Abstract
This review details the state of the art in research on top coal drawing mechanisms in Longwall top coal caving (LTCC) by examining the relevant literature over the last two decades. It starts with an introduction of the brief history and basic procedures of LTCC. The framework of research on the drawing mechanism, basic concepts, and some theoretical models of LTCC are detailed in sect. research framework of top coal drawing mechanism. The authors note that the Top coal drawbody (TCD), Top coal boundary (TCB) and Top coal recovery ratio (TCRR) are key factors in the drawing mechanism. The Body–boundary–ratio (BBR) research system has been the classic framework for research over the last 20 years. The modified Bergmark–Roos model, which considers the effects of the supporting rear canopy, flowing velocity of top coal, and its shape factor, is optimal for characterizing the TCD. A 3D model to describe the TCB that considers the thicknesses of the coal seam and roof strata is reviewed. In sect. physical testing and numerical simulation, the physical tests and numerical simulations in the literature are classified for ease of bibliographical review, and classic conclusions regarding the drawing mechanism of top coal are presented and discussed with elaborate illustrations and descriptions. The deflection of the TCD is noted, and is caused by the shape of the rear canopy. The inclined coal seam always induces a larger TCD, and a deflection in the TCD has also been observed in it. The effects of the drawing sequence and drawing interval on the TCRR are reviewed, where a long drawing interval is found to lead to significant loss of top coal. Its flowing behavior and velocity distribution are also presented. Sect. practical applications of drawing mechanisms for LTCC mines 4 summarizes over 10 cases where the TCRR of LTCC mines improved due to the guidance of the drawing mechanism. The final section provides a summary of the work here and some open questions. Prospective investigations are highlighted to give researchers guidance on promising issues in future research on LTCC.
Highlights
Longwall top coal caving (LTCC) is a special type of mining method commonly used to extract coal seams thicker than 4.5 m (Wang et al 2018a)
The hydraulic drawing support (DS) used in LTCC leads to the formation of a distinct boundary in comparison with the block caving where no DS is used, and the rear canopy of the DS influences the shape of the Top coal boundary (TCB) (Wang and Zhang 2015; Wang et al 2016d)
3.3.1.1 Effect of rear canopy of DS on Top coal drawbody (TCD) Figure 12 shows the effect of the rear canopy of the DS on the TCD based on experimental and simulation-based insights
Summary
Longwall top coal caving (LTCC) is a special type of mining method commonly used to extract coal seams thicker than 4.5 m (Wang et al 2018a). Once the DO is opened, the fractured top coal flows to the Armored face conveyor (AFC) through the DO. This process is often called top coal drawing. Many studies on top coal drawing mechanisms often use gravitational flow in block caving for reference (Wang et al 2015d; Jin et al 2016, 2017; Song et al 2018; Song and Konietzky 2019). This study reviews and summarizes of top coal drawing mechanisms in LTCC excluding those based on gravitational flow in block caving.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
