| Abundant tar-rich coals exist in the Northwest China.Although tar-rich coal had been widely exploited and utilized,and researches on tar-rich coal pyrolysis had focused on the pyrolysis process and product characteristics,pyrolysis utilization of tar-rich coal had multiple practical problems,such as unclear understanding of molecular structure and pyrolysis process,high heavy components of tar and difficult recovery of the catalyst.So,it it necessary to intensively investigate tar-rich coal.In the Northwest China,there are also a large number of low-grade iron ores with weak magnetism.Based on the catalytic effect of iron on coal pyrolysis,a fundamental study on the synergistic cooperative disposal of coal pyrolysis and iron ore reduction was proposed in this paper.Four typical tar-rich coal(XJ1,XJ2,SX1 and SX2)and two hematite ores(A and B)were selected to study the basic properties of raw materials and the rules of on functional groups and coal pyrolysis product.The effect of demineralization on surface morphology,microcrystalline and thermal transform characteristics of tar-rich coal was investigated by AFM Raman and a fixed bed reactor,and the influence formula of ash parameters on coal pyrolysis conversion was proposed.The compositions of coal pyrolysis productions during in-situ and non-in-situ catalytic pyrolysis of iron ore were compared.Thermodynamics and process phases of iron ore reduction were studied,as well as the magnetic separation parameters of iron ore.The main conclusions are as follows:(1)The proximate and ultimate analysis indicated that the descending order of the volatile matter was XJ1,SX2,SX1 and XJ2.XJ1 belonged to high-sodium coal with high CaO content,and the other three coals had high Si and Al content.FTIR analysis showed that the content of quaternary substitution of benzene ring was the highest in SX1 coal,and the other three coals were mainly ternary substitution of benzene ring;C-0 stretching vibration showed that XJ1 and XJ2 were strongly oxidized during formation process;The ratio of CH2 and CH3 indicated that XJ2 had the longest side chain and the least branch chain;Besides,it was found that the relationship between the content of C-O absorption vibration peak and the oxygen content in elemental analysis is basically the same.The strength of C-O absorption vibration peak was consistent with the content of oxygen in elemental analysis.And the pyrolysis hydrogen gas was closely related to the dehydrogenation of the hydrogenated aromatic structure.(2)TGA analysis showed that the descending order of the weightlessness was XJ1,SX1,XJ2 and SX2.The chemical bond attribution of the six sub-peaks of the fitting curve was determined by decoupling the volatiles from pyrolysis and analyzing the covalent bond fracture rule in DTG during pyrolysis.The fixed-bed pyrolysis experiments showed that the maximum yield of tar from XJ1,XJ2,SX1 and SX2 was 10.07%,9.31%,10.98%and 8.01%,respectively.The side chain of aliphatic hydrocarbon is cracked to form hydrogen radical,and the condensation of hydrogen radical resulted in increasing the yield of hydrogen.(3)It was found that the two-stage demineralization treatment(HF-HCl)reduced the ash content of the coal,increased the content of element carbon,and reduced the content of Na,Mg,Al,S and Ca in the ash.The pyrolysis experiment in fixed-bed experiment showed that demineralization treatment increased the yield of tar and gas.XRD analysis showed that demineralization treatment reduced the height of the coal crystallites and increased the diameter of the coal crystallites.Based on the AFM analysis,we found that the demineralized coal had a larger surface roughness than raw coal,and demineralization treatment caused the peaks and valleys of the surface roughness to interchange.From the Raman speetra,this study demonstrated that demineralization treatment can enhance disorder in the structure of coal,and a linear relationship between the half peak width of the Raman spectra and the coal carbon content was found in both raw coal and acid-treated coal.(4)After treating coal with potassium hydroxide,phosphoric acid,hydrochloric acid and hydrofluoric acid,the weight loss of SX1 and SX2 was significantly increased.The ash content resulted that acid treated coal can significantly reduce the alkaline components in coal ash,and the alkali treated coal can reduce the Si content and increase the Fe and Ca content.By associating the ash parameters with pyrolytic conversion(at 550?),we found that S value could predict the coal pyrolysis conversion.(5)The thermogravimetric analysis results indicated that the addition of iron ore increased the release of volatiles and decreased the temperature of the maximum weight loss rate.The fixed-bed pyrolysis experiment showed that the pyrolysis conversion rate of XJ2 and SX1 was increased by in-situ and non-in-situ pyrolysis of iron ore,the yield of char and tar was decreased,and the gas yield was increased.B iron ore had a stronger catalytic than A.The effect of in-situ catalytic pyrolysis with A iron ore was weaker than that of ex-situ catalytic pyrolysis,and iron ore B had a strong effect on ex-situ pyrolysis of XJ2 and in-situ pyrolysis of SX1,respectively.Gas composition analysis showed that iron ore increased H2,CH4 and CO2 content,and the effect of non-in-situ pyrolysis was stronger than that of in-situ pyrolysis.(6)The tar of in-situ pyrolysis with iron ore showed that the main components of XJ2 were aliphatic hydrocarbons,aromatic hydrocarbons and oxygen-containing derivatives,while the main components of SX1 were aliphatic hydrocarbons and aromatic hydrocarbons.The basic influence law of iron ore on coal in-situ pyrolysis is that the iron ore reduced aliphatic hydrocarbons content,increased the yield of monocyclic aromatic hydrocarbons and BTEXN,and reduced the integrity of oxygenated compound(phenols,aliphatic hydrocarbon oxygen-containing derivatives,and aromatic hydrocarbon oxygen-containing derivatives).The increase of monocyclic aromatic hydrocarbon content was not only related to the decomposition of polycyclic aromatic hydrocarbons,phenols and oxygen-containing derivatives of aromatic hydrocarbons,but also related to the cyclization and aromatization of saturated aliphatic hydrocarbons.The tar components analysis showed that the content of asphalt components in XJ2 and SX1 tars was high,while the asphalt content of XJ2 and SX2 decreased by 2.34%and 8.86%respectively by the addition of iron ore A and B during the in-situ pyrolysis process,and the asphalt content of XJ2 and SX2 decreased by 2.91%and 7.35%respectively by the addition of iron ore A and B during the ex-situ pyrolysis process.(7)The results of ex-situ pyrolysis tar analysis showed that the effect of catalytic deoxidation of iron ore during the ex-situ pyrolysis process was better than that of in-situ pyrolysis,and the CO2 and CO yield of coal ex-situ pyrolysis was higher than that of in-situ pyrolysis.The effect of iron ore on the aliphatic hydrocarbon cracking of tar from SX1 showed that the in-situ pyrolysis of coal with iron ore was stronger than that of ex-situ pyrolysis.The content of BTEXN from XJ2 increased by 8.30%and 3.72%respectively with the addition of A and B iron ore as the addition amount reached 20%during the ex-situ pyrolysis process,while the content increased by 0.74%and 7.73%respectively during the ex-situ pyrolysis process.Tar composition analysis reported that the asphalt component of XJ2 was reduced by 7.35%and 11.75%respectively by iron ore A and B in ex-situ pyrolysis process,while that reduced by 9.06%and 7.15%respectively during the in-situ pyrolysis process,which indicated that ex-situ pyrolysis of coal with iron ore had a better effect on improving the tar quality than in-situ pyrolysis.(8)The analysis of iron ores showed that the total iron content of A and B was 40.48%and 36.67%,respectively;the reduction temperature of hematite should be controlled below 1,000K to avoid overreduction,and the volume fractions of H2 and CO should be less than 52.93%and 41.07%,respectively(at 700?)in the cooperative disposal process.The optimum grade and recovery yield of A were 63.87%and 60.38%,respectively at the coal type of XJ2,pyrolysis mode of in-situ pyrolysis,temperature of 600?,addition amount of 20%and residence time of 30min.The optimum grade and recovery yield of B were 64.21%and 61.64%,respectively at the coal type of XJ2,pyrolysis mode of ex-situ pyrolysis,temperature of 600?,addition amount of 20%and residence time of 30min.XRD analysis of iron ores showed that the reduction path of iron ores in the process of coal pyrolysis and iron ore was Fe2O3?Fe3O4?FeO?Fe3C?Fe. |
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