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.

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.

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.

Impact of Uncertainty On Prediction of Supercritical CO2 Properties and Nusselt Numbers

2021 ◽  
Author(s):  
Neil Sullivan ◽  
Yang Chao ◽  
Sandra Boetcher ◽  
Mark Ricklick
Keyword(s):  
Heat Transfer ◽  
Critical Point ◽  
Supercritical Co2 ◽  
Transfer Rates ◽  
Nusselt Numbers ◽  
Property Data ◽  
Highly Sensitive ◽  
Fluid Properties ◽  
Temperature And Pressure ◽  
The Impact

Abstract The impact of measurement uncertainty on heat transfer coefficient correlations for supercritical CO2 is investigated. Selection of appropriate temperature- and pressure-dependent reference quantities for these correlations, such as thermal conductivity, appears to have a large effect on predicting heat transfer rates. Supercritical CO2 work heavily depends on tabular real fluid property data, which show that fluid properties have very large gradients with respect to temperature and pressure near the critical point. The sharp gradients imply heat transfer predictions are highly sensitive to the accuracy of temperature and pressure experimental measurements in this region. Root sum of squares (RSS) uncertainties of various property values indicate predictably large (on the order of 1000%) uncertainties in calculated Reynolds, Prandtl, and Nusselt numbers near the critical point. Interestingly, uncertainties remain several times the calculated value for operating pressures (between 7.5 and 8.5 MPa) common in the experimental literature, highlighting a need for careful application of correlations near the pseudocritical line, and the benefits of presenting dimensional data in the literature.

Near-Critical CO2 Flow Measurement and Visualization

2014 ◽  
Vol 137 (1) ◽  
Author(s):  
Farzan Kazemifar ◽  
Dimitrios C. Kyritsis
Keyword(s):  
Pressure Drop ◽  
Critical Point ◽  
Flow Structure ◽  
Greenhouse Gas Emission ◽  
Steel Tube ◽  
Stainless Steel Tube ◽  
Inlet Temperature ◽  
Mass Flow Rates ◽  
Inlet Conditions ◽  
Co2 Flow

Near-critical CO2 flow has been studied because of its potential application in carbon dioxide capture and sequestration, which is one of the proposed solutions for reducing greenhouse gas emission. Near the critical point the thermophysical properties of the fluid undergo abrupt changes that affect the flow structure and characteristics. Pressure drop across a stainless steel tube, 2 ft long with 0.084 in. ID, at different inlet conditions and mass flow rates have been measured. The effects of variations of inlet conditions have been studied. The results show extreme sensitivity of pressure drop to inlet conditions especially inlet temperature in the vicinity of the critical point. Also, shadowgraphs have been acquired to study the flow structure qualitatively.

Numerical Investigation of the Flow Behavior Inside a Supercritical CO2 Centrifugal Compressor

2018 ◽  
Vol 140 (12) ◽  
Author(s):  
Alireza Ameli ◽  
Teemu Turunen-Saaresti ◽  
Jari Backman
Keyword(s):  
Critical Point ◽  
Centrifugal Compressor ◽  
Supercritical Co2 ◽  
Flow Behavior ◽  
Liquid Density ◽  
Flow Solver ◽  
Real Gas ◽  
Fluid Behavior ◽  
Test Loop ◽  
Fluid Properties

Centrifugal compressors are one of the best choices among compressors in supercritical Brayton cycles. A supercritical CO2 centrifugal compressor increases the pressure of the fluid which state is initially very close to the critical point. When the supercritical fluid is compressed near the critical point, wide variations of fluid properties occur. The density of carbon dioxide at its critical point is close to the liquid density which leads to reduction in the compression work. This paper explains a method to overcome the simulation instabilities and challenges near the critical point in which the thermophysical properties change sharply. The investigated compressor is a centrifugal compressor tested in the Sandia supercritical CO2 test loop. In order to get results with the high accuracy and take into account the nonlinear variation of the properties near the critical point, the computational fluid dynamics (CFD) flow solver is coupled with a look-up table of properties of fluid. Behavior of real gas close to its critical point and the effect of the accuracy of the real gas model on the compressor performance are studied in this paper, and the results are compared with the experimental data from the Sandia compression facility.

Numerical Investigation of the Flow Behavior Inside a Supercritical CO2 Centrifugal Compressor

2016 ◽  
Author(s):  
Alireza Ameli ◽  
Teemu Turunen-Saaresti ◽  
Jari Backman
Keyword(s):  
Critical Point ◽  
Centrifugal Compressor ◽  
Supercritical Co2 ◽  
Flow Behavior ◽  
Lookup Table ◽  
Liquid Density ◽  
Flow Solver ◽  
Real Gas ◽  
Fluid Behavior ◽  
Fluid Properties

Centrifugal compressors are one of the best choices among compressors in supercritical Brayton cycles. A supercritical CO2 centrifugal compressor increases the pressure of the fluid which state is initially very close to the critical point. When the supercritical fluid is compressed near the critical point, wide variations of fluid properties occur. The density of carbon dioxide at its critical point is close to the liquid density which leads to reduction in compressor work. The investigated compressor is a centrifugal compressor tested in the Sandia supercritical CO2 compression loop. In order to get results with the high accuracy and take into account the non-linear variation of the properties near the critical point, the CFD flow solver is coupled with a lookup table of properties of fluid. Behavior of real gas close to its critical point and the effect of the accuracy of the real gas model on the compressor performance are studied in this paper and the results are compared with the experimental data from the Sandia compression facility.

Near-Critical CO2 Flow Measurement and Visualization

2013 ◽  
Author(s):  
Farzan Kazemifar ◽  
Dimitrios C. Kyritsis
Keyword(s):  
Pressure Drop ◽  
Critical Point ◽  
Flow Structure ◽  
Greenhouse Gas Emission ◽  
Steel Tube ◽  
Stainless Steel Tube ◽  
Inlet Temperature ◽  
Mass Flow Rates ◽  
Inlet Conditions ◽  
Co2 Flow

Near-critical CO2 flow has been studied because of its potential application in carbon dioxide capture and sequestration, which is one of the proposed solutions for reducing greenhouse gas emission. Near the critical point the thermophysical properties of the fluid undergo abrupt changes that affect the flow structure and characteristics. Pressure drop across a stainless steel tube, 2 ft long with 0.084 in ID, at different inlet conditions and mass flow rates have been measured. The effects of variations of inlet conditions have been studied. The results show extreme sensitivity of pressure drop to inlet conditions especially inlet temperature in the vicinity of the critical point. Also, shadowgraphs have been acquired to study the flow structure qualitatively.

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 Research on Response Characteristics and Control Strategy of the Supercritical Carbon Dioxide Power Cycle

Processes ◽  
2021 ◽  
Vol 9 (11) ◽  
pp. 1943
Author(s):  
Chunhui Dai ◽  
Ping Song ◽  
Can Ma ◽  
Kelong Zhang ◽  
Wei Zheng ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Control Strategy ◽  
Pressure Control ◽  
Inlet Temperature ◽  
Turbine Inlet Temperature ◽  
Response Characteristics ◽  
Split Ratio ◽  
Compressor Inlet ◽  
Temperature And Pressure ◽  
Main Compressor

With the development of GEN-IV nuclear reactor technology, the supercritical carbon dioxide (SCO2) Brayton cycle has attracted wide attention for its simple structure and high efficiency. Correspondingly, a series of research has been carried out to study the characteristics of the cycle. The control flexibility of the power generation system has rarely been studied. This paper carried out a dynamic performance of the 20 MW-SCO2 recompression cycle based on the Simulink software. In the simulation, the response characteristics of the system main parameters under the disturbances of cooling water temperature, split ratio, main compressor inlet temperature and pressure were analyzed. The results show that the turbine inlet temperature is most affected by the disturbances, with a re-stabilization time of 2500–3000 s. According to the response characteristics of the system after being disturbed, this study proposed a stable operation control scheme. The scheme is coordinated with the main compressor inlet temperature and pressure control, recompressor outlet pressure control, turbine inlet temperature control and turbine load control. Finally, the control strategy is verified with the disturbance of reduced split ratio, and the results show that the control effect is good.

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.

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