The Flow Behavior Of Dust Particles In Airflow Ield And Wet Purification

Belt conveyor is actively used in short conveying process of industrial for bulk materials.But the transfer station of belt conveyor often has the dust phenomenon, especially in theprimary products process of the mineral processing and smelting, cement production, etc. Dustsuppression model known as “Scattered capture, Centralized purification”is a common methodin the industry. It is not extremely suitable for the dust suppression and purification of high dustlink with the disadvantage of complex ventilation piping, easy choking, and difficultmaintenance after blockages, high energy consumption of removing dust, etc. In this paper, anew dust suppression model denoted as “Scattered capture, Local purification”（SCLP） isproposed. It based on the conveyor transfer station dust control program of Xingda sinteringplant in XuZhou city. The physical and chemistry properties of sintering ore and the basic flowbehavior, the induced air flow of conveyor transfer station, the dust-capture feature of dustexhaust hood, the main structural parameters of wet dust separator, the resistance characteristicsand the collection efficiency are studied and those are applying in the conveyor transfer stationof sintering plant.The physical and chemistry property of sintering ore dust is studied. The dust true density isabout3.854⁴.195g/cm³, and the sphericity is about0.51⁰.93, and the wetting velocity is about0.306⁰.483cm/min. The material on the belt conveying has a large amount of dust below125μm which about accounts for2.23%. There are the high level of minerals with about44⁴6%content of T.Fe in the dust. The minerals should be considered effective recycling in thepurification process.The basic flow behavior of dust particles in air flow field is studied. The free setting sizepartition of sintering ore dust is mainly at Stockes region and Allen region. The terminalvelocities can be expressed approximately as the settling velocity of dust at Stockes region, butthe accelerated settlement and uniform settlement must be considered individually at Allenregion. The respiratory dust has the weaker inertia movement and diffusion effect in a stationaryair field, but it has a stronger following performance in a horizontal turbulent flow field. The dustabove10μm in horizontal turbulent flow field has a larger slip velocity with the air flow and thetrajectories of dust need to be decided by horizontal airflow velocity and dust settling velocity.Induced airflow velocity which is produced by the dropping of conveyor transfer stationmaterial is studied and the empirical model of induced air velocity is built up. With thedimensional analysis as the starting point, two dimensionless criteria named Re andm_p/ρ_gg^1/2h^3/2D number related to the induced airflow are set up. The similar experiment showsthat the induced air velocity has a strong regularity trend with the material mass flow velocity and drop height to the same material. Because of the interaction influence on particles, theinduced airflow velocity has a poor trend with the particle diameter when the drop height is inthe experimental particle diameter range.The suction airflow velocity range of dust exhaust hood is studied. The raising dust effect ofinduced airflow is gradually replaced by catching dust effect of suction airflow with the increaseof suction airflow velocity. When suction airflow increases to a certain value, the suction airflowhas an effect on raising motionless dust which attached to the materials bed. The percentage oflarge granularity dust and total dust mass, which are caught by dust exhaust hood, increase alongwith the increase of suction airflow. The upper limit wind velocity of suction airflow should notblow a large number of dusts which attached to the materials bed （about9.20m/s）. Theminimum wind velocity should be able to completely absorb induced air flow.The main structural parameters of throttling self-excited dust separator are studied by modelexperiment. The results show that the contact cavity height directly affects the dedusting effectand its suitable height is about300mm. Two-stage throttling effect of gas-liquid mixing is betterthan single-stage. The better interstage matching is that the primary throttling intensity is bigger（α=250/300²35/300） to stimulate droplets and the secondary throttling intensity is smaller（α=150/300²20/300） to strengthen the effect of gas-liquid mixing.The liquid phase adjustment characteristic for dust separator resistance is found out. Theforce balance of gas-liquid two phase before and after of the throttle is regulated by the changingof throttle liquid-level difference Δh. Then the total resistance coefficient of dust separator ischanged for restraining the increase of gas phase resistance. Due to the influence of liquid phaseadjustment, the throttling intensity α is linearly propotional decreased to the airflow velocity ofdust separator. The total resistance coefficient ξ relatively reduces along with the increase of gasphase velocity and relatively increases along with the increase of throttling intensity. The gasphase total resistance can be indirectly express by the throttling liquid-level difference Δh. Theeconomic and suitable inlet velocity of dust separator is about3.62⁵.37m/s.Fractional collection efficiency model of throttling self-excited dust separator is established.The dust removal process is divided into catching dust on the liquid surface and catching dustwith the liquid droplet. The theoretical models show that catching dust on the liquid surface hashigher fractional collection efficiency for the large-granule dust, and catching dust with theliquid droplet has higher fractional collection efficiency for the large-granule dust and respirabledust. Collection efficiency of catching dust with the liquid droplets mainly depends on thegas-phase velocity coefficient ζ1and the dust separator airflow. The experiment results show thatthe gas-phase velocity coefficient ζ1is0.79and the collection efficiency for respirable dustreaches to98.26%. The collection efficiency raise along with the increase of air inlet dust concentration and the air outlet dust concentration increases along with the increase of air inletconcentration. When the entrance dust concentration is within the range of695.45³667.34mg/m3, the outlet dust concentration meets discharge standards. The initial liquid level b0and thedust separator airflow have a great effect on the collection efficiency. The suitable b0is-15¹4mm. And the inlet air velocity of dust separator is not lower than2.93m/s.The feasibility of “Scattered capture, Local purification”-dust suppression model is verified.The industry field application shows that the model can reduce the dust emission and greatlyreduce the jam failure rate. The total dust removal efficiency is more than98%, and the energyconsumption reduces about14.6%. The13conveyor transfer stations have currently transformed,and the transformation has a good popularization prospect, high economic and social value.