A Supercritical CO2 Gas Turbine Power Cycle for Next-Generation Nuclear Reactors

2002 ◽  
Author(s):  
Vaclav Dostal ◽  
Michael J. Driscoll ◽  
Pavel Hejzlar ◽  
Neil E. Todreas
Keyword(s):  
Gas Turbine ◽  
Oil Recovery ◽  
Supercritical Co2 ◽  
Power Plants ◽  
Ideal Gas ◽  
Working Fluid ◽  
Inlet Temperature ◽  
Brayton Cycle ◽  
Pinch Point ◽  
Good Efficiency

Although proposed more than 35 years ago, the use of supercritical CO2 as the working fluid in a closed circuit Brayton cycle has so far not been implemented in practice. Industrial experience in several other relevant applications has improved prospects, and its good efficiency at modest temperatures (e.g., ∼45% at 550°C) make this cycle attractive for a variety of advanced nuclear reactor concepts. The version described here is for a gas-cooled, modular fast reactor. In the proposed gas-cooled fast breeder reactor design of present interest, CO2 is also especially attractive because it allows the use of metal fuel and core structures. The principal advantage of a supercritical CO2 Brayton cycle is its reduced compression work compared to an ideal gas such as helium: about 15% of gross power turbine output vs. 40% or so. This also permits the simplification of use of a single compressor stage without intercooling. The requisite high pressure (∼20 MPa) also has the benefit of more compact heat exchangers and turbines. Finally, CO2 requires significantly fewer turbine stages than He, its principal competitor for nuclear gas turbine service. One disadvantage of CO2 in a direct cycle application is the production of N-16, which will require turbine plant shielding (albeit much less than in a BWR). The cycle efficiency is also very sensitive to recuperator effectiveness and compressor inlet temperature. It was found necessary to split the recuperator into separate high- and low-temperature components, and to employ intermediate recompression, to avoid having a pinch-point in the cold end of the recuperator. Over the past several decades developments have taken place that make the acceptance of supercritical CO2 systems more likely: supercritical CO2 pipelines are in use in the western US in oil-recovery operations; 14 advanced gas-cooled reactors (AGR) are employed in the UK at CO2 temperatures up to 650°C; and utilities now have experience with Rankine cycle power plants at pressures as high as 25 MPa. Furthermore, CO2 is the subject of R&D as the working fluid in schemes to sequester CO2 from fossil fuel combustion and for refrigeration service as a replacement for CFCs.

A Comparison Study for Off-Design Performance Prediction of a Supercritical CO2 Compressor With Similitude Analysis

2019 ◽  
Author(s):  
Yongju Jeong ◽  
Seongmin Son ◽  
Seong kuk Cho ◽  
Seungjoon Baik ◽  
Jeong Ik Lee
Keyword(s):  
Critical Point ◽  
Supercritical Co2 ◽  
Power Plants ◽  
Cycle Performance ◽  
Working Fluid ◽  
Brayton Cycle ◽  
Power Cycle ◽  
Design Performance ◽  
Wide Range ◽  
Phase Fluid

Abstract Most of the power plants operating nowadays mainly have adopted a steam Rankine cycle or a gas Brayton cycle. To devise a better power conversion cycle, various approaches were taken by researchers and one of the examples is an S-CO2 (supercritical CO2) power cycle. Over the past decades, the S-CO2 power cycle was invented and studied. Eventually the cycle was successful for attracting attentions from a wide range of applications. Basically, an S-CO2 power cycle is a variation of a gas Brayton cycle. In contrast to the fact that an ordinary Brayton cycle operates with a gas phase fluid, the S-CO2 power cycle operates with a supercritical phase fluid, where temperatures and pressures of working fluid are above the critical point. Many advantages of S-CO2 power cycle are rooted from its novel characteristics. Particularly, a compressor in an S-CO2 power cycle operates near the critical point, where the compressibility is greatly reduced. Since the S-CO2 power cycle greatly benefits from the reduced compression work, an S-CO2 compressor prediction under off-design condition has a huge impact on overall cycle performance. When off-design operations of a power cycle are considered, the compressor performance needs to be specified. One of the approaches for a compressor off-design performance evaluation is to use the correction methods based on similitude analysis. However, there are several approaches for deriving the equivalent conditions but none of the approaches has been thoroughly examined for S-CO2 conditions based on data. The purpose of this paper is comparing these correction models to identify the best fitted approach, in order to predict a compressor off-design operation performance more accurately from limited amount of information. Each correction method was applied to two sets of data, SCEIL experiment data and 1D turbomachinery code off-design prediction code generated data, and evaluated in this paper.

A Novel Brayton Cycle With the Integration of Liquid Hydrogen Cryogenic Exergy Utilization

2005 ◽  
Author(s):  
Na Zhang ◽  
Noam Lior
Keyword(s):  
Energy Efficiency ◽  
Gas Turbine ◽  
Liquid Hydrogen ◽  
Utilization Efficiency ◽  
Working Fluid ◽  
Inlet Temperature ◽  
Brayton Cycle ◽  
Evaporation Process ◽  
Impact Reduction ◽  
Gas Turbine Cycle

Stored or transported liquid hydrogen for use in power generation needs to be vaporized before combustion. Much energy was invested in the H2 liquefaction process, and recovery of as much of this energy as possible in the re-evaporation process will contribute to both the overall energy budget of the hydrogen use process, and to environmental impact reduction. A new gas turbine cycle is proposed with liquefied hydrogen (LH2) cryogenic exergy utilization. It is a semi-closed recuperative gas turbine cycle with nitrogen as the working fluid. By integration with the liquid H2 evaporation process, the inlet temperature of the compressor is kept very low, and thus the required compression work could be reduced significantly. Internal-fired combustion is adopted which allows a very high turbine inlet temperature, and a higher average heat input temperature is achieved also by internal heat recuperation. As a result, the cycle ha ry attractive thermal performance with the predicted energy efficiency over 79%. The choice of N2 as the working fluid is to allow the use of air as the oxidant in the combustor. The oxygen in the air combines with the fuel H2 to form water, which is easily separated from the N2 by condensation, leaving the N2 as the working fluid. The quantity of this working fluid in the system is maintained constant by continuously evacuating from the system the same amount that is introduced with the air. The cycle is environmentally friendly because no CO2 and other pollutant are emitted. An exergy analysis is conducted to identify the exergy losses in the components and the potential for further system improvement. The biggest exergy destruction is found occurring in the LH2 evaporator due to the relatively higher heat transfer temperature difference. The energy efficiency and exergy efficiency are 79% and 52%, respectively. The system has a back-work ratio only 1/4 of that in a Brayton cycle with ambient as the heat sink, and thus can produce 30.14 MW (53.9%) more work, with the LH2 cryogenic exergy utilization efficiency of 54%.

scholarly journals The Impeller Exit Flow Coefficient As a Performance Map Variable for Predicting Centrifugal Compressor Off-Design Operation Applied to a Supercritical CO2 Working Fluid

2017 ◽  
Author(s):  
Eric Liese ◽  
Stephen E. Zitney
Keyword(s):  
Centrifugal Compressor ◽  
Process Simulation ◽  
Supercritical Co2 ◽  
Flow Coefficient ◽  
Working Fluid ◽  
Inlet Temperature ◽  
Brayton Cycle ◽  
Inlet Flow ◽  
Cycle Simulation ◽  
Main Compressor

A multi-stage centrifugal compressor model is presented with emphasis on analyzing use of an exit flow coefficient vs. an inlet flow coefficient performance parameter to predict off-design conditions in the critical region of a supercritical carbon dioxide (CO2) power cycle. A description of the performance parameters is given along with their implementation in a design model (number of stages, basic sizing, etc.) and a dynamic model (for use in transient studies). A design case is shown for two compressors, a bypass compressor and a main compressor, as defined in a process simulation of a 10 megawatt (MW) supercritical CO2 recompression Brayton cycle. Simulation results are presented for a simple open cycle and closed cycle process with changes to the inlet temperature of the main compressor which operates near the CO2 critical point. Results showed some difference in results using the exit vs. inlet flow coefficient correction, however, it was not significant for the range of conditions examined. This paper also serves as a reference for future works, including a full process simulation of the 10 MW recompression Brayton cycle.

Performance Characteristics of an Operating Supercritical CO2 Brayton Cycle

2012 ◽  
Author(s):  
Thomas Conboy ◽  
Steven Wright ◽  
James Pasch ◽  
Darryn Fleming ◽  
Gary Rochau ◽  
...  
Keyword(s):  
Supercritical Co2 ◽  
Waste Heat ◽  
Electrical Power ◽  
Heat Removal ◽  
Test Facility ◽  
Working Fluid ◽  
Inlet Temperature ◽  
Brayton Cycle ◽  
Compact Size ◽  
Test Loop

Supercritical CO2 (S-CO2) power cycles offer the potential for better overall plant economics due to their high power conversion efficiency over a moderate range of heat source temperatures, compact size, and potential use of standard materials in construction [1,2,3,4]. Sandia National Labs (Albuquerque, NM, US) and the US Department of Energy (DOE-NE) are in the process of constructing and operating a megawatt-scale supercritical CO2 split-flow recompression Brayton cycle with contractor Barber-Nichols Inc. [5] (Arvada, CO, US). This facility can be counted among the first and only S-CO2 power producing Brayton cycles anywhere in the world. The Sandia-DOE test-loop has recently concluded a phase of construction that has substantially upgraded the facility by installing additional heaters, a second recuperating printed circuit heat exchanger (PCHE), more waste heat removal capability, higher capacity load banks, higher temperature piping, and more capable scavenging pumps to reduce windage within the turbomachinery. With these additions, the loop has greatly increased its potential for electrical power generation — according to models, as much as 80 kWe per generator depending on loop configuration — and its ability to reach higher temperatures. To date, the loop has been primarily operated as a simple recuperated Brayton cycle, meaning a single turbine, single compressor, and undivided flow paths. In this configuration, the test facility has begun to realize its upgraded capacity by achieving new records in turbine inlet temperature (650°F/615K), shaft speed (52,000 rpm), pressure ratio (1.65), flow rate (2.7 kg/s), and electrical power generated (20kWe). Operation at higher speeds, flow rates, pressures and temperatures has allowed a more revealing look at the performance of essential power cycle components in a supercritical CO2 working fluid, including recuperation and waste heat rejection heat exchangers (PCHEs), turbines and compressors, bearings and seals, as well as auxiliary equipment. In this report, performance of these components to date will be detailed, including a discussion of expected operational limits as higher speeds and temperatures are approached.

Micro Gas Turbine Integrated With a Supercritical CO2 Brayton Cycle Turbine: Layout Comparison and Thermodynamic Analysis

2020 ◽  
Author(s):  
Fabrizio Reale ◽  
Raniero Sannino ◽  
Raffaele Tuccillo
Keyword(s):  
Gas Turbine ◽  
Supercritical Co2 ◽  
Waste Heat ◽  
Thermal Power ◽  
Energy Systems ◽  
Working Fluid ◽  
Small Scale ◽  
Brayton Cycle ◽  
Part Load ◽  
Micro Gas Turbine

Abstract In an energetic scenario where both distributed energy systems and smart energy grids gain increasing relevance, the research focus is also on the detection of new solutions to increase overall performance of small-scale energy systems. Waste heat recovery (WHR) can represent a good solution to achieve this goal, due to the possibility of converting residual thermal power in thermal engine exhausts into electrical power. The authors, in a recent study, described the opportunities related to the integration of a micro gas turbine (MGT) with a supercritical CO2 Brayton Cycle (sCO2 GT) turbine. The adoption of Supercritical Carbon Dioxide (sCO2) as working fluid in closed Brayton cycles is an old idea, already studied in the 1960s. Only in recent years this topic returned to be of interest for electric power generation (i.e. solar, nuclear, geothermal energy or coupled with traditional thermoelectric power plants as WHR). In this technical paper the authors analyzed the performance variations of different systems layout based on the integration of a topping MGT with a sCO2 GT as bottoming cycle; the performance maps for both topping and bottoming turbomachinery have been included in the thermodynamic model with the aim of investigating the part load working conditions. The MGT considered is a Turbec T100P and its behavior at part load conditions is also described. The potential and critical aspects related to the integration of the sCO2 GT as bottoming cycle are studied also through a comparison between different layouts, in order to establish the optimal compromise between overall efficiencies and complexity of the energy system. The off-design analysis of the integrated system is addressed to evaluate its response to variable electrical and thermal demands.

Evaluation for Scalability of a Combined Cycle Using Gas and Bottoming SCO2 Turbines

2015 ◽  
Author(s):  
Leonid Moroz ◽  
Petr Pagur ◽  
Oleksii Rudenko ◽  
Maksym Burlaka ◽  
Clement Joly
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
Supercritical Co2 ◽  
Power Plants ◽  
Combined Cycle ◽  
Electricity Production ◽  
Working Fluid ◽  
Gas Temperature ◽  
Cycle System ◽  
Gas Turbine Exhaust

Bottoming cycles are drawing a real interest in a world where resources are becoming scarcer and the environmental footprint of power plants is becoming more controlled. Reduction of flue gas temperature, power generation boost without burning more fuel and even production of heat for cogeneration applications are very attractive and it becomes necessary to quantify how much can really be extracted from a simple cycle to be converted to a combined configuration. As supercritical CO2 is becoming an emerging working fluid [2, 3, 5, 7 and 8] due not only to the fact that turbomachines are being designed significantly more compact, but also because of the fluid’s high thermal efficiency in cycles, it raises an increased interest in its various applications. Evaluating the option of combined gas and supercritical CO2 cycles for different gas turbine sizes, gas turbine exhaust gas temperatures and configurations of bottoming cycle type becomes an essential step toward creating guidelines for the question, “how much more can I get with what I have?”. Using conceptual design tools for the cycle system generates fast and reliable results to draw this type of conclusion. This paper presents both the qualitative and quantitative advantages of combined cycles for scalability using machines ranging from small to several hundred MW gas turbines to determine which configurations of S-CO2 bottoming cycles are best for pure electricity production.

Computational Fluid Dynamics of a Radial Compressor Operating With Supercritical CO2

2012 ◽  
Author(s):  
Rene Pecnik ◽  
Enrico Rinaldi ◽  
Piero Colonna
Keyword(s):  
Critical Point ◽  
Gas Turbine ◽  
Supercritical Co2 ◽  
High Speed ◽  
Power Plants ◽  
Compressible Flows ◽  
High Efficiency ◽  
Fluid Dynamic ◽  
Working Fluid ◽  
Maximum Pressure

The merit of using supercritical CO2 (scCO2) as the working fluid of a closed Brayton cycle gas turbine is now widely recognized, and the development of this technology is now actively pursued. scCO2 gas turbine power plants are an attractive option for solar, geothermal and nuclear energy conversion. Among the challenges which must be overcome in order to successfully bring the technology to the market, the efficiency of the compressor and turbine operating with the supercritical fluid should be increased as much as possible. High efficiency can be reached by means of sophisticated aerodynamic design, which, compared to other overall efficiency improvements, like cycle maximum pressure and temperature increase, or increase of recuperator effectiveness, does not require an increase in equipment cost, but only an additional effort in research and development. This paper reports a three-dimensional CFD study of a high-speed centrifugal compressor operating with CO2 in the thermodynamic region slightly above the vapor-liquid critical point. The investigated geometry is the compressor impeller tested in the Sandia scCO2 compression loop facility [1]. The fluid dynamic simulations are performed with a fully implicit parallel Reynolds-averaged Navier-Stokes code based on a finite volume formulation on arbitrary polyhedral mesh elements. The CFD code has been validated on test cases which are relevant for this study, see Ref. [2,3]. In order to account for the strongly nonlinear variation of the thermophysical properties of supercritical CO2, the CFD code is coupled with an extensive library for the computation of properties of fluids and mixtures [4]. Among the available models, the one based on reference equations of state for CO2 [5,6] has been selected, as implemented in one of the sub-libraries [7]. A specialized look-up table approach and a meshing technique suited for turbomachinery geometries are also among the novelties introduced in the developed methodology. A detailed evaluation of the CFD results highlights the challenges of numerical studies aimed at the simulation of technically relevant compressible flows occurring close to the liquid-vapor critical point. The data of the obtained flow field are used for a comparison with experiments performed at the Sandia scCO2 compression-loop facility.

scholarly journals Supercritical CO2 Mixtures for Advanced Brayton Power Cycles in Line-Focusing Solar Power Plants

2019 ◽  
Vol 10 (1) ◽  
pp. 55 ◽  
Author(s):  
Robert Valencia-Chapi ◽  
Luis Coco-Enríquez ◽  
Javier Muñoz-Antón
Keyword(s):  
Supercritical Co2 ◽  
Power Plants ◽  
Solar Power ◽  
Plant Performance ◽  
Design Parameters ◽  
Working Fluid ◽  
Brayton Cycle ◽  
Power Cycles ◽  
Solar Power Plants ◽  
Dry Cooling

This work quantifies the impact of using sCO2-mixtures (s-CO2/He, s-CO2/Kr, s-CO2/H2S, s-CO2/CH4, s-CO2/C2H6, s-CO2/C3H8, s-CO2/C4H8, s-CO2/C4H10, s-CO2/C5H10, s-CO2/C5H12 and s-CO2/C6H6) as the working fluid in the supercritical CO2 recompression Brayton cycle coupled with line-focusing solar power plants (with parabolic trough collectors (PTC) or linear Fresnel (LF)). Design parameters assessed are the solar plant performance at the design point, heat exchange dimensions, solar field aperture area, and cost variations in relation with admixtures mole fraction. The adopted methodology for the plant performance calculation is setting a constant heat recuperator total conductance (UAtotal). The main conclusion of this work is that the power cycle thermodynamic efficiency improves by about 3–4%, on a scale comparable to increasing the turbine inlet temperature when the cycle utilizes the mentioned sCO2-mixtures as the working fluid. On one hand, the substances He, Kr, CH4, and C2H6 reduce the critical temperature to approximately 273.15 K; in this scenario, the thermal efficiency is improved from 49% to 53% with pure s-CO2. This solution is very suitable for concentrated solar power plants coupled to s-CO2 Brayton power cycles (CSP-sCO2) with night sky cooling. On the other hand, when adopting an air-cooled heat exchanger (dry-cooling) as the ultimate heat sink, the critical temperatures studied at compressor inlet are from 318.15 K to 333.15 K, for this scenario other substances (C3H8, C4H8, C4H10, C5H10, C5H12 and C6H6) were analyzed. Thermodynamic results confirmed that the Brayton cycle efficiency also increased by about 3–4%. Since the ambient temperature variation plays an important role in solar power plants with dry-cooling systems, a CIT sensitivity analysis was also conducted, which constitutes the first approach to defining the optimum working fluid mixture for a given operating condition.

Evaluation of Property Methods for Modeling Direct-Supercritical CO2 Power Cycles

2017 ◽  
Author(s):  
Charles W. White ◽  
Nathan T. Weiland
Keyword(s):  
Oil Recovery ◽  
Supercritical Co2 ◽  
Power Plants ◽  
Physical Property ◽  
Aspen Plus ◽  
Cost Effective ◽  
Operating Conditions ◽  
Cycle Performance ◽  
Working Fluid ◽  
Power Cycles

Direct supercritical CO2 (sCO2) power cycles have received considerable attention in recent years as an efficient and potentially cost-effective method of capturing CO2 from fossil-fueled power plants. These cycles combust natural gas or syngas with oxygen in a high pressure (200–300 bar), heavily-diluted sCO2 environment, such that the fluid entering the turbine is 90–95% CO2, with the balance composed primarily of H2O, CO, O2, N2 and Ar. After recuperation of the turbine exhaust thermal energy, water is condensed from the cycle, and the remainder is recompressed for either return to the combustor or for enhanced oil recovery (EOR) or storage. The compression power requirements vary significantly, depending on the proximity of the operating conditions to the CO2 critical point (31 °C, 73.7 bar), as well as to the level of working fluid dilution by minor components. As this has a large impact on cycle and plant thermal efficiency, it is crucial to correctly capture the appropriate thermo-physical properties of these sCO2 mixtures when carrying out performance simulations of direct sCO2 power plants. These properties are also important to determining how water is removed from the cycle, and for accurate modeling of the heat exchange within the recuperator. This paper presents a quantitative evaluation of ten different property methods that can be used for modeling direct sCO2 cycles in Aspen Plus®. REFPROP is used as the de facto standard for analyzing indirect sCO2 systems, where the closed nature of the cycle leads to a high purity CO2 working fluid. The addition of impurities due to the open nature of the direct-sCO2 cycle, however, introduces uncertainty to the REFPROP predictions. There is a limited set of mixtures available for which REFPROP can be reliably used and there are a number of species present in a coal-fired direct-fired sCO2 cycle that REFPROP cannot accommodate. Even with a relatively simplified system in which the trace components are eliminated, simulations made using REFPROP require computation times that often preclude its use in parametric studies of these cycles. Consequently, a series of comparative analyses were performed to identify the best physical property method for use in Aspen Plus® for direct-fired sCO2 cycles. These property methods are assessed against several mixture property measurements, and offer a relative comparison to the accuracy obtained with REFPROP. This study also underscores the necessity of accurate property modeling, where cycle performance predictions are shown to vary significantly with the selection of the physical property method.

Analysis of a Combined Cycle Plant Using a Small Particle Receiver to Drive a Primary Brayton Cycle

2015 ◽  
Author(s):  
Matthew Miguel Virgen ◽  
Fletcher Miller
Keyword(s):  
Heat Exchanger ◽  
Gas Turbine ◽  
Small Particle ◽  
Power Plants ◽  
Rankine Cycle ◽  
Combined Cycle ◽  
Working Fluid ◽  
Brayton Cycle ◽  
Efficiency Gains ◽  
Steam Cycle

All current commercial CSP plants operate at relatively low thermodynamic efficiency due to lower temperatures than similar conventional plants and due to the fact that they all employ Rankine conversion cycles. We present here an investigation on the effects of adding a bottoming steam power cycle to a hybrid CSP plant based on a Small Particle Heat Exchange Receiver (SPHER) driving a gas turbine as the primary cycle. Due to the high operating temperature of the SPHER being considered (over 1000 Celsius), the exhaust air from the primary Brayton cycle still contains a tremendous amount of exergy. While in the previous analysis this fluid was only used in a recuperator to preheat the Brayton working fluid, the current analysis explores the potential power and efficiency gains from instead directing the exhaust fluid through a heat exchanger to power a Rankine steam cycle. Not only do we expect the efficiency of this model to be competitive with conventional power plants, but the water consumption per kilowatt-hour will also be reduced by nearly two thirds as compared to most existing concentrating solar thermal power plants as a benefit of having air as the primary working fluid, which eliminates the condensation step present in Rankine-cycle systems. Coupling a new steam cycle model with the gas-turbine CSP model previously developed at SDSU, a wide range of cases were run to explore options for maximizing both power and efficiency from the proposed CSP combined cycle gas turbine (CCGT) plant. Due to the generalized nature of the bottoming cycle modeling, and the varying nature of solar power, special consideration had to be given to the behavior of the heat exchanger and Rankine cycle in off-design scenarios. The trade-offs of removing the recuperator for preheating the primary fluid are compared to potential overall power and efficiency gains in the combined cycle case.

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