Gas Drainage System Research Articles

Definition, theory, methods, and applications of the safe and efficient simultaneous extraction of coal and gas

Simultaneous extraction of the coal and gas is an effective method of eliminating coal mine gas disasters while safely exploiting the coal and achieving efficient gas drainage in China, which is widely accepted by the main coal-producing countries around the world. However, the concrete definition of simultaneous extraction is vague and there is little accurate theoretical support for the simultaneous extraction of coal and gas, which makes it difficult to determine an efficient gas drainage method appropriate to the features of coal seams. Based on theoretical analysis, laboratory tests and field observations, a specific definition of simultaneous extraction of coal and gas is proposed after analyzing the characteristics of coal seam occurrences in China, and we developed the mechanism of mining-enhanced permeability and established the corresponding theoretical model. This comprises a process of fracture network formation, in which the original fractures are opened and new fractures are produced by unloading damage. According to the theoretical model, the engineering approaches and their quantitative parameters of ‘unloading by borehole drilling’ for single coal seams and ‘unloading by protective seam mining’ for groups of coal seams are proposed, and the construction principles for coal exploitation and gas-drainage systems for different conditions are given. These methods were applied successfully in the Tunlan Coal Mine in Shanxi Province and the Panyi Coal Mine in Anhui Province and could assure safe and efficient simultaneous extraction of coal and gas in these outburst coal mines.

Discussion on Ways of Mine Gas Drainage and Extraction

Coal gas is a key factor in coal mine production safety, gas outburst and other threats can cause suffocation mine operating personnel, damage to human health, the gas reaches the ignition and combustion gases can cause encountered gas and coal dust explosion; while the main gas or the Earth's atmosphere sources of pollution. Therefore, effective governance gas to gas as a resource to achieve coal and gas extraction, to eliminate sudden end, and take advantage of the gas, reducing its air pollution is a major issue in the field of coal mining, the paper gas utilization, gas drainage aspects of mining, mine gas drainage system briefly described.

Experiment research on overburden mining-induced fracture evolution and its fractal characteristics in ascending mining

The simulated material model was used to simulate the formation and distribution of overburden fractures induced by ascending mining. The fracture evolution law was revealed. The fractal geometry theory and MATLAB software were applied to analyze fractal characteristics of fracture network of overburden stratum. The results showed that the overburden failure evolution is trapezoidal, accompanied with collapse in layer group and the developing height of fractures discontinuously jumps; as the mining width increased, the fractal dimension of fracture network showed an overall ascending trend, presenting three stages, namely, fast dimension rising stage, slow dimension rising stage, and stable stage. In the caving zone, fracture zone, and bending zone, the development, propagation, and closure of fractures were asynchronous and inner similar. These achievements are important to roof roadway stability control and layout of gas drainage system and contribute to the simultaneous extraction theory of coal and gas by pressure relief.

Coupling Model of Evolution of Mining Fissure Elliptic Paraboloid Zone and Methane Delivery

After mining, a dynamic distribution of mining fissure elliptic paraboloid zone in the overlying stratum would be formed. Based on the rock mechanics, seepage flow mechanics, mass transfer theory and elastic-plastic theory, the coal-rock mass deformation equation, mixture gas seepage equation and gas diffusion equation of the mining fissure elliptic paraboloid zone are deduced. Combined with various boundaries, initial conditions, the multi-field coupling mathematical model of mining fissure elliptic paraboloid is obtained. The model provides a theoretical basis for numerical simulation of gas drainage system layout.

Gas pipeline explosion resistance technology

Based on the features and requirements of gas drainage system, an optimized explosion resistance technology is done after a comprehensive analysis and research about the triple IR (Infrared Ray) flame detection technology, explosion resistance valve technology and explosion resistance control technology. An intelligent PLC (Programmable Logic Controller) resistance control system is designed which can cut off the gas branch quickly and accurately, and the controller have automatic pressure maintaining function, valve rotation limit function, remote and local control interlock function. The reliability and rationality of explosion resistance technology is verified by gas pipeline explosion propagation and resistance simulation test. Overall response time of explosion resistance system is less than 100ms, and the spread of fire in gas pipeline can be prevented effectively.

Radon mitigation by use of surface gas drainage system

The uranium mining was stopped in the Mecsek Mountains in 1997. Most of the dwelling houses, located close to a mine-tunnel, show a yearly average of indoor radon activity concentration higher than the EU recommendation for existing buildings (300 Bq/m3). To reduce the high radon concentration, new radon mitigation was completed in a selected house and the mitigation effect has been studied. Indoor radon concentration was monitored continuously for one month once before and three times after the mitigation technique was applied. Due to the mitigation, the initial radon concentration was decreased by 71% (average radon concentration before the mitigation: 1480±74 Bq/m3, after the mitigation: 420±33 Bq/m3). In the paper these results are interpreted from the point of view of functioning of the applied mitigation technique and dependence of the mitigation efficiency on the meteorological conditions.

A gas mixture enhanced coalbed methane recovery technology applied to underground coal mines

This paper presents a field trial for developing a gas mixture enhanced coalbed methane (GECBM) technology that can be integrated with underground coal mine methane (CMM) drainage systems. The field trial was carried out in a deep underground coalmine roadway in two stages, initially degassing using a conventional method for 30 days in three boreholes installed in the underground coal seam and then injecting the gas mixture from one of the boreholes for about 2 months. The field trial focuses on the investigation of the technical and economic feasibilities of G-ECBM technology applied to underground CMM drainage systems. The results revealed that the G-ECBM technology integrated with underground methane drainage systems can provide an effective method to enhance the coalbed methane (CBM) recovery from coal mines and the efficiency of underground gas drainage systems, and hence improve the mining safety. The field measurements showed that the single-borehole flow rate and concentration of CH4 for the production boreholes with G-ECBM have increased by a factor of 4.73 and 1.68 on average, respectively, compared with the conventional production boreholes without G-ECBM. The results also showed the economic prospect of applying G-ECBM technology to underground CMM drainage systems.

Graph Theory and Its Application in Optimization of Gas Drainage System in Coal Mine

Abstract Gas drainage is an important gas treatment measure. With changing the location and gas drainage quantity of the system, some reasonless phenomena would occur, Hence, the system must be optimized. According to the relation of graph theory and gas drainage system, the gas drainage system of Zhao Gezhuang mine is optimized by graph theory and the resistances are calculated. After optimization, the drainage resistance is equally distributed, which increases the quantity of gas drainage from coal mine, improves the efficiency and reliability of mine gas drainage system and enhances the safety of the mine; so the firm foundation of the gas utilization is established and the virtuous cycle of “drainage-usage -safety production” and comprehensive gas control are well realized. It shows that the graph theory can be well applied in gas drainage system optimization.

Dimensional Analysis and Scale-up of Immiscible Two-Phase Flow Displacement in Fractured Porous Media under Controlled Gravity Drainage

Oil production from a fractured reservoir, composed of a gas cap and an oil zone, is usually accomplished using surface or submersible pumps. The production method is called controlled gravity drainage (CGD). In the CGD mode of production, the pumps usually operate under a constant withdrawal rate until gas breakthrough, at which time the pumping rate would be influenced by the presence of gas at the production well. In this paper, we describe immiscible displacements in fractured porous media to have a better understanding of the process. Oil−gas CGD displacements were conducted using a laboratory flow apparatus in the fractured glass bead systems. A detailed dimensional analysis was conducted to scale up the experimental results based on the physics of the CGD process and experimental findings. Dimensional analysis of immiscible two-phase flow in porous media allows for quantification of the influences of petrophysical properties of the fractured media and physical properties of test fluids on some important aspects, such as critical pumping rate and recovery factor at gas breakthrough. In this work, an empirical model based on the dimensional groups of the system obtained from the Buckingham π theorem was employed to investigate the gravity drainage process in a fractured porous medium. A model was developed to predict the critical pumping rate, maximum withdrawal rate, distance between the gas−liquid (G−L) interface positions within the matrix and fractures, and recovery factor just before gas breakthrough for fractured porous media undergoing the CGD processes. The model was tested against experimental and field data of oil production under CGD. The results demonstrate that the model gives satisfactory prediction for the oil−gas drainage systems. The procedure outlined in this paper also has potential applications in modeling immiscible displacements.

Passive drainage and biofiltration of landfill gas: Results of Australian field trial

A field scale trial was undertaken at a landfill site in Sydney, Australia (2004–2008), to investigate passive drainage and biofiltration of landfill gas as a means of managing landfill gas emissions from low to moderate gas generation landfill sites. The objective of the trial was to evaluate the effectiveness of a passive landfill gas drainage and biofiltration system at treating landfill gas under field conditions, and to identify and evaluate the factors that affect the behaviour and performance of the system. The trial results showed that passively aerated biofilters operating in a temperate climate can effectively oxidise methane in landfill gas, and demonstrated that maximum methane oxidation efficiencies greater than 90% and average oxidation efficiencies greater than 50% were achieved over the 4 years of operation. The trial results also showed that landfill gas loading was the primary factor that determined the behaviour and performance of the passively aerated biofilters. The landfill gas loading rate was found to control the diffusion of atmospheric oxygen into the biofilter media, limiting the microbial methane oxidation process. The temperature and moisture conditions within the biofilter were found to be affected by local climatic conditions and were also found to affect the behaviour and performance of the biofilter, but to a lesser degree than the landfill gas loading.

炭鉱ガス回収利用システム日中共同実証事業の概要

Methane gas (coal mine gas) emitted into the atmosphere due to coal mining is not only a problem for mine safety but also an undesired effect on global warming. Therefore, we will accelerate to diffuse technologies for coal mine gas recovery and its effective use through demonstration project at operating coal mines. The demonstration project for effective recovery and utilization of coal mine gas has been conducted for five years, from fiscal 1998 to 2002, at Tiefa Coal Mining Company, Liaoning Province in P.R.C. The purposes of the project are to prevent global warming, to improve mine safety and to use the coal mine gas effectively as a clean energy resource with its efficient recovery and effective use. The advanced gas drainage and utilization system have been introduced and at the same time the technology transfer has been conducted. Through the project, the coal mine gas has been recovered stably in high concentration and supplied as town gas.

Control of gas emissions in underground coal mines

A high level of knowledge is now available in the extremely relevant field of underground gas emissions from coal mines. However, there are still tasks seeking improved solutions, such as prediction of gas emissions, choice of the most suitable panel design, extension of predrainage systems, further optimization of postdrainage systems, options for the control of gas emissions during retreat mining operations, and prevention of gas outbursts. Research results on these most important topics are presented and critically evaluated. Methods to predict gas emissions for disturbed and undisturbed longwall faces are presented. Prediction of the worked seam gas emission and the gas emission from headings are also mentioned but not examined in detail. The ventilation requirements are derived from the prediction results and in combination with gas drainage the best distribution of available air currents is planned. The drainage of the gas from the worked coal seam, also referred to as predrainage, can be performed without application of suction only by over or underworking the seam. But in cases where this simple method is not applicable or not effective enough, inseam-boreholes are needed to which suction is applied for a relatively long time. The reason for this is the low permeability of deep coal seams in Europe. The main influences on the efficiency of the different degasing methods are explained. Conventional gas drainage employing cross measure boreholes is still capable of improvement, in terms of drilling and equipment as well as the geometrical borehole parameters and the operation of the overall system. Improved control of gas emissions at the return end of retreating faces can be achieved by installation of gas drainage systems based on drainage roadways or with long and large diameter boreholes. The back-return method can be operated safely only with great difficulty, if at all. Another method is lean-gas drainage from the goaf. The gas outburst situation in Germany is characterized by events predominantly in the form of `nonclassical' outbursts categorized as `sudden liberation of significant quantities of gas'. Recent research results in this field led to a classification of these phenomena into five categories, for which suitable early detection and prevention measures are mentioned.

Technologies recovering and utilizing coal seam gas in Japan

In Japanese coal mines the gas drainage is employed in a practical operation in order to keep low level of methane concentration in the ventilation. In 1993, gas of 44.9 million m 3 was drained and about 90% of the drained gas was used for power generation and heating. In order to evaluate the utilization possibility of coal seam gas as natural gas resources, the gas resources in Ishikari coal field was estimated. At Taiheiyo coal mine, the long-length boreholes with a length of 500m was developed and used to degas methane from the coal and rock seams. At Sorachi Coal Mine, an auto- controlled gas drainage system to control the flow rate of a gas drainage line from sealed goaf was developed and used successfully in practical operations. This paper summarizes the resources estimation of coal seam gas in Ishikari coal field and recent technologies related to the methane gas drainage in Japanese coal mines.

Distribution of gas pressure in a radial flow field

It is still a difficult problem to find the analytical solutions for the gas flow equation, the nonlinear partial differential equation of the radial flow field in the coal seam. The approximate analytical solutions, with variable substitution and proper simplification, that is, the distribution expressions of gas pressure in a radial flow field are developed. The analytical formulas for gas drainage in the coal seam are presented. The numerical calculation with computers demonstrates that the new analytical formulas are accurate and easy to use for the design of a gas drainage system.

A new method for the rational arrangement of gas drainage boreholes

The effective radius and the rational distances between boreholes for gas drainage in coal seams are two of the fundamental parameters for the rational arrangement of boreholes in a gas drainage system. Mathematical formulae for the rational arrangement of boreholes for gas drainage in coal seams have been deduced based on the theoretical model of coal gas dynamics. It is shown, by using the formulae for calculations for actual areas in the collieries, that these formulae, which have primarily been applied in the design of a gas drainage system for the prevention of coal gas outbursts, are rapid, simple and useful.

Methane drainage in longwall coal mining : De Villiers, A W J S Afr Inst Min MetallV89, N3, March 1989, P61–72

This paper explores the behaviour of methane in the goaf during longwall mining, together with some methods for the control of methane emissions into the goaf, the working face, and the ventilation system. Experimental work done at Twistdraai Colliery, Sasol Coal, is referred to, as well as the gas-drainage system being practised at West Cliff Colliery in New South Wales, Australia. Gas drainage is discussed briefly, and certain suggestions are made in regard to coal mining in South Africa.