Abstract
A particle element approach based on continuum-discontinuum element method (CDEM) is applied to optimize the automated top-coal drawing techniques in extra-thick coal seams. Numerical models with 100 drawing openings are created according to the field engineering geological conditions of Tongxin coal mine in China. An automated coal drawing control approach in numerical modelling based on time criterion is proposed. The rock mixed rate, top-coal recovery rate and the variance of the drawn top coal amount are counted and set as the statistical indicators to evaluate the top-coal drawing techniques. The traditional top-coal drawing criterion, “rocks appear, close the opening”, leads to low recovery of top coal and waste of coal resources in extra-thick coal seams, significantly weakening the transport stability and efficiency of the scraper conveyer. A three-round unequal time top-coal drawing technique is proposed for automated top-coal drawing. Three drawing openings, corresponding to the three top-coal drawing rounds respectively, are working at the same time; in each round, the top-coal drawing sequence is from the first drawing opening at one end of the working face to last drawing opening at another end; the drawing time of each round is not equal and increases with the round number. The numerical inversion approach of iteration steps can be used for real top-coal drawing time estimation and automated drawing process design to achieve a better top coal drawing effect, while the exact time for each drawing round still needs to be corrected by engineering practice.
Highlights
The reserves and production of thick coal seams account for about 45% of underground coal resources and output in China
Numerical models with 100 drawing openings are created according to the field engineering geological conditions of Tongxin coal mine in China
For automated coal drawing techniques, the time of each top-coal drawing round is regarded as a control variable and can be adjusted according to the number of top-coal drawing rounds, which makes the size of the caving ellipsoid above each opening close to each other and realizes that top-coals move down evenly, so the difference in coal amount of each drawing opening is smaller, and the transport efficiency of scraper conveyer is improved
Summary
The reserves and production of thick coal seams account for about 45% of underground coal resources and output in China. As a major mature mining method used in thick coal seams, the longwall top-coal caving technique (LTCC) has been used in China for over 30 years for industrial testing and large-scale application [1,2,3]. Because of the complex environment of underground longwall working face, LTCC process can only be achieved by manual operation for a long time, which greatly restricts the standardization of LTCC process flow and top-coal caving efficiency. For the traditional top-coal caving technique, the coal drawing termination condition is “close coal
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