Study On Key Technologies And Scheme Of 660MW Ultra Supercritical Circulating Fluidized Bed Boiler

Ultra supercritical circulating fluidized bed boiler combined the advantages of higher parameter power generation and clean combustion technology,which is an important direction of the development of circulating fluidized bed(CFB)combustion technology.To realize the effective combination of circulating fluidized bed combustion technology and ultra supercritical steam parameter power generation technology,additionally to meet the latest national environmental emission requirements and form a safe and feasible boiler scheme is the key to whether ultra supercritical circulating fluidized bed technology can become a product.Based on the national key research and development program"660MW ultra supercritical circulating fluidized bed boiler development"(2016yff0600204),from the perspective of engineering practice,the present work focuses on the key technical bottlenecks,puts forward the solution path of technical problems,determines and completes the 660MW ultra supercritical circulating fluidized bed boiler scheme,and implements it in the Guizhou Weihe national demonstration project.The main work of this paper is as follows:1(1)On the basis of summarizing the development status and direction of circulating fluidized bed combustion technology,especially the key technologies and bottlenecks in the development and R&D process of large-scale circulating fluidized bed boiler with supercritical and ultra supercritical parameters,it is proposed that the heating surface wall temperature deviation and the further inhibition of NO_x generation on the combustion side are the key problems during the R&D of 660MW ultra supercritical circulating fluidized bed boiler.Aiming at solving these two problems and forming 660MW ultra supercritical circulating fluidized bed boiler scheme on this basis is the key research content of this paper.(2)The wall temperature deviation of the heating surface of ultra supercritical circulating fluidized bed boiler is the technical bottleneck that restricts whether the circulating fluidized bed combustion technology can realize the ultra supercritical steam parameters.In the present work,the wall temperature deviation of high temperature reheater in external heat exchanger of 600MW supercritical circulating fluidized bed boiler is tested.Through operation optimization,the wall temperature deviation can be reduced within a certain range.Additionally,in order to meet the safe operation requirements of ultra supercritical steam parameters,the present work further fits the heat load distribution of the external heat exchanger of ultra supercritical circulating fluidized bed boiler which with the same size and operation condition according to the measured data.And the wall temperature deviation problem has been sovled by throttling the working medium side.(3)In view of the wall temperature deviation of the heating surface of ultra supercritical circulating fluidized bed boiler,in order to provide further operation adjustment means in the project,the cold test rig is built and the experimental research is carried out,and the suggestions of reducing the deviation from the ash side are proposed.Combined with the solutions and suggestions from the working media side and ash side,the paper puts forward the design principles of external heat exchanger of 660MW ultra supercritical circulating fluidized bed boiler,which lays the foundation for the implementation of boiler scheme.(4)In order to meet the increasingly stringent air pollutant emission requirements of new coal-fired units in China,the paper briefly reviews the NO_x generation mechanism and influencing factors,and puts forward the idea of"delayed introduced secondary air"to reduce the original NO_x emission by raising the secondary air layout position.The feasibility of this idea is verified by the experimental study of different fuels on 3MW hot test rig,and the emission differences of different fuels are obtained.In theory,based on the overall mathematical model(COM CFD CFB model)and two-dimensional equivalent fast calculation method of ultra supercritical circulating fluidized bed boiler,three-dimensional numerical calculation of actual size and two-dimensional equivalent fast calculation numerical simulation are carried out,and suggestions on secondary air layout of 660MW ultra supercritical circulating fluidized bed boiler are put forward.(5)The operation experience of 600MW supercritical circulating fluidized bed boiler is a good reference for 660MW supercritical circulating fluidized bed boiler.This paper summarizes the problems of air cap fracture,high air leakage rate of air preheater and uniformity optimization of secondary air branch pipe in the commissioning stage,through discussing and analyzing,improvements and effects from the engineering and theoretical are suggested for similar details in the research and development of 660MW supercritical circulating fluidized bed boiler.(6)Based on the above research results and boiler design conditions,this paper discusses the key parameters to be determined during the implementation of 660MW ultra supercritical circulating fluidized bed boiler project.Through the comparison of thermal characteristics and heating surface layout,the boiler scheme and main size are determined.Through the research on hydrodynamic characteristics,the boiler hydrodynamic safety is realized;through the research on the wall temperature characteristics of the last stage heating surface in the worst environment,the wall temperature safety of the high regeneration and high superheater heating surface is realized,and finally a feasible 660MW ultra supercritical circulating fluidized bed boiler scheme is put forward.At present,in Guizhou Weihe national demonstration project,the 660MW ultra supercritical circulating fluidized bed boiler referenced this scheme is under design.It is planned to be installed and debugged in 2022,and will be put into operation in the same year.