Performance Simulation And Experimental Investigation Of A Humid Air Turbine Cycle

Energy is the basic driving force of development and economic growththroughout the world. With the development of world economy, the rapid increase inworld population and improve of people’s living standards, the world’s energyconsumption continues to grow, the importance of energy issues have becomeincreasingly prominent. Humidifying working fluid is an effective way to enhance theefficiency and power output of gas turbine. Humid air turbine (HAT) cycle is arepresentative of the new power cycle. The advantages of HAT cycle including highefficiency, high specific work, low unit investment costs, low combustion nitrogenoxide (NOx) emissions, low impact of power output by environmental conditions, andgood off-design performance. However, the current domestic and internationalresearch on the HAT technology is not sufficient. It seems to be particularly lack ofHAT cycle of experimental research and the test data is more scarce. Therefore, thisthesis will study HAT cycle performance using the method of combining theexperimental research and theoretical study. Improving understanding and awarenessof the HAT cycle performance is the base of applying HAT cycle gas turbinetechnology to the actual units and systems.The gas turbine performance simulation technology and SJGT gas turbineperformance simulation software development were first studied. The gas turbineperformance calculation method and software implementation were studied, includingthe study of thermal properties of variable specific heat, the memory sequentialiterative method and the variable partial differential coefficients deviationlinearization method. The structure and function of the SJGT software were analyzed,as well as five of the software modeling features: multi-input multi-output calculationmodule, common parts module library, dragging modeling, dynamic link librarytechnology and a friendly man-machine interface. Using SJGT software, the detailedcomponent level model of gas turbine was carried on, especially considering thecompressor air-extraction model and turbine cooling air-injection model. Finally, thecomponent modules were gathered and the module library was created, which laid thefoundation for the research of the performance of gas turbine.Then, a test investigation on Humid Air Turbine (HAT) cycle was conducted on asmall-size two-shaft gas turbine test rig. The test rig was made up of a centrifugalcompressor, a centripetal turbine, an individual direct flow flame tube, a free power turbine, a dynamometer and a saturator with structured packing. The goals of thisthesis were to study the gas turbine overall performance improvement in HAT cyclesuch as the turbine inlet temperature, power output and cycle efficiency. The effect ofthe humid air on pollutant emission was also examined.Two different test conditions were taken into account for the test investigation: inthe first case, the fuel flow rate was kept constant at48kg/h by the control system,while in the second case, the turbine inlet temperature was kept constant at650℃.The results show that the air humidification can immediately affect the performanceof HAT cycle. The saturator outlet humidity ratio is an important parameter in thestudy of HAT cycle performance. When the fuel flow rate keeps constant, increasinghumidity ratio can decrease the combustion temperature, reduce the discharge of NOxand increase the power output due to the increase of flow rate of working fluidthrough the turbine. When the turbine inlet temperature keeps constant, increasinghumidity ratio will substantially increase the power output in HAT cycle gas turbine.It provides an alternative to improve gas turbine performance without being restrictedby a higher TIT depending on the development of material technology.Retrofit design from two-shaft gas turbine to HAT cycle two-shaft gas turbinecontains changing calculation method of working medium thermal physical property,adding the saturator model and modifying the combustion model. Based on the gasturbine parts characteristics and test conditions, the off-design performance of HATcycle was calculated and its results were coincident with the test ones. The studiesshow that the humidity ratio of the HAT cycle has a huge impact on the specific workof gas turbine, increasing the humidity ratio will greatly improve the cycle specificwork and the thermal efficiency. Increasing the humidity ratio can also increase thecompressor surge margin, which improves the compressor operation safety.In order to further understand the potential of HAT cycle, improved design on theexisting HAT cycle test system was studied, by adding the regenerator, economizerand aftercooler to form a more complete HAT cycle two-shaft gas turbine system.Research shows that in theπ=3.0andπ=2.5working conditions, the regenerativeHAT cycle shows the best performance and the most energy conservation among theexisting HAT cycle, the regenerative HAT cycle and the regenerative HAT cycle withaftercooler. Increasing liquid-gas ratio of saturator can increase the humidity ratio andimprove the cycle specific work and the thermal efficiency. However, the liquid-gasratio will be restricted by the size of the test unit, pipe flow and the tank size. Theincrease of the heat regenerator efficiency contributes to the combustion process, makes the system more fuel saving, and reduces the exhaust temperature. Afterconsidering both the size of regenerator and the HAT cycle performance, theregenerator efficiency is set to0.6. The purpose of setting up the after-cooler is toreduce the saturator inlet air temperature. However, increasing after-cooler outlet airtemperature will increase the humidity ratio, enhance cycle specific work and raisethe thermal efficiency, also reduce fuel consumption rate and decrease exhaust gastemperature as well. Therefore, the after-cooler is not recommended to be added to theimproved design system.Finally, the off-design performance and dynamic performance of the three-shaftgas turbine in power generation system of were analyzed. The thesis placed emphasison study of the control strategy in the case of load rejection. At last, the research onapplying HAT technology to the three-shaft gas turbine was discussed. The resultsshow that the off-design performances of three-shaft gas turbine driving the constantspeed load and the propeller load were similar. Compare the compressor performancebetween the propeller load system and the constant speed load system, compressorsurge margin of the latter system is greater than the former one. In the powergeneration system, single-loop control system, feedforward feedback control systemand cascade system were assessed in order to control the engine in the case of loadrejection. According to the results, the cascade control system is most satisfactory dueto its fastest response and best stability and robustness. The simulation experimentalresults of the gas turbine starting progress have the important value of engineeringapplication. Comparison is made among the general cycle, the regenerative cycle withintercooler, the regenerative HAT cycle with intercooler and the regenerative HATcycle with intercooler and aftercooler. The research shows that the regenerative HATcycle with intercooler is most optimal cycle, which performs the highest power outputof65703kW, relatively high cycle efficiency of49.03%and the lowest specific fuelconsumption of0.172kg/kWh.