热解酸洗煤焦结构特性以及与其反应性关系研究

Structural characteristics of char derived from acid-washed coal pyrolysis and its corrections with char reactivity

酸洗过程可消除煤中具有显著催化作用的碱及碱土金属组分对热解煤焦的影响,从而能够单一解析热解后煤焦结构特性以及与其反应性之间的内在关系。以瞬间给料方式将酸洗煤样喷入流化床反应器内,制备不同热解温度下的酸洗煤焦样品。采用S,D,A1,A2,G和G*6个特征峰的拉曼光谱拟合方法表征煤焦结构特性。结果表明:以I(D)/I(S+D+A1+A2)特征峰比率表征的煤焦微晶结构比重随热解温度逐渐升高,以I(A1+A2)/I(D)表征的小环与大环芳香结构比重随热解温度逐渐降低,说明大小环芳香结构之间转化是煤焦不定形结构向晶体结构转化的主要过程。800℃以上热解温度下煤焦反应性随转化率分布相比600℃和700℃低温热解煤焦反应性分布更加集中,说明不同热解温度下主导煤焦反应性的结构特征不同。煤焦拉曼结构与其反应性之间的相关性表明I(D)/I(S+D+A1+A2)酸洗煤焦结构特征能够较好地关联煤焦反应性。

Acid-washed process can eliminate the effects of alkali and alkaline earth metallic species on the characteristics of char derived from pyrolysis.The evolution of char structure and its correction with char reactivity is thus to be investigated independently. Acid-washed coal is injected into a fluidized-bed reactor instantaneously to prepare the acid-washed char samples under different pyrolysis temperatures. The FT-Raman spectra of chars in this study is curve-fitted with six bands representing structural characteristics of chars. The results show that the ratio of I(D)/I(S+D+A1+A2) representing the microcrystalline degree of char increases,and the ratio of I(A1+A2)/I(D) representing the degree of small aromatic ring and large aromatic ring system in char decreases gradually with increasing pyrolysis temperature.Taking the changes of I(D)/I(S+D+A1+A2) and I(A1+A2)/I(D) together into account,it indicates that the conversion of smaller aromatic rings to the large aromatic rings would mainly account for the growth in the carbon crystallites.The differences of the reactivity of char at various conversion levels under 600 ℃ and 700 ℃pyrolysis are larger than that of the reactivity of char under 800 ℃ pyrolysis.It indicates that the char reactivity is dependent on the different structural characters of char at different pyrolysis temperatures.The relativity between the Raman structures and the char reactivity illustrates that the ratio of I(D)/I(S+D+A1+A2) could well correlate with char reactivity.