Experimental Study On The Characteristics Of Pressure-pyrolysis Char From Shenhua Bituminous Coal And Its Effect On NO Reduction

The rapid development of Chinese economy is inseparable from the use of energy.Coal is the primary energy source in China,occupying a significant share in the energy utilization structure.As one of the main places for coal utilization,coal-fired power stations emit large amounts of CO₂ and NO_x into the air every year,causing severe pollution to the environment.Based on China’s proposed strategic goal of achieving"carbon neutral"by 2060,achieving efficient CO₂ capture and NO_x emission reduction of coal-fired power stations has become the primary goal of China’s energy development.Pressure-enriched oxygen combustion technology reaches low cost and high-efficiency CO₂ capture and effectively reduces NO_x emission and gradually becomes the mainstream combustion method of coal-fired power stations in China.Char-NO reaction plays a vital role in reducing NO emissions in coal-fired power stations,while pressure and temperature changes in pressurized oxygen-enriched combustion will affect the generation and reduction characteristics of NO_x during coal combustion.Therefore,it is of great guiding significance to study the influence of environmental factors such as pressure and temperature on the char-NO reaction in the pressurized thermal conversion process of pulverized coal for NO_x emission reduction in high-pressure coal-fired power stations.In this paper,Shenhua bituminous coal was taken as the research object.Based on the experimental system of pressurized horizontal furnace,the effects of pyrolysis conditions,such as pyrolysis pressure,pyrolysis temperature and pyrolysis residence time,on carbon skeleton structure,surface C（O）active number and heterogeneous reduction ability of NO were investigated by temperature programmed desorption（TPD）method,Raman spectroscopy and XPS.The results show that,with the increase of pyrolysis pressure,pyrolysis temperature,pyrolysis residence time,the aromatic rings’structure on the char’s surface polycondense,the number of amorphous carbon structure reduces,and the graphitization degree of char increases.The change of carbon skeleton structure of char minimizes the number of defect sites on the surface,which leads to the decrease of the number of C（O）active sites on the surface of char.Reducing the number of active sites on the char surface reduces the reaction sites of O₂ and NO molecules,which reduces the reactivity of char combustion and the ability of heterogeneous reduction of NO.This paper also investigated the influence of environmental pressure,temperature,and reaction residence time on the heterogeneous reduction reaction of char-NO;and the type and quantity of nitrogen-containing functional groups on the surface of the residual char after heterogeneous reduction under different environmental conditions.The results show that with the increase of environmental pressure,the total reduction amount of NO increases,and the char-NO reaction is promoted.The content of N-5 on the residual char surface decreases gradually,while the content of N-6 and N-Q increases.The N-5,which has poor thermal stability,is converted into N-6 and N-Q under high pressure.When the char from different pyrolysis pressure reduces NO at the corresponding pressure,the char has the best NO reduction effect at 0.6 MPa in the experimental pressure range（0.3-1.2MPa）.With the increase of ambient temperature,the total reduction amount of NO increases,and the char-NO reaction becomes more obvious.The content of N-5 and N-6 structures on the surface of residual char gradually decreases,while the content of N-Q gradually increases.It is suggested that N-5 and N-6 transform into N-Q with stronger thermal stability under the action of high-temperature;When the char from different pyrolysis temperature reduces NO at the corresponding temperature,the char has the best reduction effect and the largest total reduction amount of NO at 1000℃in the experimental temperature range（800-1000℃）.With the increase of the reaction residence time,the total reduction amount of NO content of C（N）structure increased,and the contents of N-5 and N-6 on the residual char surface gradually increased.The absolute content of N-Q was stable at the early stage（0-5 min）of the char-NO reaction and then increased gradually.The C（N）structure generated in the first step of the char-NO reaction is mainly N-5 and N-6 forms of nitrogen-containing functional groups.In the later stage of the reaction,the content of N-5 decreased.In contrast,the content of N-6 and N-Q increased,which is due to the gradual polycondensation of N-5 with poor thermal stability and the formation of N-6 and N-Q structures under the action of subsequent high temperature and high pressure.