外文翻译-底板煤层的瓦斯抽放控制.doc

1、翻译部分（英文原文）Control of gas emissions in underground coal minesKlaus Noack DMT-Gesellschaft fur Forschung und Prufung mbH,Institut fur Bewetterung,Klimatisierung und Staubbekampfung,Franz-Fischer-Weg 61,Essen,GermanyReceived 2 August 2003accepted 24 February2004Abstract: A high level of knowledge is no

2、w 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

3、,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

4、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 f

5、rom 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

6、 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

7、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 c

8、an 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 ofnonclassical outbursts categorized a sudden liberation of significant quantities of gas .Recent r

9、esearch results in this field led to a classification of these phenomena into five categories,for which suitable early detection and prevention measures are mentioned.q 1998 Elsevier Science B.V.1. IntroductionCoal deposits contain mine gas (mostly methane )in quantities which are functions ofe degr

10、ee of coalification and permeability of the overburden rocks.This is the reasonhy the gas content of coal seams ?and rock layers. varies from 0 m 3rt in the flameal and gas-flame coal of the northwestern Ruhr Basin to)25 m3rt in the anthracitef Ibbenburen in Germany.When influenced by mining activit

11、ies this gas is emitted into the coal mine.For better understanding of this process a distinction has been established between basic and additional gas emissions.Basic gas emission is the gas influx from the worked coal seam,which is the equivalent of a partial influx in a multi-seam deposit and of

12、the total gas influx in a single-seam deposit.Additional gas emission represents gas influx coming from neighbouring coal seams in the case of a multi-seam deposit .and from associated rock layers.The additional gas emission may be in excess of ten times the basic gas emission.So it is mostly the ad

13、ditional gas emission which determines the measures to control the gas emission.In Germany the gas emission is considered to be under control if the gas concentra-tion of the mine air can be kept permanently at all relevant places under 1%CH4.This value is at an adequate distance to the lower explos

14、ion limit of methane-air mixtures,which under normal conditions is 4.4%CH4.In exceptional cases,the permissible limit value can be raised to 1.5%CH4.For historical reasons,different permissible limits sometimes apply in other countries,for example 1.25%CH 4in the United Kingdom and up to 2%CH 4in Fr

15、ance.Basically,the options for control of gas emission are as follows:(1) Total avoidance of gas release from the deposit.This is only possible with regard to the additional gas emission and only for mining procedures which do not affec stability;hence permeability of the overlying and underlying st

16、rata e.g.,room-and-pillar mining where the pillars are left standing during the development phase.(2) Removal of the gas from the deposit before working.For this purpose,all procedures for pre-degassing,either by vertical or by deflected cross measure boreholes drilled from the surface,or by inseam-holes drilled below ground,are technically suitable provided the natural or induced gas permeability permits pre-degassing.(3) Capture and drainage of the gas during mini