Performance of Supercritical CO2 Dry Gas Seals Near the Critical Point

2016 ◽  
Author(s):  
Mohd Fairuz Zakariya ◽  
Ingo H. J. Jahn
Keyword(s):  
Critical Point ◽  
Supercritical Co2 ◽  
Closed Loop ◽  
High Pressures ◽  
Thermal Power ◽  
Operating Conditions ◽  
Real Gas ◽  
Dry Gas Seal ◽  
Gas Seals ◽  
And Performance

The Queensland Geothermal Energy Centre of Excellence is investigating the use of supercritical CO2 closed loop Brayton cycles in the Concentrated Solar Thermal power cycle plant. One of the important components in the turbomachinery within the plant are seals. As the cycle is closed loop and operating at high pressures, dry gas seals have been recommended for future use in these systems. One of the main challenges of using supercritical CO2 dry gas seals is that operating conditions are near the critical point. In the supercritical region in the vicinity of the critical point (304 K, 7.4 MPa), CO2 behaves as a real-gas, exhibiting large and abrupt non-linear changes in fluid and transport properties and high densities. To correctly predict the seal operation and performance, the interaction between this real gas and the seal rotor (primary ring) and the seal stator (mating ring) need to analysed and investigated in detail, as they can lead to significant changes in flow and seal performance. Results from this paper show that increased centrifugal effects caused by higher gas densities can reduce the pressure in the sealing dam region. This adversely affects the loading capacity of the dry gas seal. However, it also benefits seal performances by reducing the leakage rate. The current work presents an investigation of the supercritical CO2 dry gas seals operating close to the critical point with an inlet pressure and temperature of 8.5Mpa and 370K respectively and a speed of 30000 RPM. Results highlighting the effects of the groove length or dam to groove ratio on the performance of the dry gas seal are presented. The seal is simulated using Computational Fluid Dynamics to study the flow behaviour of the supercitical CO2 in the dry gas seal. Supercritical CO2 fluid properties are based on the fluid database REFPROP. The numerical model was validated with previous work and good agreement was demonstrated.

Numerical Approach for Real Gas Simulations: Part II — Flow Simulation for Supercritical CO2 Centrifugal Compressor

2017 ◽  
Author(s):  
Swati Saxena ◽  
Ramakrishna Mallina ◽  
Francisco Moraga ◽  
Douglas Hofer
Keyword(s):  
Critical Point ◽  
Centrifugal Compressor ◽  
Supercritical Co2 ◽  
Operating Conditions ◽  
Inlet Guide Vane ◽  
Thermodynamic Quantities ◽  
3D Flow ◽  
Real Gas ◽  
The Real ◽  
Operating Range

This paper is presented in two parts. Part I (Tabular fluid properties for real gas analysis) describes an approach to creating a tabular representation of the equation of state that is applicable to any fluid. This approach is applied to generating an accurate and robust tabular representation of the RefProp CO2 properties. Part II (this paper) presents numerical simulations of a low flow coefficient supercritical CO2 centrifugal compressor developed for a closed loop power cycle. The real gas tables presented in part I are used in these simulations. Three operating conditions are simulated near the CO2 critical point: normal day (85 bar, 35C), hot day (105 bar, 50 C) and cold day (70 bar, 20C) conditions. The compressor is a single stage overhung design with shrouded impeller, 155 mm impeller tip diameter and a vaneless diffuser. An axial variable inlet guide vane (IGV) is used to control the incoming swirl into the impeller. An in-house three-dimensional computational fluid dynamics (CFD) solver named TACOMA is used with real gas tables for the steady flow simulations. The equilibrium thermodynamic modeling is used in this study. The real gas effects are important in the desired impeller operating range. It is observed that both the operating range (minimum and maximum volumetric flow rate) and the pressure ratio across the impeller are dependent on the inlet conditions. The compressor has nearly 25% higher operating range on a hot day as compared to the normal day conditions. A condensation region is observed near the impeller leading edge which grows as the compressor operating point moves towards choke. The impeller chokes near the mid-chord due to lower speed of sound in the liquid-vapor region resulting in a sharp drop near the choke side of the speedline. This behavior is explained by analyzing the 3D flow field within the impeller and thermodynamic quantities along the streamline. The 3D flow analysis for the flow near the critical point provides useful insight for the designers to modify the current compressor design for higher efficiency.

Operation and Control of a Supercritical CO2 Compressor

2021 ◽  
Author(s):  
Joshua D. Neveu ◽  
Stefan D. Cich ◽  
J. Jeffrey Moore ◽  
Jason Mortzheim
Keyword(s):  
Steady State ◽  
Critical Point ◽  
Operating Conditions ◽  
State Control ◽  
Power Cycle ◽  
Low Head ◽  
And Performance ◽  
Steady State Control ◽  
And Control ◽  
Thermal Sources

Abstract Among the list of advanced technologies required to support the energy industry’s novel Supercritical Carbon Dioxide (sCO2) power cycle is the need for a robust and responsive control system. Recent testing has been performed on a 2.5 MWe sCO2 compressor operating near the critical temperature (31C) and critical pressure (73.8 bar), developed with funding from the US DOE Apollo program and industry partners. While sCO2 compression has been performed before, operating near the critical point has many key benefits for power generation with its low head requirements and smaller physical footprint. However, with these benefits come unique challenges, namely controlling this system to steady-state operating conditions. Operating just above the critical point (35°C [95°F] and 8.5 MPa [1,233 psi]) there can be large and rapid swings in density produced by subtle changes in temperature, leading to increased difficulty in maintaining adequate control of the compressor system. This means that proper functionality of the entire compressor system, and its usefulness to a closed loop recompression Brayton power cycle, is largely dependent on variables such as thermal sources, precision and response time of the instrumentation, proper heat soaking, and strategic filling and venting sequences. While other papers have discussed the science behind and performance of sCO2 compressors, this paper will discuss the challenges associated with steady-state control of the compressor at or near operating conditions, how the fill process was executed for optimal startup, and changes that occurred while idling during trip events.

Loop Transient Performance With a Closed Loop sCO2 Brayton Cycle

2021 ◽  
Author(s):  
Stefan D. Cich ◽  
J. Jeffrey Moore ◽  
Meera Day Towler ◽  
Jason Mortzheim
Keyword(s):  
Atmospheric Pressure ◽  
Closed Loop ◽  
Operating Conditions ◽  
Department Of Energy ◽  
Brayton Cycle ◽  
Transient Performance ◽  
Start Up ◽  
The Us ◽  
Successful Testing ◽  
And Performance

Abstract Recent testing has been completed on a 1 MWe supercritical carbon dioxide (sCO2) closed loop recuperated cycle under funding from the US Department of Energy (DOE) Sunshot initiative and industry partners. Some of the goals of this funding included the development of a 1 MWe loop, a 10 MWe turbine, and performance and mechanical testing. One of the key challenges that presented itself was the filling, start-up, and shut down of the entire system. Understanding the loop transient performance is important when having to bring a turbine online, transitioning from peak to partial loading, and also managing routine and emergency shut downs. Due to large changes in density near the critical point for CO2 and its tendency to form dry ice when expanded to atmospheric pressure, managing loop filling and venting is critical in ensuring that components are not damaged. With successful testing up to 715°C and 234 bar, this paper will provide updated data to, “Loop Filling and Start Up with a Closed Loop sCO2 Brayton Cycle [1].” While the previous paper focused on early trips and start up challenges, this paper will focus on the specific challenges at maximum operating conditions, and how the loop was managed when getting up to these high temperatures and pressures and how the loop behaved during a high temperature trip when compared to a controlled shut down from maximum operating conditions.

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.

Development of a Heat Transfer Correlation for Supercritical CO2 Based on Multiple Data Sets

2012 ◽  
Author(s):  
Tiberiu Preda ◽  
Eugene Saltanov ◽  
Igor Pioro ◽  
Kamiel S. Gabriel
Keyword(s):  
Heat Transfer ◽  
Critical Point ◽  
Supercritical Water ◽  
Wall Temperature ◽  
Supercritical Co2 ◽  
Power Plants ◽  
Operating Conditions ◽  
Thermodynamic Efficiency ◽  
New Correlation ◽  
Multiple Data Sets

Currently, increase in thermodynamic efficiency of water-cooled Nuclear Power Plants (NPPs) can only be achieved by raising the coolant’s operating conditions above the supercritical point. The critical point of water is 22.06 MPa and 373.95°C, making supercritical water research very power-intensive and expensive. CO2 behaves in a similar manner once in the supercritical state, but at significantly lower pressure and temperature, since critical point of CO2 is 7.37 MPa and 30.98°C. The applications of supercritical CO2 research range from using it as a modelling fluid, to supercritical turbine applications in Liquid Metal Fast Breeder Reactors (LMFBRs), and use in a supercritical Brayton cycle. Therefore, it is of prime importance to model its behaviour as accurately as possible. For this purpose, experimental data of Koppel (1960), He (2005), Kim (2005) and Bae (2007) for CO2 were analyzed, and a new correlation was developed. The dataset consists of 1409 wall temperature points with pressures ranging from 7.58 to 9.58 MPa, mass fluxes from 419 to 1200 kg/m2s, and heat fluxes from 20 to 130 kW/m2. All runs take place in bare tubes of inner diameters from 0.948 to 9.00 mm in both vertical and horizontal configurations. The proposed correlation takes a wall-temperature approach to predicting the Nusselt number. This paper compares the new correlation with other work which has been done at the University of Ontario Institute of Technology by Mokry et al. (2009), as well as with correlations by Swenson et al. (1965) and Dittus-Boelter (1930). It was found that the new correlation has an overall RMS error of 13% for Heat Transfer Coefficient (HTC) values and 5% for calculated wall temperature values. The correlation can be used as a conservative approach to predict wall temperature values in Supercritical Water Reactor (SCWR) preliminary calculations, to predict heat transfer in secondary-loop turbine/ heat exchanger applications, as with the LMFBR, and to help validate scaling parameters used for water and other coolants.

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.

Design and Test Plan of the Supercritical CO2 Compressor Test Loop

2008 ◽  
Author(s):  
Takao Ishizuka ◽  
Yasushi Muto ◽  
Masanori Aritomi
Keyword(s):  
High Pressure ◽  
Critical Point ◽  
Thermal Efficiency ◽  
Supercritical Co2 ◽  
Thermal Power ◽  
Low Pressure ◽  
Fiscal Year ◽  
Pressure Side ◽  
Test Loop ◽  
Pressure Compressor

Supercritical carbon dioxide (CO2) gas turbine systems can generate power at a high cycle thermal efficiency, even at modest temperatures of 500–550°C. That high thermal efficiency is attributed to a markedly reduced compressor work in the vicinity of critical point. In addition, the reaction between sodium (Na) and CO2 is milder than that between H2O and Na. Consequently, a more reliable and economically advantageous power generation system can be created by coupling with a Na-cooled fast breeder reactor. In a supercritical CO2 turbine system, a partial cooling cycle is employed to compensate a difference in heat capacity for the high-temperature — low-pressure side and low-temperature — high-pressure side of the recuperators to achieve high cycle thermal efficiency. In our previous work, a conceptual design of the system was produced for conditions of reactor thermal power of 600 MW, turbine inlet condition of 20 MPa/527°C, recuperators 1 and 2 effectiveness of 98%/95%, Intermediate Heat Exchanger (IHX) pressure loss of 8.65%, a turbine adiabatic efficiency of 93%, and a compressor adiabatic efficiency of 88%. Results revealed that high cycle thermal efficiency of 43% can be achieved. In this cycle, three different compressors, i.e., a low-pressure compressor, a high-pressure compressor, and a bypass compressor are included. In the compressor regime, the values of properties such as specific heat and density vary sharply and nonlinearly, dependent upon the pressure and temperature. Therefore, the influences of such property changes on compressor design should be clarified. To obtain experimental data for the compressor performance in the field near the critical point, a supercritical CO2 compressor test project was started at the Tokyo Institute of Technology on June 2007 with funding from MEXT, Japan. In this project, a small centrifugal CO2 compressor will be fabricated and tested. During fiscal year (FY) 2007, test loop components will be fabricated. During FY 2008, the test compressor will be fabricated and installed into the test loop. In FY 2009, tests will be conducted. This paper introduces the concept of a test loop and component designs for the cooler, heater, and control valves. A computer simulation program of static operation was developed based on detailed designs of components and a preliminary design of the compressor. The test operation regime is drawn for the test parameters.

Effects of Real Gas Model Accuracy and Operating Conditions on Supercritical CO2 Compressor Performance and Flow Field

2018 ◽  
Vol 140 (6) ◽  
Author(s):  
Alireza Ameli ◽  
Ali Afzalifar ◽  
Teemu Turunen-Saaresti ◽  
Jari Backman
Keyword(s):  
Flow Field ◽  
Critical Point ◽  
Supercritical Co2 ◽  
High Efficiency ◽  
Significant Proportion ◽  
Operating Conditions ◽  
Working Fluid ◽  
Look Up Table ◽  
Compressor Performance ◽  
The Look

Rankine and Brayton cycles are common energy conversion cycles and constitute the basis of a significant proportion of global electricity production. Even a seemingly marginal improvement in the efficiency of these cycles can considerably decrease the annual use of primary energy sources and bring a significant gain in power plant output. Recently, supercritical Brayton cycles using CO2 as the working fluid have attracted much attention, chiefly due to their high efficiency. As with conventional cycles, improving the compressor performance in supercritical cycles is major route to increasing the efficiency of the whole process. This paper numerically investigates the flow field and performance of a supercritical CO2 centrifugal compressor. A thermodynamic look-up table is coupled with the flow solver, and the look-up table is systematically refined to take into account the large variation of thermodynamic properties in the vicinity of the critical point. Effects of different boundary and operating conditions are also discussed. It is shown that the compressor performance is highly sensitive to the look-up table resolution as well as the operating and boundary conditions near the critical point. Additionally, a method to overcome the difficulties of simulation close to the critical point is explained.

Loop Filling and Start Up With a Closed Loop sCO2 Brayton Cycle

2019 ◽  
Author(s):  
Stefan D. Cich ◽  
J. Jeffrey Moore ◽  
Meera Day Towler ◽  
Jason Mortzheim ◽  
Douglas Hofer
Keyword(s):  
Atmospheric Pressure ◽  
Closed Loop ◽  
Brayton Cycle ◽  
Entire System ◽  
Thermal Transients ◽  
Start Up ◽  
The Us ◽  
Proper Mass ◽  
Gas Seals ◽  
And Performance

Abstract Recent testing has been performed on a 1 MWe sCO2 closed loop recuperated cycle under funding from the US DOE Sunshot initiative and industry partners. Some of the goals of this funding included the development of a 1 MWe loop, a 10 MWe turbine, and performance and mechanical testing. One of the key challenges that presented itself was the filling, start-up, and shut down of the entire system. Understanding the loop transient performance is important when having to bring a turbine online, transitioning from peak to partial loading, and also managing routine and emergency shut downs. Due to large changes in density near the critical point for CO2 and its tendency to form dry ice when expanded to atmospheric pressure, managing loop filling and venting is critical in ensuring that components do not get damaged. Specific challenges were centered on protecting the dry gas seals, maintaining proper mass in the loop, and also thermal transients during trips. This paper will take a detailed look at the challenges encountered during start up and shut downs, and also the solutions that were implemented to successful transition between different phases of the testing.

Design, Simulation, and Construction of a Test Rig for Organic Vapors

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
Andrea Spinelli ◽  
Matteo Pini ◽  
Vincenzo Dossena ◽  
Paolo Gaetani ◽  
Francesco Casella
Keyword(s):  
Dynamic Simulation ◽  
Thermal Power ◽  
Operating Conditions ◽  
Maximum Temperature ◽  
Main Process ◽  
Test Rig ◽  
Experimental Conditions ◽  
Blow Down ◽  
Working Fluids ◽  
Real Gas

A blow-down wind tunnel for real-gas applications has been designed, validated by means of dynamic simulation, and then built. The facility is aimed at characterizing an organic vapor stream, representative of the expansion taking place in organic Rankine cycle (ORC) turbines, by independent measurements of pressure, temperature, and velocity. The characterization of such flows and the validation of design tools with experimental data, which are still lacking in the scientific literature, is expected to strongly benefit the performance of future ORC turbines. The investigation of flow fields within industrial ORC turbines has been strongly limited by the unavailability of calibration tunnels for real-gas operating probes, by the limited availability of plants, and by restricted access for instrumentation. As a consequence, it has been decided to design and realize a dedicated facility, in partnership with a major ORC manufacturer. The paper thoroughly discusses the design and the dynamic simulation of the apparatus, presents its final layout, and shows the facility “as built”. A straight-axis planar convergent-divergent nozzle represents the test section for early tests, but the test rig can also accommodate linear blade cascades. The facility implements a blow down operating scheme, due to high fluid density and operating temperature, which prevent continuous operation because of the prohibitive thermal power required. A wide variety of working fluids can be tested, with adjustable operating conditions up to maximum temperature and pressure of 400 °C and 50 bar, respectively. Despite the fact that the test rig operation is unsteady, the inlet nozzle pressure can be kept constant by a control valve. In order to estimate the duration of the setup and experimental phase, and to describe the time evolution of the main process variables, the dynamic plant operation, including the control system, has been simulated. Design and simulation have been performed with both lumped-parameter and 1D models, using siloxane MDM and hydrofluorocarbon R245fa as the reference working fluids, described by state-of-the-art thermodynamic models. Calculations show how experiments may last from 12 seconds up to several minutes (depending on the fluid and test pressure), while reaching the experimental conditions requires few hours, consistently with the performance of daily-based experiments. Moreover, the economic constraints have been met by the technical solutions adopted for the plant, allowing the construction of the facility.

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