Development Of Combustion Detection System Based On TDLAS And Research On Gas Combustion Process

Iron and steel industrial gas mainly includes converter gas,blast furnace gas and coke oven gas,which is an important secondary energy and is usually used as fuel for industrial furnaces such as reheating furnaces for steel rolling,hot blast stoves and boilers in power plants.Converter gas is a kind of medium calorific value gas,which can be used as industrial fuel to burn alone or mixed with coke oven gas.The components of iron and steel industrial gas have great influence on the combustion rate in actual industrial burners and the concentration of pollutant gas in the exhaust.In this study,for the purpose of investigating the combustion behaviour,a combustion detection system based on tunable diode laser absorption spectroscopy(TDLAS)technology is developed to simulate the combustion of metallurgical gas in industrial burners and investigate its combustion characteristics.First of all,the laser parameters of TDLAS technology were set,and CO2 absorption curves with wavelengths of 1996.89 nm and 2004.02 nm were selected for the online measurement of flame temperature and species' concentration.In the complex measurement environment,the two absorption lines were calibrated and the best measurement parameters were obtained.The wavelength of 1996.89 nm was finally set as temperature 28.14? and current 37mA,while the wavelength of 2004.02 nm was set as temperature 26.62? and current 37 mA.Then,a combustion diagnosis system was designed and develpoed.According to the combustion of iron and steel industry gas in industrial burners,the burner and gas supply circuit were designed,built and adjusted to ensure stable combustion.Automatic ignition and emergency cut-off devices were designed and built to ensure the safety of the experiment.When measuring combustion parameters,an inert gas purging device and an integrating sphere device are built to improve the signal-to-noise ratio of laser.The TDLAS measurement was compared to traditional measurement methods to verify the reliability of TDLAS measurement.Based on the combustion of converter gas(CO-CO2-H2-N2),the effects of H2 and N2 on the CO-CO2 flame characteristics and the concentration of NOx in the exhaust were experimentally studied by using the combustion detection system.The effects of 0-24%by volume of H2 and N2 in fuel flow on the flame structure,flame temperature,CO and CO2 concentration distribution in flames and the concentration of NOx in the exhaust were discussed and compared.It is found that the increase of H2 and N2 percentage will lead to the increase of flame length,but the increase of flame length and flame length after increasing H2 is greater than that after increasing equal percentage N2.The addition of H2 leads to an increase of flame temperature and chemical reaction rate in the flame,while the addition of N2 leads to a decrease of flame temperature and chemical reaction rate.The highest CO concentration in the flame increases with H2 addition.The highest CO concentration in flame decreases with N2 addition.The increase of H2 and N2 lead to the decrease of CO2 concentration in flame.The position of the highest CO2 concentration in the flame is far away from the burner nozzle with H2 addition,which remains unchange with N2 addition.The increase of H2 percentage in gas is not conducive to NOx emission reduction,while the increase of N2 percentage is beneficial to NOx emission reduction.Based on the combustion of blast furnace gas(CO-H2-CO2-N2),the flame structure,flame temperature distribution,CO and CO2 concentration distribution in flames and the NOx concentration in the exhaust were experimentally studied by using combustion detection system.The effects of 0-32%pure CO2,pure N2 and CO2-N2(50%-50%)in fuel flow on flame structure,flame temperature distribution,concentration distribution of CO and C02 in flame and concentration of nitrogen oxides in tail gas were studied.The results show that the addition of H2 in the mixed gas leads to a short the flame length,high flame temperature and high combustion rate.The addition of CO leads to a higher NOx emission reduction.Increasing CO2 and N2 in CO-H2 fuel flow will lead to the increase of flame length,but CO2 has a greater influence on flame length than N2 under the condition of equal percentage.The addition of CO2 and N2 will reduce the flame temperature and the chemical reaction rate in the flame.The influence of CO2 on the flame temperature and chemical reaction in the flame is greater than that of N2 under the condition of equal percentage.Increasing CO2 in the CO-H2 fuel stream will lead to the increase of CO concentration in the flame,while increasing N2 will lead to the decrease of CO2 concentration in the flame.Under the condition of equal percentage,the influence of CO2 on CO concentration in flame is less than that of N2,but the influence on CO2 generation in flame is greater than that of N2.Adding CO2,N2 and CO2-N2(50%-50%)to the CO-H2 fuel stream is beneficial to reduce NOX emission,but relatively speaking,increasing CO2 is more beneficial to reduce NOx emission.Based on the combustion of coke oven gas and the mixture of coke oven gas and blast furnace gas(H2-CH4-CO and H2-CH4-CO-CO2-N2),the effects of CO replacing H2 or CH4 with 0-20%by volume and CO2,N2 and CO2-N2 with 0-32%by volume(50%-50%)on the combustion characteristics were experimentally studied.It was found that when CO replaced CH4,the flame length decreased.The temperature of the flame is lower.With the increase of CO,the highest CO concentration in the flame increases.After replacing H2 with CO,the flame length and the consumption rate of CH4 in the flame increase,but the flame temperature decreases.Replacing CH4 or H2 with CO is beneficial to NOx emission reduction,but replacing CH4 with CO is more significant.Increasing CO2 and N2 in H2-CH4-CO fuel flow will increase the flame length,but under the condition of equal percentage,CO2 has a greater influence on the flame length than N2.The increase of CO2 percentage and N2 percentage reduces the temperature of H2-CH4-CO flame and the rate and intensity of chemical reaction in flame,but CO2 has a greater influence on flame temperature and chemical reaction in flame than N2.The CO concentration first increases and then decreases with the addition of CO2,and first decreases and then increases with the addition of CO2-N2.Under the condition of equal percentage,the influence of N2 on the reaction rate of CO oxidation in flame is higher than that of CO2.The CH4 concentration first decreases and then increasse with the addition of CO2-N2.Increasing CO2 and N2 will lead to the location of the highest CO2 concentration approaching to the burner nozzle,but under the condition of equal percentage,the location of the highest CO2 concentration is closer to the burner nozzle when increasing CO2 than when increasing N2.Increasing CO2 and N2 in fuel flow can reduce the concentration of NOx in exhaust gas,but increasing CO2 is more beneficial to NOx reduction than increasing N2.