Study On The Characteristics Of NO_x Emission And Coupling Control For Boiler With Slag-Tap Furnace Burning Pure High-Alakli Coal

There has rich reserves of high-alkali coal in China,which has a large heating value.But its strong pollution and slagging characteristics greatly limits the combustion and utilization of high-alkali coal.Cyclone boiler with slag-tap furnace is a new type of high-efficiency combustion equipment for high-alkali coal combustion designed to solve the problem of strong slagging burning pure xinjiang high-alkali coal.Cyclone boiler with slag-tap furnace has the characteristics of high combustion efficiency of cyclone burner and high slag captured rate of boiler with slag-tap furnace.It has been considered for burning pure high-alkali coal in order to achieve the purpose of clean and efficient utilization of high-alkali coal.Controlling nitrogen oxides?NO_x?emissions at the outlets of boiler is the key to the promotion and application of cyclone boilers with slag-tap furnace.Relevant research shows that the optimization of low-nitrogen combustion technology can effectively control the generation and emission of NO_x.In order to reveal the influence of different low-NO_x technologies on the NO_x emission of cyclone boilers with slag-tap furnace,the characteristics of NO_x emission and coupling control for boiler with slag-tap furnace burning pure high-alkali coal were conducted.The effects of primary air blade inclination,excess air coefficient,the over-fire air?OFA?rate and ammonia injection position on NO_x emission were numerically studied.The NO_x emission characteristics on coupling control of low-NO_x technology for air staging and low-NO_x technology for ammonia injection in high temperature area were obtained.An integrated low nitrogen combustion control scheme for boiler with slag-tap furnace burning pure high-alkali coal was proposed.Study on combustion characteristics for cyclone boiler with slag-tap furnace burning pure high-alkali coal.A three-dimensional 1:1 geometric model was established,and the distribution laws of the aerodynamic field,temperature field,component field and NO_x concentration field in the cyclone boiler with slag-tap furnace were mainly analyzed.The research results show that:the overall aerodynamic field in the whole boiler with slag-tap furnace is good,the flue gas is full,and the cyclone burners arranged in reverse rows can enhance combustion.The temperature distribution tends to be low in the middle and high on both sides in the cyclone burner.The temperature near the wall of the cyclone can reach 1700K?2100 K,which satisfies the requirements of liquid slag discharge.For the entire boiler,along the direction of flue gas flow,the temperature shows a trend of rising first,then decreasing,and then stabilizing.The average temperature of the furnace outlet section is 1358K,the mass fraction of O₂ gradually decreases,and the mass fraction of CO increases first,then decreases and remains stable at last,the mass fraction of CO₂ gradually increases,and the NO_x concentration increases first,then decreases,and tends to stabilize after the superheater.NO_x concentration at furnace outlet is about 704.14 mg/m³.Study on NO_x emission characteristics for cyclone boiler with slag-tap furnace burning pure high-alkali coal.Software CFD was used to numerically study the characteristics of pulverized coal combustion and NO_x emission in the cyclone boiler with slag-tap furnace burning pure high-alkali coal within a large range of parameters when the excess air coefficient changed from 1.1 to 1.25,the primary air blade inclination angle changed from 25°to 40°,the over-fire air rate changed from 0%to 15%,and the ammonia injection height Z=8m to Z=16 m.The research results show that:the blade inclination of the primary air has little effect on the combustion in the furnace.The larger the blade inclination,the higher the temperature in the furnace and the NO_x concentration at the outlet,but the variation range is small.When the blade inclination increases from 25°to 40°,the furnace outlet temperature increases by about 114 K and the NO_x concentration increases by about 91 mg/m³.With the increase of the excess air coefficient,the temperature of the flue gas at the furnace outlet first increases and then decreases,and the NO_x emissions continue to increase.The temperature under different OFA rate conditions can make the pulverized coal burn normally and ensure the fluidization of ash.The larger the OFA rate,the lower the average temperature in the furnace and the lower the NO_x concentration at the furnace outlet.The NO_x distribution trend in the cyclone boiler with slag-tap furnace under different ammonia injection conditions is the same.Along the direction of flue gas flow,the NO_x concentration first increases,then decreases,then increases,then decreases,and finally stabilizes.Within the range of working conditions studied,the higher the ammonia injection height,the higher the NO_x concentration at the furnace outlet,the lower the efficiency of NO_x reduction,the maximum efficiency of NO_x reduction is 42.11%,and the NO_x concentration at the furnace outlet is 407.63 mg/m³.Study on coupling control of NO_x emission characteristics for cyclone boiler with slag-tap furnace burning pure high-alkali coal.In order to further reveal the effect of multiple low-NO_x technology coupling control on NO_x emission,The NO_x emission characteristics on coupling control of low-NO_x technology for air staging and low-NO_x technology for ammonia injection in high temperature area were obtained were numerically studied.The results show that the characteristics of NO_x emission under the control of multiple low-NO_x combustion technologies are complex,and the emission of NO_x was controlled by the low-NO_x technology for air staging and the low-NO_x technology for ammonia injection in high temperature area together.When the over-fire air rate is large,the temperature in the boiler with slag-tap furnace is not high,and the NO_x concentration is also low.The temperature in the ammonia injection area is far from the optimal temperature?1550 K?for ammonia injection in high temperature area,and the efficiency of NO_x reduction is low.With the decrease of over-fire air rate,the temperature in the boiler with slag-tap furnace rises,the NO_x concentration increases,the temperature in the ammonia injection area is closed to the optimal temperature?1550 K?for ammonia injection in high temperature area,and the efficiency of NO_x reduction is higher.Therefore,the NO_x concentration at outlet was determined by the interaction between the NO_x generation in the boiler with slag-tap furnace and the efficiency of NO_x reduction for ammonia injection in high temperature area.Taking all factors into consideration,under the conditions of excess air coefficient of 1.2 and primary air blade inclination angle of 30°,air staging low-NO_x combustion technology and low-NO_x technology for ammonia injection in high temperature area are adopted at the same time.At the OFA rate of 5%,the ammonia injection port is in the vertical flue,arranged 2 m above the slag chamber,the combustion in the furnace is good,and the residence time of pulverized coal particles is long.At this time,the NO_x concentration at the furnace outlet was only 324.62 mg/m³,which was 53.9%lower than the NO_x concentration in the basic operating conditions.