Study On The Kinetics Of Combustion And Distribution Of Arsenic With Low Rank Coal In The Southern Junggar Coalfield

Xinjiang is featured with richness of coal resources which most of them are attributed to the low rank coal.Due to the shallow deposition of coal,dry climate and low recovery of coal mining,the coal in this region is very apt to spontaneous combustion.Besides the pollutants,such as the COx,the SOx,and the NOx,etc.which were produced from coal combustion,other harmful elements,such as the mercury(Hg),the Arsenic(As),the Gallium(Ga),Cadmium(Cd),the Chromiun(Cr)and the Lead(Pb)also were accumulated in ash of coal combustion.Especially,the arsenic(Ar)was well known due to its high toxic and carcinogenic.In the present paper,a comprehensive methods,including the SEM,the FTIR,the TPO and the TGA,etc.,were employed to quantify the kinetics of low rank coal oxidation of Sourthen Junggar Coalfield.Then,the XRD,the SEM-EDS and the HSC chemistry tool was employed to quantify the distribution of arsenic compounds during the increase of temperature of coal oxidation and combustion.(1)Results from the SEM show that the micro form and structure of raw coal which were collected from different mining areas is the same to an extent.For the heated coal samples at the temperature of less 400 Celsius degree,the coal surface shows no obvious changes.For the heated coal samples at the temperature of over 400Celsius degree,the fibers,cracks and depth as well as sizes were found on the coal surface.Results from FTIR show that the relative content of oxygen functional groups of coal samples increased with decreasing particle size,and the oxygen functional group is an important indicator in the coal oxidation,which indicates that the smaller the particle size of coal is,the more favorable the oxidation,and the Sikushu coal sample is easier to be oxidized(especially and<0.075 mm).(2)Results from TPO show that the oxygen-consumption rate of all coal samples increases exponentially with the increase of temperature.Results from TGA show that the characteristic temperature T₃ of Wudong and Dahuangshan coal samples decreases with the reduction of particle sizes,the Sikeshu's increases with the reduction of particle sizes.In the T₁-T₂ stage,the activation energy(39-59 k J·mol^-1)of Wudong coal samples lower than the other coal samplesdecreased with decreasing particle size,indicating that the raw coal was easier to be oxidized by Wudong coal samples;the activation energy(15-61 k J·mol^-1)of Sikeshu coal samples showed a decrease with increasing heated temperature,which indicated that it was easy to be oxidized after heated temperature,and the higher the temperature was,it was the easier to be oxidized.(3)Results from XRD show that the quartz,the kaolinite,the calcite and the dolomite are the major minerals within raw coal,and the quartz and the kaolinite are the major minerals within coal ash.Results from SEM-EDS show that all coal samples contains less arsenic which indicates most of them probably was released by gaseous phase with comparison of the raw coal arsenic content.(4)Results from HSC chemistry simulation show that all samples'arsenic distribution has the same trend at different pressures of air atmosphere condition.And with the increase of pressure,the solid As₂O₅ was produced prior to other arsenic compounds,and the gaseous As O₂ contents increases with the increase of temperature.The gaseous products contents,including the As O,the As₂O₃,the As₄O₆,and the As₄O₇,together with the solid As of raw coal decrease with the increase of temperature.At the condition of oxygen-rich atmosphere,the range of temperature for the gaseous As H₃was wide than that of other products with the increase of temperature,and the content of gaseous As H and As S decrease with that except the gaseous As H₂.The generating temperature of the As,the As H,the As H₂,and the As S increase with the increase of pressure.When the pressure was alternated from 0.01 MPa to 0.1 MPa and from 0.1MPa to 1.0 MPa,the generating temperature of products was higher with 300 Celsius degree than that of normal standard condition.And when the pressure was changed from1.0 MPa to 2.0 MPa,the generating temperature was higher 200 Celsius degree than that of the normal standard condition.