Study On Blasting Fume Mechanism And Control Technology In Tunnel Based On Gas-Solid Two-Phase Flow

With the development of traffic construction,there are more and more long and large tunnels.In the process of excavation with large instruments or blasting with explosives,a large amount of dust will be generated and distributed in the tunnel environment.The construction environment with high dust concentration for a long time is easy to cause workers to suffer from pneumoconiosis and other common respiratory occupational diseases.At the same time,tunnel blasting will also produce a lot of CO and other harmful gases(dust together called soot),which more heavily polluted the working environment in the tunnel working area,is not conducive to the health of professional personnel.Therefore,the study of the migration mechanism of smoke and dust in the tunnel and the control technology of effectively controlling the concentration of smoke and purifying the tunnel environment are the priority among priorities in the safe development of tunnel engineering.Based on the theory of gas-solid two-phase flow,this thesis studies the mechanism and control technology of tunnel soot migration based on gas-solid two-phase flow by means of theoretical research,model test,field monitoring and numerical simulation.The research results of this thesis are as follows:(1)Based on the gas-solid two-phase flow theory,the mechanism of fume generation in tunnel was analyzed,the governing equation of CO and dust was established,and the force exerted by CO and dust in tunnel space was analyzed.Based on this,the equilibrium equation of smoke force in tunnel space was established.Based on the theory of transport and diffusion of pollutants,a mathematical model of transport and diffusion of CO in tunnel was established,and the calculation method of initial concentration of CO was introduced.Based on the theory of dust turbulence diffusion,a mathematical model of dust migration and diffusion in tunnel was established.A simplified calculation method of dust concentration in tunnel was proposed,and the validity of the calculation results was verified by numerical simulation.(2)The self-developed model test device for studying the law of dust migration and diffusion was used to simulate the experimental study on the law of dust migration and diffusion of different particle sizes under the ventilation condition after blasting and the experimental study on the dust removal effect of humidification after blasting.Combined with python-openCV dust particle size recognition tool,the particle size of dust particles at different positions in the model after tunnel "blasting" was identified,and the research concluded: Dust particles with different particle sizes have different migration and diffusion laws under the action of air flow and reflux.Dust with large particle size(50-100μm)is easy to concentrate in the area near the palm surface,while dust with small particle size(1-10μm)has longer suspension time,longer diffusion distance and is not easy to settle in the tunnel.By comparing the dust concentration before and after humidification after tunnel blasting,it can be concluded that the addition of water mist will make dust particles aggregate into clusters,greatly reducing the diffusion distance,and increasing the humidity value can effectively reduce the dust concentration.(3)Based on the gas-solid two-phase flow theory,the field ventilation model of Jiming tunnel was established by Fluent numerical simulation software.Combined with field wind speed monitoring,the effectiveness of numerical simulation was verified,and then the migration and distribution law of dust and CO in the tunnel was explored.Finally,the significance of three ventilation parameters was analyzed by response surface method.The distribution of airflow field in the tunnel is extremely disordered,and eddy current is one of the main influencing factors leading to the irregular distribution of flow field in the tunnel.The airflow in Jiming tunnel can be divided into eddy current zone,eddy current influence zone and stable zone according to the different distance from the palm surface.At the initial stage of ventilation after blasting,the CO concentration on the tunnel plane presents a dovetail distribution,and the CO concentration in the face area is higher than that outside the blast smoke throwing area.The CO migration showed two modes of "translation" and "diffusion".The dilution rate of CO concentration near the tunnel wall was faster than that in the middle of the tunnel.Dust particles with small particle size have long residence time and are not easy to settle.Dust particles with different particle size have different diffusion speed and diffusion range in the tunnel.Dust particles with small particle size have higher dispersion degree and faster diffusion range.The Box-Benhnken response surface model of CO and dust concentration was established.The variance results of CO and dust concentration in the same ventilation time were obtained by analyzing the response surface method.The optimal ventilation parameters were proposed based on the response surface analysis results.(4)Based on the MATLAB App Designer software design tool,a set of intelligent ventilation system suitable for tunnel ventilation design was designed and developed.Four functional modules including ventilation system design,pollutant concentration prediction,pollutant concentration monitoring and intelligent ventilation device control system were carried out.The Jiming tunnel project was taken as an example to show the realization effect of the software function.This thesis also designed and proposed "follow-up type system and method for pumping and exhausting harmful gas in tunnel"(CN113982668A),and verified the application effect of the shadowing harmful gas extraction and drainage device in the tunnel through numerical simulation.The research results show that: The traceable tunnel harmful gas drainage device will make the flow field near the tunnel face more chaotic,and can accelerate the dust and CO discharge.After adding the traceable tunnel harmful gas drainage device,the trend of CO concentration near the tunnel face shows a single exponential function change.