Evaporative Gas Turbine Cycles. a Thermodynamic Evaluation of Their
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Department of Heat and Power Engineering Evaporative gas turbine cycles- A thermodynamic evaluation of their potential by Per Rosin MASTER ismm#N if ms bocmmt is wmnts FWBH SALES PltlUfTEI Dokumentutgivere HJ/LTH Dokumentnamn Ookumentbeteckning Inst f6r Varme- och kraftteknik Rapport ISRN LUTMDN/TMVK-7010-SE Hendliggare Utgivnlngsdatum Arendebetecknlng Mars 1993 FOriettere Rosdn, Per M. Dokumenxtitel och undertitol Evaporative gas turbine cycles- A thermodynamic evaluation of their potetial Relerat (semmandrag) The report presents a systematic method of thermodynamically evaluating different gas turbine cycles, treating the working fluids as ideal gases (cp = cp (T)). All models used to simulate different components in the cycles are presented in the report in detail and then connected in a computer program fully developed by the author. The report focuses on the theme of evaporative gas turbine cycles, in which low level heat is used to evaporate water into the compressed air stream between the compressor and recuperator. This leads to efficiency levels close to a comparable combined cycle but without the steam bottoming cycle! A parametric analysis has been conducted with the aim of deciding the best configuration of an evaporative cycle both for an uncooled expander and for a cooled expander. The model proposed to simulate the cooled expander is a combination between two existing models. Relerat ekrivet av Rosdn Per M. Foreleg till ytterligare nyekelord evaporation, humidification, gas turbine, intercooler, aftercooler, recuperator, economiser, air-cooled expander, humid air turbine cycle, HAT, steam injection Klattitiketionnystem och -klau(er) Indextermer (enge kella) 12 10 Omflng Ovriga bibliogretiske uppgiftei 6 2 67 sidor SIS Sprlk engelska en lig t Sekretessuppgifter ISSN ISBN ; .• e ... ISSN0282-1990 ' ; 9, % X Ookumentet.ken.erhiUai.&i'fcn | Mott agar #r>* uppgifter Instf. virme-och Aaftteknik Box 118 221 00 LUND Pris DOKUMENTOATABLAO Blanket! LU 11:25 1976-07 DISCLAIMER Portions of this document may be illegible electronic image products. Images are produced from the best available original document. Department of Heat and Power Engineering Summary Summary This thesis presents a systematic method of thermodynamically evaluating different gas turbine cycles, treating the working fluids as ideal gases (c= c_(D). To decide the thermodynamic properties of all constituents of the working fluids polynomials, a description of the thermodynamic of each constituent is made. The polynomials have their origin in works done by NASA. The report focuses on the theme of evaporative gas turbine cycles, in which low level heat is used to evaporate water into the compressed air stream between the compressor and recuperator. Water is brought into contact with the compressed air stream in a counter flow act, in a humidification tower, causing water to be evaporated into the air. The outlet humidified air temperature of the tower will decrease drastically. At the same time the gas flow will increase due to the water addition. As the mass flow through the expander will be 20-30% larger than through the compressor, the specific work output from evaporative gas turbine cycles also rises greatly. The low temperature after the humidification tower makes it possible to reuse a large amount of low level heat at the expander outlet, by means of a recuperator. Because the gas temperature after the humidification tower can always be kept low, the recuperator can reuse a very large amount of low level heat from exhaust gas at the expander outlet, causing the thermal efficiency of the cycles to rise drastically. A parametric analysis has been conducted with the aim of deciding the best configuration of an evaporative gas turbine cycle both for an uncooled expander and an air-cooled expander. The analysis shows that efficiency levels of approximately 55% are reachable, using the best configurations ( Natural gas as fuel), for a cooled expander. More advanced evaporative gas turbine cycles reach their efficiency optima at pressure ratios around 15-20, then flattens out. The specific work output, however, rises with the pressure ratio increase in the whole pressure ratio area investigatedf 5<P2/Pi<35). The model proposed to simulate the cooled expander is a combination of two existing models. It tries to evaluate the gains due to lower temperature and higher specific heat of the cooling air, when extracting the cooling air after the humidification tower, but before the recuperator. i Table of contents LUND INSTITUTE OF TECHNOLOGY Table of contents Summary.........................................................................................................................................................i Table of contents ............................................................................................................................................ii Nomenclature .................................................................................................................................................iv 1. Introduction ................................................................................................................................................. 1 1.1. Background ................................................................................................................................ 1 1.2. Objectives ................................................................................................................................... 4 1.3. Method and resources............................................................................................................... 4 1.4. Limitations ................................................................................................................................ 5 1.5. Organisation of the report .............................................................................. .......................... 5 1.6. Acknowledgements .................................................................................................................. 5 2. The compressor system...............................................................................................................................6 2.1. The low pressure compressor .....................................................................................................7 2.2. The intercooler ......................................................... ................................................................ 8 2.3. The high pressure compressor .................................................................................................. 9 3. The humidification system......................................................................................................................... 11 3.1. The aftercooler ...........................................................................................................................11 3.2. The humidification tower..........................................................................................................12 3.3. The pump for circulating water................................................................................................ 14 4. The combustion chamber ............................................................................................................................16 5. The expander ...............................................................................................................................................19 5.1. An uncooled expander ...............................................................................................................20 5.2. A simple thermodynamic model of an air-cooled expander .....................................................21 5.3. An advanced thermodynamic model of an air-cooled expander .............................................. 24 6. Heat-exchangers in the heat recovery boiler ..............................................................................................26 6.1. The recuperator ......................................................................................................................... 26 62. The economiser ......................................................................................................................... 28 6.3. The heat exchanger for district heating .................................................................................... 29 7. Results of some cycle simulations ..............................................................................................................31 7.1. One Heat-Exchanger Water Systems....................................................................................... 32 7.1.1. Uncooled Expander ..................................................................................................32 7.1.2. Air-Cooled Expander ...............................................................................................33 12. Two Heat-Exchanger Water Systems....................................................................................... 34 7.2.1. Uncooled Expander ..................................................................................................35 1.22. Air-Cooled Expander ...............................................................................................36 ii Department of Heat and Power Engineering Table of contents 73. Three Heat-Exchanger Water Systems.....................................................................................