Numerical Simulation And Improvement Of Concentrated-thin Swirl Pulverized Coal Burner

Because of the center circumfluence, which can make the high temperate gas flow back to facilitate ignition of pulverized coal and stable combustion,swirl coal burner has been widely used in engineering. There are complicated physical and chemical processes like multiphase flow, fuel decomposing, combustion etc. in the burner. With the rapid development of the technology of computer hard ware and software, the numerical simulation technology based on computational fluid dynamics develops quickly and increasingly becomes mature.It is proved truly by the high precise numerical forecasts of flow, heat transference,combustion, chemical reaction, multiphase flow in many engineering practice.In this dissertation,the Realizable k-εmodel of fluent software has been used to simulate how the wind distribution of wind channel, swirl strength and position of the secondary swirling air flow impact on circumfluence area of the swirl burner under cold condition, the distribution,size and shape of circumfluence area were analyzed. The dissertation summarized the rules to achieve the goal of guiding the improvement of burner structure. The research indicated that there was strong backflow in the swirl burner, the secondary swirling air flow mixes with the primary swirling air timely because of its entrainment and traction,the turbulent kinetic energy value was large at the mixed position. The mixed air flow spread to periphery because of its extended characteristic, the strong circumfluence appear in the neighborhood of the central axis,but it caused large velocity difference at crater also. Excessive difference may cause flame excursion,and even bifurcation. The primary air was increased to make the flame thrust force even in fact,then the coal can't combust stably.The simulation results are consistent with the known phenomena.Lagrangian stochastic trajectory model in the discrete particle model and non-premixed combustion model were used in the hot state simulation, the principle of dense thin separation and the motion characteristics of coal particles have been found out, the fields of flow, oxygen concentration and temperature have been analyzed. The research indicated that the way of separating was based on bevel collision and reflection, the dense phase was situated at inboard channel and the particles were distributed at the wall nearby when they entered furnace chamber. It was beneficial to increase the reflux temperature by enlarging the angle of the expansion cone,but it caused high temperature beside the spout wall at the same time.Methods were proposed for minishing the difference velocity according to the influencing factors and simulation verification have been done.The results showed that the velocity distribution became even, the volatile attained complete combustion, the residence time of Particles was increased, the burn-out rate of fixed carbon increased by 15%,and the temperature of flame increased by 130K.