| Manual bagging is still mainly bagged cement production existing in China's enterprises,and the use rate of fully automated equipment in the production process is not high.The problem of dust concentration exceeding the standard in semi-airtight enclosure in bagging workshop is serious,and the phenomenon of "systematic ineffectiveness" is widespread.Aiming at the specific problems existing in the semi-enclosed cover of a cement bag workshop in Tianshan Group,this thesis studies the dust diffusion and control in the cover,aiming at studying the movement law of cement dust in the cover,and exploring the best scheme of airflow organization in the cover according to the actual situation.In this thesis,combined with the current situation of ventilation in semi-enclosed hood,a three-dimensional numerical simulation model is established by ICEM pretreatment,and the numerical simulation is carried out according to the measured parameters.The simulation results are basically consistent with the field test data,which shows the correctness of the numerical simulation.Through on-site detection,the total dust concentration of TWA in breathing belt of bagging workers is 9.20mg/m3,and that of TWA in the rear of Chartered aircraft is 106.27 mg/m3.The simulation results show that the airflow organization in semi-airtight cover is unreasonable under the original ventilation conditions,and the dust concentration seriously exceeds the standard.According to the specific problems existing in semi-hermetic enclosure,the ventilation optimization scheme is put forward in this thesis.Firstly,scheme one explores the best dust control air volume based on the original ventilation conditions.The results show that when the main air duct air volume is 5700 m3/h,the dust control effect is the best.On this basis,the second scheme is put forward,and the No.2 vent is moved to the front and rear wall of the Chartered aircraft.The simulation results show that the scheme has certain control over the dust concentration in the rear of the Chartered aircraft,but the concentration still exceeds the standard seriously.Through analysis,the position of No.3 exhaust outlet is unreasonable,which makes the right side of the Chartered aircraft short-circuit,and the left side baffle of the entrance has a certain impact on the air flow into the rear of the Chartered aircraft.Therefore,on the basis of scheme 2,scheme 3 is proposed,that is,to change the size and location of the entrance and exit.The simulation results show that this scheme has the best dustcontrol effect.The simulation results show that the dust concentration near the breathing belt is about 0.01 mg/m3,and the highest dust concentration at the rear of Chartered aircraft is about 16 mg/m3.According to the third scheme,after a period of trial operation,through on-site investigation and test analysis,combined with numerical simulation results,the air distribution after the transformation is better.The test results show that the average dust concentration(TWA total dust = 0.01mg/m3)at the respiratory belt has been reduced to below the national standard limit(4mg/m3),and the total dust concentration at the rear of the Chartered aircraft in the semi-enclosed hood has also been reduced.As low as 10 mg/m3,the expected effect has been achieved.The research results have certain scientific value and practical significance for reducing the cost of ventilation system reform in cement bagging enterprises,improving the efficiency of dust removal in large-volume negative pressure semi-airtight cover,and researching dust movement and dust control methods in similar semi-confined space. |
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