| Air purification is an important part of tunnel construction.Because the tunnel is too long,the ventilation layout is not reasonable,the wind pressure is insufficient and the construction enterprise is pursuing the profit,the use of traditional mechanical ventilation will cause the dust removal rate in the tunnel too slow,and the builders often exceed the standard to carry out the work,which seriously affects the construction progress and the health of the construction personnel.The introduction of negative ion purification technology can well solve the above defects in traditional ventilation and purification.Negative ion purification technology is a new method of tunnel air purification.At present,there is no precedent for introducing negative ion purification technology into tunnel construction at home and abroad.The feasibility of the application of negative ion purification in the construction tunnel and the design of the installation parameters in the application are also rarely studied,which is the main research content of this paper.Firstly,based on the situation of tunnel field,the distribution formula of negative ion concentration distribution,the steady-state dust elimination rate calculation formula and the instantaneous dust concentration distribution formula are derived in combination with the theory of turbulent mass transfer,the ionization zone discharge theory and the theory of dust settling charge.The influence of voltage,wind speed and installation length on the efficiency of dust removal is studied by means of the derived formula.The conclusion is that the higher the voltage,the longer the installation length and the smaller the wind speed,the higher the efficiency of the negative ion purification system to dust removal.Secondly,after analyzing the related data,the minimum limit of 500/cm~3is recommended.The influence of voltage,wind speed and negative ion concentration on the reserved length of negative ion purification system is studied.The lower the voltage,the greater the wind speed and the higher the negative ion concentration standard,the longer the reserved length is.the table of reserved length under different wind speed and voltage is drawn.Thirdly,combined with indoor test and derived formula,the installation voltage of tunnel test is selected 60kV,installation height is 3m and installation length is 300m.Finally,the tunnel field test is carried out.From the test data,the negative ion concentration in the negative ion purification system section is symmetrical in U shape on the cross section.The magnitude of concentration of negative ions is basically the same on the same vertical section parallel to the middle line of the tunnel.The negative ion concentration distribution formula is basically consistent with the actual test results.When the negative ion purification system is used and unused in a construction period,the dust elimination rate is 51%and 20%respectively,and the time of exceeding the standard maximum permissible concentration 8mg/m~3 is 1 hours and 12 hours respectively,which is basically consistent with the calculation results of instantaneous dust concentration distribution formula.According to the field test data,the dust purification rate in the steady state construction stage is 74%,and the calculation results of the dust purification rate in the steady state are 82%.Considering the effect of the field complexity,it is considered that the two are basically consistent.The results show that the application of negative ion purification system in construction tunnel can effectively eliminate dust,speed up construction progress and ensure the health of construction workers.Negative ion purification technology can be applied to construction tunnels.The calculation formula is basically consistent with the actual test value,and the formula can be used for reference in the parameter design of negative ion purification system in construction tunnel. |
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