Simulation Study On Wind-driven Pollutant Dispersion During Material Unloading Around Semi-open Industrial Buildings

The unloading of bulk ore is a common production process in industrial parks with mineral productions such as steel and coal productions.When ore transportation vehicles are unloading at semi-open industrial buildings,it is easy to produce a large amount of dust pollution.Fine particulate matter(such as PM_2.5)disperses to the surrounding environment under the synergistic effect of natural wind and the induced airflow caused by the free fall of mineral materials.This kind of intermittent wind-borne pollutant dispersion not only deteriorates the ambient air quality in industrial parks,but also increases respiratory disease risk among people living around.However,there are few studies on the distribution of wind velocity fields around semi-open industrial buildings,and especially the synergistic effect of natural wind and induced airflow caused by dust diffusion in the unloading process in semi-open buildings is not clear.In view of the above problems,this paper studies the dispersion of windborne pollutants from ore unloading in semi-open industrial buildings.The research results will provide technical reference for controlling such unloading-induced dust pollution.The main work of the paper is summarized as follows:（1）A numerical model suitable for the analysis of the windborne pollution dispersion induced by unloading in semi-open industrial buildings is established.In particular,the RNG k-εturbulence model and self-defined function programming were used to set the initial and the boundary conditions.The model was validated by comparisons with the wind tunnel experiments of airflows around a semi-open building and pollutant dispersion around an isolated building.The validity of the turbulence model and the numerical method is validated.The validated model was used to obtain wind velocity and pollutant concentration distributions around the semi-open industrial building.（2）A simulation test study was carried out on different induced airflow parameters during the unloading process.In this experiment,the effect of the induced airflow velocity and the influence range on the dispersion of windborne pollutants was studied.The results show that the induced airflow increases the turbulent kinetic energy in the material pit,which not only promotes the escape of pollutants,but also increases the diffusion range of the dust-laden airflow to the outside of the workshop.When the dimensionless induced airflow velocity ug is 0.4,the projected length of the dust-laden airflow flowing out of the material pit is close to half the width of the workshop;when the influence range of the induced airflow is 100%,the projected length exceeds half the width of the workshop.In addition,with the increase of the induced flow rate and its influence range,the height of the peak pollutant concentration on the discharge side increases,while the pollutant concentration on the leeward side is higher.（3）The influence of discontinuous unloading and different wind directions on pollution diffusion was explored.The wind speed fields and the pollutant concentration fields around the semi-open industrial building under different discontinuous unloading scenarios and different inflow winds are analyzed in detail.The results show that,vehicles unloading in the outer unloading room will cause a higher concentration of pollutants to accumulate in the building,while the concentration of pollutants in the building is relatively low when unloading in the middle.Different wind directions make the wind field distribution around the building vary greatly.When the wind direction angle is 45°,the average wind speed in the building is larger,the turbulence intensity is larger,and the gust wind speed is larger,so the pollutants are not easy to accumulate in the building,but the pollutants spread farther.In other wind directions,the wind speed in the building is relatively low,especially when the wind direction angle is135°,the wind speed in the building is the lowest,the turbulence intensity is small,and the gust wind speed in the leeward side area is the smallest.In this working condition,the pollutants are mainly concentrated around the building.However,the diffusion distance of pollutants is relatively short compared with other working conditions.（4）The exposure risk of pollutants in pedestrian areas around the semi-open industrial building was assessed.The pollutant intake fractions of 4 areas around the semi-open industrial building were analyzed.The results show that higher induced flow rates and range of influence of induced air flow produce higher iF values.The iF value of the area near the discharge side of the semi-open industrial building is the highest,followed by the side of the building,and the iF value of the area 1H from the windward and leeward sides of the building is almost 0.