| New advanced pulverized coal industrial boiler system has obvious advantages compared with traditional system.The related products inported are mature but expensive.Therefore,it is of great significance to develop a high-efficiency clean pulverized coal combustion technology for industrial boilers independently.A new high-efficiency low-nitrogen pulverized coal combustion technology suitable for industrial boilers is proposed by Harbin Institute of Technology.For the development of burners with this technology for a 29 MW boiler,a 1:6 gas/particle cold-model was built.The PDA system was applied to explore the influence of the angle of the secondary air blade in the burner and the different premixing section length of primary and inner secondary air on the gas-solid flow characteristics in the furnace.The combustion and the formation of nitrogen oxides in the furnace were numerically simulated.The effects of the inner secondary air blade angle on the combustion characteristics and nitrogen oxide formation characteristics were studied.The three-dimensional gas/particle velocity and particle phase volume flow distribution in the cold-model were obtained by PDA.The results show that an inner recirculation zone(IRZ)is formed in the center of the furnace.The end of the IRZ can be larger than 3.5d.On the x/d=0.2 cross-section,the particles are mainly concentrated in the secondary air outflow of the pre-combustion chamber.A large number of particles rushes out of the pre-combustion chamber from the vicinity of the sidewall surface.After the x/d=1.5 section,the particle flow rate near the wall surface was higher.The internal secondary air blade angle has little effect on the overall distribution of gas/particle flow when changing from 45° to 64°.The process of mixing the primary air and the secondary secondary air in the pre-combustion chamber and the external secondary air is delayed when there is a premixing section,and it varies little when the length of premixing section is increased from 50 mm to 100 mm.The software Fluent was used to simulate the pulverized coal combustion process.Algorithm model was confirmed with the data abtained from real boiler.The simulation results show that,under steady operation,an IRZ is formed in the center of the pre-combustion chamber and in the furnace.As the angle of the inner secondary air blade increases from 0° to 70°,The effect of flue gas reflux caused by the IRZ in the pre-combustion chamber is strengthened,which is conducive to the early ignition of coal powder.When the blade angle is 70°,the axial velocity near the wall reaches 35m/s,the scouring and wear of the coal powder on the wall of the pre-combustion chamber is aggravated.The high temperature region of the furnace greater than 1500 K is mainly concentrated in the outer region of the inner and outer secondary airflow,wherein the highest flue gas temperature is between 1700 K and 1800 K.The separated secondary air flow envelops the flame to form oxidizing atmosphere in the vicinity of the furnace sidewall,which is beneficial to avoid high temperature corrosion and slagging of the water tube.The high concentration region of nitrogen oxides in the furnace is concentrated in the outer region of the inner and outer secondary airflow.When the blade angle is 60°,the oxygen concentration at the outlet of the furnace and the content of combustibles in the fly ash are lower,the average flue gas temperature is higher,and the oxygen concentration in the vicinity of the water tube is higher,and the wear of pre-combustion chamber is lighter.Thus the angle of 60° is recommended for the inner secondary air blade. |
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