Study On Distribution And Treatment Of Harmful Gases In Tunnels

With the rapid development of China,s economy,China,s infrastructure construction has been upgraded in terms of quality and quantity.How to effectively improve traffic efficiency in a limited urban space,urban tunnels occupy an important position.As a result,more and more urban road tunnels have emerged.However,due to the relatively closed structure of the highway tunnel,a large amount of harmful gas will be discharged after passing through the car.With the increase of time,the exhaust gas in the tunnel will be more original.When people pass through the tunnel,if they are in this environment for a long time,it will cause great harm to health.Therefore,the purification of harmful gases in tunnels has become the focus of attention.In this paper,Chongqing is a 300 m highway tunnel as the research object,using the computational fluid dynamics software and the gas diffusion model in the tunnel to build a gas diffusion model in the tunnel.And the limited solvent method was used to solve the concentration distribution of NO and NOx in the tunnel.At the same time,titanium dioxide is used as a raw material for the purification of harmful gases.Because pure titanium dioxide has a limited purification effect,titanium dioxide samples are prepared in the laboratory and nitrogen dioxide is used to change the properties of titanium dioxide to increase the activity of titanium dioxide.In the study of the distribution of harmful gases in tunnels,two main factors are considered: the wind speed in the tunnel and the traffic volume in the tunnel.The distribution of NO and NOx in the tunnel under two different conditions is also discussed.At the same time,when discussing the purification efficiency of titanium dioxide,the main considerations are: the amount of titanium dioxide,the calcination temperature,and whether nitrogen is doped.In addition,experimental analysis and comparison of the three conditions were conducted to study the surface.1)The magnitude of the wind speed in the tunnel has an important influence on the distribution of harmful gases.When the wind speed is zero,the gas in the tunnel is mainly free-diffusion,and the distribution is homogeneous and distributed in the tunnel.When the wind speed is 1m/s,the gas in the tunnel tends to increase from the inlet to the outlet.However,after 100 meters,the gas distribution is about the same.There is a zero amount of harmful gas at the inlet.When the wind speed is 2m/s,the distribution condition is approximately the same as 1m/s,but the concentration is approximately the same after 150 m,and the part where the gas at the inlet is zero is longer than 1m/s.2)The impact of traffic volume in the tunnel on the distribution of harmful gases;when discussing the impact of traffic volume,the wind speed is positioned at 1.5m/s.When the traffic volume is free-running,the gas distribution in the tunnel at this time increases gradually in the horizontal direction.When it reaches 100 m,the concentration is approximately the same,and the vertical concentration of the gas increases gradually due to gravity,and the horizontal direction is approximately the same..When the traffic volume is saturated,it is almost the same as the former,but because the increase in concentration is no longer apparent due to gravity.When traffic is in a congested state;the rest of the road is roughly the same vertically and is not affected by gravity.The concentration of each part is approximately the same,but the exhaust concentration of the car is high.3)Different loading capacity The purification efficiency of titanium dioxide is not the same.The larger the load is,the larger the load is,but the increasing trend after 3 times is not obvious.The more the load is,the higher the purification efficiency is in the purification effect,indicating that the content of titanium dioxide is greater.The better the multi-photocatalytic efficiency,but the experimental load is very small,less than one gram.At the same time,the purification efficiency of the load and whether nitrogen doping and how much temperature calcination have no effect.4)The effect of calcining temperature;because there are three types of molecular structure of titanium dioxide,and the sample molecules calcined at different temperatures are not the same,according to experiments show that the calcined sample at 500 degrees is mainly anatase,400 degrees has a part of rutile,There is a partial version of Taibei Mine at 600 degrees.Experiments show that the best result of purification is anatase.The rutile is the worst version of Taiyuan,so the best calcining temperature is 500 degrees,the best 400 degrees and 600 degrees is the worst.5)The effect of nitrogen doping;titanium dioxide itself has certain defects so the purification effect is not very satisfactory,but can improve its purification effect after doping with other elements.In this paper,doping units are used.Experiments show that after nitrogen doping,the purification effect has a With great improvement,under the same conditions,there is a 5% or more gap between the nitrogen-doped and un-doped samples.At the same time,the doped samples do not have much change in other aspects of the original sample.Therefore,the distribution of harmful gases in the tunnel was obtained through simulation.At the same time,the modified titanium dioxide sample was placed in a place where the gas distribution was relatively concentrated to improve the other environments in the tunnel.