Investigation Of NO_x Formation During Raw Coal Char And Demineralized Coal Char Combustion Process Under High Temperature Conditions In O₂/H₂O Atmosphere

The efficient and rational utilization of coal based fuel will effectively improve the increasingly serious environmental problems.Based on the technology of the third generation of oxygen enriched combustion,we put forward a feasible solution: coal based solid fuel oxygen and water vapor combustion near zero emission power generation system(OCCSS),at the same time this program involved an important basic theory needs further exploration.In this paper,the combustion of raw coal-char and demineralized coal-char was carried out under the condition of high temperature,high oxygen and high water vapor on a fixed bed,studied on the removal of ash and temperature,oxygen concentration and water vapor concentration on the effect of gaseous product release in combustion process;analyzed char surface pore structure;observed char surface structure of different carbon burning rate application of Raman spectroscopy,the reaction and degree of graphitization were analyzed;also studied related gaseous product release regularity and char surface structure change.Increasing the oxygen concentration and the reaction temperature can aggravate the combustion reaction of coal char,at the same time,it accelerates the rate of NO formation,improves its peak value,increasing oxygen concentration can improve the conversion rate of NO,but the increase in reaction temperature can reduce the conversion rate of NO,the main reason is that under the experimental conditions,NO can directly attack on C,and the higher the temperature the stronger the reaction,thereby it reduces the conversion rate of NO.Jiangjunmiao,Shenhua coal ash contains more active minerals,demineralizing weakens the char-NO reduction reaction,the conversion rate of NO increased,while Jiaozuo coal ash contains more inert component,demineralizing can enhance char-NO reaction,the conversion rate of NO decreased.The analysis of coal char pores shows that demineralizing can reduce the specific surface area and pore volume of char samples,but increase the average pore size.The combustion reaction of char was obviously promoted by adding water vapor.Under low oxygen concentration(5%),the gasification reaction is serious,generating a lot of CO,the char surface violently catalyzed NO-CO reaction,leading to a sharp decrease in NO concentration which can promote NO reduction;this phenomenon was not observed at oxygen concentrations above 10%,but the conversion rate of NO increases with the concentration of water vapor.Water vapor accelerates the polycondensation and inertness of coal char,reduces the reactivity of char,weakens the reaction of char-NO,and increases the conversion rate of NO.The results of Raman spectrum analysis shows that with the increase of burnout rate,the degree of graphitization of coal increased and the reactivity decreased continuously.Meanwhile,the overall reactivity of the char is lower than that of the original char in all stages of combustion.