Pinch Point Analysis of Air Cooler in sCO2 Brayton Cycle Operating Over Ambient Temperature Range

2019 ◽  
Author(s):  
Ankur Deshmukh ◽  
Jayanta Kapat
Keyword(s):  
Water Discharge ◽  
Ambient Air ◽  
Operating Conditions ◽  
Brayton Cycle ◽  
Pinch Point ◽  
Power Cycle ◽  
Point Analysis ◽  
Air Cooler ◽  
Set Up ◽  
Cycle Efficiency

Abstract Supercritical CO2 Brayton Power cycle is getting commercially attractive for power generation due to its numerous advantages like zero water discharge, compactness, low environmental emission and potential to reach high thermal efficiency. A typical recuperated sCO2 closed cycle consists of three heat exchangers (main heat exchanger, cooler and recuperator) and two turbomachinery (sCO2 turbine and sCO2 compressor). The cooler using ambient air for cooling is the focus of this study. Steady state air cooler model is set up to study the effect of air cooler size on cycle efficiency. The effect of change in ambient air temperature on air cooler pinch point for different air cooler sizes is analyzed using transient air cooler model. The simulation is setup for design of approximately 100MWe sCO2 cycle with operating temperature of 700° C and pressure of 250 barA. Transient calculations are done using LMS AMESim. LMS AMESim is Siemens PLM commercially available software. This work thus serves as a framework to develop a design basis for air cooler in sCO2 cycle as a function of transient operating conditions.

Pinch Point Analysis of Air Cooler in Supercritical Carbon Dioxide Brayton Cycle Operating Over Ambient Temperature Range

2020 ◽  
Vol 142 (5) ◽  
Author(s):  
Ankur Deshmukh ◽  
Jayanta Kapat
Keyword(s):  
Carbon Dioxide ◽  
Supercritical Carbon Dioxide ◽  
Water Discharge ◽  
Ambient Air ◽  
Operating Conditions ◽  
Pinch Point ◽  
Power Cycle ◽  
Air Cooler ◽  
Set Up ◽  
Supercritical Carbon

Abstract The supercritical carbon dioxide Brayton power cycle is getting commercially attractive for power generation due to its numerous advantages like zero water discharge, compactness, and low environmental emission and potential to reach high thermal efficiency. A typical recuperated closed cycle consists of three heat exchangers (main heat exchanger, cooler, and recuperator) and two turbomachinery (turbine and compressor). The cooler using ambient air for cooling is the focus of this study. The steady-state air cooler model is set up to study the effect of air cooler size on cycle efficiency. The effect of change in the ambient air temperature on the air cooler pinch point for different air cooler sizes is analyzed using the transient air cooler model. The simulation is set up for the design of the approximately 100 MWe cycle with an operating temperature of 700 °C and a pressure of 250 bar. Transient calculations are done using LMS AMESim. LMS AMESim is the Siemens PLM commercially available software. This work thus serves as a framework to develop a basis for the design of the air cooler in the power cycle as a function of transient operating conditions.

CFD–Aided Design Methodology for PCHE-Type Recuperators in Supercritical CO2 Recompression Power Cycles

2020 ◽  
Author(s):  
George Stamatellos ◽  
Antiopi-Malvina Stamatellou ◽  
Anestis I. Kalfas
Keyword(s):  
Design Methodology ◽  
High Capacity ◽  
Computation Time ◽  
Channel Length ◽  
Brayton Cycle ◽  
Power Cycles ◽  
Power Cycle ◽  
Design Options ◽  
Aided Design ◽  
Cycle Efficiency

Abstract The supercritical carbon dioxide (sCO2) cycle has emerged as a promising power cycle for various types of power conversion systems, based on its high thermal efficiency, (approaching 60%), small-size and compactness. The recompression Brayton cycle with sCO2 is based on high capacity regenerators processing a large amount of heat making their effectiveness critical for the overall cycle efficiency. Printed Circuit Heat Exchangers (PCHEs) are used in these cycles because of their high attainable effectiveness values. The design process for these regenerators is demanding, considering the peculiarities of variation of CO2 density and thermal properties near the critical temperature. On the other hand, a reduced computation time is necessary for the quick assessment of alternative design options. A hybrid design methodology for the high-temperature and the low-temperature recuperator (HTR and LTR) is presented in this paper, which employs 3D CFD conjugate heat transfer computation of the performance of a small two-channel module of the PCHE type. The results of the module computation are deployed in a 1D segmental method for the performance computation of the full heat exchanger’s channel length. Thus, the thermal effectiveness and pressure drop characteristics for the full heat exchanger are computed fast and with high accuracy. Application of the proposed methodology is carried out for the HTR and LTR computation in a recompression sCO2 Brayton cycle of a 600 MWth size power plant.

Brayton Cycle As an Alternate Power Conversion Option for Sodium Cooled Fast Reactor

2019 ◽  
Author(s):  
Jofred Joseph ◽  
Satish Kumar ◽  
Tanmay Vasal ◽  
N. Theivarajan
Keyword(s):  
Power Conversion ◽  
Rankine Cycle ◽  
Inlet Temperature ◽  
Brayton Cycle ◽  
Generation System ◽  
Fast Reactors ◽  
Turbine Inlet Temperature ◽  
Power Cycle ◽  
Power Generation System ◽  
Cycle Efficiency

Abstract Enhancing the safety and economic competitiveness are major objectives in the development of advanced reactor designs with emphasis on the design of systems or components of the nuclear systems. Innovative power cycle development is another potential option to achieve these objectives. Sodium cooled fast reactor (SFR) is one among the six reactor design concepts identified by the Gen IV International Forum for development to meet the technology goals for new nuclear energy system. Similar to the power cycle used in conventional fossil fuel based thermal power plants, sodium-cooled fast reactors have adopted the Rankine cycle based power conversion system. However, the possibility of sodium water reaction is a major concern and it becomes necessary to adopt means of early detection of leaks and isolation of the affected SG module for mitigating any adverse impact of sodium water reaction. The high exothermic nature of the reaction calls for introducing an intermediate sodium heat transport loop, leading to high overall plant cost hindering commercialization of sodium fast reactors. The Indian Prototype Fast Breeder Reactor (PFBR) also uses Rankine cycle in the power generation system. The superheated steam temperature has been set at 490 degree Celsius based on optimisation studies and material limitations. Additional Fast Breeder reactors are planned in near future and further work is being done to develop more advanced sodium cooled fast reactors. The closed Brayton cycle is a promising alternative to conventional Rankine cycle. By selecting an inert gas or a gas with milder reaction with sodium, the vigorous sodium water reaction can be avoided and significant cost savings in the turbine island can be achieved as gas turbine power conversion systems are of much smaller size than comparable steam turbine systems due to their higher power density. In the study, various Brayton cycle designs on different working gases have been explored. Supercritical-CO2 (s-CO2), helium and nitrogen cycle designs are analyzed and compared in terms of cycle efficiency, component performance and physical size. The thermal efficiencies at the turbine inlet temperature of Indian PFBR have been compared for Rankine cycle and Brayton cycle based on different working fluids. Also binary mixtures of different gases are investigated to develop a more safe and efficient power generation system. Helium does not interact with sodium and other structural materials even at very high temperatures but its thermal performance is low when compared to other fluids. Nitrogen being an inert gas does not react with sodium and can serve to utilise existing turbomachinery because of the similarity with atmospheric air. The supercritical CO2 based cycle has shown best thermodynamic performance and efficiency when compared to other Brayton cycles for the turbine inlet temperature of Indian PFBR. CO2 also reacts with sodium but the reaction is mild compared to sodium water reaction. The cycle efficiency of the s-CO2 cycle can be further improved by adopting multiple reheating, inter cooling and recuperation.

Primary Study on Carbon Dioxide Power Cycle of HTGR

2008 ◽  
Author(s):  
Chengjie Duan ◽  
Xiaoyong Yang ◽  
Jie Wang ◽  
Suyuan Yu
Keyword(s):  
Carbon Dioxide ◽  
High Temperature ◽  
Physical Properties ◽  
Critical Pressure ◽  
Working Fluid ◽  
Brayton Cycle ◽  
Power Cycle ◽  
Pressure Cycle ◽  
Cycle Efficiency ◽  
Thermal Physical Properties

At present, power cycles used in HTGR are indirect steam Rankine cycle and helium Brayton cycle. Using water or helium as working fluid which transform thermal energy into mechanical energy for HTGR power cycle has many disadvantages. Steam cycle could choose steam system which is similar to conventional coal-fired power plant, but because of the limit of material and equipments, there is big temperature difference between the steam and the helium, that makes big loss of thermal power and lowers the cycle efficiency. Helium can reach a high temperature in HTGR Brayton cycle and it has good stability, but because of helium has big isentropic exponent and low density, it is difficult to compress and makes helium turbine has shorter blades and more stages than normal gas turbine. Carbon dioxide has good thermal stability and physical properties. To avoid the reaction of CO2 with graphite and canning of fuel element at high temperature, it should be used in an indirect cycle as second loop working fluid. CO2 has appropriate critical pressure and temperature (7.38MPa, 304.19K) and can choose three types of cycle: supercritical cycle, subcritical-pressure cycle and trans-critical-pressure cycle (CO2 sometimes works under supercritical pressure, some times under subcritical-pressure). Carbon dioxide cycle works in a high pressure, so it makes pressure loss lower. When CO2 works close to its critical point, its density become larger than other conditions, and not change very much, this permits to reduce compress work. The thermal physical properties of carbon dioxide are totally different from helium due to CO2 works as real gas in the cycle. That causes the calculation of CO2 thermal physical properties, heat transfer and power cycle efficiency become difficult and need to be iterated. A systematic comparison between helium and carbon dioxide as working fluid for HTGR has been carried out. An empirical equation had been selected to estimate the thermal physical properties of carbon dioxide. Three types of carbon dioxide power cycle have been analyzed and the thermal efficiency has been calculated. A detailed introduction to the basic calculation process of the CO2 cycle thermal efficiency had been presented in the paper.

scholarly journals Thermal Performance Analysis of a Direct-Heated Recompression Supercritical Carbon Dioxide Brayton Cycle Using Solar Concentrators

Energies ◽  
2019 ◽  
Vol 12 (22) ◽  
pp. 4358 ◽  
Author(s):  
Jinping Wang ◽  
Jun Wang ◽  
Peter D. Lund ◽  
Hongxia Zhu
Keyword(s):  
Incidence Angle ◽  
Operating Conditions ◽  
Inlet Temperature ◽  
Brayton Cycle ◽  
Turbine Inlet Temperature ◽  
Beam Radiation ◽  
Solar Concentrators ◽  
Cooling Temperature ◽  
Turbine Inlet ◽  
Cycle Efficiency

In this study, a direct recompression supercritical CO2 Brayton cycle, using parabolic trough solar concentrators (PTC), is developed and analyzed employing a new simulation model. The effects of variations in operating conditions and parameters on the performance of the s-CO2 Brayton cycle are investigated, also under varying weather conditions. The results indicate that the efficiency of the s-CO2 Brayton cycle is mainly affected by the compressor outlet pressure, turbine inlet temperature and cooling temperature: Increasing the turbine inlet pressure reduces the efficiency of the cycle and also requires changing the split fraction, where increasing the turbine inlet temperature increases the efficiency, but has a very small effect on the split fraction. At the critical cooling temperature point (31.25 °C), the cycle efficiency reaches a maximum value of 0.4, but drops after this point. In optimal conditions, a cycle efficiency well above 0.4 is possible. The maximum system efficiency with the PTCs remains slightly below this value as the performance of the whole system is also affected by the solar tracking method used, the season and the incidence angle of the solar beam radiation which directly affects the efficiency of the concentrator. The choice of the tracking mode causes major temporal variations in the output of the cycle, which emphasis the role of an integrated TES with the s-CO2 Brayton cycle to provide dispatchable power.

Supercritical Carbon Dioxide Power Cycle Configurations for Use in Concentrating Solar Power Systems

2012 ◽  
Author(s):  
Craig S. Turchi ◽  
Zhiwen Ma ◽  
John Dyreby
Keyword(s):  
Carbon Dioxide ◽  
Energy Storage ◽  
Molten Salt ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Solar Power ◽  
Brayton Cycle ◽  
Concentrating Solar Power ◽  
Power Cycle ◽  
Cycle Efficiency

Concentrating Solar Power (CSP) plants utilize oil, molten salt or steam as the heat transfer fluid (HTF) to transfer solar energy to the power block. These fluids have properties that limit plant performance; for example, the synthetic oil and molten salt have upper temperature limits of approximately 390°C and 565°C, respectively. While direct steam generation has been tested, it requires complex controls and has limited options for integration of thermal energy storage. Use of carbon dioxide as the HTF and power cycle working fluid offers the potential to increase thermal cycle efficiency while maintaining simplicity of operation and thermal storage options. Supercritical CO2 (s-CO2) operated in a closed-loop recompression Brayton cycle offers the potential of higher cycle efficiency versus superheated or supercritical steam cycles at temperatures relevant for CSP applications. Brayton-cycle systems using s-CO2 have smaller weight and volume, lower thermal mass, and less complex power blocks versus Rankine cycles due to the higher density of the fluid and simpler cycle design. Many s-CO2 Brayton power cycle configurations have been proposed and studied for nuclear applications; the most promising candidates include recompression, precompression, and partial cooling cycles. Three factors are important for incorporating s-CO2 into CSP plants: superior performance vs. steam Rankine cycles, ability to integrate thermal energy storage, and dry-cooling. This paper will present air-cooled s-CO2 cycle configurations specifically selected for a CSP application. The systems will consider 10-MW power blocks that are tower-mounted with an s-CO2 HTF and 100-MW, ground-mounted s-CO2 power blocks designed to receive molten salt HTF from a power tower.

Thermodynamic Optimization of Recuperated S-CO2 Brayton Cycles for Solar Tower Applications

2013 ◽  
Author(s):  
Mahmood Mohagheghi ◽  
Jayanta Kapat
Keyword(s):  
Temperature Difference ◽  
Optimization Process ◽  
Limiting Factors ◽  
Limiting Factor ◽  
Inlet Temperature ◽  
Brayton Cycle ◽  
Pinch Point ◽  
Point Temperature ◽  
Decision Variables ◽  
Cycle Efficiency

Supercritical carbon dioxide (S-CO2) Brayton cycle represents significant advantages in solar tower application. Various configurations of S-CO2 Brayton cycle employing recuperation, recompression, intercooling and reheating have been investigated. The thermodynamic performance of each cycle configuration is optimized by using Genetic Algorithm in which the maximum cycle efficiency is defined as the objective function. The optimization process is comprehensive, i.e., the decision variables such as temperature and pressure of turbines, compressors, re-heaters, inter-coolers, and the pinch point temperature difference are optimized simultaneously. The recompression inlet temperature and mass flow fraction are also optimized along with other decision variables where that is the case. The main limiting factors in the optimization process are maximum cycle temperature, minimum heat rejection temperature, and pinch point temperature difference. The maximum cycle pressure is also a limiting factor in all studied cases except the simple recuperated cycle. The optimized cycle efficiency can vary from 55.77% to 62.02% where the highest value is obtained for the recompression recuperated cycle with reheating and intercooling. The optimization is based on thermodynamic analysis only, even though decision making for practical systems should be based on thermo-economic optimization.

scholarly journals Influence of selected cycle components parameters on the supercritical CO2 power unit performance

2018 ◽  
Vol 240 ◽  
pp. 05035
Author(s):  
Marcin Wołowicz ◽  
Jarosław Milewski ◽  
Gabriel Ziembicki
Keyword(s):  
Power Unit ◽  
Cycle Performance ◽  
Brayton Cycle ◽  
Split Ratio ◽  
Compressor Inlet ◽  
Set Up ◽  
Cycle Efficiency ◽  
Unit Performance ◽  
Isentropic Efficiency

The paper presents the influence of selected components parameters on the performance of supercritical carbon dioxide power unit. For this analysis mathematical model of supercritical recompression Brayton cycle was created. The analysis took into consideration changes in the net cycle power and efficiency for different compressor inlet temperatures. The results were obtained for a fixed minimum pressure of 7.4 MPa and fixed recompression split ratio. The studies conducted in this paper included also consideration of sensitivity of the cycle efficiency to a change in recuperators heat transfer area. In order to determine how each recuperator influences the cycle performance, an analysis of efficiency dependence on the recuperators area was made. Another parameters that were investigated are to a change in turbine and compressors isentropic efficiency and their influence on the cycle efficiency. In the reference cycle, isentropic efficiencies were set up as 88% for both the main and recompression compressor, and 90% for the turbine. Since isentropic efficiency is a sort of measure of broadly defined quality of a turbine or compressor, including airfoil shape, sealing, etc., it may be a significant cost factor that should be considered during cycle design. Therefore, a sensitivity analysis of cycle efficiency to both compressors and turbine isentropic efficiencies was conducted.

Transient Thermodynamic Modeling of Air Cooler in Supercritical CO2 Brayton Cycle for Solar Molten Salt Application

2019 ◽  
Author(s):  
Ankur Deshmukh ◽  
Jayanta Kapat ◽  
Akshay Khadse
Keyword(s):  
Molten Salt ◽  
Heat Exchangers ◽  
Supercritical Co2 ◽  
Water Discharge ◽  
Transient Behavior ◽  
Operating Conditions ◽  
Air Cooler ◽  
Temperature Operating ◽  
Transient Study ◽  
Start Ups

Abstract Supercritical CO2 Brayton power cycle is getting commercially attractive for power generation due to its numerous advantages like zero water discharge, compactness, low environmental emission and potential to reach high thermal efficiency at lower costs. A typical recuperated sCO2 closed cycle consists of three heat exchangers (main heat exchanger, cooler and recuperator) and two turbomachinery (sCO2 turbine and sCO2 compressor). The cooler which can use air or water as heat sink is the focus of this study. The purpose of the paper is investigation of behavior of thermodynamic parameters of cooler during transient operations. In this study, dynamic simulation is performed to analyze the transient behavior of air cooler in sCO2 cycle using molten salt as heat source from solar energy. Transient study is critical to understand the thermodynamic behavior of each system with time. Rapid changes in ambient temperature, operating loads, start-ups and shutdowns affect the performance of the turbomachinery and heat exchangers. The change in the thermal performance of air cooler with the change in boundary conditions is demonstrated here. The simulation is setup by having a steady state design of 100MWe sCO2 cycle with operating temperature of 700°C and pressure of 250 barA. Dynamic calculations are done using LMS AMESim. Transients studied in this paper include (i) step variation (ii) standard variation (iii) linear variation of air temperature. This work thus serves as a framework to develop a design basis for sCO2 cycle components as a function of transient operating conditions.

Selecting the Optimum Supercritical CO2 Cycle for Indirect-Fired Applications

2019 ◽  
Author(s):  
Brittany Tom ◽  
January Smith ◽  
Aaron M. McClung
Keyword(s):  
Carbon Dioxide ◽  
Supercritical Carbon Dioxide ◽  
Supercritical Co2 ◽  
Operating Conditions ◽  
Working Fluid ◽  
Performance Goals ◽  
Brayton Cycle ◽  
Power Cycle ◽  
And Performance ◽  
Supercritical Carbon

Abstract Existing research has demonstrated the viability of supercritical carbon dioxide as an efficient working fluid with numerous advantages over steam in power cycle applications. Selecting the appropriate power cycle configuration for a given application depends on expected operating conditions and performance goals. This paper presents a comparison for three indirect fired sCO2 cycles: recompression closed Brayton cycle, dual loop cascaded cycle, and partial condensation cycle. Each cycle was modeled in NPSS with an air side heater, given the same baseline assumptions and optimized over a range of conditions. Additionally, limitations on the heater system are discussed.

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