Migration And Partition Of Trace Elements In Coal During Gasification In Entrained-flow Gasifier

Coal gasification,as a clean and efficient technology of coal conversion,is the fundamental and core technology for modern coal chemical industry.Currently,entrained-flow gasification develops rapidly as one of the key development directions because of its high efficiency and environmentally friendly.Some trace elements?TEs?in coal are thought to pose a potential risk for the public health and natural environment,even if present only at the parts-per-million level.However,the migration and transformation of TEs during coal gasification in entrained-flow gasifier is lack of intensive and thorough study.In order to predictive to the transformation form and release direction of TEs during coal gasification in entrained-flow gasifier,research on the migration and redistribution of TEs during coal gasificaton in entrained-flow gasifier is necessary.And a theoretic approach is offered for controlling the toxic TEs in coal during coal gasification at last.The behavior of TEs in coal during modern coal gasification is closely related to the occurrence characteristics of TEs and the technical characteristics of coal processing.In this study,the in-depth coal analysis and evaluation,the compositon and content of minerals,the distribution and enrichment of TEs in coal are all attribute to obtain the effects of the modern coal gasification in entrained-flow gasifier on the release,migration,redistribution of TEs in coal.What's more,some samples are collected from the industrial coal gasification plant in a large-scale coal chemical industry base to analyze,so as to gain the migration law of TEs in coal during gasification.The different ranks coal including lignite,subbituminous coals,meager coal and anthracite are chosen as representative raw materials for coal pyrolysis and gasification.Coal gasification in entrained-flow gaisifer is decoupled into the fast pyrolysis?⁹00??,the high temperature pyrolysis?1000¹500??and the gasification after the touching between coal/char and gasification agent.The samples obtained from different stages are collected in a fast pyrolysis device and a gasification experimental system respectively.A comprehensive investigation using X-ray diffraction analysis,X-ray fluorescence analysis,Fourier transform infrared spectroscopy,gas chromatography,a mercury analyzer,ion-selective electrode measurements,inductively coupled plasma mass spectrometry is performed to reveal the law of the transformation behavior of TEs in coal.The main contents of the paper conclude:?1?the relationship between process parameters?temperature,O₂/coal,H₂O/coal,carrier gas?and gasification with different ranks of coal;?2?the migration behavior of TEs in different coals during fast pyrolysis?⁹00??;?3?the migration behavior of TEs in different coals during high temperature pyrolysis?1000¹500??;?4?the migration behavior of TEs in different coals during gasification in entrained-flow gasifier.Based on the result of experiment study,the partitioning mechanism of TEs in coal during entrained-flow gasification has been obtained.And the migration and partition of TEs in coal during entrained-flow gasification is explained by using the gray-box model of gasification in entrained-flow gasifier.The main conclusions are as following:?1?The gasification performance of low rank bituminous coal,such as Lingwu coal and Datong coal,is better than that of lignite,meager coal and anthracite.The increasing of temperature can promote the gasification performance.The content of CO and effective gas?CO+H₂?in syngas can be increased by substituting CO₂ for N₂ as carrier gas.The result also proves that bench-scale unit can simulate large-scale industrial gasifier well.?2?Wulantuga coal,with high-sulfur and low-ash yield,is enriched with As,Be,Ge,Sb,Hg.The concentrations of As,Be,Ga,Sb,U and W in char samples are higher than those in coal.Hg is the most volatile element.The concentrations of Se and Ge are initially higher but decrease with the increasing pyrolysis temperature.?3?The gasification performance of Lingwu coal is better than other coals',and it has a low-ash yield and low concentration of TEs.The contents of most rare earth elements?REEs?show a tendency to increase in chars during fast pyrolysis,especially the increase of Eu followed by Gd and Er.In contrast to the negative anomaly of Eu and Ce in coal is conspicuous,the negative anomaly of Eu in chars is unconspicuous.The distribution pattern curves of REEs in coal and char samples are similar,which is conspicuous negative anomaly of Eu in coal.And the distribution pattern curves of light rare earth elements move up obviously with the increasing temperature,while unobviously for heavy rare earth elements.?4?Ganhe meager coal has high-sulfur and high-ash yield,and it is enriched with As,F,Ga,Hg,Rb,Se and U.During fast pyrolysis,the concentrations of Li,Be and U in the char samples are higher than those in raw coal,while the opposite are observed for Hg,As,Ga and Rb.The concentrations of F and Se are initially higher but decrease with pyrolysis temperature.The analysis of the minerals and organic structure of Ganhe coal and chars indicate that: Hg releases when the pyrite decomposes,and the concentration of F decreases while the fluoride minerals disappears.Under the same pyrolysis condition,the behavior of Se,Hg,Be,U in different coals is similar,while other elements' is not.?5?During high temperature pyrolysis,the concentrations of V,Ga and U in Ganhe chars increase with the increasing temperature,while the opposite are observed for Be,Cr,Ni,Sr.The concentrations of Pb and Cs increase initially and decrease at last,while the opposite is observed for Li.The concentrations of V,Cr,Ga,Ni,Li,Sr,Cs and U in Lingwu chars increase.The concentration of Be decreases,while the concentration of Pb decreases only if the temperature beyond 1100?.?6?The behavior of TEs in Ganhe and Lingwu residue is affected by the temperature obviously.The concentrations of V,Be,Cr in Ganhe residues increase initially and then decrease with the increasing temperature.The behavior of U and Ni are same in the both kinds of coal.CO₂,substituting for N₂ as carrier gas,has little effect on the migration of TEs,except for Ganhe residues.?7?The fast pyrolysis,high temperature pyrolysis and gasification experiments are accomplished based on the decoupling of gasification in entrained-flow gasifier.The migration law of TEs in laboratory agrees with the variation of TEs in on-site samples of gasification plant.The partition mechanism of TEs during gasification in entrain-flow gasifier is gained and the behavior is explained by the gray-box model of gasification in entrained-flow gasifier.The volatile TEs,such as Hg,releases to gaseous phase during the fast pyrolysis.Pb can enrich at solid phase products during pyrolysis,while be carried away from coarse residue.The REEs enriches at solid phase products during gasification.