Characteristics Of Particulate Matters From Unorganised Emitting Sources Of Steel Plants

Steel industry is a significant contaminant emitter with a large scale of production and multiply particulate matter(PM)emitting sources.It is important for source apportionment of PM and improvement of dedusting technology by clarifying the characteristics of PM from steel plants.However,previous studies on the PM characteristics of steel plants mostly foucus on organized emitting sources,whilst few reports on unorganized emitting sources are reported.Aiming to find out the characteristics of PM from unorganized emitting sources of the whole process of steel production,a steel plant,with the yield of 20 Mt/a,in China is investigated.The morphological,chemical,and physical characteristics of PMs from unorganized emitting sources of the selected plant are comprehensively and quantitatively analysed through on-site sampling and laboratory testing.The main tasks of this work are as follows:(1)Total suspended particle(TSP)and PM10 were collected from 18 unorganized emitting sources in the steel plant using the IFC-2 explosion-proof dust sampler and the Anderson impactor.The morphological characteristics of the PMs are studied by using a scanning electron microscopy and a laser particle size distribution analyzer.The microscopic morphology of PMs from unorganized emitting sources can be mainly divided into:irregularly Fe-,Si-,Ca-and Mgrich mineral particles produced by physical means such as mechanical crushing,belt conveying and discharge dropping;layered carbonaceous particles produced by mechanical crushing and combustion cracking;spherical Si-,Al-and Fe-rich particles in a high temperature molten state;chain and agglomerate particles formed by the polymerization of high temperature flue gas and some volatile minerals.The particle size of the TSP from unorganized emitting sources is mainly within 0.1-716 ?m,with the forms of both single peak and double peaks.The size of PMs with a single peak distribution are larger than 15 ?m,whilst PMs with bimodal distribution are partially gathered around the size of 1,3,4,and 5 ?m and partially dispersed around 40,120,30,and 110?m.In addition,PMs from unorganized emitting sources are mostly large particles,and the share of cumulative PM10 is 25%-35%.(2)Chemical characteristics are studied by using an x-ray fluorescence spectrometer,an infrared carbon sulfur analyzer and an inductively coupled plasma optical emission spectrometer.The dominant harmful components in the PMs from unorganized emitting sources are TMn,As,Cr2O3,Al2O3,S and Zn,of which Al2O3 and S are mainly from the crushing chamber,coke oven top and transferring station.The mass fractions of Al2O3 are 3.20%,3.79%and 1.85%,respectively;whilst S are 0.81%,0.98%and 0.38%,respectively.TMn is mainly from LF refining furnace with a mass fraction of 1.28%.The recyclable components in PMs from unorganized emitting sources are TFe,CaO,SiO2,C and MgO.The mass fraction of TFe ranks first in sintering,ironmaking and steelmaking processes,with the values of 7.26%-57.79%.(3)Physical characteristics such as electrical resistivity,magnetic properties and wettability are studied by using a resistivity tester,a magnetometer,and a contact angle tester.The resistivity of the PMs is generally within the range of 104-1013 ?·m.The resistivity decreases as the mass fraction of water in the PMs increases.The saturation magnetization and coercivity of the PMs are 11.69-245.21 emu·cm-3 and 11.08-100.62 Oe,respectively.The magnitude of coercivity is related to not only the mass fraction of TFe,but also the PM size.In addition,the mass fraction of particles with the size of less than 1 ?m has a strong correlation with the ratio of residual saturation magnetization to saturation magnetization(Mrs/Ms),showing a strong single domain property.The contact angle between the PMs and the pure water droplet is generally lower than 90°,showing a good wettability.The contact angle generally decreases with increasing temperature.In the initial state,the contact angle of the particles from the hot metal relading station reaches the maximum at 58.9°;whilst from the ring cooler is the smallest,only 20.1°.In addition,the contact angle of the particles from the top of the coke oven is most sensitive to temperature.When the temperature raises from 30? to 80?,its contact angle drops from 57.2° to 24.8°.The particles from the ground of returning ore tank are least sensitive to temperature,with the contact angle reducing from 32.6° to 29.8°.