Research On Equalization Technology Of Primary Air Velocity And Coal Powder Concentration For Power Plant Boiler

Nowadays,the distribution uniformity of primary air velocity and coal powder concentration in primary air feeding pipes of power plant boilers can't meet the requirement of accurate combustion control of boilers.In the dissertation,the primary air feeding pipes of actual power station boiler were taken as research object and the numerical simulation and experiment methods were applied to study the distribution characteristics and adjusting methods of coal and air in parallel pipes.Two techniques to improve the distribution uniformity of primary air velocity and coal powder concentration were mainly discussed.1)Online equalization technology of coal and air based on the regulating valve.The continuously adjustable regulating valve of grille type was designed,and the vertical single-pipe simulation model was established to study the effects of grille size(while throttle ratio is certain),inlet velocity,and coal powder concentration on the flow characteristics and resistance characteristics of the regulating valve.The simulation results showed that the regulating valve with the largest grille size had the least resistance coefficient and the best inherent flow characteristics(hyperbolic)while other conditions were similar.Besides,the fitting relation between the flow resistance coefficient and coal powder concentration and the valve opening was obtained.Moreover,the regulating valve with largest grille size was applied to the parallel branch pipes to balance coal and air,and then coal and air online balancing strategy based on the regulating valve was proposed.Afterwards,coal and air online equalization system was designed and project implementation and verification were conducted.The experimental results indicated that air and coal distribution deviation of parallel pipes were respectively decreased by 2.40%and 7.07%after the equalization system was applied to the power station compared with before.2)Equalization technology of coal and air based on jet methodThe feasibility of jet method to improve the performance of diffusion distributor or forked tube was studied by numerical simulation.The simulation results showed that the jet flow can regulate the coal and air flow of outlet of the distributor separately.In theory,the distribution deviation of the inherent coal concentration of the distributor can be reduced by more than half,and at this time the pressure drop increment of the distributor was below 200Pa.Both of the above two techniques can reduce the distribution deviation of coal and air in primary air feeding pipes.In comparison,the first technique can only regulate air and coal flow of parallel branch pipes in the same direction and is suitable for a lower maximum distribution deviation of coal powder concentration less than 16%in the outlet of branch pipes,while the advantage of the second technique lies in the fact that the maximum distribution deviation of coal powder concentration between 15%and 25%in the outlet of branch pipes can be reduced significantly.