| In 2007,the new edition of National Occupational Health Standard"Occupational Contact Limits for Hazardous Factors in Industrial Places"was implemented,which stipulates that for dust containing 10%~50%free silica,the time-weighted average permissible concentration is 1mg/m~3and the short-term permissible concentration is 2mg/m3.In 2017,the emission limit of atmospheric pollutants in foundry industry was put into effect,which stipulates that the emission limit of dust from foundry equipment in industrial zone is 15mg/m3and the emission limit of average concentration of atmospheric pollution in any one hour is 5mg/m3.In 2018,the Environmental Protection Tax Law of the People's Republic of China began to be implemented,which stipulates that enterprises and institutions that discharge dust directly into the atmosphere will pay taxes ranging from 1.2 to 12 yuan per 4 kg of pollution equivalent.This series of new standards and the implementation of the tax law show that the environmental pollution problem in our country is serious at present,which proves the government's firm determination to improve the environment without delay.Dust removal and dust isolation of grinding station in industrial foundry workshop has always been the focus of improving the air environment inside the workshop and the working environment of workers.At present,most of the domestic workshops adopt dust-removing and dust-isolating measures for grinding workplaces in the form of grinding room plus personal protection,but this has limited effect on improving the air environment in the workshop and the working environment of workers.In this paper,air curtain is installed on the basis of grinding chamber,and its physical model is modeled by CFD technology.After verifying the correctness of the model calculation results,the local ventilation situation of workers in grinding chamber under different working conditions and the dust-proof effect of air curtain are analyzed by numerical calculation combined with theoretical calculation.Different working conditions include different exhaust volume and different exhaust hood size.Taking a sand foundry workshop in Jiangsu Province as an example,combined with the actual situation of the grinding station and relevant design specifications,the exhaust air volume was selected as 8000m3/h,10000 m3/h and 12000 m3/h,and the exhaust hood size was 0.6m×0.6m,0.9m×0.9m,1.2m×1.2m and 1.5m×1.5m.The size of the grinding room is 4.5 m long,3.6 m wide and 3.6 m high.It is planned to set an air curtain on the top of the open surface of the grinding room and an exhaust hood with an external dust collector fan on the opposite side.Through the analysis and comparison of the simulation results,it is concluded that different exhaust air volume has great influence on the air velocity field and dust concentration field in the grinding room,while different exhaust hood size only has influence on the dust concentration field,and the influence on the air velocity field can be neglected.Through comparison,the optimum operating conditions were selected as 10 000 m3/h exhaust air volume and 0.9 m×0.9 m exhaust hood size.The dust-producing forms of grinding dust are divided into two types.Under the optimum working conditions,the dust-proof efficiency of air curtain for the second type of dust-producing forms is close to 100%,and for the first type of dust-producing forms,the dust-proof efficiency is 61.5%.In order to further improve the efficiency of dust isolation,after theoretical calculation,a baffle with a height of 1 m can be installed at the bottom of the doorway of the grinding room.The baffle will not affect the effect of the air curtain on the air distribution in the grinding room. |
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