1、翻译部分Control of gas emissions in underground coal mines Klaus Noack*DMT-Gesellschaft fr Forschung und Prfung mbH, Institut fr Bewetterung, Klimatisierung und Staubbekmpfung, Franz-Fischer-Weg 61, Essen, GermanyReceived 2 August 1996; accepted 24 February 1997. Available online 24 November 1998. Abstr
2、act 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, fur
3、ther 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 undisturbe
4、d 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 ai
5、r 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 need
6、ed 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
7、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 l
8、ong 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 non-classical outbursts categorized
9、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.Author Keywords: gas emission; prediction; pre-degassing; gas drainag
10、e; gas outbursts1. Introduction Coal deposits contain mine gas (mostly methane) in quantities which are functions of the degree of coalification and permeability of the overburden rocks. This is the reason why the gas content of coal seams (and rock layers) varies from 0 m3/t in the flame coal and g
11、as-flame coal of the northwestern Ruhr Basin to 25 m3/t in the anthracite of Ibbenbren in Germany.When influenced by mining activities 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
12、 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 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)
13、 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 additional 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 concentr
14、ation 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 explosion 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 h
15、istorical reasons, different permissible limits sometimes apply in other countries, for example 1.25% CH4 in the United Kingdom and up to 2% CH4 in France. Basically, the options for control of gas emission are as follows:(1) Total avoidance of gas release from the deposit. This is only possible wit
16、h regard to the additional gas emission and only for mining procedures which do not affect stability; hence permeability of the overlying and underlying strata (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
