Methane Formation by the Reaction of Coalbed Carbon with Water

There is proposed a mechanism of methane and carbon dioxide formation by the direct reaction of carbon with water during catastrophic events in the mining of coal deposits. Thermodynamics of the reaction is dis-cussed.

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.

Simulation of the interaction of methane,carbon dioxide and coal

Gas adsorption has an important influence on gas flow in a coal body.Research on the characteristics of coal and gas adsorption is the theoretical basis for studying gas flow in coal.In this paper,the interaction between methane,carbon dioxide and surface molecules of anthracite was simulated using the quantum chemistry method.Adsorption energy and adsorption configurations of different quantities of gas molecules absorbed on the coal surface were calculated.The results show that adsorption between coal and the two kinds of gas molecules is a physical adsorption process and there is an optimal configuration.Gas molecules are more easily adsorbed in the hydroxyl-containing side chain,while it is difficult for them to be adsorbed at the position of the benzene ring.Besides,carbon dioxide molecules are more readily adsorbed on the coal surface than methane molecules.The findings have an important significance in revealing the nature of gas adsorption in coal.

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.

Carbon Dioxide/Methane Separation by Adsorption on Sepiolite

In this work, the use of sepiolite for the removal of carbon dioxide from a carbon dioxide/methane mixture by a pressure swing adsorption （PSA） process has been researched. Adsorption equilibrium and kinetics have been measured in a fixed-bed, and the adsorption equilibrium parameters of carbon dioxide and methane on sepiolite have been obtained. A model based on the LDF approximation has been employed to simulate the fixed-bed kinetics, using the Langmuir equation to describe the adsorption equilibrium isotherm. The functioning of a PSA cycle for separating carbon dioxide/methane mixtures using sepiolite as adsorbent has also been studied. The experimental results were compared with the ones predicted by the model adapted to a PSA system. Methane with purity higher than 97% can be obtained from feeds containing carbon dioxide with concentrations ranging from 34% to 56% with the proposed PSA cycle. These results suggest that sepiolite is an adsorbent with good properties for its employment in a PSA cycle for carbon dioxide removal from landfill gases.

Molecular simulation studies of hydrocarbon and carbon dioxide adsorption on coal

Sorption isotherms of hydrocarbon and carbon dioxide （CO2） provide crucial information for designing processes to sequester CO2 and recover natural gas from unmineable coal beds. Methane （CH4）, ethane （C2H6）, and CO2 adsorption isotherms on dry coal and the temperature effect on their maximum sorption capacity have been studied by performing combined Monte Carlo （MC） and molecular dynamics （MD） simulations at temperatures of 308 and 370 K （35 and 97 ~C） and at pressures up to 10 MPa. Simulation results demonstrate that absolute sorption （expressed as a mass basis） divided by bulk gas density has negligible temperature effect on CH4, C2H6, and CO2 sorption on dry coal when pressure is over 6 MPa. CO2 is more closely packed due to stronger interaction with coal and the stronger interaction between CO2 mole- cules compared, respectively, with the interactions between hydrocarbons and coal and between hydrocarbons. The results of this work suggest that the ＂a＂ constant （pro- portional to TcPc） in the Peng-Robinson equation of state is an important factor affecting the sorption behavior of hydrocarbons. CO2 injection pressures of lower than 8 MPa may be desirable for CH4 recovery and CO2 sequestration. This study provides a quantitative under- standing of the effects of temperature on coal sorptioncapacity for CH4, C2H6, and CO2 from a microscopic perspective.

Decomposition of carbon dioxide hydrate in the samples of natural coal with different degrees of metamorphism

Methane and carbon dioxide hydrates are one of the possible forms in which these gases exist in natural coal(for more detailed discussion see Refs [1,2]). In this work, the decomposition of carbon dioxide hydrate in five samples of natural coal differing from each other in metamorphism degree was investigated experimentally. Carbon dioxide hydrate dispersed in coals was synthesized from water adsorbed in these coals. During a linear temperature rise in an autoclave with the coal + hydrate sample the hydrate decomposition manifests itself as a step of increase in gas pressure, accompanied by a decrease/stabilization of the temperature of coal sample. The dependencies of the amount of hydrate formed on initial coal humidity and on gas pressure during hydrate formation were studied. It was demonstrated that each coal sample is characterized by its own humidity threshold below which hydrate formation in natural coal is impossible. With an increase in gas pressure, the amount of water transformed into hydrate increases. For the studied coal samples, the decomposition of carbon dioxide hydrates proceeds within a definite temperature and pressure range, and this range is close to the curve of phase equilibrium for bulk hydrate.

Study of methane and carbon dioxide adsorption-desorption hysteresis in coals from Sydney Basin:A theoretical and experimental approach OA

Methane(CH_(4))and carbon dioxide(CO_(2))are primary components of coal seam gas(CSG).Understanding their adsorption-desorption hysteresis characteristics,along with the fundamental mechanism,is crucial for CSG exploitation and related hazards mitigation.This research focused on the representative Bulli coal seam in the Sydney Basin,Australia.Through the purpose-built indirect gravimetric high-pressure isothermal adsorption-desorption hysteresis experiment,a novel Langmuir-based desorption model,incorporating hysteresis effect and residual gas,was proposed.Quantitative characterization of the adsorption-desorption hysteresis degrees of CO_(2)and CH_(4)i n coal particles of various sizes and inΦ50mm 100 mm intact coal samples were achieved using the improved hysteresis index(IHI).The experimental findings validated that the proposed desorption model accurately describes the desorption behavior of CO_(2)and CH_(4)in coal(R2>0.99).Based on the adsorption-desorption properties of inkbottle-shaped micropores and pore deformation caused by gas adsorption-induced coal expansion,the occurrence mechanism of adsorption–desorption hysteresis and the fundamental reasons for the presence of residual gas were elucidated.Furthermore,the study explored the impact of CO_(2)and CH_(4)adsorption-desorption hysteresis effects on coal and gas outbursts,suggesting that coal seams rich in CO_(2)do not have a higher propensity for outbursts than those rich in CH_(4).

Early Opportunity of CO_2 Storage in Coal Bed of China

A study to identify potential early opportunities for CO2 storage in coal bed has been performed. CO2-ECBM can enhances the recovery of coalbed methane,and also store CO2 in coal for geological time.CO2-ECBM is an effective measure for CO2 mitigation,and also enhance the recovery of coalbed methane that can reduce the cost of CO2 geological storage.The evaluation index system of feasibility

Industrial Feasiblity of Direct Methane Conversion to Hydrocarbons over Fe-Based Fischer Tropsch Catalyst

Recently, as a direct consequence of the dwindling world oil reserves and the growing awareness of the environmental problems associated with the use of coal as energy source, there is growing interest in cheaper, abundant and cleaner burning methane. The Gas-to-Liquid technology offers perhaps the most attractive routes for the exploitation of the world huge and growing natural gas resources. Using this process the erstwhile stranded gas is converted to premium grade liquid fuels and chemicals that are easily transported. However, a widespread application of the GTL process is being hampered by economical and technical challenges. The high cost of synthesis gas, for instance, weighs heavily on the economics and competitiveness of the process limiting its wider application. This work presented a modified Gas-to-Liquid process that eliminates the costly synthesis gas production step. The proposed process utilized an alternative pathway for methane activation via the production of chloromethane derivatives which are then converted to hydrocarbons. It established that hydrocarbons mainly olefins can be economically produced from di- and tri-chloro- methanes over a typical iron-based Fischer Tropsch catalysts in a moving bed reactor at industrially relevant conditions. Some of the attractions of the proposed process include a) the elimination of the costly air separation plant requirement b) high process selectivity and c) significant reduction of carbon dioxide emissions thereby saving on feedstock loss and the costly CO2 removal and isolation processes.

Recovery of greenhouse gas as cleaner fossil fuel contributes to carbon neutrality

Under the context of carbon neutrality of China,it is urgent to shift our energy supply towards cleaner fuels as well as to reduce the greenhouse gas emission.Currently,coal is the main fossil fuel energy source of China.The country is striving hard to replace it with methane,a cleaner fossil fuel.Although China has rich geological resources of methane as coal bed methane(CBM)reserves,it is quite challenging to utilize them due to low concentration.The CBM is however mainly emitted directly to atmosphere during coal mining,causing waste of the resource and huge contribution to greenhouse effect.The recent work by Yang et al.demonstrated a potential solution to extract low concentration methane selectively from CBM through using MOF materials as sorbents.Such kind of materials and associated separation technology are promising to reduce greenhouse gas emission and promote the methane production capability,which would contribute to carbon neutrality in dual pathways.

Interactions of dynamic supercritical CO_(2) fluid with different rank moisture-equilibrated coals: Implications for CO_(2) sequestration in coal seams

The interactions between CO_(2) and coals during CO_(2)-ECBM(CO_(2) sequestration in deep coal seams with enhanced coal-bed methane recovery)could change pore morphology and chemistry property of coals,thereby affecting adsorption,diffusion and flow capability of CO_(2) and CH_(4) within coal reservoirs.To simulate CO_(2)-ECBM process more practically,the dynamic interactions of supercritical CO_(2)(sc CO_(2))and moisture-equilibrated coals were performed at temperature of 318.15 K,pressure of 12.00 MPa,and duration of 12.00 h.The impacts of the interactions on physicochemical properties of coals were investigated.Results indicate that sc CO_(2)/H_(2)O exposure shows minor effect on micropores of coals.However,the exposure significantly decreases the mesopore surface area of bituminous coals,while increases that of anthracites.The mesopore volume and the average mesopore diameter of all the coals after sc CO_(2)/H_(2)O exposure decrease.The multi-fractal analysis verifies that the sc CO_(2) exposure can enhance the pore connectivity of various rank coals.Apart from the pore morphology,the exposure of sc CO_(2)/H_(2)O also affects the oxygenic functional groups on coal surface.Particularly,the exposure of sc CO_(2)/H_(2)O reduces the content of CAO and C@O of coals.The content of COOH of low rank coals including Hehua-M2#coal,Zhongqiang-4#coal,Buliangou-9#coal and Tashan-5#coal decreases,while the high rank Laochang^(-1)1#coal and Kaiyuan-9#coal witness a growth in COOH.The content of total oxygenic functional groups of all coals after interaction with sc CO_(2)/H_(2)O decreases;on the contrary,that of CAC/CAH of all coals after sc CO_(2)/H_(2)O exposure increases.In summary,the interaction with sc CO_(2)/H_(2)O significantly changes the pore system and oxygenic functional groups of various rank coals,which needs further attention regarding CO_(2)-ECBM.

A review on transport of coal seam gas and its impact on coalbed methane recovery

This paper presents a summary review on mass transport of coal seam gas(CSG)in coal associated with the coalbed methane(CBM)and CO_(2) geo-sequestration enhanced CBM(CO_(2)-ECBM)recovery and current research advances in order to provide general knowledge and fundamental understanding of the CBM/ECBM processes for improved CBM recovery.It will discuss the major aspects of theory and technology for evaluation and development of CBM resources,including the gas storage andflow mechanism in CBM reservoirs in terms of their differences with conventional natural gas reservoirs,and their impact on CBM production behavior.The paper summarizes the evaluation procedure and methodologies used for CBM exploration and exploitation with some recommendations.

碳中和目标下中国天然气工业进展、挑战及对策

天然气在21世纪中叶将迈入“鼎盛期”,“天然气时代”正在到来。回顾全球天然气工业历程,梳理美国页岩革命启示,总结中国天然气发展历史与成果进展,分析天然气在能源绿色低碳转型中的地位与挑战,提出当前和未来中国天然气工业的发展对策。中国天然气工业经历了起步、增长、跨越3个发展阶段,已成为世界第4大天然气生产国与第3大消费国;天然气勘探开发理论技术取得重大成就,为储量产量规模增长提供了重要支撑。碳中和目标下,推动绿色可持续发展,天然气工业发展挑战与机遇并存。天然气低碳优势显著,“气电调峰”助力新能源发展;同时,开采难度与成本加大等问题更突出。为保障国家能源安全,实现经济社会与生态环境和谐共生,碳中和进程中,立足“统筹布局、科技创新;多能互补、多元融合;灵活高效、优化升级”,完善产供储销体系建设,加速推动天然气工业发展:①加大天然气勘探开发力度,规划部署重点勘探开发领域,突破关键理论,强化技术攻关,持续支撑增储上产;②推进天然气绿色创新发展,突破新技术,拓展新领域,融合新能源;③优化天然气供需转型升级,加大管道气、液化天然气布局和地下储气库建设,建立储备体系,提升应急调节能力和天然气一次能源消费比例,助力能源消费结构转型,实现资源利用低碳化、能源消费清洁化。

煤层气制乙炔流程模拟与分析

为缓解电石法制乙炔中高污染、高能耗的现状、推广甲烷部分氧化法工艺,同时改善国内煤层气(Coal-Bed Methane,CBM)利用率,本文搭建了一套以煤层气为原料且采用部分氧化法生产乙炔的工艺模型。结合乙醇胺(MEA)脱碳工艺吸收CO_(2),利用Aspen Plus软件完成了煤层气制乙炔的全流程模拟,并进行了技术经济和环境影响分析。结果表明:本工艺年产乙炔3×10^(4) t(纯度大于99%),乙炔成本为12423.73 CNY/t,还可以副产1.86×10^(4) t氢气(纯度99.99%),具备良好的综合经济效益;本工艺每生产1 t乙炔排放3048.66 kg CO_(2),仅为主流电石法碳排放量(6560 kg)的46.5%,碳减排优势突出。

二氧化碳驱替煤层气技术发展现状分析

在“双碳”背景下,CO_(2)驱煤层气(CO_(2)-ECBM)工业化应用是促进煤炭清洁高效利用和CO_(2)利用的重要途径之一,CO_(2)驱煤层气技术既可实现CO_(2)的地下封存利用又能提高煤层气采收率。与发达国家相比,我国的CO_(2)驱煤层气技术研发工作发展较慢,因而需从机制机理、现场实验方面阐述CO_(2)驱煤层气技术研究进展。首先从实验室模拟试验介绍煤吸附CO_(2)之后的体积膨胀、渗透率和力学性质的影响研究,然后从世界各地的现场试验介绍CO_(2)驱煤层气技术的发展历程和研究进展。低渗透煤层的注入性是制约该技术可行性的关键因素,因而低渗透煤层增渗技术的突破是中国驱替煤层气技术推广应用的前提。由于现有监测技术还不能完全满足驱替过程优化调控及安全性监测的需要,在CO_(2)驱煤层气技术的发展实施过程中需考虑气源、工艺、腐蚀、安全及投资等问题。针对驱替煤层气技术在工业应用中存在成本较高、市场激励机制不足等问题,需从国家和地方层面进一步完善煤层气开发利用政策,推进驱替煤层气技术健康发展。

小庄煤矿液态二氧化碳驱替技术研究与应用

煤层瓦斯抽采效率不足是高瓦斯及突出矿井采掘接续困难和瓦斯事故频发的主要原因,为了提高煤层采前瓦斯预抽效率,降低矿井瓦斯灾害治理成本,基于液态二氧化碳对煤层进行低温致裂增透和对煤层瓦斯进行相变交换置换驱替的两方面影响,针对彬长小庄煤矿低透气性、瓦斯难以抽采的问题,以40205工作面为研究对象,通过对其进行液态二氧化碳驱替煤层气技术深入分析和工程应用,分析了现场抽采效果。现场应用表明,驱替后的钻孔内瓦斯浓度平均增加1.425倍,纯量平均增加1.33倍,瓦斯抽采效率明显提升。该结果初步证实了液态二氧化碳驱替技术的适用性,为煤矿瓦斯抽采提供了一定的技术支撑。

超临界CO_2驱替煤层CH_4装置及试验研究

自主研发了MCQ-Ⅱ型大试件(100mm×100mm×200mm)超临界CO2驱替煤层CH4试验装置,该装置不仅能够保障试验过程中CO2始终处于超临界状态,而且可测量煤体吸附过程中的体积膨胀。借助本装置对同一温度不同体积应力条件下的超临界CO2的渗透性及其驱替CH4效果进行了试验研究。试验结果表明:在50℃、恒定体积应力为48~60MPa条件下,超临界CO2的渗透率与注入渗透压呈正相关关系,与体积应力呈负相关关系。超临界CO2在煤体中的渗透特性远远高于其在常态条件下的渗透性。试验同时发现,超临界CO2在煤体中的吸附量与孔隙压力及体积应力均呈正相关,在48和60MPa的体积应力下,单位体积的煤体分别可累计吸附10.82~17.52体积和16.12~20.40体积的CO2;试验还测得了不同条件下煤体吸附CH4、超临界CO2及超临界CO2驱替煤体CH4过程中,煤体体积膨胀百分比。在超临界CO2驱替CH4试验中,2号焦煤煤样试件中注入气体体积(包括CH4,CO2)均小于1号弱黏煤煤样,但是两煤样中的CO2/CH4置换比及CO2最终储存率相当,分别为4.01/4.16,20.05%/20.09%。

甲烷及二氧化碳在不同煤阶煤内部的吸附扩散行为

采用容量法确定吸附量的方法,基于Fick第二定律,在吸附平衡压力约为1.4 MPa,温度为35～65℃的实验条件下,研究了甲烷(CH4)和二氧化碳(CO2)在不同煤阶煤内部的吸附扩散行为。研究结果表明:Fick第二定律能够很好地描述CH4及CO2在不同煤阶煤内部的扩散行为;CH4和CO2有效扩散系数随着吸附温度的升高而增大,同时有效扩散系数和煤阶(利用镜质组最大反射率Ro,max表征)之间呈现"U"形关系;相同条件下,同种煤样的CO2有效扩散系数高于CH4;CH4和CO2在不同煤阶煤内部的扩散主要受微孔内部的表面扩散控制。

注二氧化碳提高煤层甲烷采收率的实验模拟

针对我国煤层气开发中存在的产气率低、回采周期长的问题,开展了注二氧化碳驱替煤层甲烷的实验模拟研究.根据实验数据,利用扩展Langmuir方程计算了驱替过程中CH4组分的产出特征,并与纯CH4的解吸过程进行了比较.结果表明,在CO2驱替实验中,CH4在单位压降下的解吸率,明显高于纯CH4解吸时单位压降下的解吸率.其中晋城煤层CH4单位压降下的解吸率提高了150%,潞安煤层CH4单位压降下的解吸率提高了270%.由此可见,采用二氧化碳注入技术,可以显著提高煤层甲烷的采收率.