| With the increasingly strict environmental protection requirements,in order to reduce the unorganized emissions of VOCs in the painting and coating process and improve the job hygiene conditions in the painting workplace,the painting operation is required to be concentrated in the painting room.Mobile telescopic paint booths are widely used because of their simplicity of use,low investment,non-occupancy of the workplace,and applicability of paint booth size.However,through on-site research,it is found that the mobile telescopic paint booth generally adopts the side exhaust method,and the airflow organization inside the paint spraying booth is disordered,and there are problems such as paint spraying operation and closed ventilation process are not synchronized,paint VOCs exhaust gas cannot be collected completely,the collection efficiency of VOCs exhaust gas is low,and the unorganized emission seriously exceeds the standard.Therefore,in this paper,by analyzing the diffusion law of VOCs exhaust gas in the process of painting and coating,we use a combination of numerical simulation and physical test to optimize the ventilation method of mobile telescopic paint booth,and propose a combined ventilation mode combining air supply and exhaust system,which can improve the collection efficiency of painting exhaust gas to more than 95% without increasing the processing air volume of the original purification system while ensuring the synchronization of painting operation and closed ventilation process.It has significantly improved the working environment of the workshop and achieved the purpose of effectively reducing the emission of paint VOCs.First,the combination of numerical simulation and physical test is used to verify the reliability and accuracy of numerical simulation.Then,the effects of four factors,namely the horizontal position of the spraying point,the height of the spraying point,the amount of toluene volatilization,and the amount of ventilation,on the ventilation effect of the mobile telescopic paint booth were discussed,and the horizontal position of the spraying point,the height of the spraying point,the amount of toluene volatilization,and the amount of ventilation were also determined for the subsequent study.Secondly,the diffusion characteristics and velocity distribution of VOCs in the mobile telescopic paint spray booth and the upward and downward spray booth under mechanical ventilation conditions were analyzed to provide a basis for the optimal design of the mobile telescopic spray booth.Finally,different ventilation strategies were developed for the horizontal positions of the three paint spraying points,so that the collection efficiency of VOCs in the mobile telescopic spray booth could reach more than 95% in the paint spraying stage,and the effects of air supply and exhaust on the ventilation effect of the mobile telescopic spray booth were also discussed separately.The following conclusions were mainly obtained.(1)By comparing the variation curves of toluene concentration with time at test points 1,2,3 and 4 under numerical simulation and physical test conditions,it was found that the numerical simulation results agreed well with the physical test results,and the accuracy and reliability of the numerical simulation were effectively verified.(2)In the discussion of the horizontal position of the spraying point,the height of the spraying point,the amount of toluene volatilization,ventilation on the effect of mobile telescopic spray booth ventilation found that: 1)The spraying point is located in the spray booth cross-sectional velocity of the location,such as near the exhaust or air inlet is more conducive to improving labor hygiene conditions in the spray booth;2)The increase in the height of the spraying point will aggravate the average volume concentration of toluene in the spray booth.3)The height of the spray paint point closer to the human respiratory surface will have a greater impact on the average concentration of toluene on the human respiratory surface;4)The increase in ventilation can effectively improve the average volume concentration of toluene in the painting room,but the increase in ventilation within a certain range does not have an impact on the discharge efficiency;5)Finally,the horizontal position of the spraying point L=3.45 m,the height of the spraying point h=1.35 m,the toluene volatilization f=0.5g/s,and the ventilation quantity Q=15000m~3/h were chosen as the basis of the subsequent chapters.(3)By comparing the dispersion characteristics of VOCs exhaust gases in a mobile telescopic paint booth and the upward-feeding downward-venting spray booth under mechanical ventilation conditions,it was found that the upward-feeding downward-venting spray booth can effectively control the diffusion range of VOCs and improve the collection efficiency of spraying VOCs.For this reason,the ventilation method of the mobile telescopic spray booth was optimized by considering the integration of the ventilation method of the upward-feeding and downward-venting booth.(4)The ventilation method of the mobile telescopic spray booth was optimized by setting one air supply outlet of 200 mm in length and the same width of the booth at1500 mm intervals on the top of the booth.By developing ventilation strategies for each of the three horizontal painting points,it was found that the collection efficiency of toluene in the painting stage could be increased from 88.6% to more than 95% by opening only the nearest air supply outlet at the back end of the painting point,which improved the synchronization rate between painting operation and ventilation process and significantly improved the phenomenon of toluene pollution in the painting room.(5)By studying the effect of exhaust air volume and air supply volume on the ventilation effect separately,it was found that although the increase of exhaust air volume helps to improve the average volume concentration of toluene in the painting room,the improvement effect will become limited as the exhaust air volume continues to increase,while the collection efficiency of toluene at the painting stage is reduced as the exhaust air volume increases;the increase of air supply volume helps to improve the average volume concentration of toluene in the painting room and also helps to improve the collection efficiency of toluene at the painting stage. |
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