Advanced Gas Turbine Cycles with Water-Air Mixtures as Working Fluid

Abstract: Since the early 80's, the worldwide utilization of gasturbines for thermal power generation has increased rapidly.They have less pollution than any other major combustion energyconverters. One important development trend in gas turbinetechnology is new processes for better flue gas heat recovery(gaining better efficiency, power density and environmentalimpact), so called advanced cycles. The purpose of this workhas been to evaluate the performance and process system andsubsystems of advanced gas turbine cycles with air/watermixture as working medium. The focus of the thesis is on theevaporative gas turbine cycle. This cycle has extraordinaryheat recovery possibilities. An increased understanding of theinteraction of the different process components is sought, withan emphasis on modeling the high pressure humidificationcolumn. Efforts have been made to synthesize innovativestrategies for EvGT humidification. Theoretical andexperimental work concerning the water recovery andpurification issues are also presented.Some important results are that the flow of air through thehumidifier should be optimized. For the differentcasespresented in this thesis, the optimal fraction (with regard toefficiency) varies from about 12% to 40% of the compressorinlet air. Savings in heat exchanger area and reduced pressurework for booster fan are advantages of using only a part of thecompressor air in the humidifier. For obtaining best efficiencyof the evaporative cycle, the heat flows above the boilingpoint should preferably be taken care of by conventionalboilers for steam injection or by a separate humidifier sectionworking only slightly below boiling temperature. This isparticularly important in gas turbines without intercooling orwithout recuperation due to high temperatures in exit streams.The unique nature of the humidifier is its ability to evaporatewater below the boiling point, by the use of air dilution.However, the best temperature performance (lowest temperatureof outlet water from humidifier) is reached if the thermalloading on the humidifier is not excessive.The need for large quantities of demineralized water haspreviously been identified as a possible drawback for the EvGTcycle. In favor of the EvGT-technology, the first water testingexperiments on a pilot EvGT-plant, presented in this work,contradict this notion. It is theoretically and experimentallyshown that an EvGT-plant can be run with no external water feedat all, by means off lue gas condensation and condensaterecovery. After internal condensate treatment, the recycledcondensate was of equal quality or better than the deionizedfresh feed used for initial system fill-up.