Simulating Research On Gas Turbine And Its Combined Cycle In Part Load

In the 21 century,the development of power station required of high efficiency,good economics,low pollution,that's to say,to combine the energy,economic,environment together. This requirement broke down the long time governing status of steam turbine in the world power generation,and gas turbine and its combined cycle will replace it,because of their advantage of low cost rate,short building time,high efficiency,low pollution.So it is very necessary to predict the characteristics of the combined cycle system and optimize its operating strategy by developing a simulation system.The most troublesome part in developing component based gas turbine simulation system is the performance characteristics estimation of the compressors at low rotational speed, due to the strong dependency of its performance on rotational speed and variable geometry. Thus the accuracy of compressor characteristic calculation is the critical factor in gas turbine system simulation.The high pressure and high accuracy calculation requirement of modern heavy duty gas turbine and its combined cycle system has resulted in acid challenge on modeling and simulation based on components characteristic,which request improve the compressor characteristic extrapolate computational method.Consequently,developing a wide margin varying duty gas turbine and its combined cycle simulation system then to study its operation stratagem become an significance task.The aim of this study is to research compressor characteristic extrapolate estimation method based on limited compressor high rotational speed lines to quantitative analysis compressor characteristic at wide margin varying duty,then develop a wide margin varying duty gas turbine and its combined cycle dynamic simulation system.Furthermore,study the characteristic at various work condition and to determine its corresponding operation stratagem.Main contents and conclusions of the research are described in the following:1.Introduce feature-stage method to compressor part load characteristicThe inlet and outlet flow coefficient of compressor are mismatch in part load,and the gas flow angle deviate from designed flow angle,due to the high pressure ratio of compressor. Thus,the analogy theory is not appropriate to extrapolate the characteristic map for compressors directly.Based on the discussion of the compressibility of work medium effect on compressor efficiency,the feature-stage is introduced.With the idea of dividing the compression process into infinite number of infinitesimal processes,the feature-stage characteristics are determined based on analogy theory and system identification method,and the total characteristic of compressor can be calculated stage by stage based on the characteristic of feature-stage.The feature-stage present theoretical dividing of the compressor compression process,but unnecessary to consider the pressure ratio distribution and stage characteristic relation.The physical meaning of feature-stage is it presents the average stage feature of total compressor.The similarity condition can be approach while the number of feature-stage is big enough.2.Regress compressor feature-stage characteristic based SVMBased SVM(SVM)regression method,the global feature-stage characteristic line is regressed from multiple feature-stage characteristic lines identified from different compressor rotational speed lines.Instead of statistic the characteristics of any other compressors, this method can reflect the own characteristics of the original compressor accurately.Since the stage characteristics are estimated from multi-curves of the compressor characteristic maps,this method can make a good use of available information. Furthermore,SVM method decreases the error of compressor reconstruction characteristic map.3.Extrapolate part load characteristic of feature-stage,and study variable geometry characteristic calculation methodBased on the feature-stage characteristic at referenced rotational speed,the overall performance characteristic map of compressor is reconstructed by analogy theory.Beside the part load performance characteristic estimation problem,the variable stationary vane performance characteristic estimation is a critical problem in gas turbine performance estimation.Based on the interdependence between the blade work and the blade flow angle,the relationship of the feature-stage pressure ratio and efficiency characteristic between fix and variable geometry are derivate.4.Develop gas turbine simulation model and analysis its part load operation strategy Based on component characteristic,a single shaft gas turbine simulation system with VSV compressor is developed,and analysis its performance during start up,loading, decreasing load and shutdown.Simulation test show that,the gas temperature and exhaust temperature are both increased after adjust VSVs,thus the increasing waste heat losses counteract the high T₃^* effect on efficiency.But at part load,the gas flow rate decrease after closing VSVs,which reduce idle fuel.During start up,there are a peak of T₄^* and T₃^*.So,the increment of fuel corresponding rotational speed incensement must be restricted during ignition and trip to control starting speed and to avoid over temperature.5.Develop gas turbine combined cycle simulation system and analysis its part load operation strategyA gas turbine combined cycle with natural cycle HRSG simulation system is developed and dynamical analysis.Simulation test show that,operating condition drastic variation of gas turbine and steam turbine lead to false drum water level,which should be paid attention to in exercise management,analysis of start up,loading,decreasing load and shutdown performance show that,constant T₄ adjust scheme is beneficial than constant T₃^* adjust scheme to control compressor VSVs angle while decreasing load. Which can attain high combined cycle efficiencyη_CC^N as constant T₃ adjust scheme and avoid turbine over temperature during decreasing load,then avoid HRSG over temperature. The HRSG thermal inertia is the most important influencing factor on starting speed,due to most of the startup process is spend on heating HRSG.Consequently,it should adopt warm start to decrease start period as far as possible.