Coal Seam CO Research Articles

Study on the Adsorption/Desorption Characteristics of Protogenetic CO in Coal Seams

ABSTRACT In recent years, abnormal CO gas overruns have often occurred in coal mining workings. CO overruns were thought to be caused by the underground blasting work or spontaneous combustion of coal seams; however, minimal attention has been given to the causes of the desorption and release of adsorbed CO in the coal seams. Additionally, insufficient research has been conducted on the generation, distribution and adsorption and desorption characteristics of protogenetic CO in coal seams. Therefore, a self-built comprehensive testing system for coal seam adsorption and desorption was used to study the characteristics of the depressurization desorption and thermal desorption of coal with different degrees of metamorphism during coal seam mining. The results showed that under isothermal conditions, the amount of CO adsorption and desorption of coal samples increased with increasing pressure; under temperature rise conditions, the gas adsorption-desorption was in a dynamic equilibrium process under certain conditions. When the temperature increased, the equilibrium was beneficial to the desorption direction. The initial temperature range of CO production at different equilibrium pressures was 45–55°C. With increasing pressure, the initial temperature point of CO gas production moves forward and was significantly lower than the initial temperature of coal spontaneous combustion. Our research results further supplement the source of underground protogenetic CO gas and provide theoretical support for the accurate prediction of CO coal spontaneous combustion.

Relationship Between the Nanopore Structure and Basic Characteristics of Coal with the Protogenetic CO Content.

In the prediction and forecasting of spontaneous coal combustion, protogenetic CO produced in the process of coal oxidation is used as the indicator gas, but the sources of CO gas in coal seams are extensive. Protogenetic CO in coal seams often interferes with predictions of spontaneous coal combustion. To predict the content of protogenetic CO gas in coal seams and its emission, this study established an experimental system of protogenetic CO content and emission in coal seams. Six groups of coal samples were tested, and the CO emission content was determined per hour within 24 hours of obtaining each coal sample. Four kinds of protogenetic CO gas emission indexes were defined. Then, internal factors of coal, including industrial components, elemental content and pore structure, were analysed. Finally, the relationship between the protogenetic CO gas emission index of coal seams and the internal factors of coal was obtained. The results indicate that the relation between the CO dispersion concentration and the time of the coal sample follows an exponential power distribution. The internal factors of coal influence the content and emission of protogenetic CO in coal seams, but there is no strict correlation with each parameter as it is a multi-parameter correlation synthesis process.

Study on the influence of mining conditions on the occurrence law of CO in coal seams with low metamorphic grade

ABSTRACT The CO emission during the coal mining process is easy to cause the index gas prediction method to be out of alignment. Through the self-developed gas constant temperature desorption experiment device, combined with FLAC simulation, the influence of mining conditions on the occurrence of CO is studied. The results show that the mining stress can affect the occurrence of CO by affecting the permeability of coal. The coal seams not affected by mining have the same tendency to desorb the primary CO as the coal seams affected by mining. The desorption process of primary CO is fitted by Matlab and its content in lignite is mathematically analyzed. The results show that the desorption process of primary CO is consistent with the binomial exponential fitting and contains about 380 mL of native CO per ton of lignite.

Analysis of Effects of CO2 Injection on Coalbed Permeability: Implications for Coal Seam CO2 Sequestration

A proper understanding of permeability reductions of CH4-containing coal seams after CO2 injection is essential, as coal permeability is the key parameter influencing the efficiency of enhanced coa...

Identification of Primary CO in Coal Seam Based on Oxygen Isotope Method

ABSTRACTAnalysis on the source of CO is very important for prevention of coal spontaneous combustion. In this article, a method of identifying primary CO in coal seams based on an oxygen isotope method is proposed through research. Tests on the oxygen isotopes (δ18O) of CO were generated in coal oxidization reaction and coal pyrolysis reaction. It is found that δ18O of CO will reduce with rising temperature in both reactions, with δ18O of CO being 15–20‰ in air atmosphere and that being 25–28‰ in argon atmosphere in the temperature range of 130–220°C, confirming that the sources of oxygen atoms of CO vary with different atmospheric conditions. Through collecting and testing a number of gas samples from the coal seam and roof in the coal mine, their δ18O of CO is found to be 35.2–37.3‰. The result would improve the prevention of coal spontaneous combustion.

The Application Research of Coal Seam CO Source Identification Based on the D-S Evidence Conflict

In the paper, we introduce the distance function of K-L information to replace the conflict coefficient in order to solve the constraint problem of D-S evidence theory in information fusion and achieve the feature recognition aggreation of Multi-source information under the conflict condition. Simulating results show that: the effective conflict identification of K-L information distance can complete the application constraint of D-S theorys synthetic rule, obtaining the optimized convergence results for synthesis of normal conflicting evidences, isolating the highly conflicting evidence.

CO adsorption-diffusion model in coal seams

Through the adsorption experiment for CO at different temperatures and different pressures, we get a result showing that, at a normal temperature, adsorption isotherms of CO in coal seams is part of class Iadsorption isotherm. The CO adsorption quantity can be calculated by the Langmuir equation. Diffusion mode of gas in coal seam is determined by the index Kn, which determines the magnitude of coal hole diameter and average free moving distance of molecules. According to the calculation value of Kn, it is confirmed that diffusion modes of CO in coal seams are mainly Knudsen style and transition type diffusion. The samples of coal are mainly in the bituminous coal of low metamorphic grade, and the coal hole structure is mainly pore and transition hole. Therefore, in the coal seams, the proliferation transition model of proliferation of CO is mainly the Knudsen proliferation.

The mechanical behaviour of coal with respect to CO 2 sequestration in deep coal seams

Carbon dioxide displays a strong affinity for coal due to its propensity to adsorb to the coal surface. The process of CO 2 adsorption on coal causes lowering of surface energy and, it is hypothesised that an associated decrease in surface film confinement results in a decrease in material tensile resistance. Following the results of work carried out on the mechanical influence of CO 2 on brown coal under in situ conditions [Viete DR, Ranjith PG. The effect of CO 2 on the geomechanical and permeability behaviour of brown coal: implications for coal seam CO 2 sequestration. Int J Coal Geol 2006;66(3):204–16], a theoretical explanation is proposed for the perceived lack of a weakening effect with the adsorption of CO 2 to coal at significant confining pressures. We propose that at significant hydrostatic stresses, resistance to failure is otherwise provided (by external confinement) and the effects of adsorptive weakening are concealed. Our model predicts that adsorptive weakening, fracturing under in situ stresses, and associated permeability increases are not an issue for coal seam CO 2 sequestration for sufficiently deep target seams. Lowering of the elastic modulus of coal upon introduction of CO 2 may proceed by means other than surface energy lowering and could well occur irrespective of the depth of sequestration. The effect of elastic modulus lowering under in situ conditions would be beneficial for the long-term retention of sequestered gases.

The effect of CO2 on the geomechanical and permeability behaviour of brown coal: Implications for coal seam CO2 sequestration

Abstract Theory from fracture mechanics and thermodynamics coupled with the results of experimental studies provides evidence to suggest that the adsorption of carbon dioxide on coal causes a decrease in the coal strength. Coal weakening by the introduction of CO 2 to a coal seam may induce fracturing, causing a permeability increase under in situ conditions. Such effects present significant implications for proposals regarding the storage of CO 2 in coal seams. A uniaxial and triaxial laboratory study was carried out to explore the effects of the adsorption of CO 2 on the compressive strength and permeability of southeast Australian brown coal. Comparison of the stress–strain response of air-saturated and CO 2 -saturated specimens revealed a compressive strength decrease in the order of 13% and an elastic modulus decrease of about 26% for the uniaxial testing, but no significant strength or elastic modulus decrease for the triaxial testing. The absence of an adsorptive effect on the mechanical behaviour of the triaxial specimens may have been due to an insufficient saturation period under simulated ground conditions, or due to mechanical variability in the brown coal test specimens, however, further testing is required to reveal the reason for the apparent negligible strength reduction with CO 2 adsorption at the higher confinement. Carbon dioxide outflow measurements during the stress–strain process demonstrated an initial permeability decrease with pore closure, followed by a significant increase in specimen permeability with fracturing. Issues that require consideration in the application of these results to coal seam CO 2 sequestration include: whether the expected regional and localised in situ stresses are sufficient to initiate fracturing with adsorptive weakening; how coal properties (e.g. rank, moisture content) are likely to affect the geomechanical influence of CO 2 adsorption, and the expected magnitude of the proposed fracture related permeability increase.