煤吸附超临界状态甲烷—水蒸气规律及注热增产机理研究

发布时间：2018-02-27 14:10

本文关键词： 超临界状态吸附注热吸附势理论密度泛函理论最优注热比　出处：《太原理工大学》2017年硕士论文　论文类型：学位论文

【摘要】：注热增产煤层气是时下煤层气增产的有效方法之一。储层条件多数超过甲烷的临界温度和临界压力,所以煤层中的甲烷更多以超临界状态存在。注热增产煤层气时,面临的首要问题是如何置换出吸附态的超临界状态甲烷。当煤层中注入水蒸气时,水蒸气同样会在煤孔隙裂隙表面上吸附,打破煤吸附超临界状态甲烷的吸附平衡。由于煤层中的超临界甲烷大多以吸附态存在的,所以研究煤吸附超临界状态甲烷吸附模型和水蒸气吸附机理与吸附规律显得尤为重要。本文依据热力学理论分析了吸附过程热量的变化;依据表面物理化学原理分析了不同煤阶煤吸附超临界甲烷和水的吸附特性;依据有机化学知识分析了煤分子结构,并采用密度泛函理论(DFT)模拟计算不同煤阶与甲烷、水的竞争吸附机理,探索注热开采机理。主要结论如下:(1)以超临界状态甲烷为研究对象,分别根据吸附势理论模型和等量吸附热吸附模型,构建了两种由超临界吸附等温方程和任意两组等温吸附实验数据预测计算任意等温度条件下的超临界吸附量的方法。根据27.5℃、50℃下的实测吸附等温线,采用两种计算方法分别计算了40℃下的超临界吸附等温线。计算结果与40℃实测的吸附等温线比较,两种计算方法都与实测结果基本一致,吸附势模型计算过程更简单。(2)根据量子化学密度泛函理论,采用Gaussian软件模拟了褐煤分子、高挥发分烟煤分子、无烟煤分子等不同煤阶煤分子与CH_4分子之间、水分子之间的吸附机理和注热开采煤层气的增产机理。模拟计算结果表明:(1)不同煤阶的煤分子吸附CH_4的吸附位点不同,褐煤分子吸附CH_4最稳定的位点在褐煤分子上方3.9683×10-10m处,吸附能为-20.92k J/mol;高挥发分烟煤分子最稳定吸附位点在于高挥发分烟煤分子上方,六元环侧,分子之间的距离为4.596×10-10m,吸附能为-27.79k J/mol;无烟煤分子吸附最稳定位点在无烟煤分子平面上方4.6107×10-10m处,吸附能为-38.92k J/mol。上述三种煤阶吸附CH_4的作用范围都在范德华力有效作用范围以内,无论煤阶如何,煤分子与CH_4之间是物理吸附,且随着变质程度增加,吸附CH_4的吸附能增加,即煤阶越高,吸附越稳定。(2)当水分子吸附平衡时,H_2O和褐煤分子、高挥发分烟煤分子和无烟煤分子中的羟基形成氢键。通过Mulliken电荷布局分析,得知煤分子中的羟基为氢键给予体,水分子为氢键受体,由于电荷偏移,导致了煤分子中的羟基键能和水分子中的羟基键能都发生了改变。褐煤分子中含氧官能团种类较多,羧基吸附H_2O能力最强,此时的吸附结构最稳定。通过比较吸附CH_4时的和H_2O时的吸附能,得到不同煤阶煤分子对H_2O的吸附能力均要强于CH_4,氢键的作用强于范德华力。(3)当CH_4、H_2O同时存在吸附体系中时,H_2O会抢占CH_4的吸附位,并且H_2O与煤分子之间的距离均要比CH_4近,吸附H_2O的能力要强于吸附CH_4。由于水与煤的吸附能大,与煤分子间距离近,H_2O与CH_4之间存在竞争吸附,所以注热蒸汽能提高煤层气采出率。(3)为最大限度的置换出吸附态下的超临界甲烷,又不注入过量水蒸气,提高注气效果,根据单组分吸附势模型计算的单组分吸附量和吸附能,再根据多组分N-A吸附模型计算混合气体总吸附量,最后导出了单纯考虑水蒸气和超临界甲烷竞争吸附下最优注热比。该参数对注热工艺设计具有一定指导意义。
[Abstract]:Note the hot coal gas production is one of the effective methods nowadays for enhancing coalbed reservoir conditions. The critical temperature and the critical pressure of methane over the majority, so in the coal seam methane more in supercritical state. Heat injection enhancing coalbed methane production, the primary problem facing is how to replace supercritical methane adsorbed. When steam injection in coal seam, water vapor will also be adsorbed on coal pore and fracture surface, breaking the adsorption equilibrium of supercritical methane adsorption of coal. Because of coal in supercritical methane mostly exist in the adsorbed state, so research on coal adsorption supercritical methane adsorption model and water vapor adsorption mechanism and adsorption law is this is particularly important. Based on the theory of thermodynamics analysis of the change of the adsorption process of heat; based on the surface physical chemistry principle analysis of adsorption characteristics of supercritical methane and water adsorption of different rank coals According to the knowledge of organic chemistry; analysis of the molecular structure of coal, and using density functional theory (DFT) simulation of different rank coal and methane, the competitive adsorption mechanism of water, to explore the mechanism of heat injection exploitation. The main conclusions are as follows: (1) uses the supercritical methane as the research object, according to the model and the isosteric adsorption potential theory the heat adsorption model, and constructs two kinds of prediction methods of supercritical adsorption and calculation of arbitrary temperature conditions by supercritical adsorption isotherm and the adsorption isotherm any two groups of experimental data. According to the measured 27.5 DEG C, adsorptionisotherm 50 C, 40 C under supercritical adsorption isotherms were calculated by two the calculation method respectively. Adsorption isotherm calculation results and measured 40 degrees, two kinds of calculation methods are basically consistent with the measured results, the adsorption potential model process is more simple. (2) according to quantum chemical density functional theory, using G Aussian software to simulate the lignite molecules, high volatile bituminous coal, anthracite and other molecules between different rank coals and CH_4 molecules, water molecules between adsorption mechanism and heat injection exploitation of coalbed gas production mechanism. The simulation results show that: (1) adsorption sites of coal molecular adsorption of CH_4 with different coal ranks of lignite CH_4 is the most stable adsorption sites in the molecule above 3.9683 * 10-10m lignite, adsorption energy of -20.92k J/mol; high volatile bituminous coal is the most stable molecular adsorption sites of high volatile bituminous coal molecule above six membered ring side, the distance between the molecules is 4.596 * 10-10m, the adsorption energy is -27.79k J/mol the most stable adsorption; Anthracite location above the molecular plane of 4.6107 * 10-10m anthracite, the adsorption energy range above three J/mol. -38.92k rank CH_4 adsorption were within the effective range of fan Edward force, regardless of rank as Where, between the coal molecule and CH_4 physical adsorption, and with the degree of metamorphism increases, the adsorption of CH_4 increases, the rank is higher, more stable adsorption. (2) when the water molecular adsorption, H_2O molecules and lignite, high volatile bituminous coal and anthracite molecules in molecular hydrogen bond formation. Through hydroxyl Mulliken charge distribution analysis, that the coal molecule hydroxyl donor hydrogen bonds, water molecules are hydrogen bond acceptor, because the charge migration leads to hydroxyl bond hydroxyl bond in coal molecular energy and water molecules can be changed. The oxygen molecule to many kinds of lignite, adsorption capacity of the strongest H_2O carboxyl group at this time, the most stable adsorption structure. By comparing the adsorption adsorption of CH_4 and H_2O when the can, get the adsorption capacity of different rank coals of molecular H_2O were stronger than CH_4, the role of strong hydrogen bonds in Van Edward. (3) when CH_4, H_2O and adsorbent System, the adsorption of H_2O will occupy the CH_4 bit, and between H_2O and coal molecular distance than the CH_4, the adsorption of H_2O is stronger than CH_4. adsorption due to the adsorption of water and energy of coal, and coal molecular distance between near, existence of competitive adsorption between H_2O and CH_4, so the steam injection can improve the recovery rate of CBM. (3) a supercritical methane adsorption state for the replacement of maximum limit, and the excess water vapor injection, improve gas injection effect, according to the single component adsorption potential calculation model of single component adsorption capacity and adsorption energy, according to the multicomponent adsorption of N-A mixed model calculation the total gas adsorption capacity, finally derived only consider the adsorption of water vapor and supercritical methane injection. The optimal competition ratio parameter has certain guiding significance on the heat injection process design.

【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O647.3;TE37

【相似文献】