Study On Transformations Of Mineral Matter During Pulverized Coal Combustion By Infrared Spectroscopy

Thermal transformations of mineral matter in the pulverized coal combustion have important effects on the burning of the organic matter and the dopistion and slagging of minerals.Therefore,accurate analysis of mineral composition of coal and coal ash is of vital importance.The most commonly used method of analysis of mineral matter in coal and coal ash is X-ray diffraction(XRD)technique.However,the XRD technique is limited by the detection of amorphous minerals.In recent years,Fourier transform infrared spectroscopy(FTIR)technique has been increasingly used in characterization of minerals.FTIR technique is another effective method for the identification of minerals because is not limited by the degree of mineral crystalline.In this article FTIR technique is applied to study on thermal transformations of the high silicon aluminium ratio and high-calcium coal in O2/N2 and O2/CO2 combustion atmosphere,and compared with the results of XRD analysis.(1)Thermal transformations of mineral matter in the high Si/Al ratio and high-calcium coal in the coal combustion has been investigated.FTIR analysis results show that absorption bands of kaolinite(3696,3619,938 and 913 crm-1)disappears at 500 ? in coal ash,and kaolinite removal of crystal water to form metakaolinite(1041 and 559 cm-1),and transformed into mullite at 900 ?(1090,790 and 550 cm-1).The muscovite in coal ash complete dehydroxylation process at 900 ?,and 840 cm-1 peak disappear.Muscovite internal tetrahedron structure was destroyed when 1100 ?,and transform into alkali-feldspar,and the peaks of 470 and 430 cm-1 disappear.The calcite in coal ash begins to decompose at 500 ?,and the peaks of calcite(1447,875 and 712 cm-1)disappear at 900 ?.The aluminosilicate minerals in coal ash react with CaO to form gehlenite(974,934,853,706 and 669 cm-1)at 900 0C.The metakaolinite in coal ash reacts with CaO to form anorthite(991,911,755 and 684 cm-1)at 1100 ?.(2)FTIR and XRD can well reflect the thermal transformation process of quartz,calcite,anhydrite,anorthite and gehlenite in coal ash.XRD analysis results show that the kaolinite in coal ash disappear at 500 ?.The ash content of muscovite in present the trend of increase after decreases first,and muscovite in coal ash completed the thermal transformation process at 1100 ?.The hematite,alkaline feldspar and quartz in coal ash are involved in the thermal transformation process at high temperature,and their contents are decreased.Comparison of FTIR and XRD results show that there is not metakaolinite and mullite bands in the XRD spectrum;therefore,FTIR is more specific to the thermal transformation process of kaolinite in coal.FTIR results showed that muscovite finish dehydroxylation reaction in 900 ?,and thermal conversion process of muscovite is more specific.FTIR is more sensitive to feldspar identification in coal,and the identification of hematite in coal is not as sensitive as XRD.(3)The effect of the combustion atmosphere(O2/N2 and O2/CO2)to the transformation of mineral matters in coal has been studied.It is found that the aluminosilicate minerals in coal ash are not affected by the combustion atmosphere.The decomposition of calcite.is inhibited by CO2,and a little calcite is still decomposed at 900? in O2/CO2 atmosphere.High concentrations of CO2 both promote the formation of anhydrite and inhibit the decomposition of anhydrite.The O2/CO2 combustion atmosphere is favorable for the formation of anorthite and gehlenite in coal ash,and the relative content of anorthite and gehlenite in this atmosphere is higher.