To improve the ignition behavior and to reduce the high NOx emissions of blended pulverized fuels(PF)of semicoke(SC),large-scale experiments were conducted in a 300 kW fired furnace at various nozzle settings,i.e.,rat...To improve the ignition behavior and to reduce the high NOx emissions of blended pulverized fuels(PF)of semicoke(SC),large-scale experiments were conducted in a 300 kW fired furnace at various nozzle settings,i.e.,ratios(denoted by hf/b)of the height of the rectangular burner nozzle to its width of 1.65,2.32,and 3.22.The combustion tests indicate that the flame stability,ignition performance,and fuel burnout ratio were significantly improved at a nozzle setting of hf/b=2.32.The smaller hf/b delayed ignition and caused the flame to concentrate excessively on the axis of the furnace,while the larger hf/b easily caused the deflection of the pulverized coal flame,and a high-temperature flame zone emerged close to the furnace wall.NOx emissions at the outlet of the primary zone decreased from 447 to 354 mg/m3(O2=6%),and the ignition distance decreased from 420 to 246 mm when the hf/b varied from 1.65 to 3.22.Furthermore,the ratio(denoted by SR/SC)of the strong reduction zone area to the combustion reaction zone area was defined experimentally by the CO concentration to evaluate the reduction zone.The SR/SC rose monotonously,but its restraining effects on NOx formation decreased as hf/b increased.The results suggested that in a test furnace,regulating the nozzle hf/b conditions sharply reduces NOx emissions and improves the combustion efficiency of SC blends possessing an appropriate jet rigidity.展开更多
The influences of air preheating temperature, oxygen concentration, and fuel inlet temperature on flame properties, and NOx formation and emission in the furnace were studied with numerical simulation. The turbulence ...The influences of air preheating temperature, oxygen concentration, and fuel inlet temperature on flame properties, and NOx formation and emission in the furnace were studied with numerical simulation. The turbulence behavior was modeled using the standard k-ε model with wall function, and radiation was handled using discrete ordinate radiation model. The PDF （probability density function） /mixture fraction combustion model was used to simulate the propane combustion. Additionally, computations of NOx formation rates and NOx concentration were carried out using a post-processor on the basis of previously calculated velocities, turbulence, temperature, and chemical composition fields. The results showed that high temperature air combustion （HiTAC） is spread over a much larger volume than traditional combustion, flame volume increases with a reduction of oxygen concentration, and this trend is clearer if oxygen concentration in the preheated air is below 10%. The temperature profile becomes more uniform when oxygen concentration in preheated air decreases, especially at low oxygen levels. Increase in fuel inlet tempera- ture lessens the mixing of the fuel and air in primary combustion zone, creates more uniform distribution of reactants inside the flame, decreases the maximum temperature in furnace, and reduces NOx emission greatly.展开更多
基金This work was supported by the National Key Research and Development Program of China(No.2017YFB0602002)National Natural Science Foundation of China(Grant No.51536002).
文摘To improve the ignition behavior and to reduce the high NOx emissions of blended pulverized fuels(PF)of semicoke(SC),large-scale experiments were conducted in a 300 kW fired furnace at various nozzle settings,i.e.,ratios(denoted by hf/b)of the height of the rectangular burner nozzle to its width of 1.65,2.32,and 3.22.The combustion tests indicate that the flame stability,ignition performance,and fuel burnout ratio were significantly improved at a nozzle setting of hf/b=2.32.The smaller hf/b delayed ignition and caused the flame to concentrate excessively on the axis of the furnace,while the larger hf/b easily caused the deflection of the pulverized coal flame,and a high-temperature flame zone emerged close to the furnace wall.NOx emissions at the outlet of the primary zone decreased from 447 to 354 mg/m3(O2=6%),and the ignition distance decreased from 420 to 246 mm when the hf/b varied from 1.65 to 3.22.Furthermore,the ratio(denoted by SR/SC)of the strong reduction zone area to the combustion reaction zone area was defined experimentally by the CO concentration to evaluate the reduction zone.The SR/SC rose monotonously,but its restraining effects on NOx formation decreased as hf/b increased.The results suggested that in a test furnace,regulating the nozzle hf/b conditions sharply reduces NOx emissions and improves the combustion efficiency of SC blends possessing an appropriate jet rigidity.
基金Item Sponsored by National Natural Science Foundation of China (90210028)
文摘The influences of air preheating temperature, oxygen concentration, and fuel inlet temperature on flame properties, and NOx formation and emission in the furnace were studied with numerical simulation. The turbulence behavior was modeled using the standard k-ε model with wall function, and radiation was handled using discrete ordinate radiation model. The PDF （probability density function） /mixture fraction combustion model was used to simulate the propane combustion. Additionally, computations of NOx formation rates and NOx concentration were carried out using a post-processor on the basis of previously calculated velocities, turbulence, temperature, and chemical composition fields. The results showed that high temperature air combustion （HiTAC） is spread over a much larger volume than traditional combustion, flame volume increases with a reduction of oxygen concentration, and this trend is clearer if oxygen concentration in the preheated air is below 10%. The temperature profile becomes more uniform when oxygen concentration in preheated air decreases, especially at low oxygen levels. Increase in fuel inlet tempera- ture lessens the mixing of the fuel and air in primary combustion zone, creates more uniform distribution of reactants inside the flame, decreases the maximum temperature in furnace, and reduces NOx emission greatly.
