Seam Conditions Research Articles

Impact analysis of the oxidant in the process of underground coal gasification

Technology of Underground Coal Gasification (UCG) is still under developing and providing alternative for conventional underground coal mining. Underground coal gasification is a process with may be environmentally and economically attractive for widespread use in the future. The quality of the produced gas from UCG can vary substantially depending on the injected oxidant used, operating pressure, oxidizer flow rate, type of coal, hydrological conditions of the coal seam, coal type and the mass and energy balance of the underground reactor. Paper analyzes the impact of the oxidant on calorific value of the syngas in a laboratory and operating conditions. Also is analyzed the effect of temperature in the oxidation zone of gasifier on gas composition and calorific value. Effect of oxidant on the gasification process has been verified on experimental gasifier equipment. The paper describes an experimental gasifier and devices that were used for measurement and control.

Chemometric study of trace elements in hard coals of the upper Silesian Coal Basin, Poland.

The objective of the study was the analysis of trace elements contents in coals of the Upper Silesian Coal Basin (USCB), which may pose a potential threat to the environment when emitted from coal processing systems. Productive carbon overburden in central and southern zones of the USCB is composed mostly of insulating tertiary formations of a thickness from a few m to 1,100 m, and is represented by Miocene and Pliocene formations. In the data study the geological conditions of the coal seams of particular zones of the USCB were taken into account and the hierarchical clustering analysis was applied, which enabled the exploration of the dissimilarities between coal samples of various zones of the USCB in terms of basic physical and chemical parameters and trace elements contents. Coals of the northern and eastern zones of the USCB are characterized by high average Hg and low average Ba, Cr, and Ni contents, whereas coals of southern and western zones are unique due to high average concentrations of Ba, Co, Cu, Ni, and V. Coals of the central part of the USCB are characterized by the highest average concentration of Mn and the lowest average concentrations of As, Cd, Pb, V, and Zn.

Analysis of Distribution of Coalbed Methane and Geological Controlling Factors in Huanghebei Mining Area

Distribution characteristics of coalbed methane in Huanghebei mining area were studied and influence of geological factors such as faults, lithology of coal seam roof and floor, magmatic activities, burial depth and upper bedrock thickness of coal seam and hydrogeological conditions on occurrence of coalbed methane were deeply discussed in this paper. Coalbed methane content of mining area increased gradually from southeast to northwest. Coalbed methane in deep well points of mining area is dominated by methane and that in shallow parts contained higher content of nitrogen.

Numerical Simulation on the Stress Distribution of Thin Seam Containing Iron-Sulfide-Cores

Fast Lagrangian Analysis of Continua in three Dimensions was adapted to establish numerical model of thin seam with Iron-sulfide-cores, based on the conditions of thin seam in Yanzhou Mining Area, and the influence of existing cores or not, cores in different positions, cores contents on mine pressure was studied. The results showed that, stress concentration and plastic zone is more easily to be formed in the coal around cores. When there are cores in coal, the bahaviors of abutment stress foreside the working face have no significant differences, the abutment stress curve is fluctuation and width or range of plastic zone little changed, but the boundary of plastic zone is fuzzy and radial. The boundary of plastic zone has some difference with the increasing of cores contents, but other macroscopic mine pressure behaviors has no significant differences. It is helpful to understand spalling mechanism of iron-sulfide-cores in thin seam.

A Study on the Outburst Threshold Value of Gas Content in Coal

An outburst of coal and gas is a major hazard in underground coal mining. It occurs when certain conditions of coal stress, strength and gassiness are met. Based mainly on field observations related to the conditions, a number of indices are used in prediction of the outburst. Some of the indices are considered to be inadequate, inappropriate or impractical in some coal seam conditions. Significant progresses have been made in development of the technologies over the last few years. One of the major achievements is an analytical method in determination of an outburst threshold value of the gas content in a coal seam. The method combines field measurements and numerical modelling. The method is illustrated in this paper in a case study for determination of the outburst threshold value of gas content for a coal seam.

Optimization on Gateway Section of Soft Coal Seam and Hard Roof and Supporting Technology

Support invalidity of a roadway have a largely influence on production safety of coal mines, especially the soft coal roadway, which deforms heavily. To solve this problem, it began from the gateway section optimization, based on the actual geological condition of Chang-gouyu Mine. The computational model was established up to optimize tunnel shapes using FLAC3D. The scopes of plastic zone, stress field, displacement field were compared and analysed for different shapes of roadway. The irregular trapezoid section is adopted, then the bolt support parameters were designed and field application was done. By using the irregular trapezoid, the stress distribution around the roadway is improved and the deformation and plastic zone is decreased. Under the geological conditions of the soft coal seam and hard roof strata, the stability of roadway was effectively controlled by using optimized trapeziform cross-section and bolting support.

Research on the Height of Water Flowing Fractured Zone of Fully Mechanized Caving Mining in Extra-thick Coal Seam

Abstract Failure height of overlying rock mass in extra-thick coal seam conditions by fully mechanized caving mining affects the groundwater occurrence condition, which in turn, affects mine safety. Aiming at extra-thick coal seam conditions, this paper numerically stimulates the dynamic process of actual excavation. Results show that failure height increases with excavation volume, thereby increasing the location of abscission layer dropping along with increasing failure height. An abscission layer is formed along the depth, changing the condition of groundwater occurrence and exposing a hidden safety hazard in the field of continuous mining. The simulation results are in line with the fact by verification with drilling survey data.

The application of a coupled artificial neural network and fault tree analysis model to predict coal and gas outbursts

This paper proposes the use of a coupled fault tree analysis (FTA) and artificial neural network (ANN) model to improve the prediction of the potential risk of coal and gas outburst events during the underground mining of thick and deep Chinese coal seams. The model developed has been used to investigate the gas emission characteristics and the geological conditions that exist within the Huaibei coal mining region, Anhui province, China. The coal seams in this region exhibit a high incidence of coal and gas outbursts. An analysis of the results obtained from an initial application of an FTA model, identified eight dominant model parameters related to the gas content or geological conditions of the coal seams, which characterize the potential risk of in situ coal and gas outbursts. The eight dominant model parameters identified by the FTA method were subsequently used as input variables to an ANN model. The results produced by the ANN model were used to develop a qualitative risk index to characterize the potential risk level of occurrence of coal and gas outburst events. Four different potential risk alarm levels were defined: SAFE, POTENTIAL, HIGH and STRONG. Solutions to the prediction model were obtained using a combination of quantitative and qualitative data including the gas content or gas pressure and the geological and geotechnical conditions of coal seams. The application of this combined solution method identified more explicit and accurate model relationships between the in situ geological conditions and the potential risk of coal and gas outbursts. An analysis of the model solutions concluded that the coupled FTA and ANN model may offer a reliable alternative method to forecast the potential risk of coal and gas outbursts.

Similarity model tests of movement and deformation of coal-rock mass below stopes

For a study of the movement and deformation of coal-rock mass and low protected seams below a stope, as well as for fracture developments and rules of evolution of permeability, we designed a plane strain model test stand to carry out model tests of similar materials in order to improve the effect of gas drainage from low protected seams and to measure the movement and deformation of coal-rock mass using a method of non-contact close-range photogrammetry. Our results show that 1) using paraffin melting to take the place of coal seam mining can satisfy the mining conditions of a protective seam; 2) coal-rock mass under goafs has an upward movement after the protective seam has been mined, causing floor heaving; 3) low protected seams become swollen and deformed, providing a good pressure-relief effect and causing the coal-rock mass under both sides of coal pillars to become deformed by compression and 4) the evolution of permeability of low protected seams follows the way of initial values→a slight decrease→a great increase→stability→final decrease. Simultaneously, the coefficient of air permeability increased at a decreasing rate with an increase in interlayer spacing.

Prediction model of bottom hole temperature and pressure at deep injector for CO2 sequestration to recover injection rate

Abstract The field test of CO 2 -ECBM was carried during 2003 to 2007 in order to evaluate technical feasibility of injecting CO 2 into the coal seam while producing CH 4 at Yubari City, Hokkaido, Japan. It aims to resolve global warming and to develop a system for injection and sequestration of CO 2 into coal seams. The targeted coal seam is located about 900 m below the surface. The absolute pressure at the bottom hole is approximately 15.5 MPa and the CO 2 temperature is about 28 ∘ C before the injecting into the coal seam. Thus, CO 2 is injected in liquid phase to the coal seam and supercritical condition of CO 2 has not been satisfied due to heat loss along the deep injection well. Replacements of usual tubing pipes with thermal insulated tubings were applied, however the temperature at the bottom hole was still lower than the CO 2 critical temperature. The project had a problem about decreasing injection rate after starting injection CO 2 . It was evaluated by analysing the field test data that the maximu m decreasing ratio of the coal seam permeability was 0.065 and permeability around injection well was became 6 times larger than the original one. We assumed that its reason is caused with swelling of the coal seam around the injection well by liquid CO 2 injection. Present study has focused on the keeping supercritical CO 2 in the tubing because viscosity of supercritical CO 2 that is 40% smaller than that of liquid CO 2 . The CO 2 temperature has been successfully predicted in order to keep CO 2 in supercritical condition from the surface to the bottom for various CO 2 injection rates and electric heater power. The minimum injection rate has been presented in order to keep CO 2 in the supercritical condition at the bottom hole of the injection tubing. Injected CO 2 is expected to be super critical over 12 ton/day of injection rate without any heating in the tubing.

CO2 storage through ECBM recovery: An experimental and modeling study

The permeability of the coal seam is the main petrophysical property controlling the performance of the ECBM operation, since it affects both the CO2 injection and CH4 recovery. In the present paper, coal swelling of intact coal samples is studied both under unconstrained and constrained conditions. Unconstrained swelling experiments are performed in a view cell under a static high pressure gas atmosphere, whereas gas injection experiments are carried out in a flow cell, where the sample is subjected to a given hydrostatic confinement. Both experiments are performed by using different gases, namely He, CO2, CH4 and N2, and under typical coal seam conditions, i.e. at high pressure and at 45 ∘C. The results of the unconstrained coal sample showed that swelling increases monotonically with pressure up to a few percents for adsorbing gases, with CO2 swelling coal more than CH4 that swells more than N2, whereas for helium, a non-adsorbing gas, volume changes are negligible. The results of the flow experiments were successfully described using a mathematical model consisting of mass balances accounting for gas flow and adsorption, and mechanical constitutive equations for the description of porosity and permeability changes during injection. Results showed increase in permeability with decreasing effective pressure on the sample. Moreover, when CO2 is used a permeability reduction was observed compared to Helium, which can be explained by taking into account the effects of swelling on the flow dynamics.

Research on the sudden changes and the controlling factors of deep coal mining conditions

It was illustrated that the mining conditions inducing disasters changed with depth both in regularity of gradual and sudden change. The sudden change depth for different disaster conditions are different and controlled by different factors. The high temperature and its change with depth are mainly controlled by strata structures and rock heat conductivity property, the high rock stress and dynamical engineering disasters and their change with depth are mainly controlled by tectonic conditions, roof strata rock property and deep rock mechanical property, coal mine water disasters and their change with depth are mainly controlled by rock mechanical property of coal seam floor and regional groundwater circulation conditions, gas disaster conditions and their change with depth are mainly controlled by buried conditions of coal seam and opening conditions of geological structures. It is mentioned that the key point for the control of deep coal mining disaster is to clearly understand the sudden change depth of different factors causing disasters.

Void detection at an anthracite mine using an in-seam seismic method

An in-seam seismic (ISS)-based void detection technique was developed at Penn State University. Among various features, the most important one is its capability of acquiring high quality and broadband signals ranging from 50 to 5000 Hz. This feature is essential for acquiring and analyzing signals for a thin seam condition. The technique was tested at an underground anthracite mine. It successfully detected a mined out void at a distance of 46 m (150 ft) from the coal face. The seam height at the test site was 1.4 m (4.5 ft) on average. The transmission surveys generated well developed Love seam waves. This made it possible to reliably assess the dispersion characteristics of Love waves for this particular site. The Airy-phase had a typical frequency range of 400–600 Hz with a fairly stable velocity of 975 m/s (3200 ft/s). An elliptical method was used for void mapping in order to accommodate highly irregular sensor and source locations. The mapping error was within ± 4.6 m (15 ft) based on the test results.

Methane control for mechanised longwall top-coal caving faces in high gas content mines

In China, mechanised longwall top-coal caving technology (LTCT) has been widely used under suitable thick coal seam conditions due to its low cost, high production and productivity since it was introduced in 1982. It has even been applied in some high gas-content mines (e.g. No. 5 Mine, Yangquan coalfield), where methane is the most serious hazard affecting production in the mine. With the introduction of LTCT in 1992, the frequency of production delays greatly increased due to excess methane. In order to solve these problems, China University of Mining and Technology (CUMT) has been carrying out methane research jointly with Yangquan Coal Group Co. (YCGC) since 1993. The major focus of the research was concerned with the gas source and emission characteristics of the longwall top-coal caving face (LTCF) and the methane drainage methods from the adjacent strata during initial and normal mining. The research has helped the mine to control methane-related production delays to tolerable levels. The methane problems during normal mining were solved by the adoption of the high-level strike drainage roadway (HSDR). The methane concentration during initial mining was kept below the statutory limits by the adoption of the mid-level drainage roadway (MDR). In this way, the methane-related production delay problems were successfully solved by introduction of the HSDR in conjunction with the MDR. This paper analyses the gas source and emission characteristics of LTCF, and describes the experiences and methodologies adopted in methane control at the LTCF during normal and initial mining.

指向性ボーリングを用いた地山ガス抜きおよび断層探査技術

Taiheiyo Coal Mine is located on the southeast part of Kushiro-city in Hokkaido prefecture, Japan. The Mine, which is an underground coal mine, was established in 1920. The total output of clean coal during its 80 years of operation was more than 100 million tons. Its mining fields gradually expanded into sea beds in the Pacific Ocean from land areas ; and since 1951 its entire mining fields have been under the sea bed. Currently, the main fields for mining are areas located 600 to 700 meters under sea level. The production of clean coal in 1999 was 2.13 million tons and R.O.M was 4.08 million tons. The Coal Mine has commenced present directional drilling system applied in Australia for in-seam gas drainage since 1997. However, due to the coal seam condition in the Mine that collapse easier than in Australia and contain clay parting, it was difficult to keep the borehole in open. Hence we modified drilling system, in order to drill both in the coal seam and in the rock strata. This change required some modification on bit, bent sub and rod and also development of new drilling machine. After these modifications, three directional drilling systems have been installed for gas drainage and exploration underground, and another two systems will be installed by the end of March 2001. In this paper, outline of the directional drilling system and the typical result of trials for in-seam gas drainage and exploration drilling by the system are descried.

大口径ボーリングによる排出繰粉量とガス湧出について

In this paper, the measuring results of gas emission and cuttings volume exhausted by the large diameter (250mmφ) boring for a prevention of gas outburst are described. The large diameter boring has been carried out from the heading of gateroad into advancing direction up to the depth of 20-30m.Main results obtained are as follows.(1) It is probably assumed that complicated seam condition is existent under such circumstances as cuttings volume over 1, 000l/m, boring time over 30 min./m or gas emission volume per cuttings over 100m3/m3 on the large diameter boring.(2) The relation between cuttings volume and boring depth are classified into three patterns as shown in Fig. 7. In such a case that the peak position of pattern B-curve is located within the safety depth of existing borehole from the heading, it i s desirable to shift pattern B to A or C by new large diameter boring.

Signal Processing For Crosshole Seismic Imaging

Boreholes are normally drilled on a wide grid pattern over potential coal mine sites to evaluate coal reserves, etc., but further drilling or geophysical methods are required for detailed coal seam mapping. Surface seismic methods are useful to find seam conditions without drilling, but are limited by the low frequencies used (<150 Hz even for high resolution surveys) to resolutions of the order of 10 m, which is inadequate for good mine planning. Higher frequencies cannot be transmitted through the surface soil and weathered layers.