Heterogeneous Coal Research Articles

Study of the Change in the Coal-and-Liquid-and-Gas Interfacial Angle

The use of surfactants has a significant impact on the safety of mining operations in order to prevent dynamic processes, prevent dust. The interfacial angle is the main indicator characterizing the interfacial interactions for heterogeneous multicomponent solid bodies, coal and solutions. The problem of development of modern methods for determining the interfacial angle at the coal-water-gas boundary is considered. The results of the research study of the change in the coalliquid-gas interfacial angle are presented. The influence of various coal properties and characteristics on the interfacial angle value is shown. The influence of the interfacial angle on wetting and filtration processes, the features of the experimental methods for the interfacial angle determination are shown. A model of the coal surface consisting of four main components is proposed. The main attention is paid to the moisture content of coal and capillaries as the main factors determining the properties of coal. An analytical method for determining the interfacial angle of coalwater-gas is proposed.

Permeability evolution and mesoscopic cracking behaviors of liquid nitrogen cryogenic freeze fracturing in low permeable and heterogeneous coal

Fracking to approach permeability enhancement is indispensable to enhance coalbed methane recovery, which can significantly reduce greenhouse gas emissions and produce substantial clean energy. To access efficient fracking, samples of Permian low permeable coal reservoir were cracked into different sizes or scales of blocks and particles with liquid nitrogen cryogenic freeze fracturing (FF) by maximizing the underlying heterogeneity of coal. To investigate the crack efficacy, this study systematically examined the permeability evolution and mesoscopic cracking behaviors of coal with different water contents and cleat–fracture systems in the context of cryogenic FF. Results showed that the permeability enhancement and microcracking tended to occur with increasing water content of coal sample; and the efficacy of cryogenic FF on the tighter coal sample was more remarkable. However, the permeability does not strictly increase with the cycles of cryogenic FF and has a close relationship with water content, structural plane direction, efficacy of cryogenic FF, and porosity compaction. The mesoscopic cracking behaviors indicate that numerous smaller pores are iteratively, not strictly sequentially, cracked and become connective in this process. The permeability evolution of coal sample is identified as significantly associated with the mesoscopic cracking behaviors. Notably, the first cycle of cryogenic FF acted on the detected several scales of pores and micro fissures, and partially caused these structures to be opened and interconnected to be permeable. Two main changes were observed in the microcracking of the coal samples in this study: 1) nonuniform shrinkage deformation and micro fissure expansion; and 2) pores opening mostly in the macropore and mesopore scale. It is reasoned that thermal cracking and intermittent opening of seepage pores due to the phase transition of free water in pores or micro fissures ultimately contribute to the permeability enhancement in low permeable and heterogeneous coal.

Safe and Productive Application of Hydraulic Backhoes in Coal-Bearing Areas of Complex Structured Deposits

The article describes a problem of hydraulic backhoes usage in coal-bearing areas development in complex structured deposits. At present time there is a mass replacement of previously widely used shovels with more adaptive excavation equipment—hydraulic backhoes in open pits of Kuzbass (the largest Russian coal basin, Western Siberia). On the one hand, it opens up new opportunities for reducing of coal losses and better planning of mining operations in coal-bearing area during the development of rock-and-coal blocks. On the other hand, backhoes usage with the replacement of railway transport for trucks significantly complicates rock-and-coal face parameters determination. It also impose new requirements for dispatching the “excavator—transport unit” work chain. In addition, strict requirements to excavator’s maneuverability for rock-and-coal blocks processing actualize research of safe backhoe positioning on a bench. The article describes the results of technological parameters determination for hydraulic backhoes usage in coal-bearing areas development in complex structured deposits. The most important results are the recommendations for choosing the order of heterogeneous (rock and coal) layers processing and justification of excavation blocks parameters for their layer-by-layer extraction that minimizes the coal losses. Particular attention is paid to the definition of excavated layer parameters depending on bucket capacity and excavated substance. Based on these data, the dependence of hydraulic backhoe productivity on the excavated layer height was defined. The study results are presented in the article on the example of Kuzbass coal deposits being developed by several open pit mines.

A coupled macro- and meso-mechanical model for heterogeneous coal

A thorough understanding of the deformation behavior, damage accumulation, and progressive failure of heterogeneous coal is a prerequisite for effective control of the surrounding rock and efficient exploitation of resources in underground coal mines. Such understanding can be obtained by analyzing both the macro- and meso-responses of coal to loading. Accordingly, a coupled macro- and meso-mechanical model for heterogeneous coal is developed and implemented in FLAC3D in the present study. The model is based on elasto-plastic mechanics and the energy dissipation and release principle, and heterogeneity is incorporated by the combination of a statistical approach and the discrete fracture network method. The model is calibrated by experimental data and is used to simulate stress-strain responses, the evolution of acoustic emission (AE) events, and energy conversion in compressed coal. The results reveal that: (1) the model can efficiently capture the dependency of the deformability, compressive strength and AE characteristics on the confining pressure; (2) the anisotropic behavior of heterogeneous coal is realistically realized, and the initiation, propagation and coalescence of micro-cracks can be located and tracked; and (3) stress paths, the degree of heterogeneity, and the unloading rate of confining pressure significantly influence the axial stress-strain response and AE event evolution in the stressed coal. The proposed model produces reasonable values for the roof weighting interval and expansion of the excavation-damaged zone around the gate when compared to the field data measured at the Dongzhouyao mine of China.

Powder Resistivity Inferred Differential Collection of Heterogeneous Coal Fly Ash and Powered Activated Carbon Admixtures Within a Cylindrical Electrostatic Precipitator

One of the primary goals of U.S. EPA’s Mercury Air Toxics Standards (MATS) is to remove approximately 90 % of mercury emissions from coal-fired power plants (CFPPs). Sorbent injection upstream of electrostatic precipitators (ESPs) has been the leading method for capturing mercury at CFPPs. However, electrostatic precipitators (ESPs) that are marginally sized and/or operated may face new performance challenges due to sorbent injection. Injected mercury sorbent particles having different properties (i.e., particle size, surface chemistry, or electrical properties), mixing with native fly ash, can potentially affect the collection behaviors of ESPs. The present study uses powder resistivity to study the differential collection behaviors within a cylindrical ESP by manually feeding admixtures containing Norit DarcoⓇ FGD powdered activated carbon (PAC) and fly ash samples from either Powder River Basin (PRB) or Illinois bituminous coals. Powder resistivity measurements, performed on fly ash admixtures at various PAC ratios (i.e. 0−10 wt. %) prior to ESP processing, serve as the initial resistivity data to infer the impact of PAC injection on ESP collection by comparing to powder resistivity of samples collected from the collection electrode. This study presents not only the evidence of differential collection behaviors within an ESP but also the implications for mercury emissions and the particulate matter (PM) control through ESPs.

Test Study on the Heterogeneity of Coal and Model of Coupled Gas Flow and Deformation Process

In order to obtain the heterogeneity of coal, the mechanical tests were performed. The experimental results show that the heterogeneity of the mechanical parameters for coal follow the Weibull distribution. Then the model of coupled gas flow and deformation process for heterogeneous coal was presented and the effects of heterogeneity of coal on gas flow and failure of coal were investigated. The finding is that the effect of the heterogeneity of coal on gas flow and mechanical failure of coal can be considered by the model in this paper. Failure of coal has a great effect on gas flow.

Model of coupled gas flow and deformation process in heterogeneous coal seams and its application

The heterogeneity of coal was studied by mechanical tests. Probability plots of experimental data show that the mechanical parameters of heterogeneous coal follow a Weibull distribution. Based on elasto-plastic mechanics and gas dynamics, the model of coupled gas flow and deformation process of heterogeneous coal was presented and the effects of heterogeneity of coal on gas flow and failure of coal were investigated. Major findings include: The effect of the heterogeneity of coal on gas flow and mechanical failure of coal can be considered by the model in this paper. Failure of coal has a great effect on gas flow.

Measurement and simulation of flow properties of coal ash slag in coal gasification

AbstractThe viscosities of 45 coal ash slag samples at high temperature have been measured under different temperatures and shear rates. The computer thermodynamic software package FactSage has been used to predict liquidus temperatures, volume fractions of crystallized solid particles (ϕ), and the compositions of remaining liquid phase for 45 coal ash slag samples. The flow properties of completely liquid and partly crystallized coal ash slag samples have been predicted by three viscosity models. The Urbain formalism has been modified to describe the viscosities of fully liquid slag and homogeneous remaining liquid phase in coal ash slag samples. The modified Einstein equation and Einstein–Roscoe equation have been used to describe the viscosities of heterogeneous coal ash slag samples of ϕ < 10.00 vol % and ϕ ≥ 10.00 vol %, respectively. These three models provided a good description of the experimental data of fully liquid and heterogeneous coal ash slag samples. The new models also predicted flow properties of mixtures of coal ash slags with CaO, Fe2O3, MgO, SiO2, and Al2O3. © 2010 American Institute of Chemical Engineers AIChE J, 2011

Field scale characterization and modeling of contaminant release from a coal tar source zone

A coal tar contaminated site was characterized using traditional and innovative investigation methods. A careful interpretation of hydrogeological and hydrogeochemical data allowed for the conceptualization of the heterogeneous coal tar distribution in the subsurface. Past and future contaminant release from the source zone was calculated using a modeling framework consisting of a three-dimensional steady-state groundwater flow model (MODFLOW) and two hydrogeochemical models (MIN3P). Computational time of long-term simulations was reduced by simplifying the coal tar composition using 3 composite and 2 individual constituents and sequential application of a 2D centerline model (for calibration and predictions) and a 3D model (only for predictions). Predictions were carried out for a period of 1000 years. The results reveal that contaminant mass flux is governed by the geometry of zones containing residual coal tar, amount of coal tar, its composition and the physicochemical properties of the constituents. The long-term predictions made using the 2D model show that even after 1000 years, source depletion will be small with respect to phenanthrene, 89% of initial mass will be still available, and for the moderately and sparingly soluble composite constituents, 60% and 98%, respectively.

Adsorption and gas transport in coal microstructure: investigation and evaluation by quantitative X-ray CT imaging

Natural gas (methane) production from coal seams is recognized as one of the valuable energy sources due to high storage capacity of coal to store gas at low pressures. It is known that coal composition, pore structure, and mineral matter properties affect both the amount of adsorbed quantity and kinetics of adsorption when the coals are considered for natural gas production or mediums for storing gas, mainly methane or carbon dioxide Experiments in the field of adsorption equilibrium and dynamics usually investigate the adsorption properties on crushed coal samples within a certain range of particle sizes. This data can be used to obtain an average behavior representing the very heterogeneous coal–gas system. But, although individual pores are not likely influenced by crushing, this process destroys the natural integrity and continuity of the porous medium and mixes all the lithotypes and minerals in the same batch. This makes it impossible to investigate and differentiate the behavior of different microstructures and lithotypes. In this study, gas transport and adsorption were investigated on a 3.8-cm diameter core of a medium volatile bituminous coal from Gelik seam in the Zonguldak Basin (Northwestern Turkey) by using quantitative X-ray computerized tomography (CT) imaging technique to visualize the interior of the coal during the experiment. Coal was subjected to time-varying xenon (although not a perfect analog for methane, it provides good contrast under X-rays) gas pressure for the experiment. Adsorbed amounts at different locations were determined by scanning the coal at different times. Qualitative CT images and quantitative image data were used to investigate and compare the regions where gas is transported and stored as well as the rate of adsorption at different regions having different pore structure, and composition. The SEM and CT imaging techniques used in this study enabled us to investigate the coal microstructure falling into macropore range (>1 μm with SEM and 0.3135 mm with CT). This study clearly demonstrates that, for the specific coal sample and xenon gas conditions, different structures (in the length scale given above) and lithotypes have different adsorption capacity and rate behavior. SEM images were also used to define the regions showing different adsorption behavior.