Richard C. Gilmore: Publications

Dr. Gilmore has published many articles in conferences around the world in the mining industry on topics studying coal mine ventilation safety. Conferences in the USA, Canada, Europe, Africa, and China on topics covering explosives, high-performance computing (HPC), computational fluid dynamics (CFD), methane-air explosions, coal mine rock dust, weather influencing methane accumulation, gob ventilation boreholes, nitrogen inertization, and risks of the spontaneous combustion of coal.

Peer-Reviewed Articles

2019
  • Gilmore, R. C., Brune, J. F., Johnson, R., and Schreiner, M.
    Methane-air Mixture Air-blast Approximated Using Detonating Cord in Rock Dust Dispersibility Studies
    45th Annual Conference on Explosives and Blasting Technique, International Society of Explosives Engineers (ISEE), Nashville, TN

    ABSTRACT: Explosive pockets of methane-air mixtures accumulate in underground coal mines and, when ignited, produce an air-blast wave that can disturb combustible coal dust on the floor, roof, and ribs. To prevent explosions, the coal dust must be continuously diluted through application of inert rock dust, usually powdered limestone. Application of powdered dust process creates a respiratory nuisance downwind, where miners cannot work until the dust settles. Rock dust suppliers have developed wet and foam applied products to reduce the nuisance and limit the interruption to mining during dust application. To test the effectiveness of these alternative dust products, researchers at the Colorado School of Mines (Mines) have constructed a full-scale explosion test drift located at the Mines Edgar Experimental Mine (Edgar) to study the dispersibility of different rock dust applications. This paper examines the use of Pentaerythritol tetranitrate (PETN) detonating cord to produce controlled air-blasts that simulate methane-air explosions. The air blasts are generated with curtains of detonating cord that produce shockwaves with wind speeds between 30 to 70 m/s (100 to 225 fps) depending on the length of 5.3 g/m (25 grain/ft) detonating cord used. These velocities represent the minimum air speeds required to trigger propagating coal dust explosions. Researchers have conducted 40 test blasts with various lengths of detonating cord. Results show the two primary waves and two reflected waves each decaying into air- blast waves with overpressures of 14 to 27 kPa (2 to 4 psi). Pressures were recorded with commercial piezoelectric transducers and custom-built, bi-directional probes to record the total and dynamic pressures of the wind generated in the explosion. Researchers were able to generate consistent and repeatable wind speeds and air-blast durations sufficiently similar to a methane-air explosion to study the dispersibility of various rock dust products and application methods.

  • Gilmore, R. C., and Brune, J. F.
    Coal Mine Rock Dust Dispersibility Tests after Absorbing Moisture
    17th North America Mine Ventilation Symposium, Montreal, Canada

    ABSTRACT: Pulverized limestone rock dust used in United States underground coal mines to prevent and suppress coal dust explosions must easily disperse by forces of a methane or coal dust explosion. Moisture in the mine environment causes caking of the dust. Colorado School of Mines researchers performed dispersibility tests in a full-size explosion test drift. Tests included conventional, hydrophobized, and rock dust approved for German mines. Conventional and German standard rock dust products partially agglomerate, which may not be effective in suppressing a coal dust explosion, while hydrophobic rock dust retains better dispersibility.

  • Gilmore, R. C., McMack, J, DeRosa, C, Bogin, G. E., Jr., and Brune, J. F.
    Design and Construction of a 1/40th Scale Longwall Mine Model for Physical Testing of Methane Explosions
    17th North America Mine Ventilation Symposium, Montreal, Canada

    ABSTRACT: Researchers at the Colorado School of Mines are designing and building a 1:40 scaled physical model of a fully operational longwall coal mine. The purpose of the model is to minimize the occurrence of methane explosion hazards by testing various ventilation strategies and determining optimal methane sensor placement throughout the longwall face. Fluid scaling factors were analyzed using Computational Fluid Dynamics software Ansys FLUENT™ at both full and 1/40th scales. Researchers were able to identify key scaling factors and subsequently developed suitable flow parameters that would maintain full-scale accuracy of flow patterns in the 1/40th model.

2018
  • Brune, J. F., and Gilmore, R. C.
    Explosive Testing of Rock Dust Dispersibility for Coal Dust Explosion Prevention
    11th International Mining Ventilation Congress, Xi’an, China
    ABSTRACT: Limestone rock dust is used in many coal mines to inertize coal dust and prevent mine explosions. Since rock dusting creates a nuisance to workers downwind from the dust application, suppliers are offering wet and foam-applied rock dust products. Researchers at the Colorado School of Mines have constructed a full-size explosion test drift where they can generate controlled explosions at defined wind speeds of 30 to 50 m/s, the minimum wind speed that can entrain coal dust and propagate coal dust explosions. Initial results with different wet-applied, that then dried rock dust products suggest that explosive forces break-up clumps of the rock dust, but this wet-applied dust does not disperse as easily as dry-applied dust. Also, hydrophobized rock dust and dust meeting German specifications disperses more readily.
2016
  • Brune, J. F., Grubb, J. W., Bogin, Jr., G. E., Marts, J. A., Gilmore, R. C. and Saki, S. A.
    Lessons Learned from Research about Methane Explosive Gas Zones in Coal Mine Gobs
    International Journal of Mining and Mineral Engineering, Vol. 7, No.2, pp. 155–69, Doi: 10.1504/IJMME.2016.076498
    ABSTRACT: Coal mine longwall gobs contain explosive methane gas zones (EGZs) that can cause mine fires and explosions when EGZs extend into active mining areas. The tragic explosion at the Upper Big Branch Mine in West Virginia in April 2010 cost 29 miners’ lives and may have been caused by this mechanism. This paper summarises the significant research findings from five years of computational fluid dynamics (CFD) modelling research conducted at the Colorado School of Mines (CSM) under funding from the US National Institute for Occupational Safety and Health (NIOSH). CSM research has shown that EGZ formation can be effectively controlled by progressive sealing of the gob and injecting nitrogen where necessary.
2015
  • Gilmore, R. C., Brune, J. F., Marts, J. A., Saki, S. A., Bogin, Jr., G. E., and Grubb, J. W.
    Gob Ventilation Modeling on HPC Platforms using GPGPU/CPU Combinations
    Application of Computers and Operations Research in the Mineral Industry, pp. 904-10, Fairbanks, AK
    ABSTRACT: Computational Fluid Dynamics (CFD) modeling of large scale mine gob ventilation simulations requires high performance computing to solve large systems of equations representing the flow physics. These CFD models help examine explosive gas zones (EGZs) and oxygen ingress in bleeder ventilated gobs and progressively sealed gobs for mine fire and explosion risk assessment. Researchers at Colorado School of Mines (CSM) have developed a CFD model to represent full-size underground longwall coal mine gobs with multiple adjacent panels. A newly developed advanced modular mesh design allowed researchers to significantly increase CFD model problem size and reduce processing time from days to hours using ANSYS® Fluent® on multi-node Central Processing Unit (CPU) architectures. For complex flows involving turbulent sub-models, a combination of CPU and NVIDIA® general purpose graphics processing unit (GPGPU) processing architectures have the ability to reduce computation time. CSM researchers examined the gains and limitations when using GPGPU speed up as implemented within the Fluent® solver.
  • Gilmore, R. C., Marts, J. A., Brune, J. F., Saki, S., Bogin, Jr., G. E., and Grubb, J. W.
    Simplifying CFD Modeling of Longwall Gobs with Modular Meshing Approach
    Mining Engineering, Vol. 67, No. 3, pp. 68-72
    ABSTRACT: Computational fluid dynamics (CFD) modeling involves the creation of a computation domain called a mesh or grid to solve the equations defining the physics of fluid flow. This process often comprises the majority of time spent in modeling efforts. In a project sponsored by the National Institute for Occupational Safety and Health (NIOSH), researchers at the Colorado School of Mines used an innovative meshing approach, allowing easy adaptation of the CFD model to adjust to a variety of longwall bleeder-ventilated and progressively sealed (often referred to as bleederless in the United States) mining geometries, with gob porosity and permeability scalable over a wide range. This paper presents the methodology of the meshing and scaling approach along with recommendations for using CFD modeling in longwall gob ventilation applications. The new meshing technique was utilized to evaluate the function of a back return in a progressively sealed gob and a bleeder-ventilated gob.
  • Lolon, S. A., Gilmore, R. C., Brune, J. F., Bogin, Jr., G. E., Grubb, J. W., Zipf, Jr., R. K., Juganda, A., and Saki, S. A.
    Effect of Decreasing Barometric Pressure on Explosive Gas Zones in Bleeder Ventilated Longwall Gobs
    15th Annual North American Ventilation Conference, pp. 439-44, Blacksburg, VA
    ABSTRACT: Mine explosions have long been known as a catastrophic risk in underground coal mining. Since 1970, the U.S. coal mine industry experienced 12 major disasters associated with methane explosions; most of which occurred during a significant drop in barometric pressure. Several of these disasters and numerous other explosions of lesser consequence suggest involvement of explosive gas zones (EGZs) or explosive methane-air mixture. Previous studies by researchers at the Colorado School of Mines (CSM) have been aimed at locating and reducing EGZs in longwall gobs but little work has been done to investigate the effect of barometric pressure on these EGZs. In a new research project at CSM, funded by The National Institute for Occupational Safety and Health (NIOSH), the authors investigate how the locations and volumes of EGZs in bleeder ventilated longwall gobs change with decreasing barometric pressures. This work is being done using Computational Fluid Dynamics (CFD) modeling. In the simulated longwall panel, the authors found that the decreasing barometric pressure significantly affects EGZs size and shape. During barometer drops, explosive methane may expand and migrate from the gob into active working areas, exposing miners to potential hazards of explosion and fire. Research results suggest the need for thorough gas monitoring along the periphery of the longwall and in the bleeder entries.
  • Saki, S. A., Brune, J. F., Bogin, Jr., G. E., Gilmore, R. C., Grubb, J. W., Zipf, Jr., R. K., and Marts, J. A.
    Gob Ventilation Boreholes Design Optimization for Longwall Coal Mining
    15th Annual North American Ventilation Conference, pp. 453-60, Blacksburg, VA
    ABSTRACT: Gob ventilation boreholes (GVBs) are widely used in United States underground coal mines for longwall gob degasification purposes. GVBs can recover 30 to 50% of methane emissions from the longwall gob depending on geologic conditions.  Generally, GVBs are considered useful for reducing methane concentrations in working areas, explosion hazards and creating safer working conditions for the longwall section. Computational fluid dynamics (CFD) modeling efforts at the Colorado School of Mines (CSM) under a National Institute for Occupational Safety and Health (NIOSH) funded research project have confirmed that gob ventilation boreholes are helpful to reduce the methane concentrations at the face. However, they may also draw fresh air from the face into the gob, creating explosive gas zones (EGZs) within the gob. GVBs operation may thereby increase oxygen ingress into the gob and create explosive gas mixtures. It is important to identify the locations for GVBs placement to maximize the methane extraction and to minimize any explosion hazards. In this paper, CFD studies will be presented to analyze the effect of GVBs design and operating parameters on methane extraction, formation of EGZs in the gob and methane concentrations at the longwall face and tailgate. The distance of GVBs from the tailgate and the working face, the borehole diameter, the distance from the top of the coal seam being mined, the wellhead vacuum pressure and number of GVBs operating on the panel all have a significant effect on methane extraction, explosive gas mixtures volume and methane concentration in working areas. CFD studies at the CSM identified optimal GVBs design and operating parameters, which can maximize the benefits and minimize the risks.
  • Brune, J. F., Grubb, J. W., Bogin, Jr., G. E., Zipf, Jr., R. K., Marts, J. A., and Gilmore, R. C.
    A Critical Look at Longwall Bleeder Ventilation
    15th Annual North American Ventilation Conference, pp. 427-32, Blacksburg, VA
    ABSTRACT: Bleeder ventilation is common and legally required in underground longwall coal mines in the United States. This ventilation technique originated with room-and-pillar retreat mining and is intended to clear mined-out areas or gobs of any explosive methane-air mixtures. A system of bleeder ventilation entries surrounds the gob, intended to draw explosive methane accumulations directly towards a dedicated system of return airways and to a dedicated bleeder fan. Bleeder entries are traveled regularly for inspection purposes and the methane content within these travel ways is limited to 2%. With the arrival of longwall mining in the United States in the 1970s, bleeder ventilation was extended to controlling methane in longwall gobs. Researchers at the Colorado School of Mines (CSM), under a research project funded by the CDC-NIOSH Office of Mine Safety and Health Research, have studied bleeder ventilated longwall gobs by examining gas compositions and gas flows using computational fluid dynamics (CFD) modeling techniques. Researchers found that bleeder ventilated gobs are surrounded by a fringe of methane-air mixtures in the explosive range. Investigations of numerous mine explosions indicate that these explosive mixtures may have either ignited within the gob or may have been pushed into the active mine workings. This paper characterizes the explosion and fire hazards stemming from bleeder ventilated gobs and suggests improvements for ventilation practices that reduce or eliminate these hazards.

  • Grubb, J. W., Brune, J. F., Zipf, Jr., R. K., Bogin, Jr., G. E., Marts, J. A., Gilmore, R. C., Saki, S. A., and Lolon, S. A.
    Managing the Risk of Spontaneous Combustion in Underground Coal Mines
    15th Annual North American Ventilation Conference, pp. 547-54, Blacksburg, VA
    ABSTRACT: Spontaneous combustion events leading to thermal runaway and a fire or explosion in underground coal mines are low in frequency but can have severe consequences in terms of both fatalities and business losses. The propensity of coal seams to spontaneously combust and reach thermal runaway varies and is not fully understood. Recent fire events at Elk Creek Mine in Colorado and Deer Run Mine in Illinois and possibly the Soma Mine in Turkey are reminders that the spontaneous combustion risk remains insufficiently mitigated in some sectors of the coal mining industry. Coal mine regulations in the United States are minimal in addressing the spontaneous combustion risk in underground mines. As compared to other coal mining risks, the regulations offer minimal prescriptive solutions for managing this risk. In other countries where spontaneous combustion events have been more prevalent in occurrence including the loss of life and business, the regulations and accepted practices are more aggressive in addressing the risk. Findings from five years of computational fluid dynamics (CFD) modeling conducted at Colorado School of Mines (CSM) under funding from the National Institute for Occupational Safety and Health (NIOSH) have shown that explosive gas zones can exist in a longwall gob in areas where the spontaneous combustion of coal could develop into an ignition source. This paper will summarize measures that have been collected from a leading practice survey for assessing and managing the spontaneous combustion risk. A deductive modeling approach will be presented that can assist mine management teams in their cost-benefit analysis of the extent of implementation of a management program for the risk. As a minimum, mine management teams must assess the risk of a spontaneous combustion event at their mine. Once technically informed regarding the propensity of their coal and the potential existence of contributing factors, the decision on how extensive a preventative program is required can be made. A major spontaneous combustion event is infrequent but the consequences can be devastating.

2014
  • Gilmore, R. C., Marts, J. A., Brune, J. F., Bogin, Jr., G. E., Grubb, J. W., Saki, S. A.
    CFD Modeling Explosion Hazards – Bleeder vs. Progressively Sealed Gobs
    10th International Mine Ventilation Congress, pp. 47-53, Sun City, South Africa, Doi: 10.13140/RG.2.2.28080.56322
    ABSTRACT: Researchers at the Colorado School of Mines have developed a series of computational fluid dynamic models to study the air flows and gas distributions in longwall gobs or goaves. Models were verified using tube bundle gas composition analysis and other mine air quality data. The studies found that oxygen penetration distance into sealed gobs and formation of explosive methane air mixtures depends on face ventilation flow rates and nitrogen injection rates. Studies indicate that, with bleeder ventilated gobs common in U.S. coal mines, oxygen penetration tends to reach deeper into the gob and extend along the fringes of the gate roads where explosive gas mixtures may form. Researchers found a contiguous explosive fringe along the bleeder entries surrounding the gob. Similar patterns were not observed with progressively sealed gobs. Oxygen penetration also has an impact on the occurrence of spontaneous combustion. CFD modeling demonstrates that progressively sealed gobs provide better opportunities to control spontaneous combustion through inert gas injection compared to bleeder ventilated gobs.
  • Marts, J., Gilmore, R., Brune, J., Bogin, G., Jr., Grubb, J., and Saki, S.
    Accumulations of Explosive Gases in Longwall Gobs and Mitigation through Nitrogen Injection and Face Ventilation Method
    6th Aachen International Mining Symposia, pp. 347-58, Aachen, Germany
    ABSTRACT: Researchers at the Colorado School of Mines (CSM) have developed a series of computational fluid dynamic models to study the air flows and gas distributions in longwall gobs or goaves. Progressively sealed gobs are used to limit oxygen ingress into the gob for spontaneous combustion (spon com) prevention. The most common scheme is U- Type ventilation, another variation is the back return. Zones of explosive methane – air mixtures, so-called Explosive Gas Zones (EGZs) can accumulate in either type of gob. A back return is utilized to move the point of lowest ventilation pressure from the tailgate corner further inby the face, thereby clearing the tailgate corner of methane and gob gases. The aim of modeling the gob gas compositions and flows is to determine the size and location of the EGZs and evaluate targeted nitrogen injection and other ventilation controls to reduce the EGZ’s size and explosion hazard. Models were verified using tube bundle gas analysis and other mine air quality data. The CSM studies found that oxygen penetration distance and EGZ hazard could be controlled by the face ventilation scheme. Oxygen penetration is a contributing factor to the occurrence of spontaneous combustion. CFD modeling demonstrates that back return utilization can partially mitigate EGZ hazards near the face but the amount of oxygen ingress is increased. Studies also indicate that nitrogen was an effective control measure for both schemes.
2013
  • Gilmore, R. C., Marts, J. A., Brune, J. F., Worrall, Jr., D. M., Bogin, Jr., G. E., and Grubb, J. W.
    Control of Explosive Zones in Longwall Gobs Through Nitrogen Injection
    23rd World Mining Congress, Montreal, Canada
    ABSTRACT: Underground longwall coal mining sections may develop explosive mixtures of methane-air in the mined-out gobs. If the panels are operated as bleederless or sealed gobs, progressive sealing along the gateroads as the longwall face retreats limits the flow of fresh air into the gob and thus deprives potentially explosive atmospheres of oxygen. In a project sponsored by the National Institute for Occupational Safety and Health (NIOSH), researchers at the Colorado School of Mines have used computational fluid dynamics (CFD) modelling to simulate the flow of gases in longwall gobs. Modelling indicates that targeted injection of nitrogen through the seals along the gateroads inbye the face can be used to control the size and location of methane and air clouds within the gob and to minimize or eliminate the explosion hazard resulting from the formation of flammable methane-air mixtures in longwall gobs.
  • Marts, J., Brune, J., Gilmore, R., Worrall, D., and Grubb, J.
    Impact of Face Ventilation and Nitrogen Inertization on Hazardous Gas Distribution in Bleederless Longwall Gobs
    Mining Engineering, Vol. 65, No. 9, pp. 71-7
    ABSTRACT: Underground longwall coal mining sections are operated as sealed gobs if the coal is prone to spontaneous combustion. Sealing along the gate roads during longwall face retreat limits the flow of fresh air (oxygen) into the gob and, thus, deprives the spontaneous combustion reaction of oxygen. In a project sponsored by the National Institute for Occupational Safety and Health (NIOSH), researchers at the Colorado School of Mines have used computational fluid dynamics modeling to simulate the flow of gases in sealed longwall gobs. The models were validated using measurements and observations from the field and demonstrate that targeted injection of nitrogen along the gate roads inby the face can be used to control the size and location of explosive methane clouds within the gob and to minimize or eliminate the explosion hazard resulting from the formation of flammable methane-air mixtures.

Conference Proceedings

2019
  • Gilmore, R. C., and Brune, J. F.
    Dispersibility of Rock Dust for Coal Dust Explosion Prevention (PrePrint 19-133)
    SME Annual Meeting and Exhibit. Preprint, Denver, CO
    ABSTRACT: Underground coal mines apply finely powdered limestone rock dust to inertize explosive coal dust deposits created during the mining process. Rock dusting creates a cloud of nuisance dust downwind, preventing other work in the area. Applying a wet or foam mix of rock dust eliminates the nuisance dust, but may impact the dispersion and explosion prevention capability and thus, may render the rock dust ineffective. Dispersibility tests were conducted in a full-size mine explosion test drift at the Colorado School of Mines. Tests include dry, wet, dry-misted, and foam applications using three types of rock dust: conventional, hydrophobic, and rock dust meeting stricter German specifications. Results show that dried dust forms large, agglomerated particles that may not be effective in suppressing coal dust explosions. Hydrophobic rock dust maintains better dispersibility even when applied wet or applied dry then misted. German specification dust disperses better than U.S. conventional rock dust.
  • Mcmack, J. and Derosa, C. and Zurhorst, M. and Bogin, G. E. and Brune, J. (Gilmore as Presenter)
    Design and Construction of a 1/40th Scale Longwall Mine Model for Physical Testing of Methane Explosions (Preprint 19-118)
    SME Annual Meeting and Exhibit. Preprint, Denver, CO
    ABSTRACT: Researchers at the Colorado School of Mines are designing and building a 1:40 scaled physical model of a fully operational longwall coal mine. The purpose of the model is to minimize the occurrence of methane explosion hazards by testing various ventilation strategies and determining optimal methane sensor placement throughout the longwall face. Fluid scaling factors were analyzed using Computational Fluid Dynamics software Ansys FLUENTTM at both full and 1/40th scales. Researchers were able to identify key scaling factors and subsequently developed suitable flow parameters that would maintain full-scale accuracy of flow patterns in the 1/40th model.
2016
  • Gilmore, R. C., Brune, J. F., Lolon, S. A., Juganda, A., Saki, S. A., Bogin, Jr., G. E., Zipf, Jr., R. K., and Grubb, J. W.
    Explosive Gas Zone Formation in Underground Coal Longwall Bleeder Ventilated Gobs with an Adjacent Panel Using CFD Modeling
    SME Annual Meeting and Exhibit. Preprint, Phoenix, AZ. Doi: 10.13140/RG.2.1.3356.0721
    ABSTRACT: Methane-air mixtures form explosive gas zones (EGZs) in underground longwall coal mine gob ventilation systems. Such EGZs have caused a number of fatal mine explosions, including the 2010 disaster at the Upper Big Branch mine, where 29 miners lost their lives. Researchers at the Colorado School of Mines use Computational Fluid Dynamics (CFD) modeling to predict EGZ locations. In this paper, a model of a bleeder-ventilated gob system includes two adjacent panels, an active longwall, and a mined-out gob. Boundary conditions for the simulations match statutory ventilation conditions for methane concentrations and air flow rates at common measurement points throughout the mine. The modeling results predict the persistence of EGZs in the gob that may compromise the effectiveness of the bleeder ventilation system.
  • Lolon, S. A., Brune, J. F., Gilmore, R. C., Bogin, Jr., G. E., Grubb, J. W., Saki, S. A., Juganda, A.
    CFD Studies on the Phenomenon of Gob Breathing induced by Barometric Pressure Fluctuation
    SME Annual Meeting and Exhibit. Preprint, Phoenix, AZ. Doi: 10.13140/RG.2.1.4093.7365
    ABSTRACT: In longwall mines, atmospheric or barometric pressure fluctuations can disturb the pressure balance between the gob and the ventilated working area of the mine, resulting in a phenomenon known as ” gob breathing “. Gob breathing triggers a gas flow across the gob and the working areas and may result in a condition where a methane accumulation in the gob flows into the face area forming an explosive mixture. This paper discusses results of Computational Fluid Dynamics (CFD) modeling carried out to analyze this phenomenon and its impact on the explosive mixture development under a bleeder-ventilated longwall gob panel scheme. Modeling results indicate that the gas inflow and outflow across the gob and the formation of Explosive Gas Zones (EGZs) are directly affected by the barometric pressure changes. Methane gas and EGZs in the gob expand out toward the face and bleeder entries during the falling barometric pressure. Where methane zones interface with mine air, EGZ fringes may form along the face and in the bleeder entries. When the atmospheric pressure increases, an ingression of oxygen into the gob is observed that can also increase EGZs in volume. The findings from this study help assess the methane ignition and explosion risks associated with fluctuating atmospheric pressures.
  • Saki, S. A., Brune, J. F., Bogin, Jr., G. E., Grubb, J. W., Gilmore, R. C., and Lolon, S. A.
    Optimization of Gob Ventilation Boreholes Completion Parameters
    Proceedings of the SME Annual Meeting and Exhibit. Preprint, Phoenix, AZ. Doi: 10.13140/RG.2.1.3637.1601
    ABSTRACT: Gob ventilation boreholes (GVBs) are widely used in underground coal mines for longwall gob degasification purposes. GVBs are often drilled within 10 to 30 m above the top of the coal bed into the fractured zone, completed with 20 cm (8 in.) diameter casing and 60 m of slotted pipe at the bottom. The purpose of this completion strategy is to create a pressure sink to capture the emissions before they can enter into the underground workplace. For GVBs to work effectively, they must be drilled close enough to the working areas to capture methane from the fractured zone while the setting depth must be kept above the caved zone to minimize the amount of ventilation air that is drawn into the GVBs. Well completion parameters are important for creating safe working conditions. In this paper, computational fluid dynamics (CFD) studies will be presented to analyze the effect of different practices for GVBs completion parameters for methane extraction, formation of explosive gas zones in the gob and methane concentrations at the longwall face and tailgate. Authors have identified the optimum completion parameters for GVBs, which can maximize the benefit and minimize fire and explosion risk.
2015
  • Gilmore, R. C., Marts, J. A., Brune, J. F., Saki, S. A., Bogin, Jr., G. E., and Grubb, J. W
    Impact of Regulator Settings on the Formation of Explosive Gas Zones in Bleeder Ventilated Longwall Gob
    SME Annual Meeting and Exhibit. Preprint, Denver, CO
    ABSTRACT: Researchers at the Colorado School of Mines have studied the influence of headgate side ventilation controls near the longwall start-up room on the formation of explosive gas zones (EGZs) in underground coal longwall bleeder ventilated gobs. In a project funded by the National Institute for Occupational Safety and Health (NIOSH) researchers developed a Computational Fluid Dynamics (CFD) model to study the formation of methane-air mixtures in the gob, start-up room, and bleeder entries. The relative change in size and location of EGZs are examined in response to ventilation controls in the headgate side bleeder entries near the start-up room. Modeling suggests that adjustments to the ventilation controls can be made to minimize the size of the EGZ. However, the EGZ may form in or around active working areas regardless of the ventilation control settings. Research found regulators on the crosscuts into start-up room and first entry inby can force air into to crosscuts outby the start-up room causing more air to flow through the gob
  • Marts, J. A., Gilmore, R. C., Brune, J. F., Saki, S. A., Bogin, Jr., G. E., and Grubb, J. W.
    Optimizing Nitrogen Injection for Progressively Sealed Panels
    SME Annual Meeting and Exhibit. Preprint, Denver, CO
    ABSTRACT: Researchers at Colorado School of Mines (CSM) have developed computational fluid dynamic (CFD) models to study gas distributions and explosion and fire hazards in longwall gobs. In underground coal mines, methane continuously emitted from surrounding strata mixes with air from active mine workings and may form explosive gas zones (EGZs). Some western United States coal mines are also prone to spontaneous combustion (spon com). Insight into oxygen concentrations within the gob is crucial for assessing spon com hazards and mitigation strategies. Nitrogen injection used in conjunction with progressive gob sealing can reduce EGZs and spon com hazards by forming a dynamic seal that separates the methane in the gob from the air that ingresses from the face. This paper describes CFD modeling simulations studying the formation of such dynamic seals by optimizing the nitrogen injection locations. The impact of nitrogen on oxygen ingress and formation of EGZs is discussed. Optimum nitrogen injection quantities and injection locations were determined. Dynamic seal formation is most effective if the headgate nitrogen injection locations are split between the first crosscut inby the face and a second location about 300 m (1,000 ft) further inby.
  • Saki, S. A., Marts, J. A., Gilmore, R. C., Brune, J. F., Bogin, Jr., G. E., and Grubb, J. W.
    CFD Study of Face Ventilation Effect on Tailgate Methane Concentration and Explosive Mixture of Gob in Underground Longwall Coal Mining
    SME Annual Meeting and Exhibit. Preprint, Denver, CO
    ABSTRACT: The main purpose of mine ventilation design is to provide sufficient quantity and quality of air to the workers and to dilute methane and other contaminants. It is generally perceived that the additional air along the longwall face will improve methane dilution on the face and in the tailgate. However, computational fluid dynamics (CFD) modeling efforts at the Colorado School of Mines (CSM) under a National Institute for Occupational Safety and Health (NIOSH) funded research project have found that higher flow velocities along the longwall face are shown to increase the pressure differential between the gob and longwall face allowing more methane to be entrained in the active face and tailgate (TG) area, thereby negating the dilution effect. The increased face ventilation causes an increase in pressure along the headgate side which allows more oxygen to ingress into the gob area, thereby increasing the amount of oxygen available to form explosive methane-air mixtures in the gob and to support spontaneous combustion of the coal. Two things are happening at two different locations along the longwall face, increase in pressure as the flow enters the active area cause an increase in pressure which forces more oxygen into the gob, but as the flow is developed along the longwall face, the higher velocities causes greater pressure drop allowing methane to enter the active face further downstream from the headgate (HG) towards the tailgate side. In this paper, a parametric study will be presented to discuss the effect that varying the face air quantity has on methane concentrations in the tailgate and formation of explosive gas zones (EGZs) in the gob. Counter to conventional wisdom, it appears that increased longwall face air quantities may increase the explosion hazard as they result in increased EGZ volumes in the gob, along with increased methane quantities in the tailgate return.
  • Brune, J. F., Grubb, J. W., Bogin, Jr., G. E., Marts, J. A., Gilmore, R. C., and Saki, S. A.
    Lessons Learned from Research about Methane Explosive Gas Zones in Coal Mine Gobs
    SME Annual Meeting and Exhibit. Preprint, Denver, CO
    ABSTRACT: Most, if not all longwall gobs contain explosive gas zones (EGZs), i.e., zones of explosive methane-air mixtures that can cause – and have caused – mine fires and explosions. If the coal is prone to spontaneous combustion, oxygen penetration into the gob must be avoided. This paper summarizes the significant research findings from five years of computational fluid dynamics (CFD) modeling research conducted at the Colorado School of Mines (CSM) under funding from the National Institute for Occupational Safety and Health (NIOSH). CSM Researchers have developed CFD modeling techniques to identify where and under what circumstances EGZs can form in longwall gobs and how EGZ formation and oxygen penetration depend on the ventilation method, face and bleeder ventilation parameters, injection of inert gases and the operation of gob ventilation boreholes. Recognizing these explosion and fire hazards is an important first step in improving the safety of longwall coal mines. CSM modeling research has shown that EGZ formation can be effectively controlled by adjusting ventilation parameters, choosing the proper ventilation pattern and injecting inert gases where necessary.
2014
  • Gilmore,  R. C., Marts, J. A., Brune, J. F., Saki, S., Bogin, Jr., G. E., and Grubb, J. W.
    An Innovative Meshing Approach to Modeling Longwall Gob Gas Distributions and Evaluation of Back Return using Computational Fluid Dynamics
    SME Annual Meeting and Exhibit. Preprint, Salt Lake City, UT.
    ABSTRACT: Computational fluid dynamics (CFD) has been used to model gas compositions in underground longwall coal mine gobs to study oxygen ingress and the development of potentially explosive methane-air mixtures that may form in the gob. The scenarios studied involve various headgate and tailgate ventilation and inertization schemes and controls. In a project sponsored by the National Institute for Occupational Safety and Health (NIOSH), researchers at Colorado School of Mines have used an innovative meshing approach, allowing easy adaptation of the CFD model to adjust to a variety of bleeder and bleederless mining geometries, with gob porosity and permeability scalable over a wide range. This paper presents the methodology of the meshing and scaling approach along with recommendations for using CFD modeling in longwall gob ventilation applications. The new meshing technique was utilized to evaluate the function of a back return in a progressively sealed gob. The back return was successful in maintaining sufficient oxygen concentrations in the tailgate corner of the longwall face.
  • Marts, J. A., Gilmore, R. C., Brune, J. F., Bogin, Jr., G. E., and Grubb, J. W.
    Dynamic Gob Response and Reservoir Properties for Active Longwall Coal Mines
    SME Annual Meeting and Exhibit. Preprint, Salt Lake City, UT.
    ABSTRACT: Reservoir properties including porosity and permeability distributions in longwall coal mine gobs have direct application to modeling the flow patterns and gas distributions in the gobs. Proper assessment of these distributions is required to assess gob gas hazards such as spontaneous combustion and explosive methane mixtures and to optimize gob gas venthole operation and nitrogen inertization. Determining the reservoir properties is difficult given that the gob is inaccessible and direct measurements cannot be easily taken. Several techniques have been used by previous researchers and will be discussed. This paper will present the methodology used to model the gob compaction by simulating the sequential extraction of coal. Two Western US coal mines were used for case studies. By determining volumetric strain, the porosity and permeability distributions in the gob can be calculated. The geo-mechanical model predicts an axisymmetric volumetric strain distribution with a steeper slope near the start-up room and a shallower slope near the active face.
2013
  • Marts, J., Brune, J., Gilmore, R., Worrall, D., and Grubb, J.
    Impact of Nitrogen Inertization on Methane Distribution in Bleederless Longwall Gobs
    SME Annual Meeting and Exhibit. Preprint, Denver, CO
    ABSTRACT: Underground longwall coal mining sections are operated as sealed gobs if the coal is prone to spontaneous combustion. Sealing along the gate roads during longwall face retreat limits the flow of fresh air (oxygen) into the gob and thus deprives the spontaneous combustion reaction of oxygen. In a project sponsored by the National Institute for Occupational Safety and Health (NIOSH), researchers at the Colorado School of Mines have used computational fluid dynamics modeling to simulate the flow of gases in sealed longwall gobs. The models were validated using measurements and observations from the field and demonstrate that targeted injection of nitrogen along the gate roads inby the face can be used to control the size and location of explosive methane clouds within the gob and to minimize or eliminate the explosion hazard resulting from the formation of flammable methane-air mixtures.

Other Publications

2013
  • Gilmore, R. C., Marts, J., Saki, S., Grubb, J., and Worrall, D.
    Gob Explosions
    World Coal, No. 5, pp. 45-50, Farnham, Surrey, UK