Effect of Compressor Inlet Condition on Supercritical Carbon Dioxide Compressor Performance

2019 ◽  
Author(s):  
Haoxiang Chen ◽  
Weilin Zhuge ◽  
Yangjun Zhang ◽  
Hongdan Liu
Keyword(s):  
Carbon Dioxide ◽  
Supercritical Carbon Dioxide ◽  
Critical Point ◽  
Inlet Pressure ◽  
Inlet Temperature ◽  
Inlet Condition ◽  
Compressor Inlet ◽  
Compressor Performance ◽  
Inlet Conditions ◽  
Compressor Power

Abstract Supercritical carbon dioxide (S-CO2) Brayton power cycle has attracted a lot of attention around the world in energy conversion field. It takes advantage of the high density of CO2 near the critical point while maintaining low viscosity to reduce compressor power and achieve high cycle efficiency. However, as CO2 approaches to its critical point, the thermodynamic properties of CO2 vary dramatically with small changes in temperature or pressure. As a result, the density of the working fluid varies significantly at the compressor inlet in the practical cycle if operating near the critical point, especially for small-scale cycles and air-cooled cycles, which leads to compressors operating out of the flow range, even being damaged. Concerns of large density variations at the inlet of the compressor result in S-CO2 compressor designers selecting compressor inlet conditions away from the critical point, thereby increasing compressor power. In this paper, a criterion to choose inlet pressure and inlet temperature of compressors as the design inlet condition is proposed, which is guaranteeing ±50% change in inlet specific volume within ±3 °C variation in inlet temperature. By the criterion, 8 MPa and 34.7 °C is selected as the design inlet condition. According to design requirements of the cycle, a S-CO2 centrifugal compressor is designed through 1-D design methodology. Based on the two-zone model, the effects of compressor inlet condition including inlet pressure and inlet temperature on the compressor performance are analyzed in detail. In practical operation, the compressor inlet condition is varied. Thus, an accurate prediction of compressor performance under different inlet conditions is necessary. The traditional correction method is not suitable for S-CO2 compressor. Dimensionless specific enthalpy rise is used to correct pressure ratio by the real gas table. And the S-CO2 compressor performance can be predicted correctly under different inlet conditions.

Comparison of Compressor Performance Map Predictions to Test Data for a Supercritical Carbon Dioxide Brayton Power System

2021 ◽  
Author(s):  
Eric Clementoni
Keyword(s):  
Carbon Dioxide ◽  
Supercritical Carbon Dioxide ◽  
Critical Point ◽  
Power Cycles ◽  
Real Gas ◽  
Performance Map ◽  
Compressor Inlet ◽  
Compressor Performance ◽  
Inlet Conditions ◽  
Supercritical Carbon

Abstract Supercritical carbon dioxide (sCO2) Brayton power cycles are typically designed to operate with compressor inlet conditions near the critical point to take advantage of the high density of the fluid at these conditions. While designing the cycle to operate here improves cycle efficiency, it also creates challenges for designing the compressor and predicting off-design compressor performance due to real gas fluid properties near the critical point. Multiple compressor performance map evaluation methodologies which incorporate real gas corrections have been proposed in literature with only limited evaluation of the accuracy of these methods compared to operational data from compressors designed for sCO2 power cycles. This paper evaluates compressor performance from the 100 kWe Integrated System Test (IST), which was operated at the Naval Nuclear Laboratory, over a range of compressor inlet conditions and rotational speeds relative to one real gas performance map correction methodology and assesses the impact of additional terms proposed in literature for improving the accuracy of off-design performance predictions.

Effect of Compressor Inlet Pressure on Cycle Performance for a Supercritical Carbon Dioxide Brayton Cycle

2018 ◽  
Author(s):  
Eric M. Clementoni ◽  
Timothy L. Cox
Keyword(s):  
Carbon Dioxide ◽  
Supercritical Carbon Dioxide ◽  
Critical Point ◽  
Inlet Pressure ◽  
Cycle Performance ◽  
Brayton Cycle ◽  
Power Cycle ◽  
Compressor Inlet ◽  
Cycle Efficiency ◽  
Supercritical Carbon

Supercritical carbon dioxide (sCO2) Brayton power cycles take advantage of the high density of CO2 near the critical point to reduce compressor power and increase cycle efficiency. However, thermophysical properties of CO2 vary drastically near the critical point. Concerns of large property variations and liquid formation within the compressor can result in sCO2 cycle designers selecting compressor inlet operating conditions substantially above the critical point, thereby reducing cycle performance. The Naval Nuclear Laboratory has built and tested the 100 kWe Integrated System Test (IST) to demonstrate the ability to operate and control an sCO2 Brayton power cycle over a wide range of conditions. Since the purpose of the IST is focused on controllability, the design compressor inlet conditions were selected to be 8.2°F (4.6°C) and 270 psi (18.4 bar) above the critical point to reduce the effect of small variations in compressor inlet temperature and pressure on density. This paper evaluates the effect of design compressor inlet pressure on cycle efficiency for a simple recuperated Brayton cycle and the performance of an operating Brayton power cycle with a fixed design over a range of compressor inlet pressures.

scholarly journals Performance Analysis of the Supercritical Carbon Dioxide Re-compression Brayton Cycle

2020 ◽  
Vol 10 (3) ◽  
pp. 1129 ◽  
Author(s):  
Mohammad Saad Salim ◽  
Muhammad Saeed ◽  
Man-Hoe Kim
Keyword(s):  
Carbon Dioxide ◽  
Performance Analysis ◽  
Supercritical Carbon Dioxide ◽  
Mass Fraction ◽  
Inlet Temperature ◽  
Brayton Cycle ◽  
Exergy Destruction ◽  
Turbine Inlet Temperature ◽  
Turbine Inlet ◽  
Compressor Inlet

This paper presents performance analysis results on supercritical carbon dioxide ( s C O 2 ) re-compression Brayton cycle. Monthly exergy destruction analysis was conducted to find the effects of different ambient and water temperatures on the performance of the system. The results reveal that the gas cooler is the major source of exergy destruction in the system. The total exergy destruction has the lowest value of 390.1   kW when the compressor inlet temperature is near the critical point (at 35 °C) and the compressor outlet pressure is comparatively low ( 24   MPa ). The optimum mass fraction (x) and efficiency of the cycle increase with turbine inlet temperature. The highest efficiency of 49% is obtained at the mass fraction of x = 0.74 and turbine inlet temperature of 700 °C. For predicting the cost of the system, the total heat transfer area coefficient ( U A T o t a l ) and size parameter (SP) are used. The U A T o t a l value has the maximum for the split mass fraction of 0.74 corresponding to the maximum value of thermal efficiency. The SP value for the turbine is 0.212 dm at the turbine inlet temperature of 700 °C and it increases with increasing turbine inlet temperature. However the SP values of the main compressor and re-compressor increase with increasing compressor inlet temperature.

scholarly journals Impact of volumetric system design on compressor inlet conditions in supercritical CO2 cycles

2021 ◽  
Vol 5 ◽  
pp. 104-110
Author(s):  
Alexander Hacks ◽  
Sebastian Schuster ◽  
Dieter Brillert
Keyword(s):  
Simple Model ◽  
System Design ◽  
Critical Point ◽  
Static Pressure ◽  
Inlet Pressure ◽  
Cooling Power ◽  
Closed Cycle ◽  
Model Based ◽  
Compressor Inlet ◽  
Inlet Conditions

The paper aims to improve the understanding of the dependency of compressor inlet conditions close to the critical point in supercritical CO<sub>2 </sub> (sCO<sub>2 </sub>) cycles on different volumetric cycle designs. The compressor inlet conditions are fixed by the specific static outlet enthalpy of the main cooler and the static pressure determined by the mass of CO<sub>2 </sub> in the closed cycle. While in a previous study the authors analyzed effects on the compressor inlet conditions with respect to the specific static enthalpy in the pseudocritical region for constant inlet pressure, this paper focuses on the influence of the volume of the heater and cooler. The analysis is based on experimental observations from two different experimental sCO<sub>2 </sub> cycles, the SUSEN loop and the HeRo loop. The change of compressor inlet pressure upon change of the cooling power is substantially different and caused by the different volumetric design of the cycles. A simple model based on the volumes of the hot and cold sections in the cycle is developed to understand the dependency of compressor inlet conditions on the volumetric design. In terms of the volumetric design of the cycle, the paper will improve the knowledge of the challenges in stable compressor operation close to the critical point.

scholarly journals Characterization of Non-Equilibrium Condensation of Supercritical Carbon Dioxide in a de Laval Nozzle

2017 ◽  
Author(s):  
Claudio Lettieri ◽  
Derek Paxson ◽  
Zoltan Spakovszky ◽  
Peter Bryanston-Cross
Keyword(s):  
Carbon Dioxide ◽  
Supercritical Carbon Dioxide ◽  
Critical Point ◽  
Laval Nozzle ◽  
Experimental Measurements ◽  
Fluid Properties ◽  
Inlet Conditions ◽  
Direct Extrapolation ◽  
Supercritical Carbon

On a ten-year timescale, Carbon Capture and Storage could significantly reduce carbon dioxide (CO2) emissions. One of the major limitations of this technology is the energy penalty for the compression of CO2 to supercritical conditions, which can require up to 15% of the plant’s gross power output. To reduce the power requirements supercritical carbon dioxide compressors must operate at reduced temperatures and near saturation where phase change effects are important. Non-equilibrium condensation can occur in the high-speed flow at the leading edge of the compressor, causing performance and stability issues. The characterization of the fluid at these conditions is vital to enable advanced compressor designs at enhanced efficiency levels but the analysis is challenging due to the lack of data on the metastable fluid properties. In this paper we assess the metastable behavior and nucleation characteristics of high-pressure subcooled carbon dioxide during the expansion in a Laval nozzle. The assessment is conducted with numerical calculations, supported and corroborated by experimental measurements. The Wilson line is determined via optical measurements in the range of 41 and 82 bar and near the critical point. The state of the metastable fluid is fully characterized through pressure and density measurements, with the latter obtained in a first of its kind laser interferometry set up. In a systematic analysis the inlet conditions of the nozzle are moved close to the critical point to allow for large gradients in fluid properties and reduced margin to condensation. The results of calculations using a direct extrapolation of the Span and Wagner equation of state model are compared with the experimental measurements. The analysis suggests that the direct extrapolation using the Span and Wagner model yields results within 2% of the experimental data, with improved accuracy at conditions away from the critical point. The results are applied in a pre-production supercritical carbon dioxide compressor and are used to define inlet conditions at reduced temperature but free of condensation. Full-scale compressor experiments demonstrate that the new inlet conditions can reduce the shaft power input by 16%.

scholarly journals Characterization of Nonequilibrium Condensation of Supercritical Carbon Dioxide in a de Laval Nozzle

2017 ◽  
Vol 140 (4) ◽  
Author(s):  
Claudio Lettieri ◽  
Derek Paxson ◽  
Zoltan Spakovszky ◽  
Peter Bryanston-Cross
Keyword(s):  
Carbon Dioxide ◽  
Supercritical Carbon Dioxide ◽  
Laval Nozzle ◽  
Optical Measurements ◽  
Inlet Temperature ◽  
De Laval Nozzle ◽  
Inlet Conditions ◽  
Nonequilibrium Condensation ◽  
Supercritical Carbon

Carbon capture and storage could significantly reduce carbon dioxide (CO2) emissions. One of the major limitations of this technology is the energy penalty for the compression of CO2 to supercritical conditions. To reduce the power requirements, supercritical carbon dioxide compressors must operate near saturation where phase change effects are important. Nonequilibrium condensation can occur at the leading edge of the compressor, causing performance and stability issues. The characterization of the fluid at these conditions is vital to enable advanced compressor designs at enhanced efficiency levels but the analysis is challenging due to the lack of data on metastable fluid properties. In this paper, we assess the behavior and nucleation characteristics of high-pressure subcooled CO2 during the expansion in a de Laval nozzle. The assessment is conducted with numerical calculations and corroborated by experimental measurements. The Wilson line is determined via optical measurements in the range of 41–82 bar. The state of the metastable fluid is characterized through pressure and density measurements, with the latter obtained in a first-of-its-kind laser interferometry setup. The inlet conditions of the nozzle are moved close to the critical point to allow for reduced margins to condensation. The analysis suggests that direct extrapolation using the Span and Wagner equation of state (S–W EOS) model yields results within 2% of the experimental data. The results are applied to define inlet conditions for a supercritical carbon dioxide compressor. Full-scale compressor experiments demonstrate that the reduced inlet temperature can decrease the shaft power input by 16%.

scholarly journals Stabilizing Effects of Supercritical CO2 Fluid Properties on Compressor Operation†

2019 ◽  
Vol 4 (3) ◽  
pp. 20
Author(s):  
Alexander Johannes Hacks ◽  
Sebastian Schuster ◽  
Dieter Brillert
Keyword(s):  
Critical Point ◽  
Supercritical Co2 ◽  
Cooling Power ◽  
Inlet Temperature ◽  
Stabilizing Effect ◽  
Fluid Properties ◽  
Compressor Inlet ◽  
Applicable Range ◽  
Temperature And Pressure ◽  
Inlet Conditions

This paper aims to give an understanding of an effect which stabilizes the inlet conditions of compressors for supercritical CO2 (sCO2) operating close to the critical point. The effect was observed during testing of the turbomachine within the sCO2-HeRo project, and is caused by the sCO2 real gas properties close to the pseudocritical line. Under theoretical consideration, strong gradients in the fluid properties around this line—dependent on the static temperature and pressure of sCO2—can result in strong variation of compressor performance and finally lead to unstable cycle behavior. However, this paper demonstrates reduced gradients in density at the compressor inlet when varying the cooling power and taking advantage of a stabilizing effect. The applicable range and the significance of this stabilizing effect depended on the cooler inlet temperature and pressure, and was used to evaluate the relevance for individual cycles. Controlling the cooling power and the measurement of the inlet density allowed control of the compressor inlet conditions equally well, independent of the operating point, even close to the critical point.

Numerical Simulation of the Performance of an Axial Compressor Operating With Supercritical Carbon Dioxide

2018 ◽  
Author(s):  
Jinlan Gou ◽  
Wei Wang ◽  
Can Ma ◽  
Yong Li ◽  
Yuansheng Lin ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Numerical Simulation ◽  
Supercritical Carbon Dioxide ◽  
Critical Point ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Axial Compressor ◽  
Brayton Cycle ◽  
Supercritical Carbon

Using supercritical carbon dioxide (SCO2) as the working fluid of a closed Brayton cycle gas turbine is widely recognized nowadays, because of its compact layout and high efficiency for modest turbine inlet temperature. It is an attractive option for geothermal, nuclear and solar energy conversion. Compressor is one of the key components for the supercritical carbon dioxide Brayton cycle. With established or developing small power supercritical carbon dioxide test loop, centrifugal compressor with small mass flow rate is mainly investigated and manufactured in the literature; however, nuclear energy conversion contains more power, and axial compressor is preferred to provide SCO2 compression with larger mass flow rate which is less studied in the literature. The performance of the axial supercritical carbon dioxide compressor is investigated in the current work. An axial supercritical carbon dioxide compressor with mass flow rate of 1000kg/s is designed. The thermodynamic region of the carbon dioxide is slightly above the vapor-liquid critical point with inlet total temperature 310K and total pressure 9MPa. Numerical simulation is then conducted to assess this axial compressor with look-up table adopted to handle the nonlinear variation property of supercritical carbon dioxide near the critical point. The results show that the performance of the design point of the designed axial compressor matches the primary target. Small corner separation occurs near the hub, and the flow motion of the tip leakage fluid is similar with the well-studied air compressor. Violent property variation near the critical point creates troubles for convergence near the stall condition, and the stall mechanism predictions are more difficult for the axial supercritical carbon dioxide compressor.

scholarly journals Dynamic simulation of the oscillation characteristics of supercritical carbon dioxide impacting jets

2018 ◽  
Vol 25 (1) ◽  
pp. 61-71 ◽  
Author(s):  
Xinwei Zhang ◽  
Yiyu Lu ◽  
Jiren Tang ◽  
Zhe Zhou ◽  
Qian Li
Keyword(s):  
Carbon Dioxide ◽  
Numerical Model ◽  
Supercritical Carbon Dioxide ◽  
Oscillation Frequency ◽  
High Speed ◽  
Rock Breaking ◽  
Target Distance ◽  
Inlet Pressure ◽  
Oscillation Characteristics ◽  
Supercritical Carbon

A numerical model was established to investigate the dynamic oscillation characteristics of supercritical carbon dioxide (sc-CO2) impacting jets. The jet hydrodynamics, heat transfer, and physical properties of sc-CO2 fluid were incorporated into the model. The coupling of multiple fields with large velocity and pressure gradients was achieved using a modified SIMPLE segmentation algorithm. Laboratory experiments validated the reliability of the numerical model by detecting dynamic changes in the pressure on the centerline of the sc-CO2 impacting jet. Analysis of the flow field showed single or double high-speed sc-CO2 mass structures for the sc-CO2 impacting jet, revealing the generation mechanism of the impacting oscillation frequency and the mechanism of improved rock-breaking efficiency by sc-CO2 jet. The oscillation frequency equation was obtained through a quantitative treatment of the velocity and motion area of the sc-CO2 mass. Finally, the equation and simulation results were used to analyze the influences of the target distance, inlet pressure and temperature on the sc-CO2 jet oscillation characteristics. The results showed that the oscillation frequency and amplitude first increased and then decreased with increases in the target distance. The oscillation frequency and amplitude both increased with increasing inlet pressure; the oscillation frequency increased slowly with increasing temperature.

Visualization of Supercritical Carbon Dioxide Flow Through a Converging-Diverging Nozzle

2019 ◽  
Author(s):  
Chang Hyeon Lim ◽  
Gokul Pathikonda ◽  
Sandeep Pidaparti ◽  
Devesh Ranjan
Keyword(s):  
Carbon Dioxide ◽  
Supercritical Carbon Dioxide ◽  
Critical Point ◽  
High Speed ◽  
Operating Conditions ◽  
Higher Plant ◽  
Two Phase ◽  
Pressure Profiles ◽  
Flow Through ◽  
Supercritical Carbon

Abstract Supercritical carbon dioxide (sCO2) power cycles have the potential to offer a higher plant efficiency than the traditional Rankine superheated/supercritical steam cycle or Helium Brayton cycles. The most attractive characteristic of sCO2 is that the fluid density is high near the critical point, allowing compressors to consume less power than conventional gas Brayton cycles and maintain a smaller turbomachinery size. Despite these advantages, there still exist unsolved challenges in design and operation of sCO2 compressors near the critical point. Drastic changes in fluid properties near the critical point and the high compressibility of the fluid pose several challenges. Operating a sCO2 compressor near the critical point has potential to produce two phase flow, which can be detrimental to turbomachinery performance. To mimic the expanding regions of compressor blades, flow through a converging-diverging nozzle is investigated. Pressure profiles along the nozzle are recorded and presented for operating conditions near the critical point. Using high speed shadowgraph images, onset and growth of condensation is captured along the nozzle. Pressure profiles were calculated using a one-dimensional homogeneous equilibrium model and compared with experimental data.

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