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At least 127 records · Page 7

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DOE OSTI2024

Hydrogen-Steam Separation Using Mechanical Vapor Recompression Cycle

Solar thermochemical hydrogen and fuel production is a promising pathways for producing sustainable fuels and chemicals. One of the main challenges in the development of these systems is their low steam conversion extent, dictated by its restrictive thermodynamics requiring extremely high temperatures and low oxygen partial pressure to obtain conversions over 10 \%. While condensing the unreacted steam is technically simple, the latent heat is thus lost, which can be larger than the producd hydrogen higher heating value. We propose to use a modified mechanical vapor recompression cycle, allowing to recover the latent heat by compressing the steam-hydrogen mixture prior to the condensation process, thus creating a temperature different between the hot exhaust and cold inlet streams. We show that this method can recover over 90 % of the latent heat, thus increasing the viability of solar thermochemical hydrogen production cycles even under limited conversion conditions.

hydrogen technology↗

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 OSTI2023

Sintering inhibition enables hierarchical porosity with extreme resistance to degradation during redox cycling of Fe-Mo foams

High-temperature (800 ºC) steam-hydrogen redox cycling, relevant to grid-scale energy storage, is studied for iron-based freeze-cast lamellar foams. In contrast to previously studied Fe, Fe-Ni, and Fe-Co foams that rapidly degrade, Fe-25Mo foams feature a much-enhanced structural damage resistance. Utilizing in-situ x-ray diffraction, microscopy, and x-ray tomography, strong sintering inhibition is observed in Fe-Mo foams, creating a hierarchically porous lamellar structure. This leads to (i) wide channels between lamellae, enabling high macroscopic porosity (~78%) which can accommodate gas flow as well as volumetric expansion without lamellar contact, and (ii) microporosity within lamellae, providing additional free volume to accommodate expansion during oxidation, limiting both swelling of the lamellae and the formation of Kirkendall pores. Finally, these combined effects enable a near-complete reversibility of the microstructure during cycling, preventing damage produced via internal lamellar buckling, cracking, contacting and sintering, with a remarkably high porosity (65%) remaining after 50 consecutive redox cycles.

36 MATERIALS SCIENCE↗

DOE OSTI2024

Creep Degradation of Austenitic Steels in CO2 Environments

Steels have a proven track record of safe operation in steam power plants for decades. Interest in developing supercritical CO2 power cycles as a more efficient and sustainable alternative to steam cycles has driven a need to understand steel performance in these new environments. In particular, the potential of the high temperature CO2 environment to influence the creep behavior of the steel must be determined. Prior research on this topic between the 1960s and 1980s found conflicting conclusions, but nevertheless raised the possibility that carburization during CO2 exposure may strongly affect the creep behavior. This raises concerns particularly for thin-sectioned components such as compact heat exchangers, where even small rates of carburization can become problematic over long operating lifetimes. To shed light on this issue, this research investigates the creep behavior of austenitic stainless steel 347H and 309H (a higher Cr alternative) at 650°C. Specimens of 0.5, 1.0, and 2.0 mm thickness were tested to further assess the effect of steel thickness. Both steels show a reduction in creep life in CO2 relative to air, with 309H showing slightly better performance than 374H. Analysis is ongoing to determine the reason for degraded creep properties.

Rozman, Kyle A.↗

DOE OSTI2024

Creep behavior of austenitic steels in CO2 and the effect of specimen thickness

Rozman, Kyle A.↗

NASA NTRS1978

Effect of thermal barrier coatings on the performance of steam and water-cooled gas turbine/steam turbine combined cycle system

An analytical study was made of the performance of air, steam, and water-cooled gas-turbine/steam turbine combined-cycle systems with and without thermal-barrier coatings. For steam cooling, thermal barrier coatings permit an increase in the turbine inlet temperature from 1205 C (2200 F), resulting in an efficiency improvement of 1.9 percentage points. The maximum specific power improvement with thermal barriers is 32.4 percent, when the turbine inlet temperature is increased from 1425 C (2600 F) to 1675 C (3050 F) and the airfoil temperature is kept the same. For water cooling, the maximum efficiency improvement is 2.2 percentage points at a turbine inlet temperature of 1683 C (3062 F) and the maximum specific power improvement is 36.6 percent by increasing the turbine inlet temperature from 1425 C (2600 F) to 1730 C (3150 F) and keeping the airfoil temperatures the same. These improvements are greater than that obtained with combined cycles using air cooling at a turbine inlet temperature of 1205 C (2200 F). The large temperature differences across the thermal barriers at these high temperatures, however, indicate that thermal stresses may present obstacles to the use of coatings at high turbine inlet temperatures.

Nainiger, J. J.↗

DOE OSTI2021

Simulation of the supercritical CO 2 recompression Brayton power cycle with a high-temperature regenerator

The supercritical carbon dioxide (sCO 2 ) recompression Brayton cycle promises higher efficiency and lower capital cost than traditional steam Rankine power cycles. However, achieving high efficiency requires large, highly effective recuperators. Regenerators may be a low-cost alternative to printed circuit and micro-tube heat exchangers for recuperation in sCO 2 power cycles. Regenerators are a periodic heat exchanger in which thermal energy is extracted from the hot stream, stored in solid media, and then released to the cold stream at a later time. Fixed bed regenerators with valves to direct fluid are the preferred method for implementing regenerators in power cycles, but the inherently transient nature of these systems has not been characterized for this application. This study presents the simulation of a high-temperature regenerator within a 10 MWe sCO 2 recompression Brayton cycle. A transient, one-dimensional regenerator model presented in a previous study is used to simulate the regenerator. Dynamic heat exchanger models are also developed for the precooler, low-temperature recuperator, and primary heat exchanger, and the compressors and the turbine are modeled with off-design performance maps. We assess two regenerator-valve design options; one for fast switching, and one for reduced flow rate fluctuations. System simulation finds that both designs see significant fluctuations in turbomachinery flow rate, turbomachinery and system power, and regenerator discharge process outlet temperature. While designing the regenerator-valve subsystem for lower fluctuations is possible, the regenerator cold discharge temperature and net power still fluctuate by ±77.6°C and 6%, respectively. Increasing buffer volume is not effective at sufficiently reducing these fluctuations, but adding a packed bed in between the regenerator and the primary heat exchanger can reduce regenerator discharge process outlet temperature fluctuations to 6.4°C. Further reductions could be possible by increasing the size of this packed bed.

42 ENGINEERING↗

NASA NTRS1976

Comparison of geothermal power conversion cycles

Geothermal power conversion cycles are compared with respect to recovery of the available wellhead power. The cycles compared are flash steam, in which steam turbines are driven by steam separated from one or more flash stages; binary, in which heat is transferred from the brine to an organic turbine cycle; flash binary, in which heat is transferred from flashed steam to an organic turbine cycle; and dual steam, in which two-phase expanders are driven by the flashing steam-brine mixture and steam turbines by the separated steam. Expander efficiencies assumed are 0.7 for steam turbines, 0.8 for organic turbines, and 0.6 for two-phase expanders. The fraction of available wellhead power delivered by each cycle is found to be about the same at all brine temperatures: 0.65 with one stage and 0.7 with four stages for dual stream; 0.4 with one stage and 0.6 with four stages for flash steam; 0.5 for binary; and 0.3 with one stage and 0.5 with four stages for flash binary.

Elliott, D. G.↗

NASA NTRS1981

Jay Carter Enterprises, Incorporated steam engine

The Small Community Solar Thermal Power Experiment (SCSE) selected an organic rankine cycle (ORC) engine driving a high speed permanent magnet alternator (PMA) as the baseline power conversion subsystem (PCS) design. The back-up conceptual PCS design is a steam engine driving an induction alternator delivering power directly to the grid. The development of the automotive reciprocating simple rankine cycle steam engine and how an engine of similar design might be incorporated into the SCSE is discussed. A description of the third generation automotive engine is included along with some preliminary test data. Tests were conducted with the third generation engine driving an induction alternator delivering power directly to the grid. The purpose of these tests is to further verify the effects of expander inlet temperature, input thermal power level, expansion ratio, and other parameters affecting engine performance to aid in the development of an SCSE PCS.

Source record↗

DOE OSTI2023

Evidence of redox cycling as a sub-mechanism in hydrogen production during ethanol steam reforming over La 0.7 Sr 0.3 MnO 3-x perovskite oxide catalysts

Ethanol steam reforming (ESR) is of societal interest. Here, in this work, experiments were conducted to ascertain if some of the H 2 is produced by a redox cycle involving H 2 O filling oxygen vacancies over reducible oxide catalysts. Redox cycling experiments were performed over La 0.7 Sr 0.3 MnO 3-x (100) in ultra-high vacuum. It was found that H 2 was produced from redox cycling with alternating ethanol and water exposures over La 0.7 Sr 0.3 MnO 3-x (100), with both half-cycles occurring at temperatures ≤800 K. In the first half-cycle, ethanol ‘directly’ reduced the surface to create oxygen vacancies (not by a CO intermediate), and in the second half-cycle water filled oxygen vacancies to make H 2 . The H 2 production during the water exposure has a half-cycle turnover frequency of >3.2 × 10 -2 molecules site -1 s -1 in the temperature range of 700–800 K, which is fast enough to be part of the ESR full catalytic cycle. Flowing both reactant gases together, ethanol and water, over La 0.7 Sr 0.3 MnO 3-x (100) and La 0.7 Sr 0.3 MnO 3-x powders significantly increases hydrogen production compared to pure ethanol. The results suggest that steady state ESR includes a sub-mechanism of ethanol ‘directly’ reducing the surface to create oxygen vacancy, and water filling oxygen vacancy to make some of the H 2 by a Mars van Krevelen type mechanism.

08 HYDROGEN↗

NASA NTRS1983

Advanced technology cogeneration system conceptual design study: Closed cycle gas turbines

The results of a three task study performed for the Department of Energy under the direction of the NASA Lewis Research Center are documented. The thermal and electrical energy requirements of three specific industrial plants were surveyed and cost records for the energies consumed were compiled. Preliminary coal fired atmospheric fluidized bed heated closed cycle gas turbine and steam turbine cogeneration system designs were developed for each industrial plant. Preliminary cost and return-on-equity values were calculated and the results compared. The best of the three sites was selected for more detailed design and evaluation of both closed cycle gas turbine and steam turbine cogeneration systems during Task II. Task III involved characterizing the industrial sector electrical and thermal loads for the 48 contiguous states, applying a family of closed cycle gas turbine and steam turbine cogeneration systems to these loads, and conducting a market penetration analysis of the closed cycle gas turbine cogeneration system.

Mock, E. A. T.↗

NASA NTRS1982

Steam chugging analysis in single-vent vapor injection

A complete cycle of the periodic steam chugging phenomenon is analyed. Steam velocity and pressure variations in the vent are described by one-dimensional conservation equations. This is coupled either to the water slug model when water is in the vent, or, the infinite pool spherical bubble model at the vent exit during bubble growth. An isolated spherical bubble model is used for computing the collapse pressures. Comparisons of the model predictions with the UCLA 1/12-scale and the Japan 1/6-scale data indicate that the vent-pipe model predicts the vent-clearing times and the bubble growth times well. In addition, the predicted maximum chugging heights compared well with those measured in the Japan data. On bubble collapse pressures, the comparison with the spherical bubble model predictions is only fair. The model generally overpredicts the magnitude of the spikes. On examining the effects of pool subcooling and steam mass flux, general agreement is found between the predicted trends and those measured.

Lee, C. K. B.↗

DOE OSTI2020

Design analysis of a particle-based thermal energy storage system for concentrating solar power or grid energy storage

Energy storage is becoming indispensable for expanding renewable energy integration, and it is critical to the future low-carbon energy supply. Large-capacity, grid scale energy storage can support the integration of solar and wind power and support grid resilience with the diminishing capacity of baseload fossil power plants. With the development of thermal energy storage (TES) for concentrating solar power systems, standalone TES for grid integration becomes attractive due to the declining renewable generation cost and an increasing need for energy storage. The standalone TES system introduced in this paper can play a big role in the carbon-free energy future with capacity larger than batteries and cost likely lower than other energy storage methods such as pumped storage hydropower and compressed air energy storage, both of which also have geological limitations. To this end, we describe a TES system that uses stable, inexpensive solid particles as a TES media to provide scalable, low cost energy storage. The particle-based TES has the ability to drive various thermal power cycles including conventional steam-Rankine, air Brayton turbine with combined-cycle ability, or the emerging supercritical carbon dioxide Brayton power cycle. This work describes the containment design method including a concrete silo and an internal-insulation layer for the particle-TES system. The economic analysis shows significantly low storage cost when the particle-TES is integrated with Brayton combined-cycle power generation. The paper shows the design approach of the particle-TES system and its economic potential for bulk energy storage. The advantage of the particle-TES system as a promising bulk energy storage method is its ability to economically support dispatchable renewable grid penetration for larger capacity and longer discharging hours than current battery storage technologies.

25 ENERGY STORAGE↗

DOE OSTI2021

CSP Gen3: Liquid-Phase Pathway to SunShot

The United States Department of Energy (DOE) established the Concentrating Solar Power Generation 3 (CSP Gen3) program to promote the development of advanced CSP systems capable of producing electricity at a levelized cost of energy (LCOE) less than $60/MWh, based on criteria published in the CSP Gen3 Roadmap and a subsequent funding opportunity announcement (Gen3 FOA). This report documents the progress and potential of the “Liquid Pathway” to meet these objectives. The Liquid Pathway proposes the use of low-cost molten chloride salts for energy storage, mated with an operationally flexible solar receiver that employs liquid-metal sodium for heat capture and transfer to the storage salt. This approach leverages molten-salt technology from the current state-of-the-art CSP power towers embodied by plants such as Gemasolar, Crescent Dunes, Noor III, and the DEWA 700 CSP project. Furthermore, the design builds on the knowledge gained over decades of use of liquid-metal sodium as a high-temperature heat transfer fluid (HTF) in solar tests and nuclear-power applications. The commercial representation of the proposed Gen3 design incorporates a high-efficiency sodium receiver operating at ~740°C, with a liquid-liquid heat exchanger feeding a two-tank, molten-chloride salt storage system. Chloride salt is dispatched to a supercritical CO 2 (sCO 2 ) power cycle to provide electric power to the grid. The design integration is a conceptual match for the current sodium receiver → solar salt storage → steam-Rankine power cycle promoted by developer Vast Solar, which may facilitate commercial acceptance and development.

14 SOLAR ENERGY↗

DOE OSTI2021

Technoeconomic Benefits of Film-Forming Amine Products Applied to Steam Surface Condensers

In a conventional Rankine cycle, the majority of power plants employ surface condensers that use pumped cooling water to reject heat from the cycle. In such cases, heat rejection occurs in a shell and tube heat exchanger by film-wise condensation of low-pressure steam on stainless steel, titanium, brass, or copper-nickel tubing. To improve the thermal performance of steam surface condensers, a replenishable film-forming substance (FFS) can be ap-plied to the condenser tubing to promote efficient dropwise condensation. Conventionally, film-forming amine prod-uct (FFAP) coatings protect boiler surfaces from oxidative corrosion, which substantially reduces the operation and maintenance costs. To quantify the technical and economic benefits of FFAP coatings applied to condenser tubing due to the promotion of dropwise condensation, a thermal resistance network model was established. Using a rep-resentative steam surface condenser, the improvements in thermal performance (overall heat transfer coefficient) and process parameters (net plant efficiency, cooling water flowrate, and turbine backpressure) were determined due to the enhancement in the condensation heat transfer coefficient. Experimentally measured condensation heat transfer coefficients for common condenser materials were compared with the modeling results and were found to be within attainable bounds. Lastly, the trend in total heat exchanger cost reduction is generalized to understand the trade-off between reduced surface area for heat rejection and increase in coating application costs for a re-plenishable coating system.

20 FOSSIL-FUELED POWER PLANTS↗

DOE OSTI2020

Burst behavior of nuclear grade FeCrAl and Zircaloy-2 fuel cladding under simulated cyclic dryout conditions

A novel experiment to simulate cyclic dryout in boiling water reactors has been developed to better understand the performance of nuclear grade FeCrAl cladding in a BWR during dryout conditions caused by an Anticipated Operational Occurrence or Anticipated Transient Without SCRAM - both of which are Design Basis Accidents. Internally pressurized C26 M FeCrAl alloy cladding and Zircaloy-2 cladding were subjected to rapid 300°-650 °C thermal cycling in a steam environment; actual maximum temperatures were found to vary between materials but were always above 650 °C. In the range of 32–55 MPa hoop stress, Zircaloy-2 cladding burst within 1–16 cycles (about 100 s of dryout duration above 600 °C), while at 76 MPa hoop stress, C26 M cladding remained virtually undeformed after completing 54 cycles (over 1000 s of dryout duration above 600 °C). Higher temperature 300°-700 °C and 300°C–800 °C cycling experiments had to be performed to induce C26 M burst – failure occurred after 20 cycles in the former and during the first cycle in the latter. Zircaloy-2 and C26 M failure criteria were used to generate hoop stress specific dryout lifetimes. Overall, the simulated cyclic dryout experiments show that nuclear grade C26 M cladding has significantly enhanced survivability under dryout conditions relative to Zircaloy-2.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

NASA NTRS1987

Technical and economic study of Stirling and Rankine cycle bottoming systems for heavy truck diesel engines

Bottoming cycle concepts for heavy duty transport engine applications were studied. In particular, the following tasks were performed: (1) conceptual design and cost data development for Stirling systems; (2) life-cycle cost evaluation of three bottoming systems - organic Rankine, steam Rankine, and Stirling cycles; and (3) assessment of future directions in waste heat utilization research. Variables considered for the second task were initial capital investments, fuel savings, depreciation tax benefits, salvage values, and service/maintenance costs. The study shows that none of the three bottoming systems studied are even marginally attractive. Manufacturing costs have to be reduced by at least 65%. As a new approach, an integrated Rankine/Diesel system was proposed. It utilizes one of the diesel cylinders as an expander and capitalizes on the in-cylinder heat energy. The concept eliminates the need for the power transmission device and a sophisticated control system, and reduces the size of the exhaust evaporator. Results of an economic evaluation indicate that the system has the potential to become an attractive package for end users.

Kubo, I.↗

DOE OSTI2024

In-situ strain behavior and BISON simulations of Zircaloy cladding subjected to temperature cycling separate-effects tests in a steam environment

Understanding fuel system performance during anticipated transients without scram (ATWSs) in boiling water reactors (BWRs) is necessary for refining current and future safety limits. High-fidelity material models and simulations are fundamental to rigorous assessment of zirconium-based cladding performance. However, experimental thermomechanical data during simulated ATWSs to validate these modes are limited. To provide relevant in-situ data, Zircaloy-4 cladding was subjected to cyclic heating in a steam environment to simulate an out-of-pile BWR ATWS. Digital image correlation was used to capture the cladding strain behavior in-situ for comparison against simulations using the BISON finite element code. Conventional high-temperature models were compared using multiple schemes to gain a better understanding of the applicability of three BISON models to BWR ATWS: (1) the default combination of creep models in BISON, (2) the high-temperature Erbacher model alone, and (3) the low-temperature Limback-Andersson model alone. The cases run with the Limback-Andersson model alone produced the lowest root mean square error (RMSE). The lowest RMSE for the Limback-Andersson model alone was 0.659%, and the highest RMSE reported was 4.22%. A data gap within the model in the temperature regime of interest was also identified, and to account for this gap, the current model in BISON is linearly interpolated between two separate datasets. In conclusion, this evaluation highlights the need to either develop a new model or to improve the existing model to capture transient creep effects resulting from a cyclic temperature transient.

Anticipated transient without SCRAM↗