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Thermodynamic properties of humid air and their application in advanced power generation cycles
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Water or steam is added into the working fluid (often air) in gas turbines to improve the performance of gas turbine cycles. A typical application is the humidified gas turbine that has the potential to give high efficiencies, high specific power output, low emissions and low specific investment. A heat recovery system is integrated in the cycle with a humidifier for moisturizing the high-pressure air from the compressor as a kernel. Based on today’s gas turbines, the operating temperature and pressure in the humidifier are up to about 523 K and 40 bar, respectively. The operating temperature of the heat exchanger after the humidifier is up to 1773 K. The technology of water or steam addition is also used in the process of compressed air energy storage (CAES), and the operating pressure is up to 150 bar.

Reliable thermodynamic properties of humid air are crucial for the process simulation and the traceable performance tests of turbomachinery and heat exchanger in the cycles. Several models have been proposed. However, the application range is limited to 400 K and 100 bar because of the limited experimental data for humid air. It is necessary to investigate the thermodynamic properties of humid air at elevated temperatures and pressures to fill in the knowledge gap.

In this thesis, a new model is proposed based on the modified Redlich-Kwong equation of state in which a new cross interaction parameter between molecular oxygen and water is obtained from the fitting of the experimental data of oxygen-water system. The liquid phase is assumed to follow Henry’s law to calculate the saturated composition.

The results of the new model are verified by the experimental data of nitrogen-water and oxygen-water systems from ambient temperature and pressure to 523 K and 200 bar, respectively. Properties of air-water system are predicted without any additional parameter and compared with the available experimental data to demonstrate the reliability of the new model for air-water system. The results of air-water system predicted using the new model are compared with those calculated using other real models. The comparison reveals that the new model has the same calculation accuracy as the best available model but can be used to a wider temperature and pressure range. The results of the new model are also compared with those of the ideal model and the ideal mixing model from ambient temperature and pressure to 1773 K and 200 bar to investigate the effect of the models on the thermodynamic properties of humid air.

To investigate the impact of thermodynamic properties on the simulation of systems and their components, different models (ideal model, ideal mixing model and two real models) are used to calculate the thermodynamic properties of humid air in the simulation of the compressor, humidification tower, and heat exchanger in a humidified gas turbine cycle. The simulation reveals that a careful selection of a thermodynamic property model is crucial for the cycle design. The simulation results provide a useful tool for predicting the performance of the system and designing the humidified cycle components and systems.

Place, publisher, year, edition, pages
Stockholm: KTH , 2006. , 75 p.
Series
Trita-KET, ISSN 1104-3466 ; 229
Keyword [en]
air-water mixture, humid air, properties, wet cycles, dry air, water, enthalpy, entropy, heat capacity, density, evaporative gas turbine, compressed air energy storage
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-4129ISBN: 91-7178-437-3 (print)OAI: oai:DiVA.org:kth-4129DiVA: diva2:10856
Public defence
2006-10-23, F3, KTH, Lindstedtsvägen 26, Stockholm, 13:30
Opponent
Supervisors
Note
QC 20100902Available from: 2006-10-06 Created: 2006-10-06 Last updated: 2010-09-02Bibliographically approved
List of papers
1. Saturated thermodynamic properties for the air-water system at elevated temperature and pressure
Open this publication in new window or tab >>Saturated thermodynamic properties for the air-water system at elevated temperature and pressure
2003 (English)In: Chemical Engineering Science, ISSN 0009-2509, Vol. 58, 5069-5077 p.Article in journal (Refereed) Published
Abstract [en]

A new thermodynamic model is proposed to calculate the thermodynamic properties for the air-water system in which the dry air was assumed to be a mixture of nitrogen and oxygen with the mole fractions of 0.7812 and 0.2188, respectively. For the vapor phase, fugacity coefficients were calculated with the modified Redlich-Kwong equation of state in which a new interaction parameter of oxygen and water was correlated from the experimental data of oxygen-water system. The dissolved gas followed Henry's law. Henry's constant of nitrogen was calculated with the Helgeson equation of state and that for oxygen was correlated from the experimental data of oxygen-water system. The proposed model was verified by comparing the calculated results with the available experimental data. It is shown that the proposed model is suitable for predicting saturated thermodynamic properties for the air-water system up to 300°C and 200 atm. Furthermore, the prediction results of the proposed model are better than those calculated with the model of Rabinovich and Beketov (Moist Gases, Thermodynamic Properties. Begell: House, 1995), and the application range is wider than that of the model of Hyland and Wexler (ASHRAE Trans. 89(2A) (1983a, b) 500-519, 520-535) which are among the best of today's models

Keyword
Air-water system, Gases, Humid air, Modelling, Phase equilibria, State equation
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-6205 (URN)10.1016/j.ces.2003.08.006 (DOI)000186677800011 ()
Note
QC 20100902Available from: 2006-10-06 Created: 2006-10-06 Last updated: 2010-12-06Bibliographically approved
2. Survey of experimental data and assessment of calculation methods of properties for the air–water mixture
Open this publication in new window or tab >>Survey of experimental data and assessment of calculation methods of properties for the air–water mixture
2003 (English)In: Applied Thermal Engineering, ISSN 1359-4311, Vol. 23, no 17, 2213-2228 p.Article in journal (Refereed) Published
Abstract [en]

Thermodynamic properties of the air-water mixture at elevated temperatures and pressures are of importance in the design and simulation of the advanced gas turbine systems with water addition. In this paper, comprehensive available experimental data and calculation methods for the air-water mixture were reviewed. It is found that the available experimental data are limited, and the determined temperature is within 75 °C. New experimental data are needed to supply in order to verify the model further. Three kinds of models (ideal model, ideal mixing model and real model) were used to calculate saturated vapor composition and enthalpy for the air-water mixture, and the calculated results of these models were compared with experimental data and each other. The comparison shows that for the calculation of saturated vapor composition, the reliable range of the ideal model and ideal mixing model is up to 10 bar. The real model is reliable over a wide temperature and pressure range, and the model proposed by Hyland and Wexler is the best one of today. However, the reliability of the Hyland and Wexler model approved by experimental data is only up to 75 °C and 50 bar, and it is necessary to propose a new predictive model based on the available experimental data to be used up to elevated temperatures and pressures. In the calculation of enthalpy, compared to the ideal model, the calculated results of the ideal mixing model are closer to those of real model.

Keyword
Air, Humid air, Method, Model, Properties, Water
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-6206 (URN)10.1016/S1359-4311(03)00191-1 (DOI)000185939600005 ()
Note
QC 20100902Available from: 2006-10-06 Created: 2006-10-06 Last updated: 2010-12-06Bibliographically approved
3. Saturated humidity, entropy and enthalpy for the nitrogenwater system at elevated temperature and pressure
Open this publication in new window or tab >>Saturated humidity, entropy and enthalpy for the nitrogenwater system at elevated temperature and pressure
2003 (English)In: International journal of thermophysics, ISSN 0195-928X, Vol. 24, no 6, 1681-1696 p.Article in journal (Refereed) Published
Abstract [en]

A model is used to calculate saturated thermophysical properties (humidity, entropy, and enthalpy) of a nitrogen-water mixture at elevated temperatures and pressures. In the model, a modified Redlich–Kwong equation of state is used to calculate fugacity coefficients for the vapor phase, and the liquid phase follows Henry's law. The model has been investigated by comparing the calculated results with the available experimental data. The comparison shows that the model can be used to calculate saturated thermodynamic properties for the nitrogen-water mixture reliably up to 523.15 K and 300 bar.

Keyword
enthalpy - entropy - humidity - mixtures, nitrogen, saturation, thermodynamics, vapor, liquid equilibrium, water
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-6207 (URN)10.1023/B:IJOT.0000004099.06582.98 (DOI)000186637200012 ()
Note
QC 20100902Available from: 2006-10-06 Created: 2006-10-06 Last updated: 2010-12-06Bibliographically approved
4. Thermodynamic property models for the simulation of advanced wet cycles
Open this publication in new window or tab >>Thermodynamic property models for the simulation of advanced wet cycles
2003 (English)In: American Society of Mechanical Engineers, International Gas Turbine Institute, Turbo Expo (Publication) IGTI, 2003, Vol. 3, 211-219 p.Conference paper, Published paper (Refereed)
Abstract [en]

Advanced gas turbine cycles with water or steam addition (i.e., wet cycles) have attracted much interest in recent years and some commercial systems are available. Because water is added into different points of a gas turbine depending on the methods of water addition, the working fluid of gas turbine has been changed to air-water (humid air) mixture at elevated pressure. Thus, the thermodynamic properties of working fluid are different as conventional gas turbines. Accurate calculation models for thermodynamic properties of air-water mixture are of importance for process simulation, and traceable performance test of turbomachinery and heat exchangers in the wet cycle systems. However, the impacts of thermodynamic properties on the simulation of systems and their components have been overlooked. This paper is to present our study and provide a comprehensive comparison of exiting thermodynamic models of air-water mixtures. Different models including ours have been used to calculate some components including compressor, humidification tower, heat exchanger etc. in wet cycles for investigating the impacts of thermodynamic properties on the system performance. It reveals that a careful selection of thermodynamic property model is crucial for the design of cycles. This paper will provide a useful tool for predicting the performance of the system and design of the wet cycle components and systems.

Keyword
Humid air; Humid air turbine, Simulation, Thermodynamic property model, Wet cycles
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-6208 (URN)10.1115/GT2003-38298 (DOI)0-7918-3686-X (ISBN)
Conference
2003 ASME Turbo Expo, Atlanta, GA, 16 June 2003 through 19 June 2003
Note
QC 20100902Available from: 2006-10-06 Created: 2006-10-06 Last updated: 2010-09-02Bibliographically approved
5. Phase equilibria for the oxygen-water system up to elevated temperatures and pressures
Open this publication in new window or tab >>Phase equilibria for the oxygen-water system up to elevated temperatures and pressures
2004 (English)In: Fluid Phase Equilibria, ISSN 0378-3812, E-ISSN 1879-0224, Vol. 222-223, 39-47 p.Article in journal (Refereed) Published
Abstract [en]

A new thermodynamic model was presented to calculate the phase equilibria for the oxygen-water system. The modified Redlich-Kwong equation of state with a new correlated cross-interaction parameter was used to calculate fugacity coefficients for the vapor phase. The dissolved oxygen followed Henry's law. A new expression was correlated from the experimental data to calculate Henry's constant of oxygen. The calculated results of equilibrium composition were compared with the available experimental data and those calculated by other models with different parameters. The comparison revealed that the new model is suitable for calculating both liquid and vapor compositions while the empirical method is only suitable for estimating the liquid composition. Furthermore, compared to the model proposed by Rebenovich and Beketov, the calculated results of the vapor composition with the new model are better.

Keyword
oxygen, water, equation of state, vapor-liquid equilibrium, Henry's constant
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-6209 (URN)10.1016/j.fluid.2004.06.029 (DOI)000223777100007 ()2-s2.0-4344672952 (Scopus ID)
Note
QC 20100902Available from: 2006-10-06 Created: 2006-10-06 Last updated: 2017-12-14Bibliographically approved
6. Thermodynamic properties for humid gases from 298 to 573 K and up to 200 bar
Open this publication in new window or tab >>Thermodynamic properties for humid gases from 298 to 573 K and up to 200 bar
2006 (English)In: Applied Thermal Engineering, ISSN 1359-4311, Vol. 26, no 2-3, 251-258 p.Article in journal (Refereed) Published
Abstract [en]

For the needs of process design, the model proposed in our previous papers was extended to calculate the thermodynamic properties of humidity, heat capacity, molar volume, partial pressure of water vapour, enthalpy and entropy for humid gases (nitrogen, oxygen, air or a nitrogen-oxygen mixture). The comparison with other models from 300 to 473 K and I to 100 bar shows that the results calculated with different models are consistent within 50 bar and 400 K; out of this range, there is some difference. Meanwhile, mole ratios of nitrogen to oxygen in the saturated humid air were calculated from 323 to 523 K and 50 to 250 bar. It is found that the mole ratio of nitrogen to oxygen keeps almost constant, and the effect of the slight changes in the ratio of nitrogen to oxygen on the humidity, enthalpy and entropy of humid air is small enough to be neglected. Moreover, the enthalpy of dry air was predicted, and the comparison with other models again proved the reasonable assumptions and prediction capability of the new model

Keyword
equation of state, property, humid gas, nitrogen, oxygen, air
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-6210 (URN)10.1016/j.applthermaleng.2005.05.005 (DOI)000233062300015 ()2-s2.0-27144513265 (Scopus ID)
Note
QC 20100902Available from: 2006-10-06 Created: 2006-10-06 Last updated: 2010-12-06Bibliographically approved

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