Research On The Modeling Of The Whole Process Mechanism And The Key Issues In The Operation And Control Optimization For The Coal-Fired Power Plant

In the foreseeable future,thermal power plant,especially the coal-fired units,will remain the dominant in the electrical industry in China.However,due to the complex mechanism,the incomplete measurements,and the inherent features of the coal-fired unit such as time-varying,nonlinear,great time constant and lag time,multiple variables,much interference,etc.,there are a lot of pressing problems to be investigated in the process,operation,and control optimization.Under the ever increasing pressure on environment protection,the demand for the operation and control optimization becomes more and more urgent.In this study,the modeling of the whole process mechanism and the key issues in the operation and control optimization for the coal-fired power plant are investigated.The major innovative achievements are as follows:(1)The calculation formula of thermodynamic properties of the water and steam in Region 3 of the IAPWS-IF97 is improved.Combining the iteration and the state criterion law,the possible multi-solution problem of the direct iteration is avoided.(2)The online composition estimation method of the flue gas is proposed based on the online oxygen content measurement and the offline ultimate analysis of the coal.Then,a generic calculation method of the thermodynamic properties of flue gas based on the online composition estimation is presented with the validity range as 273.15 ~2000 K and 0~200 kPa.(3)The whole process mechanism model of the coal-fired unit is established.The lumped or quasi-distributed parameter mechanism models in the boiler-side include the pulverizing system,evaporation system,heat exchanger system,metal wall energy compensation,and heat loss.The mechanism models in the turbine-side include the steam turbine system,regenerative extraction system,and cold end system.(4)The online identification approach of the lower heating value of the coal entering the furnace is presented based on the boiler-side mechanism model.Then,the online identified lower heating value is validated using the original and rectified(got rid of the assay error)assay value in the time scales of 72 hours and one month,respectively.The results show the proposed approach has high accuracy.Based on the online identified lower heating value,an improved fuel master control strategy is proposed.Also,the online efficiency assessment for the boiler-side system is carried out.(5)An online determination and rolling update approach of coal consumption characteristic is presented.Then,the unit load dispatch in four different modes is researched based on the online coal consumption characteristic.The validation shows that the reasonable load dispatch can achieve significant coal saving benefit.(6)The white and black box models of the steam turbine system are developed.Based on their equivalence,an online identification approach of the exhaust steam wetness fraction of the low pressure cylinder is developed.On the basis of that,a generic calculation procedure of the cold end optimization problem is researched for both of the single and double back-pressure condensers.The simulation result proves that the cold end system has potential optimization space.Then,the online efficiency assessment for the turbine-side system is also performed.(7)Based on the simplified whole process mechanism model,a fourth-order nonlinear state space model of the boiler-turbine system with two inputs and two outputs is established,whose parameters are identified and validated with the history data from a real 300 MW coal-fired unit.Then,the coordinated control strategies based on feedback linearization,i.e.FL-PID and FL-SMC,are presented.Finally,the simulation results based on the three control strategies,i.e.PID,FL-PID,and FL-SMC,are compared.