Study Of Humidification And Condensation Dynamics In An .
Study of humidification and condensation dynamics inan evaporative gas turbine cycleM.Sc. ThesisbyKajsa JohnsonLund, 020420Advisors:Gustaf Olsson, Department of Electrical Engineering and AutomationMartin Råberg, Sycon Energikonsult ABJörgen Svensson, Sycon Energikonsult AB
AcknowledgementsThis work has been carried out from November 2001 to April 2002 at SyconEnergikonsult AB in Malmö, Sweden.I would like to thank the personnel at Sycon Energikonsult AB for showing interest in mywork during the last six months. Especially, thanks go to my advisors Martin Råberg andJörgen Svensson for their support with the simulation tool Dymola and Martin’sthermodynamic skills. Fredrik Olsson at Sycon Energikonsult AB has supported me withbasic reading material.Sydkraft AB, who has made the thesis work possible through financing, deserves a bigthank.Torbjörn Lindquist and Marcus Thern at the Department of Heat and Power Engineeringat LTH also deserve a special thank for showing me the pilot plant and supporting mewith measurement values.I also own Sebastian Courel big thanks for his work with reviewing the report.At last, my most grateful thanks go to my supervisor at the Department of ElectricalEngineering and Automation, Professor Gustaf Olsson, who has really supported me withhis great knowledge and experience during the thesis work.Kajsa JohnsonLund, April 2002
AbstractThe electricity demand is forecasted to increase during the next decades, especially in thedeveloping countries. Renewable power production technologies are promising, thoughthey are not expected to be able to satisfy the complete future need. Therefore theEvaporative Gas Turbine, EvGT, is assumed to be a good complement to renewablepower sources. There are also ongoing experiments about using renewable fuels in anEvGT.The EvGT project is a co-operation between universities, gas turbine manufacturers,utility power companies, and research organisations in Sweden. It started in 1989 andsince then an evaporative gas turbine pilot plant has been built at LTH to demonstrate thetechnology. The project has finished three phases and is now in phase four. Read moreabout the project in (Rosén, 2000).Sydkraft AB is one of the members of the EvGT project, to whom Sycon EnergikonsultAB has performed technical work. The contribution of Sycon Energikonsult AB hasincluded modeling of the EvGT model. The gas cycle in the EvGT process has beenmodeled and the flue gas condenser is the missing component to close the water cycle.The objective of this thesis has been to study the evaporative and condensation process ofthe EvGT cycle by means of modelling and simulating two components, thehumidification tower and the flue gas condenser.One conclusion is that the same model can be used as a humidification tower and as acondenser. The difference that defines humidification respectively condensation is thetemperature of the gas and water, and the pressure. These temperatures are derived frommeasurement values from the pilot plant at LTH.The most critical part when modelling was found to be the evaporation or condensation,i.e. when water changes phase between liquid and gas. To further improve the model thisis where the effort should be made.
Table of contentsTERMINOLOGY. 61 INTRODUCTION . 71.1 BACKGROUND . 7What is EvGT?. 7The EvGT project. 7Modelling the EvGT. 81.2 OBJECTIVE. 81.3 ORGANISATION OF THE REPORT . 92 OUTLINE OF THE WORK. 102.1 A NOTE ON VERIFICATION AND VALIDATION . 113 EVAPORATIVE GAS TURBINE . 133.1 APPLICATION AREAS . 133.2 THE PILOT PLANT. 133.3 THE EVGT CYCLE . 14Turbo set. 15Recuperator . 15Economiser . 16Humidification Tower. 16Flue gas condenser. 164 BASIC STRUCTURE OF THE MODELS . 174.1 DYMOLA. 17ENERGY . 17Graphic interface. 174.2 BASIC EQUATIONS . 195 CHARACTERIZING THE HUMIDIFICATION TOWER. 225.1 OVERALL DESCRIPTION . 225.2 HEAT AND MASS TRANSFER . 23Water and Gas flow (mw, mg). 24Structured package heat transfer (Qsp). 24Water Film heat and mass transfer (mevap, Qw, Qg) . 245.3 THE HUMIDIFICATION TOWER MODEL . 26The evaporation segment model . 285.4 STATIC VALIDATION OF THE HUMIDIFICATION TOWER. 291.Create a test bench . 292.Insert measurement values from the pilot plant at LTH . 303.Simulate until static values are reached . 304.Validate . 305.5 ANALYSIS/EVALUATION. 316 FLUE GAS CONDENSER . 336.1 CONDENSATION . 336.2 WET OR DRY CONDENSER? . 346.3 CHARACTERISTICS OF THE FLUE GAS CONDENSER . 34Packing . 35Mantle wall . 366.4 IDEAS ABOUT THE CONDENSER MODEL . 366.5 MODELLING THE CONDENSER. 37Created sub-models . 39
Evaporation segment . 41New mass transfer calculation. 416.6 VERIFICATION OF THE CONDENSER. 43Dynamic validation of the condenser model. 446.7 ANALYSIS/EVALUATION. 457 DISCUSSION AND CONCLUSION . 468 FURTHER WORK. 47NOMENCLATURE . 48APPENDIX A. 49GAS . 49EVAPORATION . 49FLOW. 49APPENDIX B. 51APPENDIX C. 53APPENDIX D. 56APPENDIX E. 59REFERENCES . 60
ionDiffusionDymolaENERGYEvaporationEvGTWater FilmHumidificationLTHMantle wallPackageValidationVerificationWater that before the condensation process was water vapor.The process where water vapour is transformed into water.Heat transfer between two substances, for example water andcopper.Heat transfer between a solid surface and a gas or liquid that is inmotion. Convection involves the combined effects of conductionand fluid motion.The process where a soluble substance is solved and mixed withanother one.The simulation tool that has been used during the thesis work.Sycon’s library of thermodynamic models.The process where water is transformed into water vapor.Evaporative Gas Turbine.Representation of the interface between gas and water.The process when gas is humidified with water vapour.Lunds Tekniska Högskola.The outermost wall of a real component in the EvGT cycle.Material used in the condenser and humidification tower toincrease the area between gas and water.Comparing of the simulation results with real measurement valuesfrom the pilot plant.Evaluation of the simulation results to see if the model seems tobehave as desired.
1 IntroductionThis chapter describes the background of the thesis. It explains the need of gas turbines,the EvGT project and the part Sycon Energikonsult AB plays in the project. Finally, thepurpose and erection of this thesis will be handled.1.1 BackgroundWhat is EvGT?The Evaporative Gas Turbine (EvGT) is an example of a wet gas turbine cycle, alsocalled water vapour addition cycle. This means that compressed air mixed with watervapour is used in the gas turbine. Sometimes the evaporative gas turbine is called HAT,Humid Air Turbine. This is a patented variant of EvGT. Another example of thetechnology with humid air is STIG, STeam Injected Gas turbine. More about wet cyclescan be read in (Ågren, 2000).The electricity demand is forecasted to increase during the next decades, especially in thedeveloping countries. Renewable power production technologies are promising, thoughthey are not expected to be able to satisfy the complete future need. Therefore theEvaporative Gas Turbine, EvGT, is assumed to be a good complement to renewablepower sources. There are also ongoing experiments about using renewable fuels in anEvGT.For long-term electricity and heat production the aspects of pollution and efficiency areimportant. Today’s electricity producing gas turbines have a satisfying efficiency but thepollution is too high. The evaporative gas turbine has shown to be a good alternative tokeep the NOx discharge low. The characteristic of the cycle is that water is evaporated ata low temperature to increase the humidity of the combustion air. The result of thisevaporation is higher efficiency and lower NOx discharge, which is highly desired. Toclose the water cycle and reuse the added water a flue gas condenser is used.The EvGT projectThe EvGT project is a co-operation between universities, gas turbine manufacturers,utility power companies, and research organisations in Sweden. It started in 1989 andsince then an evaporative gas turbine pilot plant has been built at LTH to demonstrate thetechnology. The project has finished three phases and is now in phase four. Read moreabout the project in (Rosén, 2000).The overall purpose of the project is to evaluate the evaporative gas turbine technology.The erection of the pilot plant was used to determine efficiency, pollutants, and dynamicbehaviour. It also helped identify the potential of the cycle.7
Modelling the EvGTModelling is a way to reduce problems with simplifying complex relationships. Themodelling is especially useful for verifying requirements and process optimization.Modelling also reduces the risk of problems when the component is put into operation.This of course saves a lot of money and time.Sydkraft AB is one of the members of the EvGT project, to whom Sycon EnergikonsultAB has performed technical work. The contribution of Sycon Energikonsult AB hasincluded modelling of the EvGT model. The gas cycle in the EvGT process has beenmodelled and the flue gas condenser is the missing component to close the water cycle.The flue gas condenser resembles a humidification tower, which is another component inthe EvGT cycle. This tower has been modelled but a validation of it, i.e. to make themodel fit the measurements from the pilot plant at LTH, is needed. This is done by meansof measurements from the pilot plant. After the validation the flue gas condenser can bemodelled on the basis of the humidification tower, after which it can be verified.Verification means to check that the model works as desired. Since real measurementvalues are missing a validation of the flue gas condenser can not be done.The modelling tool used at Sycon Energikonsult AB is Dymola1. The modelling languageof Dymola is Modelica. This is an object oriented language, which makes exchange andreuse of different models possible. Dymola includes a standard library consisting of e.g.mathematical functions, mechanical components, and electrical components. SyconEnergikonsult has also built its own library, ENERGY. The library contains usefulcomponents for thermodynamic modelling like gas volumes, flows, and heat exchangers.In Chapter 4 more information about Dymola and ENERGY can be found.1.2 ObjectiveThe objective of this thesis is to validate the already existing humidification tower modelwith measurement values from the pilot plant at LTH. The validation mainly includesstatic values.The next goal of the thesis is to build a model of the flue gas condenser on the basis ofthe humidification tower. A decision has to be made whether the condenser should be awet or dry one, of which the differences are explained later on in the thesis. The flue gascondenser is built with Sycon’s ENERGY library to make it possible to connect with thealready existing models. The model needs to be verified for reliability with both staticand dynamic values.1More about Dymola at www.dynasim.se8
1.3 Organisation of the reportIn Chapter 2 there is a short description of the work done during the time at SyconEnergikonsult AB. It will handle what was done, why, and in what order.Chapter 3 describes the basics about the evaporative gas turbine cycle.Chapter 4 explains the facts necessary to understand the two following chapters. Thebasic equations used when modelling are explained in Chapter 4.1 while the basics aboutthe modelling tool Dymola are explained in Chapter 4.2.The following chapter, Chapter 5, will handle the humidification tower; first a descriptionof how it works in reality, and later an explanation of the model of the tower. After that inChapter 5.3 the validation work is treated. Similar work as for the humidification tower isdone for the flue gas condenser in Chapter 6.Chapter 7 summarises what can be further done on the models, problems that haveoccurred during the work, and an analysis of how well the created model is working wastreated.The last Chapter 8 suggests further work that can be done on this thesis.In addition, to achieve a more fluent text, a nomenclature page is added in end of thethesis. Here all units of the mentioned variables and properties in the text are gathered.The terminology page in the beginning of the thesis contains a short explanation of themost important and frequent used words and abbreviations in the text.9
2 Outli
Evaporative Gas Turbine, EvGT, is assumed to be a good complement to renewable power sources. There are also ongoing experiments about using renewable fuels in an EvGT. The EvGT project is a co-operation between universities, gas turbine manufacturers, utility power companies, and
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