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Coal and Coalbed Gas - Future Directions and Opportunities (2nd Edition)
This book introduces the latest in coal geology research and the engineering of gas extraction. Importantly, the second edition examines how, over the last 10 years, research has both changed focus and where it is conducted. This shift essentially depicts \"a tale of two worlds\"-one half (Western Europe, North America) moving away from coal and coalbed gas research and production towards cleaner energy resources, and the other half (Asia-Pacific region, Eastern Europe, South America) increasing both research and usage of coal. These changes are marked by a precipitous fall in coalbed gas production in North America; however, at the same time there has been a significant rise in coal and coalbed gas production in Australia, China, and India. The driver for higher production and its associated research is a quest for affordable energy and economic security that a large resource base brings to any country like Australia's first large-scale coalbed gas to liquid natural gas projects supplying the demand for cleaner burning LNG to the Asian-Pacific region. Since the last edition of this book, global climate change policies have more forcibly emphasized the impact of methane from coal mines and placed these emissions equal to, or even more harmful than, CO2 emissions from fossil fuels in general. Governmental policies have prioritized capture, use, and storage of CO2, burning coal in new highly efficient low emission power plants, and gas pre-drainage of coal mines. The Organization for Economic Cooperation and Development (OECD) countries and China are also introducing new research into alternative, non-fuel uses for coal, such as carbon fibers, nanocarbons, graphene, soil amendments, and as an unconventional ore for critical elements.
eBook
Experimental Study of Coal–Gas Outburst: Insights from Coal–Rock Structure, Gas Pressure and Adsorptivity
Coal–gas outburst is a complex dynamic phenomenon in underground coal mines that has occurred frequently over the past 150 years. This phenomenon has seriously restricted the efficient development of coal resources and it poses a great threat to global energy security. Physical simulation experiments under different conditions that considered the coal–rock combination structure and gas adsorptivity were carried out by using a true triaxial coal–gas outburst experimental system, and the experiments controlled for the type of adsorbable gas, the presence (or absence) of a roof and the gas pressure. The influence of the coal–rock structure and gas adsorptivity on the disaster occurrence conditions and dynamic response characteristics was discussed, and the gas–solid-coupling disaster-inducing mechanisms of coal–gas outburst under unloading were obtained. The results show that outburst pulverized coal does not present an obvious sorting performance under the experimental conditions of this work. All the outburst holes are characterized by small openings and large cavities. Coal walls around the holes are damaged by spallation, and the strength of the outburst holes is low, but relatively stable. Stronger gas adsorptivity and greater gas pressure correspond to more intense outburst dynamic effects. Moreover, greater outburst intensity corresponds to more obvious coal spallation characteristics. Whether there is roof or not has no significant effect on the sweeping and handling of thrown pulverized coal. Compared with the condition without roof, the existence of a roof will promote an increase in the outburst intensity and more obvious spallation damage of the outburst coal. The coal–gas outburst process includes four stages: outburst occurrence, rapid development, deceleration development and outburst termination. The research results have certain guiding significance for studies on the mechanism of coal–gas outburst.
Journal Article
Quantitative Characteristics of Energy Evolution of Gas-Bearing Coal Under Cyclic Loading and its Action Mechanisms on Coal and Gas Outburst
It is very important and effective to characterize the failure mechanism of coal and rock materials from the perspective of energy. Energy dissipation and release are important causes of rock mass failure. To qualitatively and quantitatively characterize the energy evolution process of gas-bearing coal and the energy evolution mechanisms of coal and gas outburst, experimental studies were conducted on gas-bearing coal under different stress paths. The research results demonstrate that the energy evolution of gas-bearing coal has nonlinear characteristics and that the energy density is a quadratic function of stress. The total energy density is mainly stored as elastic energy density and is unrelated to loading paths. According to the distribution characteristics of abutment pressures in a stope, the energy distribution can be divided into an energy dissipation and release zone, an increasing-energy zone, and a stable energy storage zone. During coal mining, abutment pressure in front of the coal wall is an important factor causing energy accumulation, and the stress concentration area is a key area to prevent and control dynamic disasters of coal and rock masses. Furthermore, based on the principle of energy conservation, this study established an energy balance model for coal and gas outburst and derived energy criteria for coal and gas outburst. When Υ>1, there is a risk of coal seams have outburst. If Υ=1, the system is in a state of limit equilibrium, and mining disturbances could trigger outburst.
Journal Article
Coal and Coalbed Gas
Bridging the gap in expertise between coal and coalbed gas, subfields in which opportunities for cross training have been nonexistent, Coal and Coalbed Gas sets the standard for publishing in these areas. This book treats coal and coalbed gas as mutually inclusive commodities in terms of their interrelated origin, accumulation, composition, distribution, generation, and development, providing a balanced understanding of this energy mix. Currently considered a non-renewable energy resource, coalbed gas, or coalbed methane, is a form of natural gas extracted from coal beds. In recent years, countries have begun to seek and exploit coal for its clean gas energy in an effort to alleviate environmental issues that come with coal use, making a book on this topic particularly timely. This volume takes into account processes of coalification, gasification, and storage and reservoir characterization and evaluation and looks at water management and environmental impacts as well. Covers environmental issues in the development of coalbed gasIncludes case studies, field guides and data, examples, and analytical procedures from previous studies and investigationsAccessible by a large multidisciplinary market by one of the world's foremost experts on the topic
eBook
Disaster-causing mechanisms of gas migration under loading and unloading conditions
The aim of studying the mechanisms of coal and gas outbursts is to master the occurrence and development process of outbursts and to determine the reasons and conditions for outburst occurrence. Gas permeability is an important parameter for characterizing the difficulty of gas migration in a coal seam and an important factor in studying coal and gas outbursts. By utilizing a THM-2 type thermo-fluid-solid coupling test system of gas-bearing coal developed at Chongqing University, China, gas-bearing coal was experimentally investigated under loading and unloading paths. The results demonstrate that permeability is significantly affected by stress paths and gradually decreases with an increase in stress. The permeability of coal samples under unloading increased with the number of loading and unloading cycles and the irreversible strain was negatively correlated with permeability. In situ stress mainly affects the difficulty of migration and the flow direction of gas in the coal seam by controlling the pore and fracture systems of the coal mass. The point of maximum bearing pressure is the boundary point of the gas migration direction. In the coal mining process, mining activities break the
in-situ
stress state and induce stress concentration. As the mining face advances, the abutment pressure curve shifts to the deep part of the coal seam as does the permeability. Gas is prone to accumulate in the area between the maximum abutment pressure and the in situ stress zone, which increases the gas concentration, thus forming a zone with increased outburst risks.
Highlights
The direction of gas transportation in the coal seam was determined, and a model was established.
The gas migration in the coal seam is divided into different areas.
It was found that the maximum supporting pressure point is the boundary point of the direction of gas migration, which is the main factor that makes gas migration difficult.
Journal Article
A review of sorbents for high-temperature hydrogen sulfide removal from hot coal gas
Integrated gasification combined cycle (IGCC) and solid oxide fuel cell (SOFC) systems are considered as the most promising clean coal technologies. Syngas derived from coal gasification is the major fuel sources for IGCC and SOFC power systems; however, large amounts of sulfur compounds, mainly in the form of hydrogen sulfide, are produced during gasification. Hydrogen sulfide has to be removed prior to syngas utilization to protect downstream equipment from high-temperature corrosion. Therefore, hydrogen sulfide removal from raw syngas plays a key role in successful application of IGCC and SOFC systems. Hot coal gas desulfurization using solid sorbents is a more efficient technique for hydrogen sulfide removal, compared with conventional cold coal gas desulfurization with amine solution. This article reviews solid sorbents for high-temperature desulfurization, e.g., transition metal oxides, rare-earth oxides, spinel oxides, perovskite oxides, nanoelemental metals and mesoporous desulfurizers. Composite oxides that combine the properties of diverse metal oxides are promising candidates for hot coal gas desulfurization. The extensive background knowledge and the state of the art on high-temperature sorbents for hydrogen sulfide removal in this review provides inspiration and guidance to develop new cost-effective sorbents.Graphical Abstract
Journal Article
A Rapid Method for the Determination of Coal Seam Gas Pressure Based on Raw Coal Adsorption
The residual gas pressure of pre‐pumped coal seams is one of the key indices to check the effect of regional outburst prevention. The success rate in direct measurement is low, and it is generally obtained indirectly by use of the Langmuir equation, but it requires many test parameters, is time consuming, and prone to significant errors. To obtain the residual gas pressure of pre‐pumped coal seams more accurately and quickly, based on the theoretical analysis, an adsorption and desorption experimental device built by the authors was used to ascertain the gas adsorption constants of raw coal and applied to the calculation of coal seam gas pressure. The calculated gas pressure value was compared with the experimental gas pressure and the field measured gas pressure. The results show that under the constant temperature (consistent with the temperature of the coal seam) and natural recovery of gas pressure of coal samples, the adsorption constants a and b of raw coal gas are quickly measured by the adsorption/desorption and degassing equilibrium experiment. The relative errors of the calculated values of coal seam gas pressure with those measured by experiments and measured on site are 4.67%–9.43% and 2.78%–5.56%, respectively. Compared with the indirect method using the Langmuir equation, this method can exclude the influences of temperature and moisture on the pressure measurement results, requiring fewer test parameters and less time. Compared with direct pressure measurement in downhole drilling, this method does not require sealing of the hole and is not limited by the location of pressure measurement. The results offer a new method for coal mines to obtain the residual gas pressure in a pre‐pumped coal seam more accurately and quickly, and provide technical support for mining engineers who need to grasp situation around coal seam gas extraction situation and regional outburst prevention, and do so timeously. The method flow of coal seam gas pressure measurement based on raw coal gas adsorption is introduced.
Journal Article
Influence of saturation level on the acoustic emission characteristics of gas hydrate-bearing coal
To study the effects of gas hydrates on the prevention and control of coal and gas protrusions, this paper reports the results of acoustic emission experiments on coal bodies containing gas hydrates with different saturation levels. The results showed that few acoustic emission events were generated in the elasticity stages of coal bodies containing gas hydrates, and the first sudden increase in the number of ringing counts generally occurred before and after the yielding point. Additionally, the acoustic emission events in the yielding stage were more active, and the cumulative number of ringing counts increased faster. The peak ringing counts appeared around the damage point, and a small number of acoustic emission events were still generated after destruction of the coal samples. The cumulative ringing counts decreased linearly with increasing saturation. The effect of saturation on the cumulative ringing counts in the elasticity stage of the gas hydrate-containing coal samples was small, but the difference between the cumulative ringing counts in the yielding stage and those in the destruction stage was larger. The total cumulative ringing counts and the cumulative ringing counts during each stage for the gas hydrate-containing coal samples decreased with increasing enclosure pressure. The energy and amplitude of the loading process were consistent with the trend for the ringing counts. The acoustic emission ringing counts of gas-containing coals were greater than those of gas hydrate-containing coals in the yielding and destructing stages.
Journal Article