased with increasing alloy Ti content under these conditions. High Al superalloys did not perform significantly better under these conditions at 800 °C.

Pint, Bruce↗