Research On The Uniformity Of Secondary Air Of Baima 600MW Supercritical CFB Boiler

Due to the adjustment in economy structure,the Chinese government vigorously advocates sustainable development of renewable energy and clean combustion technology.With high combustion efficiency,wide burnable suitability and low pollutant emissions,circulating fluidized bed(CFB)has become one of the best choices among the clean combustion technology.At present,circulating fluidized bed boiler is heading rapidly towards large-scale,high parameters and supercritical development.But with the increase in furnace size consequently,the uniformity combustion in the furnace cannot be guaranteed.Therefore,it is highly required to investigate the secondary air(SA)distribution characteristics,and its penetration and diffusion performance to obtain efficient combustion in the boiler.The research objective of this thesis is to investigate the uniformity of secondary air system and the diffusion characteristics in the world's largest single capacity boiler of Baima 600 MW supercritical CFB boiler.Both experimentation and simulation methods were used to achieve the objective.Through experimental measurement and numerical simulation,it was found that secondary air distribution of the existing system is uneven.This is possibly due to the deviation in the branch resistance of SA system,which causes the deviation of the outlet velocity in the condition that the inlet pressure is approximately equal,which leads to the poor uniformity of SA.The measurement results in cold-state furnace showed that adjustment of the air damper could improve the uniformity of the secondary air and it was easy to implement into the existing unit.However,this adjustment would also increase the flow resistance of the branch pipe.The numerical simulation analysis results show that the exit velocity deviation rate of the secondary air system could be less than 5% by changing the way of connecting and the corner angle to adjust the resistance of partial branch pipe,which is suitable for the new unit design.Furthermore,Two-Fluid model was used to simulate the diffusion characteristics of the secondary air.A new method was used to modify the secondary air considering the effect of temperature swift change.It was found that the penetration distance of secondary air and the lateral diffusion increased as the boiler load increased.In addition,this study also found that the uneven distribution of secondary air would not only reduce the secondary air diffusion uniformity,but also affect the gas-solid mixing uniformity.Therefore,it is of great significance to improve the uniformity of air distribution by optimizing the design of secondary air system,which is of great significance to improve the uniformity of gas-solid mixing and the uniformity of combustion.