Structural evolution of a bituminous coal char related to its synchronized gasification behavior with H2O and/or CO2
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摘要: 本研究以烟煤在1000 ℃热解所制得的焦样为研究对象，考察了其在H2O、CO2及两者混合气氛下的结构演变，以及气化反应性的影响。为了探究焦样在气化过程中的结构演变，利用氮吸附、SEM和拉曼光谱等表征手段分析不同碳转化率下的焦样结构。结果表明，H2O气氛对焦样结构的演变明显不同于CO2气氛，揭示了焦样在两种气氛下的反应路径不同。因结构演变的不同，随碳转化率的增加，焦样在两种气氛下表现出不同的气化反应性能。在CO2气氛下，焦样的气化反应速率随碳转化率的增加而逐渐降低，与H2O气氛存在下变化趋势相反。在H2O和CO2共气化条件下，煤焦在H2O和CO2混合气氛下的反应速率高于单气氛下的反应速率的计算值，表现出一定的协同作用。这是因为焦样与H2O反应能够产生较大的比表面积，为焦样与CO2反应提供更多的反应场所，促进了焦样与CO2的反应。
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关键词:
- 烟煤 /
- 焦气化 /
- 结构演变 /
- H2O和CO2混合气氛 /
- 协同作用
Abstract: This work aims to investigate the structural evolution of the char during gasification under a single or mixed atmosphere of H2O and/or CO2 with the synchronized investigation of the effect of the varying char structure on the gasification reactivity. The experimental char was prepared from a bituminous coal at 1000℃. The changes of the char structure along with the progress of the carbon conversion during gasification were characterized using N2 adsorption, SEM, and Raman spectroscopy. The results revealed that H2O showed a more dramatically change on the char structure than CO2 and two reactants had different reaction pathways. The different pathways of reactants affected the evolution manners of the char structure and different gasification reactivity of char was related to structural evolution. The specific reaction rate between the char and CO2 decreased monotonously with increasing carbon conversion. However, the opposite trends are observed when H2O exist, either H2O alone or the mixtures of H2O and CO2. The char gasification reactivity was under the common effect of physical and chemical structure. In terms of the mixture of H2O and CO2, the significant specific surface area caused by H2O provided more active sites for CO2. The interactions between H2O and CO2 promoted reaction between C and CO2 (C + CO2 → CO) in mixtures of H2O and CO2, leading to higher amount of CO and higher specific reaction rate than calculated.-
Key words:
- bituminous coal /
- char gasification /
- structural evolution /
- H2O and CO2 mixed atmospheres /
- active cooperation
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Figure 2 Changes of physical structure with carbon conversion of char in various atmospheres
(a): specific surface area; (b): average pore diameter ■ : H2O; ● : CO2; ▲ : H2O+CO2
Figure 3 SEM images of raw char and chars at 50% carbon conversion obtained in various atmospheres
(a): 50.0 k×; (b): 100.0 k×
Figure 4 Changes of chemical structures with carbon conversion of char in various atmospheres
(a): total Raman area; (b): I(Gr+Vl+Vr)/ID ratio ■ : H2O; ● : CO2; ▲ : H2O+CO2
Figure 5 Changes of specific reaction rate with carbon conversion of char in various atmospheres
Figure 7 Changes of intrinsic reaction rate with carbon conversion of char in various atmospheres
Figure 8 Experimental and calculated curves of gases released from char gasification in mixed atmosphere
Figure 9 Experimental and calculated values of gas release quantity at various carbon conversion ranges of char in mixed atmosphere
(a): H2; (b): CO
Table 1 Proximate and ultimate analyses of coal and char samples
Sample Proximate analysis w/% Ultimate analysis wdaf/% Mad Ad Vdaf C H O* N S BC 0.65 33.39 26.97 79.25 4.68 10.57 1.87 3.63 BC-C 0.24 45.93 3.56 93.02 0.54 1.78 1.82 2.84 note: ad: air dry base; d: dry basis; daf: dry and ash-free basis; *: by difference 
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Table 2 Analyses of ash composition in coal sample used in experiment
Composition w/% SiO2 Al2O3 Fe2O3 CaO MgO TiO2 SO3 K2O Na2O P2O5 46.48 42.51 2.09 1.2 0.25 2.27 0.3 0.58 1.92 0.06
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