Numerical Simulation Of Combustion And NO_x Emission In A Purely High Alkali Coal Fired Boiler

As the most abundant fossil energy,coal still dominates Chinese energy structure.The newly discovered Zhundong coalfield has rich reserves,which is easily to mine and has excellent combustion properties.However,due to its high alkali metals content,some problems occurred during the burning of active boiler,such as the severe situation of heating surface fouling and the operation instability of each units in the long run.At present,the best unit can only achieve 80%high-alkali coal blending proportion under full load,many mine-mouth power plant have forced to use the distant coal.Therefore,the most effective way is to design and develop the full-load furnace only burning Zhundong coal.As one of the main research contents of National Science and Technology Support Program,this paper conducts numerical simulation on the preliminary design of the 600MW supercritical hedge boiler firing Zhundong high-alkali coal purely,optimizing the operation parameters and the key design parameters of the furnace,providing a reference for the final design.First of all,this thesis summarizes characteristics of Zhundong coal and solutions of common problems in the active boiler burning process.The significance of design and development of full burning and the technical requirements for the structural parameters of the hedge boiler are put forward.Secondly,the combustion process of a demonstrated single burner boiler is numerically simulated,discussing the influence of different operating parameters,including temperature field,flame shape,the size and quality of reflux zone,the form of "wind pack fire",the gas component in deoxidization area,the devolatilization and char burnout process.In order to prevent coking in the near wall,based on the analysis,the recommended parameters are showed below.The primary air velocity is 15m/s while the axial velocity of external secondary air is 25m/s,tangential velocity 4.5m/s,the center air velocity 5m/s.Finally,the thesis simulated the combustion characteristics of the boiler designed under different key design parameters.Using ANS YS FLUENT realizes the parameterized design of the boiler structure.It is not necessary to re-divide the grid in the variable structure,but adjust these well-defined structural parameters directly.This thesis also simulates the combustion process and pollutant formation in the furnace under different operating mode,such as changing burnout height.the height of over-fire air and over-fire air rate.The simulation result shows that the burnout height of 27m is helpful to realize the goal of burning high alkali coal purely,and it is more suitable to install the over-fire air above the main combustion zone 8m.