石灰岩对褐煤模拟地下气化残焦物化性质的影响

基于煤炭地下气化过程中石灰岩可能影响煤焦的组成和结构,借助煤炭地下气化模拟实验系统对不同石灰岩掺量(质量分数为0-30%)的褐煤进行水蒸气气化,并采用低温N_2吸附-脱附、XRD和FT-IR等分析手段研究石灰岩对褐煤模拟地下气化残焦的组成、比表面积及孔结构特征、微晶结构和表面官能团等物理化学性质的影响。结果表明,石灰岩对煤焦的元素组成有较大影响。石灰岩可促使煤焦中的微孔向中孔发育,增大煤焦的比表面积和孔容积;当石灰岩掺量从0增加到30%时,煤焦的比表面积增大21.91%,介孔率增加21.49个百分点。XRD分析表明,钙的存在破坏煤焦的芳香结构,使煤焦无序化程度增加,晶面间距(d_(002))增大,抑制煤焦的石墨化发展倾向。FT-IR分析表明,石灰岩存在下,煤焦的羟基官能团减少。

Effect of limestone on physicochemical properties of the residual chars from simulated underground gasification of lignite

Based on the possible effect of limestone on composition and structure of coal chars during underground coal gasification (UCG), gasification of lignite by steam with different dosages of limestone of 0-30% (mass fraction) was performed in a simulated UCG test system. The composition, specific surface area (S_BET) as well as pore structure properties, microcrystal structure and surface functional groups of the obtained residual chars were examined by low-temperature nitrogen adsorption, XRD and FT-IR, etc. The results show that composition of coal char is significantly influenced by limestone. Limestone contributes to development of micro-pore toward meso-pore, increases S_BET and total pore volume (v_t) of residual chars. When dosage of limestone increases from 0 to 30%, the S_BET of residual chars increases by 21.91%, and the ratio of meso-pore volume to total pore volume rises percentage points of 21.49. XRD analysis shows that the presence of calcium destroys aromatic structure of coal char, increases both degree of disorder and interplanar spacing (d₀₀₂), and inhibits graphitization tendency of coal char. FT-IR analysis indicates that hydroxyl group of residual chars is reduced with the presence of limestone.