Research On Migration And Transformation Characteristics Of Nitrogen And Sulfur In Pressurized Oxy-coal Combustion

With the promulgation of the policy of"Emission peak"and"Carbon neutrality",the task of CO₂ emission reduction is imminent.CO₂ emission reduction in coal power industry is the due meaning of"Emission peak".As a new high-efficiency combustion technology,pressurized oxy-fuel combustion is one of the important means of carbon emission reduction in coal-fired power plants.The reaction conditions of pressurized oxy-fuel combustion and conventional air combustion are different,resulting in the unclear migration and transformation law of nitrogen and sulfur in the process of pressurized oxy-fuel combustion.In this paper,the experimental and theoretical research on the migration and transformation characteristics of nitrogen and sulfur in the process of pressurized oxygen enriched coal combustion was carried out.The main contents and conclusions are as follows:The migration and transformation characteristics of nitrogen and sulfur in the process of pressurized pyrolysis and gasification of pulverized coal were studied by using the pressurized drop tube furnace and fixed bed tube furnace and X-ray photoelectron spectroscopy（XPS）.The results showed that the precipitation of nitrogen and sulfur was inhibited by the increase of pyrolysis pressure,the decomposition of N-X functional group was promoted while the decomposition of thiophene and sulfone was inhibited.High pyrolysis temperature was conducive to the decomposition of nitrogen and sulfur-containing functional groups,and promoted the conversion of nitrogen and sulfur to N-Q and thiophene.The release of volatiles and the decomposition of nitrogen and sulfur-containing functional groups in coal were promoted by the increase of pyrolysis time and gasification degree.The migration of N-Q,N-X and sulfate in char was related to the coal type.The decomposition of N-6 was inhibited and the decomposition of N-Q was promoted by the high temperature rise rate.The decomposition of sulfoxide and sulfate was slow at high temperature rise rate,while the decomposition of pyrite and sulfide was accelerated.The emission characteristics of nitrogen and sulfur pollutants from pressurized oxy-fuel combustion were research at pressurized drop tube furnace.During pressurized oxy-fuel combustion in O₂/CO₂ atmosphere,due to the high specific heat capacity of CO₂,the combustion temperature under oxy-fuel condition is low,resulting in lower emissions of NO,NO₂ and SO₂ than those in air combustion.The emissions of NO,NO₂ and SO₂gradually decreased with the increase of pressure.And the emissions of NO and NO₂increased,but the emission of SO₂ decreased with the increase of oxygen concentration.In addition,the emissions of NO and SO₂ increased with the increase of temperature at all pressures,while the variation trend of NO₂ emission with temperature was opposite under pressurized combustion.The molecular dynamics simulations of pressurized air combustion and pressurized oxy-fuel combustion were carried out by ReaxFF reactive force field.The results showed that the oxidation rate of pyridine increased with the increase of temperature.The effect of CO₂ on pyridine nitrogen conversion was mainly related to temperature.At low temperature,the chemical equilibrium of CO₂ played a leading role so the conversion of pyridine to NO_x was inhibited by CO₂,while at high temperature,CO₂ participated in the reaction,the number of OH radicals with strong activity was improved,so the conversion of pyridine to NO_x was improved.