Reheat Cycle Research Articles

Characteristic evaluation of a CO2-capturing repowering system based on oxy-fuel combustion and exergetic flow analyses for improving efficiency

A CO2-capturing H2O turbine power generation system based on oxy-fuel combustion method is proposed to decrease CO2 emission from an existing thermal power generation system (TPGS) by utilizing steam produced in the TPGS. A high efficient combined cycle power generation system (CCPS) with reheat cycle is adopted as an example of existing TPGSs into which the proposed system is retrofitted. First, power generation characteristics of the proposed CO2-capturing system, which requires no modification of the CCPS itself, are estimated. It is shown through simulation study that the proposed system can reduce 26.8% of CO2 emission with an efficiency decrease by 1.20% and an increase power output by 23.2%, compared with the original CCPS. Second, in order to improve power generation characteristics and CO2 reduction effect of the proposed system, modifications of the proposed system are investigated based on exergetic flow analyses, and revised systems are proposed based on the obtained results. Finally, it is shown that a revised proposed system, which has the same turbine inlet temperature as the CCPS, can increase power output by 33.6%, and reduce 32.5% of CO2 emission with exergetic efficiency decrease by 1.58%, compared with the original CCPS. Copyright © 2010 John Wiley & Sons, Ltd.

Characteristics evaluation of a CO2‐capturing power generation system with reheat cycle utilizing regenerative oxygen‐combustion steam‐superheater

AbstractA new CO2‐capturing power generation system is proposed that can be easily realized by applying conventional technologies. In the proposed system, the temperature of medium‐pressure steam in a thermal power plant is raised by utilizing an oxygen‐combusting regenerative steam‐superheater. The CO2 generated by combusting the fuel in the superheater can be easily separated and captured from the exhaust gas at the condenser outlet, and is liquefied. The superheated steam is used to drive a steam turbine power generation system. Using a high‐efficiency combined cycle power generation system as an example, it is shown that the proposed system can increase the power output by 10.8%, and decrease the CO2 emissions of the entire integrated system by 18.6% with a power generation efficiency drop of 2.36% compared with the original power plant without CO2 capture, when the superheated steam temperature is 750 °C. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 165(1): 35–41, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20575

Enhancing the efficiency and power of the triple-pressure reheat combined cycle by means of gas reheat, gas recuperation, and reduction of the irreversibility in the heat recovery steam generator

The main methods for improving the efficiency or power of the combined cycle are: increasing the inlet temperature of the gas turbine (TIT), inlet air-cooling, applying gas reheat, steam or water injection into the gas turbine (GT), and reducing the irreversibility of the heat recovery steam generator (HRSG). In this paper, gas reheat with recuperation was applied to the regular triple-pressure steam-reheat combined cycle (the Regular cycle) by replacing the GT unit with a recuperated gas-reheat GT unit (requires two gas turbines, gas recuperator, and two combustion chambers). The Regular cycle with gas-reheat and gas-recuperation (the Regular Gas Reheat cycle) was modeled including detailed modeling of the combustion and GT cooling processes and a feasible technique to reduce the irreversibility of its HRSG was introduced. The Regular Gas Reheat cycle and the Regular Gas Reheat cycle with reduced-irreversibility HRSG (the Reduced Irreversibility cycle) were compared with the Regular cycle, which is the typical design for a commercial combined cycle. The effects of varying the TIT on the performances of all cycles were presented and discussed. The results indicate that the Reduced Irreversibility cycle is 1.9–2.15 percentage points higher in efficiency and 3.5% higher in the total specific work than the Regular Gas Reheat cycle, which is 3.3–3.6 percentage points higher in efficiency and 22–26% higher in the total specific work than the Regular cycle. The Regular Gas Reheat and Reduced Irreversibility cycles are 1.18 and 3.16 percentage points; respectively, higher in efficiency than the most efficient commercially-available combined cycle at the same value of TIT. Economic analysis was performed and showed that applying gas reheat with recuperation to the Regular cycle could result in an annual saving of 10.2 to 11.2 million US dollars for a 339 MW to 348 MW generating unit using the Regular cycle and that reducing the irreversibility of the HRSG of the Regular Gas Reheat cycle could result in an additional annual saving of 11.8 million US dollars for a 439 MW generating unit using the Regular Gas Reheat cycle.

Evaluation of component characteristics of a reheat cycle gas turbine using measured performance data

In this work, component characteristics of a reheat cycle gas turbine in a commercial combined cycle power plant were evaluated. An inverse performance analysis, in which component characteristic parameters were estimated based on measured performance data, was carried out. The measured parameters were the power, the fuel flow rates of two combustors, and the temperatures and pressures at various locations such as the compressor discharge, exits of both the high-and low-pressure turbines. The estimated parameters from the analysis include the compressor and turbine efficiencies and the inlet air flow rate. The analysis was performed for a wide operation range in terms of the ambient temperature and load, providing a database for the variations of the characteristic parameters with changes in the operating condition. In addition, a sensitivity analysis was performed to examine the influence of the uncertainties of the measured parameters on the estimated parameters. The analysis program can be further developed into a performance diagnosis tool and the obtained component characteristic data can be used as reference database.

Robust Design of Terminal ILC with H∞ Mixed Sensitivity Approach for a Thermoforming Oven

This paper presents a robust design approach for terminal iterative learning control (TILC). This robust design uses the H∞ mixed‐sensitivity technique. An industrial application is described where TILC is used to control the reheat phase of plastic sheets in a thermoforming oven. The TILC adjusts the heater temperature setpoints such that, at the end of the reheat cycle, the surface temperature map of the plastic sheet will converge to the desired one. Simulation results are included to show the effectiveness of the control law.

Multi-stage chemical looping combustion (CLC) for combined cycles with CO 2 capture

This paper presents application of the chemical looping combustion (CLC) method in natural gas-fired combined cycles for power generation with CO 2 capture. A CLC combined cycle consisting of single CLC-reactor system, an air turbine, a CO 2-turbine and a steam cycle has been designated as the base-case cycle. The base-case cycle can achieve net plant efficiency of about 52% at an oxidation temperature of 1200 °C. In order to achieve a reasonable efficiency at lower oxidation temperatures, reheat is introduced into the air turbine by employing multi CLC-reactors. The results show that the single reheat CLC-combined cycle can achieve net plant efficiency of above 51% at oxidation temperature of 1000 °C and above 53% at the oxidation temperature of 1200 °C including CO 2 compression to 110 bar. The double reheat cycle results in marginal efficiency improvement as compared to the single reheat cycle. The CLC-cycles are also compared with a conventional combined cycle with and without post-combustion capture in amine solution. All the CLC-cycles show higher net plant efficiencies with close to 100% CO 2 capture as compared to a conventional combined cycle with post-combustion capture, which is very promising.

Thermodynamic and environmental consideration of advanced gas turbine cycles with reheat and recuperator

The role of gas turbine power plants in electrical energy production has been considerably increased in the last two to three decades. Various methods have been proposed to improve the performance of gas turbine cycles. In this research, two methods, a reheat cycle and a cycle with a reheat and a recuperator, were investigated and compared with a simple cycle. The main objective of this paper is to study the performance of an simple cycle and reheat cycle under actual conditions. In this regard, all processes are treated as actual, and in particular a relatively simple and reliable approach is used to predict the amount of cooling air. The results obtained on the basis of a model developed for this research show that reheating in the context of a realistic study may lead to an improvement both in efficiency and in specific net work using recuperator cause to decrease NOx emission.

Comparative study of steam injection effects on operation of gas turbine cycles

In the present work, gas turbine cycles are modified with steam injection between the combustion chamber exit and the gas turbine inlet. Heat recovery steam generators, utilising the exhaust gases, provide these cycles with the injected steam at saturated vapour. The irreversibility of the different composing units of the cycles and the variation of gas properties owing to steam injection as well as changes in the interrelation of component performance parameters are taken into account. The isentropic temperature ratio and maximum to minimum cycle temperature ratio are varied over some ranges that slightly exceed their practically acceptable bounds in order to comprehensively investigate their effects on cycle characteristics. At the chosen values of the operating parameters, the enhancement achieved in the overall efficiency for the simple, reheat (with steam injection at high and low pressures) and partial oxidation (with steam injection at high and low pressures) gas turbine cycles are of about 20∼30%, 120∼200%, 10∼12%, 120∼260%, 20% respectively. The present modified cycles technique can be considered among the possible ways to improve the performance of gas turbine cycles-based power plants at feasible costs.

ＬＮＧ船１０ＭＰａ蒸気タービンプラントの水質管理について

The steam turbine plant is well known, good for reliability, but not good for specific fuel consumption to the diesel plant. As the demand for LNG carriers and the requirements for fuel saving are increasing year and year, more efficient steam plant is being required. In response to this requirement, a new steam plant, which adopts the reheat cycle with the steam pressure of 10 MPa, has been developed. The adoption of higher pressure steam would require the more sophisticated water quality control so that its reliability could be maintained at high level as same with the conventional 6MPa plants. This paper considers the appropriate water quality control criteria and phosphate treatment for the new plant, and makes it clear that a quite different boiler water treatment is needed from the treatment of conventional plant.

再熱プラント用舶用主ボイラ

再熱プラント用舶用主ボイラ

복합화력 발전용 재열사이클 가스터빈의 운전상태 분석

Operation conditions of a reheat cycle gas turbine for a combined cycle power plant was analyzed. Based on measured performance parameters of the gas turbine, a performance analysis program predicted component characteristic parameters such as compressor air flow, compressor efficiency, efficiencies of both the high and low pressure turbines, and coolant flows. The predicted air flow and its variation with the inlet guide vane setting were sufficiently accurate. The compressor running characteristic in terms of the relations between air flow, pressure ratio and efficiency was presented. The variations of the efficiencies of both the high and low pressure turbines were also presented. Almost constant flow functions of both turbines were predicted. The current methodology and obtained data can be utilized for performance diagnosis.

Part-load analysis of a chemical looping combustion (CLC) combined cycle with CO2 capture

Chemical Looping Combustion (CLC) is a rather novel concept of hydrocarbon fuel energy conversion with inherent CO2 separation. In CLC, a solid oxygen carrier transports oxygen from air to the fuel; hence air and fuel remain in separate environments and the combustion exhaust mainly consists of CO2 and water vapour. CLC can be applied in a circulating fluidised bed reactor system. The main objectives of this work have been the sensitivity study of CLC-reactor system in combination with different oxygen carriers, design of different CLC-combined and CLC-steam cycle configurations, off-design behaviour analysis of CLC-combined cycles and investigation of the possibility to use conventional machinery in CLC-power plants. The main efforts have been directed towards cycle design including parameter optimisation and cycle performance including off-design operation of combined cycles. The comparison of CLC-cycles with conventional natural gas-fired combined cycles has been presented at all the stages of this work.Energy and mass balance models for CLC based on the oxides of Fe, Cu and Ni in combination with inert supports of Al2O3 and NiAl2O4 have been developed. The results of study on different oxygen carriers in natural gas-based CLC indicate that NiO supported on NiAl2O4 is the most suitable oxygen carrier for achieving a conceivable reactor system. In order to be applicable in CLC-combined cycles, the reactor system and the oxygen carrier must stand a temperature of at least 1000°C and pressure of 10-26 bar.Various configurations of natural gas-fired CLC-combined cycles with NiO/NiAl2O4 oxygen carrier have been studied in this work. The results show that different designs of CLC-combined cycles consisting of single reactor system operating up to 1200°C can achieve 50-52% net plant efficiency including CO2 compression to 110 bar. Different CLCcombined cycle configurations employing multi-CLC-reactors and reheat air turbine have also been analysed. CLC-combined cycle with two reactor systems and single reheat air turbine can achieve above 51% net plant efficiency at 1000°C oxidation temperature. At the same oxidation temperature, a cycle with three CLC-reactors and double reheat air turbine achieves about 52% net plant efficiency. At 1200°C oxidation temperature, single reheat cycle achieves above 53% net plant efficiency, while double reheat results in marginal efficiency improvement. All the CLC-combined cycles proposed in this work exhibit higher net plant efficiencies with close to 100% CO2 capture compared to a conventional combined cycle with 90% post-combustion CO2 capture. The off-design analysis of CLC-combined cycles shows that a CLC-combined cycle exhibits better relative net plant efficiency at partload, compared to conventional combined cycles with and without CO2 capture. However, the CLC-combined cycles need more advanced control strategies, especially if a CO2/H2Oturbine is included. The cycles demand advanced air flow control strategies during the startup, shut-down and at part-load below 60%.Two designs of ultra-supercritical natural gas-fired CLC-steam cycles based on NiO/NiAl2O4 oxygen carrier have also been proposed and analysed in this work. The single reheat CLC-steam cycle can achieve net plant efficiency of about 43% while the double reheat CLC-steam cycle achieves 44% net plant efficiency with close to 100% CO2 capture. This work suggests that CLC has a high potential for efficient power generation with CO2 capture. However, there are some technological barriers discussed in this thesis, which need to be overcome in order to successfully realise CLC application in power plants.

Growth kinetics of secondary austenite in the welding microstructure of a UNS S32304 duplex stainless steel

A thermodynamic and kinetic assessment was made of secondary austenite (γ 2) growth in the welding microstructure of a UNS S32304 duplex stainless steel during reheat cycles, between 900 and 1250 °C. Calphad-based numerical simulation and analytical electron microscopy characterization analyses were performed. A non-monotonic relationship between the proportion of γ 2 and reheating temperature was observed, a maximum γ 2 fraction being attained at ∼1050 °C. γ 2 formed at higher reheating temperatures (above ∼1100 °C) displayed an outer shell rich in chromium and nitrogen and a core region depleted in these alloying elements; in contrast, γ 2 formed at lower reheating temperatures (under ∼1000 °C) displayed almost homogeneous chemical composition.

Performance evaluation of reheat gas turbine cycles

The role of gas turbine power plants in electrical energy production has been considerably increased in the last two to three decades. Various methods have been proposed to improve the performance of gas turbine cycles. In this research, two methods, a reheat cycle (RC) and a cycle with a reheat and a heat exchanger (RHC), were investigated and compared with a simple cycle (SC). Today, to achieve a higher efficiency and capacity in gas turbines, higher turbine inlet temperatures (1300 °C and more) are used. Basically, application of such temperatures without turbine blade cooling is impossible. Therefore, analysis of gas turbine cycles without considering blade cooling in modelling will certainly not lead to a valid and correct result. The main objective of this paper is to study the performance of an RC and RHC under actual conditions. In this regard, all processes are treated as actual, and in particular a relatively simple and reliable approach is used to predict the amount of cooling air. It should be noted that there are many attempts being made to produce ceramic turbines, for which a much-reduced cooling requirement will be necessary. The results obtained on the basis of a model developed for this research show that reheating in the context of a realistic study may lead to an improvement both in efficiency and in specific net work.

A Feasibility Study of Existing Gas Turbines for Recuperated, Intercooled, and Reheat Cycle

In the present paper, a comprehensive and simple in application design methodology to obtain a gas turbine working on recuperated, intercooled, and reheat cycle utilizing existing gas turbines is presented. Applications of the proposed design steps have been implemented on the three existing gas turbines with wide ranging design complexities. The results of evaluated aerothermodynamic performance for these existing gas turbines with the proposed modifications are presented and compared in this paper. Sample calculations of the analysis procedures discussed, including stage-by-stage analysis of the compressor and turbine sections of the modified gas turbines, have been also included. All the three modified gas turbines were found to have higher performance, with cycle efficiency increase of 9% to 26%, in comparison to their original values.

Thermodynamic analysis of reheat cycle steam power plants

In this study, a thermodynamic analysis of a Rankine cycle reheat steam power plant is conducted, in terms of the first law of thermodynamic analysis (i.e. energy analysis) and the second law analysis (i.e. exergy analysis), using a spreadsheet calculation technique. The energy and exergy efficiencies are studied as 120 cases for different system parameters such as boiler temperature, boiler pressure, mass fraction ratio and work output. The temperature and pressure values are selected in the range between 400 and 590°C, and 10 and 15 MPa, being consistent with the actual values. The calculated energy and exergy efficiencies are compared with the actual data and the literature work, and good agreement is found. The possibilities to further improve the plant efficiency and hence reduce the inefficiencies are identified and exploited. The results show how exergy analysis can help to make optimum design decisions in a logical manner. Copyright © 2001 John Wiley & Sons, Ltd.

Modeling the Air-Cooled Gas Turbine: Part 1—General Thermodynamics

AbstractThis paper is Part I of a study concerned with developing a formal framework for modeling air-cooled gas turbine cycles and deals with basic thermodynamic issues. Such cycles involve gas mixtures with varying composition which must be modeled realistically. A possible approach is to define just two components, air and gas, the latter being the products of stoichiometric combustion of the fuel with air. If these components can be represented as ideal gases, the entropy increase due to compositional mixing, although a true exergy loss, can be ignored for the purpose of performance prediction. This provides considerable simplification. Consideration of three idealized simple cycles shows that the introduction of cooling with an associated thermal mixing loss does not necessarily result in a loss of cycle efficiency. This is no longer true when real gas properties and turbomachinery losses are included. The analysis clarifies the role of the cooling losses and shows the importance of assessing performance in the context of the complete cycle. There is a strong case for representing the cooling losses in terms of irreversible entropy production as this provides a formalized framework, clarifies the modeling difficulties, and aids physical interpretation. Results are presented that show the effects on performance of varying cooling flowrates and cooling losses. A comparison between simple and reheat cycles highlights the ro^le of the thermal mixing loss. Detailed modeling of the heat transfer and cooling losses is discussed in Part II of this paper.

A finite-element analysis of the inelastic relaxation of thermal residual stress in continuous-fiber-reinforced composites

In an effort to develop a methodology for interpreting in situ high-temperature neutron diffraction measurements of thermal residual stresses in composites, a finite-element model was developed and the implications of various material and experimental parameters on the residual stress evolution were studied. The model composite comprised a continuous Al 2O 3 fiber, unidirectionally aligned in a NiAl matrix. The effects of temperature-dependent elastic, plastic or creep properties, fiber volume fraction and cooling/heating rates were explored on the relaxation mechanisms of the residual stress during an initial cooling and a subsequent heating. Thermal path-dependency in the stress evolution was investigated by comparing the cooling and re-heat cycles. The result shows that the effect of the time-dependent deformation (creep) becomes more significant as the fiber content increases and the cooling/heating rate decreases. Furthermore, the path-dependency in stress evolution becomes stronger (i.e. considering the actual thermal history in the model becomes more important) as the total inelastic relaxation increases during the cooling and/or the subsequent re-heating cycles due to; (i) the presence of creep in addition to plastic deformation, (ii) increased fiber volume fraction, and (iii) slower cooling/heating rates. It was also demonstrated that using an estimated stress-free temperature in elastic–plastic models can be problematic in predicting the high-temperature behavior due to; (i) the simple assumption of reduced Δ T, and (ii) the thermal path-dependency.

Thermodynamic analysis of reheat cycle steam power plants

In this study, a thermodynamic analysis of a Rankine cycle reheat steam power plant is conducted, in terms of the first law of thermodynamic analysis (i.e. energy analysis) and the second law analysis (i.e. exergy analysis), using a spreadsheet calculation technique. The energy and exergy efficiencies are studied as 120 cases for different system parameters such as boiler temperature, boiler pressure, mass fraction ratio and work output. The temperature and pressure values are selected in the range between 400 and 590°C, and 10 and 15 MPa, being consistent with the actual values. The calculated energy and exergy efficiencies are compared with the actual data and the literature work, and good agreement is found. The possibilities to further improve the plant efficiency and hence reduce the inefficiencies are identified and exploited. The results show how exergy analysis can help to make optimum design decisions in a logical manner. Copyright © 2001 John Wiley & Sons, Ltd.

A study of thermodynamic cycle and system configurations of hydrogen combustion turbines

A hydrogen combustion turbine is powered by steam generated from the internal combustion of hydrogen as a fuel mixed with stoichiometric oxygen. As it is possible to use a closed cycle system, benefits in cycle efficiency and a reduction of environmental pollution effects. Three different closed hydrogen combustion turbine cycles are evaluated. These are the Bottoming reheat cycle (A), the Topping extraction cycle (B) designed by Jericha and Ratzesberger, and the Rankine cycle (C). Calculations have been carried out to investigate the best cycle. This investigation consists of the comparison of thermodynamic efficiency, first stage turbine vane height of the high temperature, high pressure turbine, and maximum operating temperature of the heat exchangers. In these investigations, the component efficiencies are assumed to be the values which are expected to be achieved in the near future. As a result, the thermal efficiency of cycles (A) and (B) is the same value of 61.5%. That of cycle (C), which has the feed water heating with optimized pressure ratio of the intermediate turbine, is 58.8%. Cycle (B) has the largest first stage turbine vane height of the high temperature/high pressure turbine. The larger vane height has an advantage from the point of view of both the manufacturing of the complex cooling passage inside the vane and the turbine aerodynamic efficiency. The maximum operating temperature of the heat exchanger of cycles (A) and (B) is 870 °C, while that of cycle (C) is more than 1000 °C where some problems are anticipated in the feasibility of this heat exchanger. This investigation shows that the Topping extraction cycle (B) is considered to be the best cycle from the point of view of both the thermal efficiency and the feasibility of manufacturing.