基于CT图像的煤吸附甲烷细观变形分形特性研究

为了定量化研究煤吸附甲烷过程细观变形的各向异性特征,通过ACTIS-CT扫描实验系统,开展了恒定温度下方型无烟煤吸附甲烷过程的吸附变形CT扫描实验;根据CT图像,采用质点追踪应变计算算法定量计算了吸附过程中煤内部细观结构的应变变形,讨论了其变化规律。在此基础上,提出了一种基于CT技术煤吸附气体细观变形的非均质性定量化研究方法,应用盒计数维数法计算了分形维数,定量评价了煤细观变形的非均质性,并基于分形几何和细观应变变形分布的物理描述,讨论了分形维数和甲烷吸附各向异性变形特性的关系。研究结果表明:煤吸附气体膨胀变形首先挤压孔隙或裂缝以获得更大的膨胀空间;煤吸附甲烷后引起的细观变形,其非均质性符合分形特征;分形维数与煤吸附甲烷后的膨胀变形率呈负相关性关系,膨胀变形率值越高,分形维数越低,即煤吸附甲烷后越膨胀,煤整体的非均质应变变形的不规则程度越低;相反,膨胀变形率值越低,则分形维数越高,煤整体的非均质应变变形的不规则程度越高。

颗粒煤吸附甲烷微生物降解效能试验探究

为了探讨微生物高效降解甲烷的外部环境和有利条件,优化和完善通过生物学方法治理煤矿瓦斯灾害的基本方法,自主研制了颗粒煤吸附甲烷微生物降解试验装置,研究了Methylomarinum(甲烷氧化菌)在不同氧气体积分数、不同甲烷压力下对不同坚固性系数颗粒煤吸附甲烷的降解效能。结果表明:在24 h内甲烷降解率呈现前5 h增幅较小,而后线性增长,20 h后缓慢增长并最终趋于一定值的变化规律;在不同氧气体积分数环境中,由于甲烷氧化菌代谢机制的不同,甲烷降解率差异较大;相似变质程度煤样对比试验表明,煤体坚固性系数越大,甲烷降解率越高;当气体压力为1~2 MPa时,促进甲烷的降解,5 MPa时,甲烷降解性能受到较大的抑制。

厌氧型甲烷氧化菌降解煤吸附甲烷实验研究

以贵州六枝特区龙岭煤矿大巷中泥样作为厌氧型甲烷氧化菌富集源,以甲烷作为培养过程中唯一碳源,从中筛选出可以在低氧(1.99%)或无氧条件下对甲烷具有较高降解效能的菌种,并自主开发出甲烷氧化菌降解煤吸附甲烷实验分析系统。实验结果表明,在压力为1~5 MPa范围内无论是低氧或无氧状况下,甲烷压力越大越有利于其降解;稀氧条件下煤样对甲烷的吸附量相对于纯甲烷气体吸附量有所降低,然而在同等压力条件下稀氧环境中二氧化碳的增加量及甲烷的降解率都要明显大于无氧条件下,低氧状况下甲烷的最高降解率为47%,最大二氧化碳生成量可达40 cm^3。

用脱气仪测定煤对甲烷吸附量的新方法

根据容量法测定煤对甲烷吸附常数的技术特点，通过试验分析研究出一种用测定瓦斯含量的脱气仪测定煤对甲烷吸附常数的新方法。

深部煤层瓦斯吸附规律研究

瓦斯吸附常数是煤层瓦斯基础参数中重要组成部分,通过采集平顶山矿区深部煤层不同地点煤样,利用WY-98A型瓦斯吸附常数测定仪进行高压等温吸附试验,试验结果表明,吸附曲线符合langmuir吸附方程,吸附曲线随着吸附压力升高,先表现为吸附量急剧增大,后吸附量缓慢增加,当吸附压力达到5 MPa左右时,吸附曲线平缓,逐渐达到极限吸附量。在吸附阶段前期,吸附瓦斯量快速增加,在饱和吸附量中占比超过70%,同时瓦斯吸附量与煤质参数中挥发分关系密切,呈现出挥发分越大、吸附量越小的反比关系。

温度/压力对甲烷超临界吸附能量参数的影响机制

煤层气在储层高温高压环境中主要以超临界吸附状态赋存,温度和压力是影响煤储层含气性的重要外部控制因素,温压条件改变意味着煤-甲烷吸附体系的原始平衡状态被打破,体系能量发生变化。基于无烟煤等温吸附试验数据,通过Gibbs方程对比了甲烷超临界与亚临界吸附的差异,从吸附热力学和吸附动力学角度,分析了温度和压力对甲烷超临界吸附过程中的能量参数的影响规律。结果表明:超临界条件下的煤-甲烷吸附体系绝对吸附量大于过剩吸附量,二者间的差异随平衡压力增大而增大,随温度升高而减小。对于特定的煤-甲烷吸附体系,吸附势与吸附空间在任意温压条件下呈现单一吸附特征曲线关系,且平衡压力增加引起吸附势减小,吸附空间增大,而温度升高引起吸附势增大,吸附空间减少。甲烷分子主要以菲克型扩散方式在煤岩中传质,由于分子平均自由程受温压控制,扩散系数随压力增大而减小,随温度升高而增大。气体分子吸附活化能本质为分子动能的体现,不受体系压力影响,但受体系温度影响,温度越高,吸附活化能越大。

Monte Carlo simulation of methane molecule adsorption on coal with adsorption potential

The paper presents a Monte Carlo simulation to study the adsorption characteristics of methane molecule on coal slit pores from different aspects.Firstly,a physical model of adsorption and desorption of methane molecules on micropores was established.Secondly,a grand canonical ensemble was introduced as the Monte Carlo simulation system.Thirdly,based on the model and system,the molecule simulation program was developed with VC++6.0 to simulate the isothermal adsorption relationship between the amount of molecule absorption and the factors affecting it.Lastly,the numerically simulated results were compared with measured results of adsorption coal samples of two different coal mines with a laboratory gas absorption instrument.The results show that the molecule simulations of the adsorption constants,the adsorption quantity,and the isothermal adsorption curve at the same and different coal temperatures were in good agreement with those measured in the experiments,indicating that it is feasible to use the established model and the Monte Carlo molecule simulation to study the adsorption characteristics of methane molecules in coal.

Adsorption behavior of carbon dioxide and methane in bituminous coal:A molecular simulation study

The adsorption behavior of CO_2, CH_4 and their mixtures in bituminous coal was investigated in this study. First, a bituminous coal model was built through molecular dynamic(MD) simulations, and it was confirmed to be reasonable by comparing the simulated results with the experimental data. Grand Canonical Monte Carlo(GCMC)simulations were then carried out to investigate the single and binary component adsorption of CO_2 and CH_4with the built bituminous coal model. For the single component adsorption, the isosteric heat of CO_2 adsorption is greater than that of CH_4 adsorption. CO_2 also exhibits stronger electrostatic interactions with the heteroatom groups in the bituminous coal model compared with CH_4, which can account for the larger adsorption capacity of CO_2 in the bituminous coal model. In the case of binary adsorption of CO_2 and CH_4mixtures, CO_2 exhibits the preferential adsorption compared with CH_4 under the studied conditions. The adsorption selectivity of CO_2 exhibited obvious change with increasing pressure. At lower pressure, the adsorption selectivity of CO_2 shows a rapid decrease with increasing the temperature, whereas it becomes insensitive to temperature at higher pressure. Additionally, the adsorption selectivity of CO_2 decreases gradually with the increase of the bulk CO_2 mole fraction and the depth of CO_2 injection site.

Influence of magma intrusion on gas outburst in a low rank coal mine

The effect of magma intrusion on gas outburst is illustrated by a case study of the exposed magma intru- sion in the 313 mining area, upper coal seam Number 3, in the Qiwu Mine located in Shandong province. Vitrinite reflectance, mercury injection, and maceral statistical analysis are used to characterize the coal. The aspects of coal metamorphism include changes in micro-components as well as in coal structure, the formation of new substances, and changes in gas absorption and storage. The results show that vitrinite reflectance increases within the region influenced by magma intrusion. The metamorphosed region may be divided into a weakly affected belt, a medium affected belt, a strongly affected belt, and a completely affected belt. Compared to the unaffected coal the total pore volume, as well as the amount of big and middle sized holes, increases while the number of transition holes and micro-pores decreases. This diminishes the absorption capacity of the matrix but enlarges the total gas storage space. Vitrinite con- tent initially decreases slightly but then increases rapidly while the inertinite content increases at first but then decreases. Exinite content decreases, then increases, and finally drops to zero. Higher vitrinite, and a lower inertinite, content increase gas absorption ability. This balances reduced adsorption caused by changes to pore structure. Consequently, gas adsorption capacity is not substantially reduced as the coal rank increases. Thermal metamorphism of the coal produces CH4 and other hydrocarbons that increase the total gas content in the coal seam. Asphaltene migrates into the medium and weakly affected regions filling in the pores and fractures there. This plugs the pathway for gas transport. A barrier is formed that hinders gas flow. C02, H2S, N2, and other gases carried in by the magma react to produce C02, which increases in relative concentration and enhances the risk of gas outburst. The two barriers, magma intrusion on one side and the medium and weakly affected belts on the other, as well as the unaf- fected coal seam itself, trap a large amount of gas during the thermal activity. This is the basic reason for gas outburst. These conclusions can enlighten activities related to gas prevention and control in a low rank coal mine affected by ma^ma intrusion.

Methane Adsorption Study Using Activated Carbon Fiber and Coal Based Activated Carbon

Inlfuence of ammonium salt treatment and alkali treatment of the coal based activated carbon （AC） and activated carbon ifber （ACF） adsorbents on methane adsorption capacity was studied via high-pressure adsorption experiment. Sur-face functional groups and pore structure of two types of adsorbents were characterized by the application of infrared ab-sorption spectroscopy （IR） and low temperature liquid nitrogen adsorption method. The results show that both ammonium salt treatment and alkali treatment have obvious effect on changing BET, pore volume as well as pore size distribution of adsorbents; and methane adsorption capacity of the activated carbon ifber is the maximum after the ammonium salt treatment.

Prediction on adsorption ratio of carbon dioxide to methane on coals with multiple linear regression

The multiple linear regression equations for adsorption ratio of CO2/CH4 and its coal quality indexes were built with SPSS software on basis of existing coal quality data and its adsorption amount of CO2 and OH4. The regression equations built were tested with data collected from some s, and the influences of coal quality indexes on adsorption ratio of CO2/CH4 were studied with investigation of regression equations. The study results show that the regression equation for adsorption ratio of CO2/CH4 and volatile matter, ash and moisture in coal can be obtained with multiple linear regression analysis, that the influence of same coal quality index with the degree of metamorphosis or influence of coal quality indexes for same coal rank on adsorption ratio is not consistent.

PHYSICAL SIMULATION AND ANALYSIS OF METHANE TRANSPORT IN COAL SEAM

This paper studies the effect of ground stress, pore gas pressure and adsorbed methane on methane transport in coal seam. and researches into the applleability of Darey’s inw to methane transport. The additional expansion stress of coal induced by adsorbed methane is measured. The paper establishes the constitutive equation of methane transport, taking ground stress, pore gas pressure and Klinkenburg’s effects into consideration. The features of methane transport under the condition of given stress or strain have been analyzed.

Research on Permeability of Multiphase Medium of Middle to High-Rank Coals

The permeability of coal of middle to high ranks were tested using He,CH 4 and H 2O in single phase medium and using CH 4 and H 2O in double phase medium. The relation between adsorption and permeability of those media was discussed, and the seepage flow characteristics of methane-water medium in coals were analyzed. The result shows that the coalbed methane resource of high-rank coal reservoirs in China is still recoverable.

Molecular simulation of the CH_4/CO_2/ H_2O adsorption onto the molecular structure of coal

Clarification of the molecular mechanism underlying the interaction of coal with CH4, CO2, and H2 O molecules is the basis for an in-depth understanding of the states of fluid in coal and fluid-induced coal swelling/contraction. In terms of instrumental analysis, molecular simulation technology based on molecular mechanics/dynamics and quantum chemistry is a powerful tool for revealing the relationship between the structure and properties of a substance and understanding the interaction mechanisms of physical-chemical systems. In this study, the giant canonical ensemble Monte Carlo（GCMC） and molecular dynamics（MD） methods were applied to investigate the adsorption behavior of a Yanzhou coal model（C222H185N3O17S5）. We explored the adsorption amounts of CH4, CO2, and H2 O onto Yanzhou coal, the adsorption conformation, and the impact of oxygen-containing functional groups. Furthermore, we revealed the different adsorption mechanisms of the three substances using isosteric heat of adsorption and energy change data.（1） The adsorption isotherms of the mono-component CH4, CO2, and H2 O were consistent with the Langmuir model, and their adsorption amounts showed an order of CH4CO2〉CH4. In addition, at higher temperatures, the isosteric heat of adsorption decreased; pressure had no significant effect on the heat of adsorption.（3） CH4 molecules displayed an aggregated distribution in the pores, whereas CO2 molecules were cross arranged in pairs. Regarding H2 O molecules, under the influence of hydrogen bonds, the O atom pointed to surrounding H2 O molecules or the H atoms of coal molecules in a regular pattern. The intermolecular distances of the three substances were 0.421, 0.553, and 0.290 nm, respectively. The radial distribution function（RDF） analysis showed that H2 O molecules were arranged in the most compact fashion, forming a tight molecular layer.（4） H2 O molecules showed a significantly stratified distribution around oxygen-containing functional groups on the coal surface, and the bonding strength showed a descending order of hydroxyl〉 carboxyl〉carbonyl. In contrast, CO2 and CH4 showed only slightly stratified distributions.（5） After the adsorption of CH4, CO2, and H2 O, the total energy, the energy of valence electrons, and the non-bonding interaction of the system in the Yanzhou coal model all decreased. The results regarding the decrease in the total energy of the system indicated an order of H2O〉CO2〉CH4 in terms of the adsorption priority of the Yanzhou coal model. The results regarding the decrease in the energy of valence electrons showed that under certain geological conditions, a pressure-induced “coal strain” could lead to a structural rearrangement during the interaction of coal with fluid to form a more stable conformation, which might be the molecular mechanism of coal swelling resulting from the interaction between fluid and coal. An analysis of the contribution of Van der Waals forces, electrostatic interactions and hydrogen bonds to the decrease in non-bonding interactions revealed the mechanism underlying the interactions between coal molecules and the three substances. The interaction between coal molecules and CH4 consisted of typical physical adsorption, whereas that between coal molecules and CO2 consisted mainly of physical adsorption combined with weak chemical adsorption. The interaction between coal molecules and H2 O is physical and chemical.