Effect Of Iron Oxide On Primary Products And Characteristics Of Coal Pyrolysis

Coal pyrolysis is an important method for coal utilization and is also the main stage of coal gasification and combustion.The minerals in coal or the additional minerals have an important effect on coal pyrolysis.In this paper,two typical demineralized coals(HSQDM and DLTDM)by acid pickling of Hongshaquan and Daliuta coal samples were selected in the study,and the influences of Fe2O3 on the evolution characteristics and distribution of primary products of these two demineralized coal pyrolysis were emphatically investigated.The main research works and results are as follows:The influence of Fe2O3 on the pyrolysis products characteristics and distribution of HSQDM and DLTDM were investigated by a novel in-situ pyrolysis vacuum ultraviolet single photon ionization time-of-flight mass spectrometry.The demineralized coal sample was mechanically mixed with Fe2O3 at mass ratios of 10:1,5:1 and 2:1 for in-situ pyrolysis.Due to the characteristics of in-situ sampling,soft ionization and high vacuum environment,the initial pyrolysis volatiles including alkenes,aromatic hydrocarbons,phenols,bi-phenols and a small amount of sulfur and nitrogen-containing substances can be detected.The results showed that Fe2O3 has similar influence on the products distribution of two demineralized coal samples,and relatively stronger on DLTDM than that on HSQDM.With the increase of Fe2O3 addition,the light fractions,such as alkenes and aromatic hydrocarbons,are promoted but bi-phenols is obviously inhibited.Correspondingly,the heavy products also decrease,but the peak temperature of the product increases.The increase of aliphatic carbon(or aromatic hydrocarbon substituted carbon)during coal pyrolysis is mainly responsible for the decrease of pyrolysis peak temperature.The kinetic calculation results show that the addition of Fe2O3 can reduce the activation energy of HSQDM pyrolysis reaction and make the reaction easier to proceed.The catalytic effect of Fe2O3 on the pyrolysis products of DLTDM was studied in a fixed-bed reactor with infrared heating.The results showed that the presence of Fe2O3 increases the yield of H2,CH4 and CO2 in gas products,while decreases the yield of CO during the temperature range of 550-750 ℃.According to liquid NMR analysis of650 ℃ tar,it was found that the aromatic carbon content in the tar generated by addition of Fe2O3 increases from 53.96% to 62.16%,and the proportion of aromatic hydrogen content also increases.GC-MS analysis indicated that the contents of light aromatic hydrocarbons(LAHS),polycyclic aromatic hydrocarbons(PAHs)and oxygencontaining substances(OCSs)in tar increase,indicating that Fe2O3 can promote the aromatization reaction of components in tar to generate more aromatic hydrocarbon products,and significantly improve the aromaticity of tar,meanwhile,Fe2O3 was successively reduced to the lower valence iron oxide.