Sponge Effect on Coal Mine Methane Separation Based on Clathrate Hydrate Method

The findings were presented from laboratory investigations on the hydrate formation and dissociation processes employed to recover methane from coal mine gas.The separation process of coal mine methane(CMM) was carried out at 273.15K under 4.00 MPa.The key process variables of gas formation rate,gas volume stored in hydrate and separation concentration were closely investigated in twelve THF-SDS-sponge-gas systems to verify the sponge effect in these hydrate-based separation processes.The gas volume stored in hydrate is calculated based on the measured gas pressure.The CH4 mole fraction in hydrate phase is measured by gas chromatography to confirm the separation efficiency.Through close examination of the overall results,it was clearly verified that sponges with volumes of 40,60 and 80 cm 3 significantly increase gas hydrate formation rate and the gas volume stored in hydrate,and have little effect on the CH4 mole fraction in hydrate phase.The present study provides references for the application of the kinetic effect of porous sponge media in hydrate-based technology.This will contribute to CMM utilization and to benefit for local and global environment.

Research on numerical emulator of mine methane and coal dust explosion

The mathematical physics model of mine methane and coal dust explosion propagation was established in the research,by using continuous phase,combustion,par- ticulate equations of mathematical physics.Based upon the data from mine methane drainage roadway explosion,and mine methane and coal dust explosion propagation ex- perimental studies,the numerical emulator system of mine methane and coal dust explo- sion software was developed by using prevalent flow simulation platform,which can be used to simulate the explosion accidents process effectively.In addition,the system can also be used to determine whether coal dust involved in the explosion,and to simulate accurately the transition from deflagration to detonation in methane explosion,propagation velocity of explosion shock,attenuation pattern,and affected area of explosion.

Numerical simulation of excess-enthalpy combustion flame propagation of coal mine methane in ceramic foam

Based on the assumption of a local non-equilibrium of heat transfer between a solid matrix and gas,a mathematic model of coal mine methane combustion in a porous medium was established,as well the solid-gas boundary conditions.We simulated numerically the flame propagation characteristics.The results show that the flame velocity in ceramic foam is higher than that of free laminar flows;the maximum flame velocity depends on the combined effects of a radiation extinction coefficient and convection heat transfer in ceramic foam and rises with an increase in the chemical equivalent ratio.The radiation extinction coefficient cannot be used alone to determine the heat regeneration effects in the design of ceramic foam burners.

Combustion Characteristics of Coal Mine Methane in a Preheated-Burner Packed with Raschig Rings

The utilization of coal mine methane(CMM)through porous medium combustion(PMC)contributes to energy saving and environmental protection.In this paper,a double-layer porous medium burner with the combination of heat exchangers was designed to recycle the exhausted heat for preheating the inlet gas.The effects of Raschig ring sizes on the temperature distributions and pollutant emissions were studied under different operating conditions.The results indicate that the preheating of inlet gas greatly influenced the temperature distribution and the optimum preheating effect was shown in the burner of spiral heat exchanger together with lower pollutant emissions.With the increasing of inlet velocity and equivalence ratio,the peak temperature was increased significantly.As the Raschig ring size increased,the flame temperature increased first and then decreased gradually.Meanwhile,the highest temperature and lowest average emissions of NOx and CO appeared in the burner of 10 mm Raschig rings.This study will provide the CMM utilization engineering with the theoretical foundation on PMC.

Prevention of explosion in coal mine and management of coal mine gas

There are many problems in terms of safe coal production and the sound developmentof the coal industry.Accompanying the intensification and increasing efficiencyof coal production and the conducting of mining operations at deeper and more remoteareas of mines,the efficient recovery and utilization of Coal Mine Methane:(CMM) is animportant issue in improving and stabilizing the productivity in the coal mining industry withhigh levels of gas,where the incidence of gas outbursts is increasing.We plan to studyvarious aspects of the development of production technology and characteristics of themine site.This is to establish the technology for highly efficient coproduction coal and gasoperation rate.As a result,the productivity at the coal mine face will increase due to thereduction in gas emissions in the mining face.Effective use of recovered gas can be expectedto reduce global warming by reducing the amount of coal mine methane gas emissionin the air.

Method for designing the optimal sealing depth in methane drainage boreholes to realize efficient drainage

The purpose of underground methane drainage technology is to prevent methane disasters and enable the efficient use of coal mine methane(CMM),and the sealing depth is a key factor that affects the performance of underground methane drainage.In this work,the layouts of in-seam and crossing boreholes are considered to analyze the stress distribution and failure characteristics of roadway surrounding rock through a numerical simulation and field stress investigation to determine a reasonable sealing depth.The results show that the depths of the plastic and elastic zones in two experimental coal mines are 16 and 20 m respectively.Borehole sealing minimizes the air leakage through the fractures around the roadway when the sealing material covers the failure and plastic zones,and the field test results for CMM drainage at different sealing depths indicate that the CMM drainage efficiency increases with increasing sealing depth but does not change once the sealing depth exceeds the plastic zone.Moreover,sealing in the high-permeability roadway surrounding rock does not have a strong influence on the borehole sealing performance.Considering these findings,a new CMM drainage system for key sealing in the low-permeability zone was developed that is effective for improving the CMM drainage efficiency and prolonging the high-concentration CMM drainage period.The proposed approach offers a valuable quantitative analysis method for selecting the optimum sealing parameters for underground methane drainage,thereby improving considerably the drainage and utilization rates of CMM.

Application of long-reach directional drilling boreholes for gas drainage of adjacent seams in coal mines with severe geological conditions

This study aimed to demonstrate the application of Long Reach Directionally Drilled Boreholes(LRDD)for gas drainage of adjacent seams before and during the longwall face operations of low permeability-high gas content coals Staszic-Wujek Hard Coal Mine in the Upper Silesia Coal Basin(Poland).Five LRDD Boreholes(TM1a-TM5)with a length of 300 and 400 m were located over coal seam 501 in the fractured zone and monitored over six months of longwall face operations.LRDD Boreholes were combined with Cross-Measured Boreholes.Reservoir characterization and geological modeling supported the results obtained from gas drainage.The drainage efficiency of LRDD Boreholes was the approxi-mately 70%level,while conventional Cross-Measured Boreholes were only 30%.The highest goaf gas quality(94%methane concentration)was reported for TM4,placed at an average elevation of 41 m above coal seam 501.The highest goaf gas production(average 6.2 m^(3)/min)was reported for LRDD Borehole TM3.This borehole was placed within the fracture zone(average elevation of 24.4 m)and drilled through the sandstone lithotype with the best reservoir properties,enhancing drainage performance.LRDD Boreholes TM2 and TM4 achieved similar performance.These three LRDD Boreholes were drilled close to the maximum principal horizontal stress direction,providing borehole stability during under-mining.The lowest goaf gas production was reported for LRDD Boreholes TM1a and TM5.Both Boreholes were placed in the rubble zone.

Possibilities of Increasing the Effectiveness of Mining Methane Drainage in Conditions of Low Permeability of Coal Seams

There is very low permeability of coal seams in Polish coal mines. For this reason, pre-mining methane drainage is conducted to a small extent, which rarely brings expected results. Methane emission from roof and floor sub-economic seams has the greatest share in total methane emission to workings. Effective CMM （coal mine methane） capture is used from goaf in advance or after mining. However, due to longwall mining and ventilation systems, it is not always possible to capture methane from strata. This paper presents a method of increasing the permeability of coal seams and a method of drilling boreholes towards goaf. Initial results of the effectiveness of methane capture after applying these methods are presented.

Computational fluid dynamics simulation on the longwall gob breathing

In longwall mines, atmospheric pressure fluctuations can disturb the pressure balance between the gob and the ventilated working area, resulting in a phenomenon known as ‘‘gob breathing". Gob breathing triggers gas flows across the gob and the working areas and may result in a condition where an oxygen deficient mixture or a methane accumulation in the gob flows into the face area. Computational Fluid Dynamics(CFDs) modeling was carried out to analyze this phenomenon and its impact on the development of an explosive mixture in a bleeder-ventilated panel scheme. Simulation results indicate that the outgassing and ingassing across the gob and the formation of Explosive Gas Zones(EGZs) are directly affected by atmospheric pressure changes. In the location where methane zones interface with mine air, EGZ fringes may form along the face and in the bleeder entries. These findings help assess the methane ignition and explosion risks associated with fluctuating atmospheric pressures.