基于SEM与XPS对焦炉上升管内壁结焦炭层织构的研究

Research of Texture Structure for Coke Layer in Ascension Pipe of Coke Oven Based on SEM and XPS

以焦炉上升管内壁结焦炭层为研究对象,采用扫描电子显微镜(SEM)和X射线光电子能谱仪(XPS)研究各结焦炭层的微观形貌、元素组成及键合状态,分析结焦炭层织构形成及演化规律。SEM研究表明,焦炉上升管内壁各结焦炭层形貌呈现较大的差异性,1#结焦炭层呈现0.1~1.0μm颗粒化炭颗粒松散堆叠的多孔结构,2#和3#结焦炭层呈现粒径为1.0~3.0μm的炭颗粒堆积形貌且致密性有所提高,4#结焦炭层呈现大量花纹状致密结构。以上现象可说明结焦炭层的形成过程为:首先由荒煤气中多环芳烃形成0.1~1.0μm的颗粒状初级炭层,颗粒状初级炭层在荒煤气粉尘中金属元素(如Fe)的催化作用下相互反应,形成更为致密的1.0~3.0μm的中级炭层结构,中级炭层在高温条件下进一步形成致密的终级炭层结构。XPS分析表明,1#—4#结焦炭层含C量分别为91.78%,91.95%,92.74%和94.01%,含O量分别为5.58%,5.42%,4.39%和2.86%,C/O比分别为16.45,16.96,21.12和32.87,说明在炭层结构变化的同时,炭层中含氧基团在高温及粉尘中金属元素(如Fe)作用下发生脱除反应,使得炭层中宏观C/O比逐渐升高。在此基础上,通过对C元素键合状态分峰发现,1^#—4^#结焦炭层中C—C/C—H结构含量分别为80.42%,78.00%,75.50%和81.29%,C—O/C—N结构含量分别为10.22%,11.93%,13.54%和9.35%,C=O/C=N结构含量分别为9.36%,10.07%,10.96%和9.36%。O元素键合状态分峰发现,1^#—4^#结焦炭层中=O结构含量分别为20.40%,22.21%,19.93%,18.36%,—O—结构含量分别为24.60%,27.80%,31.35%,37.82%,O2/H2O结构含量分别为55.00%,49.99%,48.72%和43.82%。以上现象说明结焦炭层上发生如下化学变化:初级炭层中多孔结构会吸附荒煤气中的氧气(O2)和水分子(H2O)在高温条件下对炭层进行氧化。脱除反应和氧化反应使得炭层中O元素在微观键合状态发生明显改变,最终使得炭层中O2/H2O和=O结构含量降低,—O—结构含量升高。以上研究揭示了荒煤气上升管结焦炭层织构形成及演化机制,为解决焦炉荒煤气上升管内壁结焦问题,提高换热器效能,降低焦化企业能耗提供了实验基础和理论依据。

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 0.1~1.0μm 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 0.1~1.0μm;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.