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.

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.

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.

Analytical Formulation of the Performance of the Allam Power Cycle

2020 ◽  
Author(s):  
Yousef Haseli
Keyword(s):  
Power Plants ◽  
Fossil Fuels ◽  
Air Separation ◽  
Working Fluid ◽  
Inlet Temperature ◽  
Separation Unit ◽  
Power Cycle ◽  
Functional Relationships ◽  
Oxyfuel Combustion ◽  
Co2 Flow

Abstract Thermal power plants operating on fossil fuels emit a considerable amount of polluting gases including carbon dioxide and nitrogen oxides. Several technologies have been developed or under development to avoid the emissions of, mainly, CO2 that are formed as a result of air-fuel combustion. While post-combustion capture methods are viable solutions for reduction of CO2 in the existing power plants, implementation of the concept of oxyfuel combustion in future power cycles appears to be a promising technique for clean power generation from fossil fuels. A novel power cycle that employs oxyfuel combustion method has been developed by NET Power. Known as the Allam cycle, it includes a turbine, an air separation unit (ASU), a combustor, a recuperator, a water separator, CO2 compression with intercooling and CO2 pump. (Over 90% of the supercritical CO2 flow is recycled back to the cycle as the working fluid, and the rest is extracted for further processing and storage. The present paper introduces a simplified thermodynamic analysis of the Allam power cycle. Analytical expressions are derived for the net power output, optimum turbine inlet temperature (TIT), and the molar flowrate of the recycled CO2 flow. The study aims to provide a theoretical framework to help understand the functional relationships between the various operating parameters of the cycle. The optimum TIT predicted by the presented expression is 1473 K which is fairly close to that reported by the cycle developers.

The Heat Transfer Performance of Porous Gas Turbine Blades

1968 ◽  
Vol 72 (696) ◽  
pp. 1087-1094 ◽  
Author(s):  
F. J. Bayley ◽  
A. B. Turner
Keyword(s):  
Gas Turbine ◽  
Turbine Blades ◽  
Engine Performance ◽  
Operating Conditions ◽  
Maximum Temperature ◽  
Specific Power ◽  
Working Fluid ◽  
Inlet Temperature ◽  
Turbine Inlet ◽  
Compression And Expansion

It is well known that the performance of the practical gas turbine cycle, in which compression and expansion are non-isentropic, is critically dependent upon the maximum temperature of the working fluid. In engines in which shaft-power is produced the thermal efficiency and the specific power output rise steadily as the turbine inlet temperature is increased. In jet engines, in which the gas turbine has so far found its greatest success, similar advantages of high temperature operation accrue, more particularly as aircraft speeds increase to utilise the higher resultant jet velocities. Even in high by-pass ratio engines, designed specifically to reduce jet efflux velocities for application to lower speed aircraft, overall engine performance responds very favourably to increased turbine inlet temperatures, in which, moreover, these more severe operating conditions apply continuously during flight, and not only at maximum power as with more conventional cycles.

Development of the Advanced Closed-Cycle Gas Turbine System

2001 ◽  
Author(s):  
Miki Koyama ◽  
Toshio Mimaki
Keyword(s):  
Film Cooling ◽  
Cooling System ◽  
Early Stage ◽  
Turbine Blades ◽  
Thermal Conditions ◽  
Inlet Temperature ◽  
Internal Cooling ◽  
Turbine Inlet Temperature ◽  
Turbine Blade Cooling ◽  
Turbine Inlet

This aims to put the fruits of the R&D; “The Hydrogen Combustion Turbine” in WE-NET Phase I Program(1993-1998) to practical use at an early stage. The topping regenerating cycle was selected as the optimum cycle, with energy efficiency expected to be more than 60%(HHV) under the conditions of the turbine inlet temperature of 1973K(1700°C) and the pressure of 4.8MPa,in it. • As the turbine inlet temperature and pressure increase, issues to be resolved include the amount of NOx emissions and the durability of super alloys for turbine blades under such thermal conditions. In this respect, the development of the highly efficient methane-oxygen combustion technology, the turbine blade cooling technology, and the ultrahigh-temperature materials including thermal barrier coatings is being carried out. • In 1999, the results made it clear that there are little error among the three analytic programs used to verify the system efficiency, it was verified that the burning rate was going to arrive at over 98% from the methane-oxygen combustion test (under the atmospheric pressure). And the type of vane “Film cooling plus recycle type with internal cooling system” was selected as the most suitable vane.

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.

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.

A Selective Assembly Method to Reduce the Impact of Blade Flow Variability on Turbine Life

2004 ◽  
Author(s):  
Vince Sidwell ◽  
David Darmofal
Keyword(s):  
Turbine Blades ◽  
High Flow ◽  
Metal Temperature ◽  
Low Flow ◽  
Inlet Temperature ◽  
Selective Assembly ◽  
Turbine Inlet Temperature ◽  
Assembly Method ◽  
Turbine Inlet ◽  
The Impact

A selective assembly method is proposed that decreases the impact of blade passage manufacturing variability on the life of a row of cooled turbine blades. The method classifies turbine blades into groups based on the effective flow areas of the blade passages, then a row of blades is assembled exclusively from blades of a single group. A simplified classification is considered in which blades are divided into low-flow, nominal-flow, and high-flow groups. For rows assembled from the low-flow class, the blade plenum pressure will tend to rise and the individual blade flows will be closer to the design intent than for a single low-flow blade in a randomly-assembled row. Since the blade metal temperature is strongly dependent on the blade flow, selective assembly can lower the metal temperature of the lowest-flowing blades and increase the life of a turbine row beyond what is possible from a randomly-assembled row. Furthermore, the life of a nominal-flow or high-flow row will be significantly increased (relative to a randomly-assembled row) since the life-limiting low-flow blades would not be included in these higher-flowing rows. The impact of selective assembly is estimated using a model of the first turbine rotor of an existing high-bypass turbofan. The oxidation lives of the nominal-flow and high-flow blade rows are estimated to increase approximately 50% and 100% compared to randomly-assembled rows, while the life of the low-flow rows are the same as the randomly-assembled rows. Alternatively, selective assembly can be used to increase turbine inlet temperature while maintaining the maximum blade metal temperatures at random-assembly levels. For the nominal-flow and high-flow classes, turbine inlet temperature increases are estimated to be equivalent to the turbine inlet temperature increases observed over several years of gas turbine technology development.

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