The Dust Diffusion Simulation Studies Of Desert Typical Open-pit Coal Mine

As one of the three main energy sources in global economy， coal， along with oil and gas， willcontinue to be the dominant source of energy and in the foreseeable future. Coal mining is also facing moresevere situation regarding environment protection， especially the impact on the mining field itself and thesurrounding atmosphere environment from the surface mining. Without the corresponding protection andpurification facilities， the emission of coal dust during mining would result in decline of air quality. Withproven minable reserves of approximately11.7billion tons high quality coal， Wucaiwan ZhundongCoalfield in Xinjiang is one of the most important production bases of coal for energy and chemicalindustry. Meanwhile， we should pay attention to the air pollution issue that is raised from massive mining.Applying MM5and CALPUFF， this paper simulates the density of coal dust in the WucaiwanZhundong Coalfield， and analyzes the main factors that affect the density of coal dust simulatingenvironment. According to the requirements of the input source of CALPUFF air quality model， emissionsources are classified and organized as followed: the drilling， blasting， and coal loading of coal field areset as point sources： the surface mine itself， which emit with smaller the amount at low emission heightwithin a large area， is set as surface sources， the coal dust from ground transportation is set as linesources. Then the intensiveness of sources is estimated according to various intensity projectionmethodologies. Based on Mesoscale meteorological prediction model (MM5) and meteorologicaldiagnostic model (CALMET)， meteorological field within the region was simulated， and meteorologicalcharacteristics of the mine were analyzed. January， April， July and October were used as typicalrepresentatives of the four seasons， CALPUFF was utilized to conduct the quantitative simulation of thedistribution of coal dust density over time， and the characteristics of density and the relationship betweendensity and meteorology were analyzed.In the simulation of wind field， average wind speed in four seasons in coalfield following thispattern: spring> summer> winter> autumn. West wind and east wind are most dominant wind in allseasons， followed by northwest wind. Temperature inversion exists during12:00to4:00in summer， butthickness of which is only tens of meters. Compared with summer， the capability of vertical air mixing inwinter is weaker， with thicker inversion layer and longer lasting， which is not conducive to the verticaldiffusion of pollutants. Diurnal variation in different seasons shares some similarity， but the height oflargest mixing layer changes significantly (summer> spring> autumn> winter). The maximum height insummer can reach more than2500m， while maximum height in winter is only about200m. Temperaturedifference among seasons is huge， the biggest difference between maximum and minimum temperaturesin summer and winter is37℃， and diurnal temperature difference is also more than10℃.During a typical hour at21:00on July112012， dust density reaches a higher value mainly due tothe continuous wind with large speeds， the effectiveness of sprinkler and some other measures to suppressdust was undermined by high temperature，and the height of the mixed layer is too thin to diffuse coal dustoutward. On typical day， October312012， causes of high dust density in some areas are continuous lowspeed wind，and the height of mixing layer is substantially lower than the average level in autumn，whichis not conducive to the horizontal diffusion of pollutants. The average density of the coal dust showing in descending order of autumn> summer> spring> winter， and this is mainly related to weather conditionsand mining capacity. The simulation of diurnal average of dust density indicates that some points reachedthe standard，but some points exceeded the standard，which is mainly related to the location of simulatingpoints and the ability to diffuse of coal dust.In order to reduce coal dust pollution on minefield itself and surrounding environment， especiallyprotected areas， we should take some effective dust suppression measures， in addition to sprinkler， andwind-proof wall (network)， chemistry method， froth and other methods should also be considered.