Influence of inherent minerals on CO2 gasification of a lignite with high ash content
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摘要: 利用分选结合逐级酸洗的方法制备出不同灰含量和矿物组成的褐煤煤样，使用沉降管反应器（DTR）和热重分析仪（TGA）研究内在矿物在1 000-1 200℃对褐煤CO2气化的影响。结果表明，内在矿物对褐煤CO2气化具有促进作用，且促进机制具有温度敏感性。低温时（1 000℃），内在矿物可通过增加初生半焦微晶结构的无序度，间接提高气化碳转化率。高温时（1 100-1 200℃），内在矿物通过催化煤焦气化，直接促进气化碳转化率的上升。碱性指数不适用于表征本研究的褐煤内在矿物的催化作用。Ca是内在矿物中影响整体催化能力的主要成分，而且羧酸盐形式的Ca是其中的活性组分。不同的催化机制是导致煤焦中钙的催化活性因其化学形式而异的根本原因。羧酸盐形式的Ca可降低煤焦气化反应的活化能，而CaO则提高反应的表观频率因子。Abstract: Lignite samples with different ash contents and mineral composition were prepared by dry separation and acid washing. A drop tube reactor and thermogravimetric analyzer were used to study effect of inherent minerals on CO2 gasification reaction of lignite at 1 000-1 200 ℃. The results show that the inherent minerals have positive effects on gasification, which are temperature sensitive. At lower gasification temperature (1 000 ℃) the inherent minerals can improve carbon conversion indirectly by obstructing the carbon structure order of nascent char. At higher temperatures (1 100-1 200 ℃)the inherent minerals can improve carbon conversion by catalyzing nascent char gasification directly. The alkaline index is not suitable for characterizing role of the inherent minerals of lignite in this case. Ca leads to the difference in catalytic activity of the inherent minerals where the most active form is carboxylate. Various catalytic mechanisms are the root cause of different catalytic activity of Ca in different chemical forms. Ca in the form of carboxylate can reduce the activation energy of coal/char gasification reaction, while CaO only promotes the apparent frequency factor.
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Key words:
- lignite /
- inherent minerals /
- CO2 gasification /
- catalytic mechanism /
- chemical form
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图 2 煤样不同温度的气化碳转化率
Figure 2 Carbon conversion of lignite samples at different gasification temperatures
: 1 000 ℃; : 1 100 ℃; : 1 200 ℃;
图 3 煤样的碱性指数及不同温度热解半焦中可萃取AAEM总量
Figure 3 Alkaline index of lignite samples and total amount of extractable AAEM in chars from pyrolysis
图 4 热解半焦Raman光谱的ID/ I(GR +VR+VL)
Figure 4 Raman band ratio (ID/I(GR +VR+VL)) for chars form pyrolysis of lignite samples
图 5 1 000 ℃热解半焦等温气化反应性能
Figure 5 Isothermal gasification reactivity for chars from 1 000 ℃ pyrolysis of lignite samples
(a): 900 ℃; (b): 1 000 ℃
图 7 非等温气化反应的TGA曲线
Figure 7 TGA curves of non-isothermal gasification;
(a): weight loss curve; (b): weight loss rate curve —●—: char; ——: char+CaO; —▲—: char+CaCO3; ——: char+Ca(OAc)2; —■—: CaCO3; ——: Ca(OAc)2
图 8 添加不同催化剂半焦气化后的SEM照片及对应的Ca元素分布的EDS分析
Figure 8 SEM images of gasified chars added catalysts and corresponding Ca distribution obtained by EDS analysis
(a): surface morphology of char; (b): Ca distribution
表 1 煤样的工业分析和元素分析
Table 1 Proximate analysis and ultimate analysis of the coals
表 2 灰分的矿物成分
Table 2 Inorganic constituents contents in coal samples in an oxide form
表 3 热解半焦的收率
Table 3 Yield of the char
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