Study On The Mechanism Of Sulfur Evolution In Pulverized Coal Combustion

With the increasingly stringent requirements for nitrogen oxide reduction policies,more and more coal-fired power plants use new technologies to reduce nitrogen oxide emissions.Among those new technologies,because of its low cost、high efficiency and wide fuel adaptability,air staged combustion technology is the prefered technology to reduce NOx emissions in major power plants.The use of air staged combustion technology will form a high concentration of reducing gas in the initial combustion zone,and then promote the generation of higher concentration of H₂S near the water wall,which will lead to the occurrence of sulfide type high temperature corrosion.In order to take effective measures to prevent high temperature corrosion,it is necessary to reveal the evolution of sulfur elements in the combustion process of pulverized coal,especially the distribution characteristics of sulfur species during the combustion process.In this dissertation,the 3-demensional numerical simulation for 18k W direct flow burner was carried out by ANSYS Fluent 19.1 Based on different occurrence forms of sulfur element in coal,a mathematical model of organic sulfur pyrolysis release was established.The user-defined function（UDF）was used to compile and link the established organic sulfur pyrolysis release model to the pulverized coal combustion program,and coupled with the solid inorganic sulfur reaction kinetics model and the gas phase sulfur species global reaction mechanism model to achieve the prediction of the generation concentration of the main gas components and sulfur species in the pulverized coal combustion process.The reliability of the combustion model and sulfur evolution model was verified by comparing the the numerical simulation value with experimental value under the condition of excess air ratioα=0.8.Through the above verified model,numerical simulation studies were carried out on eight conditions with excess air ratio ranging from 0.6 to 0.95 to explore the influence of excess air ratio on pulverized coal combustion and the concentration distribution of sulfur species.The model verification results indicate that the currently established gas phase global reaction mechanism of sulfur species considers the synergetic reaction of CO、H₂、CO₂ and H₂O with the sulfur species of SO₂、H₂S、COS and CS₂.The error between simulation value and experimental value of main gas components at the central axis and burner outlet is less than 10%,and that between simulation value and experimental value of four sulfur species is less than 20%.By comparison and analysis the effects of excess air ratio on the combustion of pulverized coal and the concentration distribution of sulfur species under eight fuel-rich conditions,it can be concluded that with the increase of excess air ratio,the CO₂ generation concentration value has a linear incremental relationship with the O₂ concentration;The CO generation concentration value has a linear decreasing relationship with O₂ concentration;the SO₂ generation concentration value has a linear incremental relationship with O₂ concentration;the H₂S、COS and CS₂ generation concentration values have a linear decreasing relationship with oxygen concentration.The research in this paper provides theoretical support for the evolution of sulfur elements in the process of coal combustion,especially for the control of H₂S generation in pulverized coal boilers and the prevention of sulfide type high temperature corrosion in water-cooled walls.