Study On Dust Removal Efficiency Of Negative Ion System In Long Tunnel Construction Period

With the development of infrastructure construction in China,the scale of road tunnel construction is getting larger and larger.During the construction of long tunnel,the air demand for high concentration pollutants such as dust is large.The pollutants diffuse with the wind in the tunnel,spread widely and stay for a long time.Because of the low efficiency of traditional pressure ventilation and the poor working environment of the constructors,the dust concentration can hardly meet the requirements of the specifications.How to effectively reduce the tunnel smoke and dust during the construction period has become a key problem for scholars at home and abroad.The predecessors initially determined the main influencing factors of dust removal efficiency in the negative ion dust removal research,but did not study the problems of graded dust removal efficiency and effective particle size under diffusion charge and comprehensive charge effect,and the system voltage and other parameters need to be optimized.The dust removal efficiency of the negative ion purification system was systematically studied by means of field test and numerical simulation based on the Shimen Tunnel Project in Pingkan-Hanzhong Section of Shaanxi Province.The main results are as follows:(1)Through the investigation of ventilation and dust removal in tunnel during construction period,the causes and physical and chemical properties of dust were expounded.By comparing the similarities and differences between negative ion dust removal technology and traditional dust removal methods,the charge mechanism,dust removal characteristics and high efficiency purification characteristics of negative ions were discussed,the main factors affecting the efficiency of negative ion dust removal were obtained,and the two mechanisms of negative ion diffusion charge and field charge were analyzed.(2)The concentration of total dust,PM10 and PM2.5 before and after the opening of the negative ion system was obtained by field test using the developed negative ion system.The results showed that the dust removal efficiency of total dust,PM10 and PM2.5 increased by 22~40% after the use of the negative ion system.(3)Based on the basic equations of hydrodynamics,electric field and dynamic field,UDF program was compiled with the secondary development function of FLUENT software,and the three-dimensional mathematical model of negative ion dust removal process was established.The RNG two-equation turbulence model was selected and coupled with the finite volume method and SIMPLE algorithm.The flow field,electric field distribution and dust trajectory were obtained.By comparing the measured and simulated values,it was found that they have the same regularity,which verified the reliability of the numerical simulation.(4)According to the Deutsch formula,the influence of voltage,wind speed,particle size and particle concentration on dust removal efficiency under diffusion charge and combined charge were simulated by FLUENT finite element numerical simulation software.The contribution rates of diffusive charged graded dust removal efficiency were obtained,which were 50~90%,30~40% and 10~15% for particles with particle sizes of 0.1~0.5,2~5 and 5~10 microns,respectively.The effective particle sizes of diffusion charge and field charge are: 0.1~0.5?m and 5~10?m,and the reasonable range of voltage in different sections was given: 40~55kV near the palm surface and 30~40kV far from the palm surface.