Experimental Study On Flame Propagation Characteristics Of Coal Clouds Under O₂/CO₂ And Elevated Pressure Condition

At present,the global environmental problems caused by a large amount of CO₂emissions are becoming increasingly serious,and the countries of the world are looking for a way of economic and environmental protection to reduce the emission of CO₂.As an important source of CO₂ emission,the upgrading demand of that technology is imminent.Therefore,the technology of oxy-fuel combustion is put forward in the world.Under the pressure condition,the mixture of oxygen and circulating flue gas is used as oxidant to form high concentration CO₂ and water with pulverized coal in combustion reaction.Thus achieving high efficiency and low cost capture of CO₂,at the same time,it can achieve higher power generation efficiency.The study of the influence of pulverized coal concentration,particle size,mixing ratio of O₂/CO₂ atmosphere and initial combustion pressure on the flame propagation characteristics of pulverized coal cloud is an important part of the study of pulverized coal pressurized oxy-fuel combustion,which is the key link of the theoretical basis of the pressurized oxy-fuel combustion power generation system.Based on a self modified 20 L spherical constant volume combustion bomb test rig,Shenhua bituminous coal was used as the research object.The influence of coal dust cloud concentration,particle size,mixing ratio of O₂/CO₂ atmosphere and initial combustion pressure on the flame propagation characteristics in the process of pulverized coal cloud flame propagation under atmospheric conditions was investigated.The results show that the influence of pulverized coal concentration and O₂/CO₂atmosphere mixing ratio on the maximum pressure,pressure rise rate and flame propagation velocity in the process of pulverized coal flame propagation is approximately the same.With the increase of pulverized coal concentration and O₂/CO₂atmosphere,the maximum pressure,pressure rise rate and flame propagation velocity in the process of pulverized coal flame propagation are increased.With the increase of pulverized coal particle size,the maximum pressure,pressure rise rate and flame propagation velocity decreased.In view of the basic problem of the pressurized oxy-fuel combustion power generation system,the influence of the change of environmental pressure and the mixture ratio of O₂/CO₂ atmosphere on the flame propagation characteristics of pulverized coal combustion is studied in this paper.The combustion characteristics of pulverized coal under pressurized O₂/CO₂ atmosphere were analyzed by using pressurized thermogravimetric analyzer,and a series of combustion parameters of pulverized coal under this condition were obtained.The results show that when the mixture ratio of O₂/CO₂ atmosphere is 7:3,with the increase of environmental pressure（1-10 atm）,the flame propagation velocity of pulverized coal clouds increases gradually,and the increase is weak after 8 atm.When the oxygen concentration is 30-50%,the ambient pressure reaches 4 atm,the coal clouds will no longer propagate.Combined with the analysis of the combustion parameters obtained by the pressurized thermogravimetric analyzer,it is found that the activation energy needed in the phase of volatilization and combustion of pulverized coal increases significantly with the increase of environmental pressure when the oxygen concentration is low,which makes the pulverized coal difficult to catch fire,resulting in no coal clouds flame propagation under this condition.Under the same external conditions,there is a certain degree of positive correlation between the flame propagation characteristics and combustion characteristics of pulverized coal...