Thermodynamic Performance Analysis And Operation Optimization Of Gas-steam Combined Cycle Power Plants Under Off-design Conditions

It is crucial to exploit renewable energy and increasing untilization efficiency of traditional fossil energy,which may be one of the most effective routes to solve the three significant issues of energy shortage,environment pollution and greenhouse effect caused by exploitation and utilization of fossil fuels.Gas turbines own many advantages,including rapid startup,high thermodynamic efficiency,and excellent load regulating capacity,therefore,gas turbines are used widely in power industry.The combined cycle gas turbines(CCGTs)often run at partial load conditions because it is frequently constrained to peak regulation in a power grid and it is sensitive to the environment conditions.With the decrease in the gas turbine load,the thermal efficiency of gas turbines also decline,therefore,it is essential to investigate the design/off-design performances and characteristics for gas-steam comnbined cycle power plants.This paper focus on the off-design characteristics of combined cycle power plants,the highly efficienct operation strategies and design plans are proposed.In addition,integrating new combined cycle system and optimizing the corresponding combined cycle thermaldynamic performance are also conducted in this paper.The detailed research contents as bfollow.(1)Modelling the PG9351 FA gas turbine combined cycle under design/off-design conditions.The relactively advanced F class gas turbine combined cycle unit are modeled,which is applied widely by thermal power plants in this paper.The stage-stacking method is adopted to model the compressor and the thermal balance equation is used to model the combustion chamber under off-design conditions,the Flügel equation is employed to describe the off-design characteristics of turbine.As for HRSG model,the off-design performances of HRSG is simulated based on the method proposed by Ganapathy.The off-design model of gas-steam combied cycle will be as a foundation for the further studies of combined cycle off-design characteristics.(2)The thermodynamic performances analysis of the influence of topping and bottoming cycle parameters on gas-steam combined cycle performances under design/off-design conditions.Based on the PG9351 FA gas tubine combined cycle units,other two combined cycle units are redesigned through increasing and decreasing compressor pressure ratio,thus,redividing the topping and bottoming cycle temperature utilization interval for given turbine initial temperature,and analyzing the design/off-design thermodynamic characteristics of main components of these three units,and the differences of thermodynamic characteristics of three units are compared,finally the gas-steam combined cycle power plants highly efficient operation strategies and design plans are proposed.(3)Research on concise semi-empirical,semi-theoretical integral thermodynamic performance calculation equations of triple pressure reheat bottoming cycle.The concise semi-empirical and semi-theoretical integral thermodynamic performance calculation equations of bottoming cycle are deduced and proposed based on comprehensive analysis of design/off-design heat transfer characteristics of HRSGs and energy conversion characteristics of steam turbines.Finally,these concise performance calculation equations are verified by real operation datas of gas-steam combined cycles and three simulation units.These equatiuons is simpler and more easily to be grasped than previous HRSG off-design models.(4)Research on cooling the compressor inlet air by novel LNG cold energy untilization method.The traditional LNG cold energy utilization systems exist relatively large heat transfer temperature diference betwwen the LNG and inlet air,therefore it will cause the relactively exergy destruction and the LNG cold energy can not be utilized sufficiently.The noval LNG cold energy utilikzation system is proposed in this paper,which consist of CO2 Rankine cycle and CO2 compression-refrigeration system,based on energy integrated cascade utilization principle.This novel system reduces immensely heat transfer temperature diference in heat exchanger and increases the output of cold energy.In addition,the sensitivity analysis and thermodynamic optimization are applied to the novel LNG cold energy utilization system.Finally the thermodynamic performances of combined cycle integrated the conventional and novel LNG cold energy utilization system under different environmental conditions are evaluated and compared.