A 600 MW coal-fired boiler with a four-corner tangential combustion mode is considered here to study the combustion features and pollutant emissions at different loads for large-percentages of blending dried sludges.T...A 600 MW coal-fired boiler with a four-corner tangential combustion mode is considered here to study the combustion features and pollutant emissions at different loads for large-percentages of blending dried sludges.The influence of the over-fired air(OFA)coefficient is examined and the impact of the blending ratio on the boiler operation is explored.The results show that for low blending ratios,a slight increase in the blending ratio can improve the combustion of bituminite,whereas a further increase leads to the deterioration of the combustion of blended fuels and thus reduces the boiler efficiency.Enhancing the supporting capability of the secondary air effectively reduces the slagging degree in the bottom ash hopper and improves the burnout rate of coals.For a large-percentage blending case at full load,it is found that the OFA coefficient must be reduced appropriately,otherwise,a secondary high-temperature combustion zone can be generated in the vicinity of the furnace arches,causing high temperature slagging and superheater tube bursting.Considering the influences of combustion and pollutant emissions,the recommended OFA coefficient is 0.2.Blending dried sludge under low loads increases the flue gas temperature at the furnace exit.While reducing the flue gas temperature in the main combustion region,which is beneficial to the safe operation of the denitrification system.Increasing the blending ratio and reducing load lead to an increase in NOx concentration at the furnace exit Sludges with low nitrogen content are suggested for the practical operation of boilers.展开更多
In practical operations,the carbon monoxide(CO)distribution in an opposite-wall-firing furnace(OWFF)is characterized by a high concentration near the side walls and a low concentration in the center,accompanied by a s...In practical operations,the carbon monoxide(CO)distribution in an opposite-wall-firing furnace(OWFF)is characterized by a high concentration near the side walls and a low concentration in the center,accompanied by a series of combustionrelated issues.To find the reasons for the CO distribution,a numerical study was conducted on a 660 MWe OWFF.The CO concentration profiles,distribution coefficients of coal and air,mixing coefficients,and the aerodynamic characteristics were extracted for analysis.The CO distribution within the furnace greatly depends on the mixing of coal and air.A mismatch between the aerodynamic behaviors of coal and air causes the non-uniform distribution of CO.Taking into consideration that distinctive flow patterns exist within the different regions,the formation mechanisms of the CO distribution can be divided into two components:(1)In the burner region,the collision of opposite flows leads to the migration of gas and particles toward the side wall which,together with the vortexes formed at furnace corners,is responsible for unburned particles concentrated and oxygenized from the furnace center to the side wall.Thus,high CO concentrations appear in these areas.(2)As the over-fire air(OFA)jet is injected into the furnace,it occupies the central region of furnace and pushes the gas from the burner region outward to the side wall,which is disadvantageous for the mixing effect in the side wall region.As a consequence,a U-shaped distribution of CO concentration is formed.Our results contribute to a theoretical basis for facilitating the control of variation in CO concentration within the furnace.展开更多
文摘A 600 MW coal-fired boiler with a four-corner tangential combustion mode is considered here to study the combustion features and pollutant emissions at different loads for large-percentages of blending dried sludges.The influence of the over-fired air(OFA)coefficient is examined and the impact of the blending ratio on the boiler operation is explored.The results show that for low blending ratios,a slight increase in the blending ratio can improve the combustion of bituminite,whereas a further increase leads to the deterioration of the combustion of blended fuels and thus reduces the boiler efficiency.Enhancing the supporting capability of the secondary air effectively reduces the slagging degree in the bottom ash hopper and improves the burnout rate of coals.For a large-percentage blending case at full load,it is found that the OFA coefficient must be reduced appropriately,otherwise,a secondary high-temperature combustion zone can be generated in the vicinity of the furnace arches,causing high temperature slagging and superheater tube bursting.Considering the influences of combustion and pollutant emissions,the recommended OFA coefficient is 0.2.Blending dried sludge under low loads increases the flue gas temperature at the furnace exit.While reducing the flue gas temperature in the main combustion region,which is beneficial to the safe operation of the denitrification system.Increasing the blending ratio and reducing load lead to an increase in NOx concentration at the furnace exit Sludges with low nitrogen content are suggested for the practical operation of boilers.
文摘In practical operations,the carbon monoxide(CO)distribution in an opposite-wall-firing furnace(OWFF)is characterized by a high concentration near the side walls and a low concentration in the center,accompanied by a series of combustionrelated issues.To find the reasons for the CO distribution,a numerical study was conducted on a 660 MWe OWFF.The CO concentration profiles,distribution coefficients of coal and air,mixing coefficients,and the aerodynamic characteristics were extracted for analysis.The CO distribution within the furnace greatly depends on the mixing of coal and air.A mismatch between the aerodynamic behaviors of coal and air causes the non-uniform distribution of CO.Taking into consideration that distinctive flow patterns exist within the different regions,the formation mechanisms of the CO distribution can be divided into two components:(1)In the burner region,the collision of opposite flows leads to the migration of gas and particles toward the side wall which,together with the vortexes formed at furnace corners,is responsible for unburned particles concentrated and oxygenized from the furnace center to the side wall.Thus,high CO concentrations appear in these areas.(2)As the over-fire air(OFA)jet is injected into the furnace,it occupies the central region of furnace and pushes the gas from the burner region outward to the side wall,which is disadvantageous for the mixing effect in the side wall region.As a consequence,a U-shaped distribution of CO concentration is formed.Our results contribute to a theoretical basis for facilitating the control of variation in CO concentration within the furnace.
