Study On The Regularity Of Dust Emission In Coal Dropping Transpersite Based On Kinetic Analysis Of Induced Air

Belt conveyor is actively used in conveying process of industrial for bulkmaterials. But the transfer station of belt conveyor often has the dust phenomenon,especially in the primary products process. Coal preparation shop is the most acuteworking section for dust pollution with high concentration and multiform ways aboutdustproducting in coking plant. In this paper, the dust sources in coal preparation shopand plant parameters, the physical and chemistry properties of coking coal and coaldust, the rheologic characteristics and praticle fluid mechanics, the material throwingtrajectory of coking coal and the quantity of induced air, the upper limit of suction airflow and the dust catching plant’ structure are studied based on the conveyor transferstation dust control program of a coking plant..The dustproducting means in transfer points of coal preparation process whichcontains four means in existence, that are belt to belt, belt to facilities, facilities to beltand dropping from facilities to another, the plant parameters, the physical andchemistry properties of coking coal and coal dust are studied in detail based on threeaspects that are quantities of dust sources, the level of difficulty for dust discharge anddust production. The coal dust dispersion pattern is studied according to theconcentration and particle size distribution of exhausted and position dust. The resultsshowed that dust dispersion is effected by gaseous phase and coking coal’scharacteristics and that it’s useful to construct a sealed space adopting dust catchingplant for dustlaying.The material throwing movement in transfer point is divided into fourcharacteristic movement region that are balance zone, separation zone, sliding zone(or material throwing zone without chute) and impact zone in order to analyze coal’sthrowing location, velocity vectors, throwing trajectory and material flow’s shape indifferent belt transport ways, operating condition and plant parameters from kinematicanalysis. Material throwing attributes in transfer points is analyzed by graphic methodand the centre of gravity place is calculated in order to draw the material throwingtrajectory in different operating condition which contains radius of tumbler, coal’sthrowing location and velocity vectors and drop height, etc. The basic flow behaviorof coal particles in air flow field is studied. The critical particle sizes and droppingterminal velocity of coking coal in different stream boundary is calculated, and it isshowed that the terminal velocities can be expressed approximately as the dropping velocity of coking coal at Stockes region, but the accelerated dropping stage anduniform dropping stage must be considered individually at Allen and Newton region,and almost all coking coal on the surface of material bed can reach to terminalvelocity in transfer points of coal preparation process. Dispersed entrainment zoneand collision extrusion zone are named for dust emission process to analysis inducedair’s movement qualitabively.The rules exploring experiment is designed to study the air entrainmentmechanisms in advance in order to build on experience for the model experiment.Induced airflow velocity which is produced by the dropping of conveyor transferstation material is studied based on the dimensional analysis, two dimensionlesscriteria named Re andd2p m p A/gH7g pnumber related to the induced airflow areset up and the empirical model of induced air velocity is built up. The similarexperiment shows that the induced air velocity has a strong regularity trend with thematerial mass flow velocity, drop height, chute angle, particle size, dynamic viscositycoefficient of air, chute sectional area, air moisture content and chute sectional shapefactor. Relational expression between induced air velocity and the above-mentionedfactors is built up.The upper limit of suction air flow is definition as that the upper limit windvelocity of suction airflow should not blow a large number of dusts which attached tothe materials bed when it is used to replace the raising dust effect of induced airflowby its catching dust effect. An exploring work is designed to study the relationshipbetween quantity of raising dust and suction airflow on the basis of model experiment.Finally, the dymamic force of suction air flow is calculated based on theabove-mentioned model experiments that the quantity of suction airflow shouldgreater than the quantity of induced air which is0.25~1.33×10-2m3/s and notexceeding the upper limit which is in the range of2.03~2.21×10-2m3/s。...