Performance of N2O4 Gas Cycles for Solar Power Applications

1979 ◽  
Vol 193 (1) ◽  
pp. 313-320 ◽  
Author(s):  
G. Angelino
Keyword(s):  
Waste Heat ◽  
Working Fluid ◽  
Inlet Temperature ◽  
Turbine Inlet Temperature ◽  
Power Cycles ◽  
Average Temperature ◽  
Power Stations ◽  
Turbine Inlet ◽  
Compressor Inlet ◽  
Cycle Efficiency

The use of N2O4 as the working fluid in gas turbine power cycles is recognized as a potential instrument for improving cycle efficiency at moderate top temperatures while maintaining the technical advantages connected with the waste heat rejection at a comparatively high average temperature. Solar central receiver power stations, whose economic effectiveness is very sensitive to cycle efficiency and which must often reject their waste heat into the atmosphere, could usefully adopt this fluid. The thermodynamic reasons which explain the peculiar behaviour of N2O4 as the Brayton cycle working fluid are discussed. With respect to inert gas cycles, N2O4 permits, for a given efficiency, a reduction in turbine inlet temperature by 200-250°C. At a given turbine inlet temperature, the dissociating character of N2O4 allows overall efficiencies similar to those of steam cycles (at least for moderate plant capacities and provided N2O4 and steam cycles reject their waste heat at comparable temperatures). The relatively long relaxation time of the second step of the N2O4 dissociation can represent a problem mainly for the regenerator. A cycle is presented where regeneration at a pressure higher than the compressor inlet pressure can alleviate this problem.

scholarly journals Performances of Transcritical Power Cycles with CO2-Based Mixtures for the Waste Heat Recovery of ICE

Entropy ◽  
2021 ◽  
Vol 23 (11) ◽  
pp. 1551
Author(s):  
Jinghang Liu ◽  
Aofang Yu ◽  
Xinxing Lin ◽  
Wen Su ◽  
Shaoduan Ou
Keyword(s):  
Heat Recovery ◽  
Waste Heat Recovery ◽  
Waste Heat ◽  
Cycle Performance ◽  
Inlet Temperature ◽  
Turbine Inlet Temperature ◽  
Power Cycles ◽  
Split Ratio ◽  
Turbine Inlet ◽  
Organic Fluids

In the waste heat recovery of the internal combustion engine (ICE), the transcritical CO2 power cycle still faces the high operation pressure and difficulty in condensation. To overcome these challenges, CO2 is mixed with organic fluids to form zeotropic mixtures. Thus, in this work, five organic fluids, namely R290, R600a, R600, R601a, and R601, are mixed with CO2. Mixture performance in the waste heat recovery of ICE is evaluated, based on two transcritical power cycles, namely the recuperative cycle and split cycle. The results show that the split cycle always has better performance than the recuperative cycle. Under design conditions, CO2/R290(0.3/0.7) has the best performance in the split cycle. The corresponding net work and cycle efficiency are respectively 21.05 kW and 20.44%. Furthermore, effects of key parameters such as turbine inlet temperature, turbine inlet pressure, and split ratio on the cycle performance are studied. With the increase of turbine inlet temperature, the net works of the recuperative cycle and split cycle firstly increase and then decrease. There exist peak values of net work in both cycles. Meanwhile, the net work of the split cycle firstly increases and then decreases with the increase of the split ratio. Thereafter, with the target of maximizing net work, these key parameters are optimized at different mass fractions of CO2. The optimization results show that CO2/R600 obtains the highest net work of 27.43 kW at the CO2 mass fraction 0.9 in the split cycle.

Gas Properties as a Limit to Gas Turbine Performance

2002 ◽  
Author(s):  
R. C. Wilcock ◽  
J. B. Young ◽  
J. H. Horlock
Keyword(s):  
Gas Turbines ◽  
Industrial Development ◽  
Pressure Ratio ◽  
Cycle Performance ◽  
Working Fluid ◽  
Inlet Temperature ◽  
Turbine Inlet Temperature ◽  
Turbine Inlet ◽  
Cycle Efficiency ◽  
Gas Properties

Although increasing the turbine inlet temperature has traditionally proved the surest way to increase cycle efficiency, recent work suggests that the performance of future gas turbines may be limited by increased cooling flows and losses. Another limiting scenario concerns the effect on cycle performance of real gas properties at high temperatures. Cycle calculations of uncooled gas turbines show that when gas properties are modelled accurately, the variation of cycle efficiency with turbine inlet temperature at constant pressure ratio exhibits a maximum at temperatures well below the stoichiometric limit. Furthermore, the temperature at the maximum decreases with increasing compressor and turbine polytropic efficiency. This behaviour is examined in the context of a two-component model of the working fluid. The dominant influences come from the change of composition of the combustion products with varying air/fuel ratio (particularly the contribution from the water vapour) together with the temperature variation of the specific heat capacity of air. There are implications for future industrial development programmes, particularly in the context of advanced mixed gas-steam cycles.

Approximate Relations for Optimum Turbine Operating Parameters in Allam Cycle

2020 ◽  
Author(s):  
Yousef Haseli
Keyword(s):  
Turbine Blades ◽  
Air Separation ◽  
Cycle Performance ◽  
Working Fluid ◽  
Operating Parameters ◽  
Inlet Temperature ◽  
Turbine Inlet Temperature ◽  
Power Cycle ◽  
Turbine Inlet ◽  
Cycle Efficiency

Abstract The Allam power cycle is a novel method for clean power generation which employs the concept of oxyfuel combustion with carbon dioxide as the main working fluid. To date, only a few studies have appeared in the literature in that the performance of the Allam cycle has been assessed using a commercial software. The objective of this article is to explore relations between the cycle performance and the main operating parameters of the Allam cycle through a simplified thermodynamic analysis and mathematical modeling. The cycle efficiency is maximized with respect to turbine parameters. Expressions are derived for estimation of optimum turbine inlet temperature and pressure as well as optimum turbine exhaust pressure. Main simplifications include no portion of the recycled CO2 is used for turbine blades cooling and single stage CO2 compressor without intercooling. The cryogenic air separation process developed by Allam is employed which produces supercritical oxygen at combustion pressure. Typical numerical results are presented using the new expressions for optimum turbine parameters. The highest cycle efficiency is found to be 66.4% at a turbine inlet temperature/inlet pressure/exhaust pressure of 1306 K/300 bar/39.4 bar and a CO2 compressor exit pressure of 60 bar. The newly derived relationships among the key process parameters allow a better understanding of the operation of Allam cycle.

Combined Steam-Turbine Power Producing Concept With Recirculating Steam Compressor

2007 ◽  
Author(s):  
Branko Stankovic
Keyword(s):  
High Temperature ◽  
Steam Turbine ◽  
Waste Heat ◽  
Combined Cycle ◽  
Steam Flow ◽  
Working Fluid ◽  
Inlet Temperature ◽  
Turbine Inlet Temperature ◽  
Turbine Inlet ◽  
High Temperature Steam

This concept shows that an efficient combined cycle, comprising topping & bottoming cycle, does not have to be privilege of gas turbine plants only, but could also be achieved with steam turbine plants. An efficient power-producing concept of a combined steam-turbine cycle with addition of a recirculating steam compressor is disclosed. Topping part of such a combined steam-turbine cycle operates at elevated steam turbine inlet temperature and pressure, while its “waste heat” is recovered by the bottoming part of the combined cycle in a heat-recovery boiler (steam heat exchanger). The recirculating steam compressor pumps the cooled majority of the entire steam flow to the maximum cycle pressure, while smaller steam flow fraction continues its full expansion to some low pressure in a condenser. The cycle waste heat could be transferred to the bottoming part of the combined cycle in a variety of modalities, depending on the chosen main high-temperature steam-turbine inlet temperature and inlet pressure (supercritical/subcritical). At an assumed constant steam-turbine inlet temperature of 900°C (∼300 bar), a very high gross cycle thermal efficiency could potentially be achieved, ranging from 56 to 62% with the high-temperature steam-turbine pressure ranging from subcritical (30 bar) to supercritical (300 bar). Such a combined steam-turbine cycle seems to be a suitable energy conversion concept that could be applied in classic thermal power plants powered by coal, but also seems as an ideal option for application in the new generation of gas-cooled nuclear rectors, where the gaseous reactor coolant, heated up to 1000°C, would indirectly transfer its heat content to working fluid (superheated steam) of the topping part of the combined steam-turbine cycle. Alternatively, the proposed concept may be combined with renewable energy sources of a sufficient temperature level.

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 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.

Advanced High Temperature Gas-Cooled Reactor Systems

2008 ◽  
Author(s):  
Yasuyoshi Kato
Keyword(s):  
Gas Turbine ◽  
Power Conversion ◽  
Inlet Temperature ◽  
Turbine Inlet Temperature ◽  
Co2 Gas ◽  
Flow Channels ◽  
Turbine Inlet ◽  
Conversion System ◽  
Gas Turbine Cycle ◽  
Cycle Efficiency

Three systems have been proposed for advanced high temperature gas-cooled reactors (HTGRs): a supercritical carbon dioxide (S-CO2) gas turbine power conversion system; a new MicroChannel Heat Exchanger (MCHE); and a once-through-then-out (OTTO) refueling scheme with burnable poison (BP) loading. An S-CO2 gas turbine cycle attains higher cycle efficiency than a He gas turbine cycle due to reduced compression work around the critical point of CO2. Considering temperature lowering at the turbine inlet by 30°C through the intermediate heat exchange, the S-CO2 indirect cycle achieves efficiency of 53.8% at turbine inlet temperature of 820°C and turbine inlet pressure of 20 MPa. This cycle efficiency value is higher by 4.5% than that (49.3%) of a He direct cycle at turbine inlet temperature of 850°C and 7 MPa. A new MCHE has been proposed as intermediate heat exchangers between the primary cooling He loop and the secondary S-CO2 gas turbine power conversion system; and recuperators of the S-CO2 gas turbine power conversion system. This MCHE has discontinuous “S”-shape fins providing flow channels with near sine curves. Its pressure drop is one-sixth reference to the conventional MCHE with zigzag flow channel configuration while the same high heat transfer performance inherits. The pressure drop reduction is ascribed to suppression of recirculation flows and eddies that appears around bend corners of zigzag flow channels in the conventional MCHE. An optimal BP loading in an OTTO refueling scheme eliminates the drawback of its excessively high axial power peaking factor, reducing the power peaking factor from 4.44 to about 1.7; and inheriting advantages over the multi-pass scheme because of the lack of fuel handling and integrity checking systems; and reloading. Because of the power peaking factor reduction, the maximum fuel temperatures are lower than the maximum permissible values of 1250°C for normal operation and 1600°C during a depressurization accident.

Analysis of Energetic, Design and Operational Criteria When Choosing an Adequate Working Fluid for Small ORC Systems

2009 ◽  
Author(s):  
Jorge Faca˜o ◽  
Armando C. Oliveira
Keyword(s):  
Thermal Stability ◽  
Low Temperature ◽  
Heat Source ◽  
Specific Volume ◽  
Saturated Vapor ◽  
Saturation Pressure ◽  
Working Fluid ◽  
Inlet Temperature ◽  
Turbine Inlet ◽  
Cycle Efficiency

Small cogeneration (CHP) systems may lead to a significant reduction of primary energy consumption and harmful emissions. Low temperature Rankine cycles, that can be assisted by solar energy, are a possible solution for producing combined electricity and useful heat. These cycles usually use an organic working fluid. This study presents an analysis of the energetic, design and operational features, that have to be taken into account when choosing an adequate working fluid for these Organic Rankine Cycles (ORC). When using renewable energies as a heat source, like solar or geothermal, the cycles may operate at temperatures between 120°C and 230°C. A system producing 5 kW of electricity was considered as a basis of comparison. Several fluids were analysed: n-dodecane, water, toluene, cyclohexane, n-pentane, HFE7100, R123, isobutane and R245fa. The organic dry fluids, with a positive slope of the saturated vapor curve in a T-s diagram, are in principle desirable for low temperature applications, simplifying turbine design. The degree to which the fluids are drying, is generally related to their molecular weight or molecular complexity. Practical issues, like thermal stability, toxicity, flammability and cost are considered. The thermodynamic cycle efficiency is also important. The saturated vapor specific volume gives an indication of condenser size, which is related to system initial cost. A super-atmospheric (>100 kPa) saturation pressure eliminates infiltration gases, which is important for operational reasons, because infiltration reduces system efficiency. The degree of superheating was optimized for maximum cycle efficiency, with a quadratic approximation method. This optimization makes it possible to decide if it is better to have saturated vapor or superheated vapor at turbine inlet, for a fixed turbine inlet temperature. For a heat source temperature of 120°C, only toluene and isobutane present a small advantage in superheating. It is difficult to find the best fluid, which has simultaneously: high cycle efficiency, low vapor specific volume at turbine outlet, super-atmospheric saturation pressure, good thermal stability, small environmental impact, small toxicity and no flame propagation. From the point of view of cycle efficiency, n-dodecane presents the best performance. However, this fluid presents the highest saturated vapor specific volume (resulting in a larger condenser) and the smallest condenser saturation pressure (resulting in infiltration of gases). The best candidates for the cycle regarding all the aspects are: toluene, cyclohexane and n-pentane. Comparing the three fluids, toluene presents the highest efficiency, the highest impact in environment and the biggest vapor specific volume. N-pentane presents the smallest cycle efficiency and smallest vapor specific volume, but is the unique fluid with super-atmospheric saturation pressure. Cyclohexane is the fluid with lowest impact in environment.

Effects of Steam Injection on the Performance of Gas Turbine Power Cycles

1979 ◽  
Vol 101 (2) ◽  
pp. 217-227 ◽  
Author(s):  
W. E. Fraize ◽  
C. Kinney
Keyword(s):  
Gas Turbine ◽  
Waste Heat ◽  
Steam Injection ◽  
Combined Cycle ◽  
Thermodynamic Efficiency ◽  
Inlet Temperature ◽  
Exhaust Gas ◽  
Turbine Inlet Temperature ◽  
Power Cycles ◽  
Determine Effect

The effect of injecting steam generated by exhaust gas waste heat into a gas turbine with 3060°R turbine inlet temperature has been analyzed. Two alternate steam injection cycles are compared with a combined cycle using a conventional steam bottoming cycle. A range of compression ratios (8, 12, 16, and 20) and water mass injection ratios (0 to 0.4) were analyzed to determine effect on net turbine power output per pound of air and cycle thermodynamic efficiency. A water/fuel cost tradeoff analysis is also provided. The results indicate promising performance and economic advantages of steam injected cycles relative to more conventional utility power cycles. Application to coal-fired configuration is briefly discussed.

scholarly journals Parametric Investigation and Thermoeconomic Optimization of a Combined Cycle for Recovering the Waste Heat from Nuclear Closed Brayton Cycle

2016 ◽  
Vol 2016 ◽  
pp. 1-12
Author(s):  
Lihuang Luo ◽  
Hong Gao ◽  
Chao Liu ◽  
Xiaoxiao Xu
Keyword(s):  
Mass Fraction ◽  
Waste Heat ◽  
Combined Cycle ◽  
Cycle Performance ◽  
Inlet Temperature ◽  
Brayton Cycle ◽  
Turbine Inlet Temperature ◽  
Turbine Inlet ◽  
Overall Efficiency ◽  
Economic Analyses

A combined cycle that combines AWM cycle with a nuclear closed Brayton cycle is proposed to recover the waste heat rejected from the precooler of a nuclear closed Brayton cycle in this paper. The detailed thermodynamic and economic analyses are carried out for the combined cycle. The effects of several important parameters, such as the absorber pressure, the turbine inlet pressure, the turbine inlet temperature, the ammonia mass fraction, and the ambient temperature, are investigated. The combined cycle performance is also optimized based on a multiobjective function. Compared with the closed Brayton cycle, the optimized power output and overall efficiency of the combined cycle are higher by 2.41% and 2.43%, respectively. The optimized LEC of the combined cycle is 0.73% lower than that of the closed Brayton cycle.

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