Experimental And Simulated Investigation On The Combustion Characteristics Of Pulverized Coal Particles Under High Temperature And Low Oxygen Environments

Moderate and intense low oxygen dilution（MILD）oxy-fuel combustion can improve the uniformity of the temperature distribution and enhance radiation heat transfer in the furnace.And the high concentration of CO₂ in flue gas is beneficial for carbon dioxide capture and sequestration（CCS）.The technology has great advantage and potential in high combustion efficiency and ultra-low pollutants emission.MILD combustion is mainly achieved by high-velocity jet to entrain high temperature flue gas in industrial applications whose essence is to creat a high temperature and low oxygen concentration environment for fuel combustion.Therefore,the influence of the reaction temperature and oxygen concentration on ignition and combustion characteristics of pulverized coal particles under O₂/N₂ atmosphere and O₂/CO₂ atmosphere is studied to provide a theoretical basis for the application of pulverized MILD oxy-coal combustion technology.Experiments are performed in the diffusion-flamelet-based Hencken burner coal combustion system.The burner can produce hot coflow with different temperatures and oxygen concentrations by adjusting supply gas flow rate.Then temperatures and oxygen concentrations at different radial and axial positions are measured by using the type-B thermocouple and flue gas analyzer.The experimental results show that the well-designed burner could provide nearly one-dimensional stable hot coflow for studying the combustion characteristics of pulverized coal particles.Secondly,the radiation spectrums of burning coal particles in hot coflow are measured by the fiber spectrometer,and then the temperature and emissivity of burning particle can be deduced according to the Planck’s law and two-color ratios.The experimental results show that the increased temperature can significantly shorten the ignition distance of pulverized coal particle and produce a brighter flame as a result of higher burning particle temperature.The ignition distance extends and burning particle temperature reduces accompanied by weaker flame under lower oxygen concentration.When carbon dioxide is used as diluting gas instead of nitrogen,the ignition distance of coal particles is increased by 0.07⁰.49 cm.The temperature of the burning particles in O₂/N₂ atmosphere is50¹15 K higher than those in O₂/CO₂ atmosphere at the same condition,and the average temperature difference is 85 K under two kinds of atmospheres.Finally,the combustion characteristics of pulverized coal particles in high temperature and low oxygen concentration environment are simulated with computational fluid dynamic（CFD）method.The numerical results show that higher coflow temperature could lead to higher temperature rising rate of coal particles,earlier devolatilization and higher carbon monoxide volume fraction.And the temperature of the burning particle decreases with lower coflow oxygen concentration above the burner tip of 2 cm.