Experimental Research On Sulfur Release And NO_x Control Of Coal During Oxy-fuel Combustion

At present,the policy of energy-saving and emission reduction and how to achieve efficient clean utilization of energy have been the focus of social attention.In the current CCUS technology,Oxy-fuel combustion technology is the most suitable development of the way to reduce the CO₂;meanwhile,it is the most likely to achieve the transformation and utilization of existing units of large-scale carbon emission reduction technology.Nowadays,the research of oxy-fuel combustion technology is still widely carried out in domestic and abroad.However,due to the complexity of coal structure and the difference of the combustion characteristics of different coals in oxy-fuel combustion,it is very necessary to study the combustion characteristics and pollutant release characteristics in different kinds of coal in the experiment of oxy-fuel combustion.Based on the engineering background,this paper took the drop tube furnace?DTF?as the coal combustion platform,which is similar to the actual pulverized coal fired boiler.This experiment was carried out with the aid of thermal gravimetric analyzer?TGA?,flue gas analyzer,Fourier transform infrared spectrometer?FTIR?,gas chromatograph and laser particle size analyzer.In this experiment,the method of combining theoretical analysis and experimental measurement is carried out,which is guided by the theory of coal powder combustion in oxy-fuel atmosphere and in air atmosphere.This paper selects the typical coal used in thermal power plant: Shenhua bituminous coal?SH?and Anshun anthracite?AS?.This experiment researched the release characteristics of CO and H₂ as the main gaseous products? sulfur gas products?SO₂,H₂ S,COS??NO_x and the burnout characteristics of pulverized coal,reducing characteristics of total sulfur release characteristics and the reduction characteristics of NO are in the condition of air classification.To explore the relations and differences in combustion characteristics and pollutant emissions between the oxy-fuel combustion and air combustion,this paper changed the equivalent ratio,combustion temperature and combustion distance under different environment.The research shows that the release amount of CO and H₂ decreased significantly with the increase of the equivalence ratio,and it decreasd to none when the equivalence ratio is reduced to 0,but it was almost unaffected by the temperature.The release amount of CO and H₂ was controlled by the coal species.The gasification effect of CO₂ in oxy-fuel combustion can't be ignored.The burnout rate is determined by the combustion environment of the oxygen concentration,CO₂ concentration and the activity of coal.The high oxygen concentration,CO₂ concentration,and volatile content contribute to the burnout of pulverized coal.SO₂ is the main gas phase sulfur content in the combustion of pulverized coal in the oxy-fuel environment.the higher the sulfur content of coal,the higher the outlet concentration of SO₂ is.There was only a small amount of H₂ S and COS in the gas phase,and its release concentration was not related to the sulfur content of coal,but positively correlated with the content of H₂,CO and activated carbon in the combustion environment.The high concentration of oxygen in the oxy-fuel combustion promotes the sulfur release by promoting the combustion of the pulverized coal.The gas phase sulfur products?H₂S and COS?are greatly affected by the equivalence ratio,and the concentration of the gas phase is decreased with the increase of the equivalence ratio,and the concentration of H₂ S and COS is decreased to 0 when the combustion environment is oxidizing atmosphere.The sulfur release rate of SH and AS are related to the content of char and sulfur.When the coal has low sulfur content and high volatile content,coal sulfur release rate lags behind the burnout rate.When the sulfur content is higher and volatile content is low,it will make the sulfur release rate much outstrip than the burnout rate.With the increase of equivalence ratio and temperature,the burning rate of pulverized coal is accelerated,the oxidation atmosphere is strengthened,and the ratio of volatile and coke nitrogen is increased,which leads to the increase of NO concentration.Shenhua coal?SH?produce large amounts of nitrogen intermediate products of HCN and NH3 with high volatile and activity,leading the NO content in the atmosphere rather low at the initial stage of combustion.Anshun anthracite?AS?'s low volatile content and high ash content leads slow burning rate.In the beginning of combustion,the oxidizing atmosphere in the environment is strong,and the nitrogen content is oxidized to NO_x.But in the late stage of combustion,a large amount of oxygen is consumped,reducing the atmosphere strengthened,a large number of NO is reduced to N2.It was found that the oxy-fuel environment promoted the reduction of NO in SH,and the oxidation of nitrogen containing substances was promoted in SH.Maintain a constant condition in total volume,adding over fire air?OFA?effect on the reduction of NO significantly.With the increase of the proportion of OFA,the proportion of NO outlet concentration decreases firstly increases and then decreases.The optimum OFA air ratio is related to the combustion atmosphere and coal species.For SH,the optimal OFA ratio is reduced from 0.35 under KQ to 0.3 at FY2;while AS is increased from 0.48 to 0.5.And the reduction efficiency of NO was affected by the coal species,in the vicinity of the optimal OFA ratio,the proportion of NO decreased by SH was significantly higher than that of AS.