Development Of Compact Adjustable Pulverized Coal Distributor And Its Performance Research

In the pulverized coal preparation system of coal fired boiler,the balanced distribution of the primary air and powder in each branch pipe has an important influence on the security,economy and environmental protection.The common method to solve the unbalanced distribution is to install pulverized coal distributor between the coarse powder separator and the downstream branch pipes.The pulverized coal distributors at present have the disadvantages of poor performance,too large volume and complex structure.In view of this situation,a compact adjustable pulverized coal distributor,which can be installed directly at the outlet of the coarse powder separator,is designed in this paper,and its performance is researched with modeling test and numerical simulation.In the modeling test part,firstly,based on the past experience of design,debugging and operation of pulverized coal distributor,a design concept is put forward to adjust the powder distribution by changing the inlet area of the downstream branch pipe.Then,according to the design idea and the modeling theory,two distributor models with different powder adjusting mechanisms are designed and manufactured.Finally,the experimental research on the performance of the distributor models is carried out on the gas-solid two-phase flow test rig.The test contents include the resistance characteristics of powder adjusting baffle,leveling test of air and powder,influence of resistance of downstream branch pipes,system air speed and the folding door opening of coarse powder separator on the distribution characteristic.In the part of numerical simulation,we first briefly introduce the basic theoretical knowledge related to the simulation,including the basic control equations of fluid mechanics,the mathematical description methods and numerical models of turbulence and gas-solid two-phase flow.Then the gas-solid flow in the distributor is simulated with FLUENT software.The flow field characteristics of the velocity field of the air phase and the particle trajectory are obtained in a typical working condition.Through the analysis of the flow field,the optimization suggestion for the structure design of the distributor is put forward.Lastly,the distribution characteristics are compared in working conditions that the direction of the airflow rotation in the diffusion section is opposite.The reasons for the different distribution characteristics in the two working conditions are discussed,which provides guidance for the practical application of the distributor.The results of the study show that:(1)The developed distributor can achieve the design purpose that achieving the distribution of air and powder by adjusting the inlet area and resistance of the branch pipes.The regulation of air and powder is relatively independent;(2)The distribution performance of the two models is approximately the same.However,due to the reasons of structural design,the adjustment range of the powder adjusting baffle on the inlet area of model II is smaller.Model I is more suitable for practical application;(3)In the influence factors of distribution characteristics,the downstream branch resistance has the greatest influence on the air,and the influence of the folding door opening on the powder is the largest.In actual operation,the distributor should be readjusted when the downstream branch resistance or folding door opening is changed;(4)The flow field characteristics in the diffuser section are complex.There are large eddy currents at low speed.The distribution of coal particles is obviously uneven in the radial direction.It is suggested that the diffusion section of Venturi structure should be adopted to reduce the generation of large size eddy current,and strengthen the mixing of air and powder;(5)In the actual application,the swirling direction that flows through the cavity first and then into the branch pipe should be used,so that the adjustment effect of the powder adjusting baffle on the powder deviation will be more obvious.The compact and adjustable pulverized coal distributor in this paper meets the industry standard in terms of distribution performance,has the advantages of small volume,simple structure and independent adjustment of air and powder,and will achieve certain practical application value after subsequent optimization design.