Experimental analysis of coal bed methane desorption and seepage under sonic vibrating of cavitation water jets

A way to enhance coal bed methane desorption and seepage by sonic vibrating of cavitataion water jets is proposed because the gas coal seams have the intrinsic properties of micro-porosity, low permeability and high adsorption. The mechanisms of how the sonic vibrating effects promote methane desorption and seepage are analyzed, and the contrast experiments of methane desorption and seepage under sonic vibrating effects are also provided. The results show: when the cavitation number is 0.020 0, under sonic vibrating effects, the volume of coal bed methane desorption increases by 36.9%, and the time for coal bed methane desorption reduces by 19.6%. The speed of coal seams methane seepage is significantly increased by 35.3% and arrives at 0.383 3 ml/s.     

Study on Adsorption Characteristics of Coal to Gas in Geophysical Field

It is very important to mine safe exploitation, gas drawing and predict of coal and gas outburst that adsorption characteristics of coal to gas in geophysical field are studied. Adsorption and desorption characteristics of coal to gas in geophysical field have been reviewed in detail, then it is obtained that adsorption characteristics of coal to gas in electromagnetic field should be further studied . Adsorption and desorption characteristics of coal to methane in alternating electric field (AEF) have been studied mainly. Adsorption characteristics of three coal samples in AEF have been studied by means of Volume Method. The result shows that chemical properties and matter constituent of coal surface are no changed , adsorption and desorption of the coal samples in AEF well accord with Langmuir equation and two constants empirical formula, and because coal potential energy is increased and coal temperature is raised caused by Joule heat effect , adsorption ability of coal is decreased, and the desorption process is slowed down in AEF.     

Multi-field coupling effect on coalbed methane seepage characteristics and numerical simulation

This paper studies the seepage of coal samples under the influence of each single factor, the axial stress, confining pressure, gas pressure, and temperature by experiments. It uses Ansys12.0 to numerically simulate the law of coalbed methane seepage, coal deformation, pore pressure, the distribution of flow field under the influence of each single field and multi-field coupled. The numerical simulation show that the result of numerical simulation of gas seepage law in the coal under each single fields is basically the same as the experimental result. The curve of gas seepage and average effective stress under the condition of multi-field coupled is negative exponential relationship. Stress influenced the deformation of the specimen is greater than the seepage field. The axial stress on the deformation of the specimen is greater than confining presses The influence on the flow field by confining pressure is greater than axial stress, the influence of axial stress on the pore pressure is greater than confining pressure, pore-pressure under the action of multi-field is bigger than pro-pressure under each single field. To study the seepage law of coalbed methane, it should consider the influence of gas-solid-heat at the same time.     

Study on the Factors Affecting Gas Permeability of Coal

In this paper,the permeability of coal from Nantong colliery is studied in a labo-ratory. The effects of desorbed gas temperature and water content on gas permeability were investi-gated. The results of experiments indieatd that decreasing gas pressure without desorption , the permeability of coal decreases, However, below the desorption pressure, the permeability of coal formethane increases, The reaults suggest that the logarithm of permeability of coal is a linear functionof the temperature and the permeability of coal saturated with water is lass than the permeability ofdry coal; with the increase of water content, the permeability of coal for methane is increasing.     

Experimental study of coalbed methane seepage in fuxin basin

Taking raw coal samples collected from the wangying colliery in Fuxin basin as the research object, the experiment of coalbed methane seepage law is conducted by the triaxial osmoscope and the relationship between effective stress and coal permeability is presented. The experiment results indicate that the coal permeability is of stress sensitivity and tended to decline in exponent with the increment of effective stress, which is consistent with the former research results. The seepage flow curves from experiments demonstrate the nonlinear characteristics under different confining pressures and moisture contents, and it accurately reflecte the effect of coal body deformation on the coalbed methane seepage flow in the experimental process. Therefore considering the influence of effective stress on the coal body deformation, a new motion equation for the nonlinear percolation characteristic of coalbed methane is established. Moreover, the motion equation is correlated well with the experimental data, and the fitting correlation coefficients are above 99.6%.     

Experimental analysis of matrix shrinkage’s influence on mechanical permeability of gas filled coal

Based on the coal seam of Zhao zhuang coal mine and Si he coal mine belong to Jin cheng anthracite Mining Group in Shanxi province, by using the self developed three axial servo controlled seepage equipment for hot fluid solid coupling of coal containing methane, parallel experiments for permeability of helium and methane under different gas pressures are carried out to quantitatively study the influence of Klinkenberg effects on the permeability of coal. Meanwhile, the problem of permeability decreasing caused by fluid pressure decreasing and gas desorption is eliminated by controlling the effective stress. The results show thatthe Klinkenberg effect is obvious under low gas pressure. With the increase of gas pressure, the permeability of coal decreases at first and then increases. The inflection points of gas pressure for Klinkenberg effect are about 0.9 MPa both for coal samples in Zhao zhuang coal mine and Si he coal mine. When the effective stress is constant, with the increase of gas pressure, the permeability increment caused by Klinkenberg effect decreases, while permeability increment caused by coal matrix shrinkage increases. Coal matrix shrinkage has a close relationship with the mechanical properties of coal rock mass. For the coal sample with a poor mechanical property, coal matrix shrinkage is more obvious.     

The Influence of In-situ Stress Gradient and Geothermal Temperature on The Calculation of Coalbed Gas Pressure

On the basis of coal seam having outcrop of coal seam and outlet on ground,the method for calculating coalbed gas pressure from the one-dimensional stable gas flow equation by considering deeply the influence of in-situ stress gradient and geothermal temperature is presented. In some mine, the theoretically computing and measuring results of coalbed gas pressure show that the in-situ stress gradient and the geothermal temperature have important influence on the calculation of coalbed gas pressure, and if the factors are drew into the calculation of coaled gas pressure,it will make the results much more accurate.     

Numerical simulation of seepage field of gas extraction drilling of single bedding of mining-coal bed

Aiming at the problem of reasonable decorate of coal gas extraction drilling, combining with the initial and boundary condition of borehole extraction, the solid and gas coupling mathematical model of gas seepage of borehole extraction is deduced based on established control equations of seepage field and deformation field. Taking gas extraction of stone coal slit as an example, according to the characteristics of coal seam in the research, the numerical simulation method is used to obtain the distribution rule of gas pressure, coalbed gas permeability, and coalbed gas seepage velocity as well as seam deformation. The effective radius of gas extraction drilling of single bedding about mining-coal bed is determined, which provides the basis for optimum arrangement of gas extraction drilling of single bedding. The results show that the effective radius of stone coal is about 4 m. If the prolonging drilling drainage time is less than 20%, the drilling quantities would reduce by about 50%.     

Mechanism and application of protection againstoutburst for abrasive water jet slotting technology

Aiming at the status quote of long time for methane extraction and slow speed for laneway excavating in coal seams of Liziya south 2JHJ well, abrasive water jet slotting technology is adopted to improve the methane desorption and increase excavating speed in semi-coal laneway. Through analyzing damage model and protection against outburst mechanism, the process of Coal-Rock Mass being cut and fractured is studied. Through lab test on abrasive water jet cutting coal-bed gangue, a new abrasive water jet cutting device is successfully designed and made and all parameters are determined. It is showed that abrasive water jet can cut through a coal-bed gangue with thickness 60~80 mm and uniaxial compressive strength 62 MPa. After cutting coal seams by abrasive water jet, the surface area for methane is enlarged and then coal seams pressure fell rapidly. Therefore the permeability and desorption of coal seams are greatly increased. The results are as follows: the average productivity of single-hole was enhanced by 2.83 times.     

Pressure Sweep Adsorption Processes for the Concentration of Methane from Coal-bed Gas Extracted

The coal-bed gas was usually extracted from mine in order to avoid coal gas outburst.The Methane(CH4),a main component in coal-bed gas,is a kind of excellent gas fuel and raw material for chemical industry.China is very rich in the resource of coal bed gas,however,most of the coal bed gas extracted from mine is wasted because of the too low concentration of methane. Pressure sweep adsorption(PSA) technique is noticeable among the methods for the concentration of methane from coal-bed gas.However,there are a few studies about this field.Studies on the pressure sweep adsorption(PSA) process for the separation of CH4/N2 using actived carbon as adsorbent are summarized.The thermodynamic relationships and kinetic processes and the influence of the operate parameters on the concentration of methane are investigated.These results have a direct application in coal-bed gas.Some suggestions for the problems need to be solved in PSA process for the separation of methane are also proposed.     

Economic Benefit Analysis on the Exploitation and Utilization Coal bed Methane

The gas accident in Coal Mine is an important safe hidden trouble.The notion on the prevention and cure of gas accident should be changed.Coal gas is a kind of deleterious gas,but it is a clean energy resource.The actualities of coal bed methane resources and its use in our country are reviewed.The foreground for the use of coal bed methane is analyszed.The economic benefit of coal bed methane utilization is evaluated by the Net Present Value(NPV) and the Internal Rate of Return(IRR)method.The results are shown that the utilization of the coal bed methane can decrease the gas accident,save energy source,reduce the environmental pollution,and have remarkable economic benefit.     

Numerical simulation on low calorific value coal-bed gascombustor and structural design optimization

This paper conducts the full size three-dimensional combustion numerical simulation study on the low-calorific value coal bed gas combustor. It explors the effects of different ratios of swirling wind and straight wind on flow field,temperature field and concentration field when this combustor combusts coal bed gas which methane volume concentration is 30 percent. The optimal ratio of swirling wind and straight wind is gained. Based on this,the number and obliquity of cyclone vane in gas pipeline are further optimized. The results show that when ratio of straight wind is 80 percent and ratio of swirling wind is 20 percent,the good jet flow rigidity is not only possessed,but also the strong spin momentum is brought. Reverse axial velocity grads and reverse velocity in central backflow region are also big,the burning temperature and combustion efficiency are high,and high-temperature region is diffusely distributed. When the number and obliquity of cyclone vane are respective 6 and 60,the mass fraction of methane descends quickly,the mass fraction of methane is low in outlet of combustion region,and the combustion efficiency is high.     

Exploration on the Principle of ECMB

ECMB, which is developed by Amoco company in USA, has very prospective. On the basis of the study on adsorption characteristics of mixture gas in coal, the principle of ECMB has been explored. The order of adsorption capacities of coal for several gases is: CO 2>CH 4>N 2>H 2 when coal adsorbs gas. In 2 member mixture gases, adsorption capacities of coal for mixed gases, methane and carbon dioxide tally with Langmuir equation, but not does for nitrogen and hydrogen. The substance of the increasing drawing ratio of coal seam gas by using ECBM is decreasing adsorption amount of methane in coal by emptying the other gas or gases into coal seam. N 2 is better gas than CO 2 in the process of using ECMB.     

Key Layer and Stress Dike Mechanism of Coal and Gas Outbursts

The outburst coal mass is a geologic body which had objectively existed before outbursts occurred.The authors think the occurrence and development of coal and gas outbursts are controlled by comprehensive factors according to a host of facts of outbursts in their researches,and all the factors belong to the system of "rock coal gas rock".Therefore the authors put forward a completely hypothesis,i.e.key layer and stress dike mechanism of coal and gas outbursts.This hypothesis emphasizes that the outbursts are the result of comprehensive action by coalbed gas,abutment stress and physical and mechanical properties of coal.Of special interest is emphasizing the geologic backgroud and conditions of outbursts to a great extent.Any phenomenon of outbursts which a person could observe could be qualitatively explained with the hypothesis so that the hypothesis can serve the study of geophysical field of outbursts perfectly.     

Character of Coalbed Methane Enrichment Controlled by Hydrological Geology in Libi Gorge Anticlines

The drain character and hydraulic linking are studied by analyzing the property of water-bearing and water-resisting, groundwater flowing and hydrochemistry character in Libi Gorge anticline. According this, the character of methane enrichment controlled by hydrological geology in the region is researched. It is indicated that Libi Gorge belongs to block anticline gas pool sealed by water pressure. In shallow layers, the water-bearing layers are controlled obviously by atmospheric water. The groundwater flows actively, drains nearby, but has no influence on the coalbed methane; in middle layers, the coal-bearing layers contain water weakly and the water flows slowly. The water has a roof and bottom enclosed effect on gas in water network ; in deep layers, the layers contain water weakly. The groundwater stops running and has a bottom enclosed effect on gas in water network. The most of faults are pressure faults, upper of them is water guiding, lower of them resisting. They enclose the gas by pressure. In addition, it is important for thickening rock character to enclose the gas.     

Wavelet denoising method of temperature signal in the process of coal gas absorption and desorption

The study on the temperature evolutionary trend under both the ground stress and gas pressure is significant in the process of coal gas absorption and desorption. However, the valid signal is difficult to gain because of much noise in the experimental data, so according to the characteristics of the temperature signal gained under different experimental conditions of coal gas absorption and desorption, this essay filtrates noise and restores the valid signal by using the wavelet denoising of MATLAB to obtain the valid temperature evolutionary curve. Through contrasting and analyzing wavelet basis function and different decomposition levels, the essay chooses the sym8 wavelet basis function which has a higher order of vanishing moments and better smoothness. The reconstructed signal filtrates most of high frequency signal, and keep low frequency, as well as smooth signal. The result shows that the de-noising effect is good and the temperature evolution rule can be well reflected in the process of the coal gas absorption and desorption.     

Analysis on rock cross-cut coal uncovering using high pressure water jet slotting in close distance seam group

Safe production and procedures at the driving face are restricted in mines of Guizhou province by the long periods required for rock cross-cut coal uncovering in high gas coal seam group. A new method is proposed to solve this problem using high pressure water jet slotting in penetration boreholes. This is proposed to increase the gas desorption rate and reduce drilling hole, which will shorten the cycle of rock cross-cut coal uncovering. Numerical simulation is used to compare the pressure relief effects of different slotting methods in penetration boreholes. The results show that the pressure relief effect of slotting all coal seams is more ideal. Field application indicates that high pressure water jet slotting has good effect of the pressure relief in coal seam group. The drilling number is reduced by 30, the drilling length is shortened by 610 m and the standard time of gas pre-pumping decreases by 39 days.     

水稻植株对稻田甲烷排放的影响及其生物学机理研究进展

稻田是主要的农业甲烷排放源之一,对全球温室气体排放有着重要影响。稻田甲烷排放包括土壤产甲烷菌的产甲烷过程、好氧甲烷氧化菌的氧化甲烷过程及甲烷通过水稻植株体、土壤溶液中冒气泡及分子扩散三种运输途径的排放过程,水稻植株地上部和根系影响着稻田甲烷排放。本文简要介绍了稻田甲烷的产生、氧化和运输排放过程,综述了水稻根系特征（形态、通气组织、分泌物、根系泌氧）、地上部特征（株高、分蘖数、生物量和同化物分配）、水肥管理措施对稻田甲烷排放的影响及内在机理。本文也讨论了今后稻田甲烷排放的主要研究方向,并认为高产与减排的协同应是一个重要切入点。     

The Kinetic Study of Adsorption of Methane on Anthracite and Its Char

The adsorption quantities of methane on anthracite and its char at different tem-perature and time were measured by using volumetric niethod. The corresponding adsorption formula-is presented. The experimental results have shown that the diffusion acti-vation energies of methane in the anthracite and its char are 14.3 kJ/mol and 26. 3 kJ/mol.It issuggested that the diffusion process of methane could be the flow through the micropores in the an-thracite and its char.     

THE EFFECT OF THE STRESS OF LONGWALL AND STRUCTURE OF COAL ON THE BUMP OF COAL AND METHANE

The problems that the bump of coal and methame in the mine is contraled by the stress of longwall and that the coal and methane bump in the mine is affected by the physical properties of the coal are analysed and discussed through some specific bump cases. It is shown that the compressive stress, the content of the methane of the coal, and the bump of coal and methane are directly affected by the content of the ash and the volatile of the coal.