基于SEM与XPS对焦炉上升管内壁结焦炭层织构的研究

doi:10.3964/j.issn.1000-0593(2019)11-3333-07

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Abstract In this work, the coke layer on the surface of ascension pipe is investigated, and scanning electron microscope (SEM) and X-ray photoelectron spectrometer (XPS) are applied to research microscopic appearance, elemental composition and bonding state of different coke layers, and further analyze texture formation and evolution law of the coke layer. SEM analysis displays that: coke layer on the surface of ascension pipe presents different microscopic appearance, 1^# coke layer presents porous structure with 0.1～1.0 μm carbon particle loosely stacked; 2^# and 3^# coke layer show enhanced compactness with 1.0～3.0 μm carbon particle stacked; 4^# coke layer displays lots of compact patterned structure. The phenomenon indicates the formation process of the coke layer as follows: the polycyclic aromatic hydrocarbons react to form primary coke layer with particle size of 0.1～1.0 μm；primary coke layer react with each other to form compact intermediate coke layer with particle size of 1.0～3.0 μm in catalysis of metal element (Fe, et al) of dust in raw gas; intermediate coke layer further to form ultimate layer at high temperature. XPS analysis displays that, 1^#—4^# coke layer present C element content of 91.78%, 91.95%, 92.74% and 94.01%, O element content of 5.58%, 5.42%, 4.39% and 2.86%, corresponding to the C/O ratio of 16.45, 16.96, 21.12 and 32.87, indicating at the same time of structure change for the coke layers, oxygen-containing groups in coke layer conduct removal reaction under the condition of metal element (Fe, et al) of dust in raw gas, resulting the macroscopic increase of C/O ratio. Furthermore, peak fitting for bonding state of C element shows that 1^#—4^# coke layer present C—C/C—H structure content of 80.42%, 78.00%, 75.50% and 81.29%, C—O/C—N structure content of 10.22%, 11.93%, 13.54% and 9.35%, C═O/C═N structure content of 9.36%, 10.07%, 10.96% and 9.36%. Peak fitting for bonding state of O element shows that 1^#—4^# coke layer present ═O structure content of 20.40%, 22.21%, 19.93%, 18.36%, corresponding to —O— structure content of 24.60%, 27.80%, 31.35%, 37.82% with O₂/H₂O structure content of 55.00%, 49.99%, 48.72% and 43.82%. The above phenomenon indicates that the following chemical process are conducted on the coke layer: the porous structure of primary coke layer absorbs oxygen gas (O₂) and water molecule (H₂O), which oxidizes coke layer at high temperature. The oxidation reaction and removal reaction result in significant change of microscopic bonding state of O element in coke layer, decreasing content of O₂/H₂O and ═O structure and increasing —O— structure. The above research reveals texture formation and evolution mechanism of coke layer on the surface of ascension pipe, providing experimental and theoretical basis for solving coke problem of ascension pipe, enhancing heat exchange efficiency and decreasing energy consumption of coking enterprises.

Key words：Spectroscopy analysis; Coking mechanism; Texture; Scanning electron microscope; X-ray photoelectron spectrometer; Peak fitting

Received: 2019-01-04 Accepted: 2019-04-26

ZTFLH:

TQ522.15

Corresponding Authors: JIN Bao-sheng E-mail: bsjin@seu.edu.cn

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https://www.gpxygpfx.com/EN/10.3964/j.issn.1000-0593(2019)11-3333-07 OR https://www.gpxygpfx.com/EN/Y2019/V39/I11/3333