Research on Special Support Technology of Gob-side Entry Retaining with Filling the Non-roadway Side in the Thin Coal Seam

By taking a certain mining area of No.2 coal seam in a coal mine as the research object, special support technology of gob-side entry retaining with filling the non-roadway side was researched. Based on the geologic features of this mining area, support method of gob-side entry retaining was proposed. The method replaced the dense wood prop with single prop, and cooperated intersection hinge roof. The support parameters were calculated, and time-space coordination between each support process was researched. The field measured data showed that this support method had a remarkable effect and strictly controlled the deformation of gob-side entry. This research formed a support system and mining system based on this condition. It has important reference meaning to safe and efficient mining coal resource with similar geologic condition.

New advances in automatic shearer cutting technology for thin seams in Chinese underground coal mines

Automatic mining technology is the ideal path and the inevitable way to improve production efficiency, reduce labour intensity and ensure safety for thin coal seam. Recently, while automatic mining technology is increasingly applied in China for thin seams, the corresponding automatic cutting technology has made new advances. Among them, mnemonic cutting technology has been fruitful industrial tested with suitable conditions. Simultaneously, another one called cutting trace pre-set technology of the shearer has been put forward. Using this method, the cutting trace in the area with coal thickness changed and geological structures can be preset. What's more, self-adaptive regulation strategy of cutting trace based on coal-rock recognition by monitoring current of cutting motor was discussed. Then, the main problems and development trends of automatic mining in China was also proposed.

Hydraulic Fracture Propagation and Permeability Evolution in the Composite Thin Coal Seam

Hydraulic fracturing can improve the permeability of composite thin coal seam. Recently, characterizing hydraulic fracture (HF) propagation inside the coal seam and evaluating the permeability enhancement with HF extension remain challenging and crucial. In this work, based on the geological characteristics of the coal seam in a coal mine of the southwest China, the RFPA2D-Flow software is employed to simulate the HF propagation and its permeability-increasing effect in the composite thin coal seam, and a couple of outcomes were obtained. (1) Continuous propagation of the hydraulic microcrack-band is the prominent characteristic of HF propagation. With the increment of the injection-water pressure, HF generation in the composite thin coal seam can be divided into three stages: stress accumulation, stable fracture propagation, and unstable fracture propagation. (2) The hydraulic microcrack-band propagates continuously driven by the fluid-injection pressure. The microcrack-band not only cracks the coal seam but also fractures the gangue sandwiched between the coal seams. (3) The permeability in the composite thin coal seam increases significantly with the propagation of hydraulic microcrack-band. The permeability increases by 1~2 magnitudes after hydraulic fracturing. This study provides references to the field applications of hydraulic fracturing in the composite thin coal seam, such as optimizing hydraulic fracturing parameters, improving gas drainage, and safe-efficient mining.

Effects of Coal Mining Height and Width on Overburden Subsidence in Longwall Pier-Column Backfilling

Longwall pier-column backfilling is a partial backfilling technique initially designed in thin coal seam mines. With the increase of mining intensity, the mining height and width of the backfilling working face will also increase. It is necessary to analyze how changes in working face dimensions influence the control effect of overburden subsidence in pier-column backfilling. In this study, a mining model with a combination of 25 conditions (five different mining heights (1~3 m) × five different mining widths (80~240 m)) was designed using a FLAC3D(Vision 5.0) numerical simulation. The simulation was used to analyze the control effect of overburden subsidence with varying mining heights and widths. In addition, according to the field working face conditions, two physical similarity models were performed to explore the overburden subsidence law in pier-column backfilling with different mining heights and widths. It was observed from the above study that mining heights and widths will have a different influence on the overburden subsidence in longwall pier-column backfilling. The result of this study provides strong theoretical support for evaluating the control effect of overburden subsidence in longwall pier-column backfilling.

Distribution Law of Mining Stress of the Gob-Side Entry Retaining in Deep Mining Thin Coal Seam

In order to explore the mining pressure development rule of gob-side entry retaining during deep thin coal seam mining, FLAC3D numerical simulation is applied to analyze the stress distribution rule of gob-side entry retaining, observing the left third working face of 49# coal seam in No. 8 mining area of Xinxing Coal Mine as the research object. The results show that the working face stress field is asymmetrical which is caused by the reserved roadway and the over goaf. After roadway tunneling, features of obvious stress redistribution are formed. The vertical and horizontal stress in the coal seam develop a U-shaped distribution. The vertical stress in the roadway is less than that in the lower roadway, and the horizontal stress is half that in the lower roadway. The phenomenon of high stress “nucleation” appears and becomes more obvious in the process of working face advancing, and the nuclear body disappears after working face advanced to the boundary line. With the working surface advancing, the trend of horizontal stress of gob-side entry retaining decreases gradually and the vertical stress of gob-side entry retaining is less than the original rock stress. The research findings provide a basis for the supporting design of gob-side entry retaining in the deep thin coal seam and the stability control of surrounding rock.

Recent Patents on Thin Coal Seam Mining Equipment

Background:: China's thin and extremely thin coal seam resources are widely distributed and rich in reserves. These coal seams account for 20% of the recoverable reserves, with 9.83 billion tons of industrial reserves and 6.15 billion tons of recoverable reserves. Objective: Due to the complex geological conditions of the thin coal seam, the plow mining method cannot be effectively popularized, and the drum mining method is difficult to be popularized and applied in small and medium-sized coal mines, so it is necessary to find other more advantageous alternative mining methods. Methods: The equipment integrates mining operations, conveying operations, and supporting operations, and is suitable for mining short and extremely thin coal seam with a height of 0.35m-0.8m and width of 2m-20m. It has the advantages of the low body of the shearer, no additional support on the working face, and small underground space. The mining efficiency of thin coal seam and very thin coal seam can be improved and the mining cost can be reduced. Results: Thin coal seam shear mining combines mining, conveying, and supporting processes together and has the advantages of a low fuselage, no extra support required for the working face, and feasibility in a small underground space. Conclusion: The summarized mining method can improve the mining efficiency of thin and extremely thin coal seams, reduce mining costs, and incorporate green mining practices, which take both mining economy and safety into account.

OPTIMASI BATUBARA TIPIS (THIN COAL SEAM) DI PIT A SITE SENAKIN PT ARUTMIN INDONESIA

ABSTRAK Konservasi cadangan batubara adalah upaya dalam rangka optimalisasi pengelolaan, pemanfaatan, dan pendataan batubara secara terukur, efisien, bertanggung jawab, dan berkelanjutan. Pengelolaan ini dilaksanakan dengan cara melakukan proses penambangan sesuai dengan perencanaan untuk memperoleh recovery penambangan yang optimal serta mengendalikan dilusi dan kehilangan (losses) batubara. Di dalam KEPMEN ESDM No. 1827 K/30/MM/2018 lampiran VII disebutkan bahwa cut off thickness minimum batubara adalah 30 cm. Batas minimum ini diterapkan dalam rangka mengoptimalkan recovery penambangan dan meminimalisir adanya dilusi yang diperoleh selama proses penambangan. Risiko dari penggalian batubara dengan ketebalan kecil dari 30 cm adalah semakin besarnya potensi terjadinya dilusi. Hal ini dikarenakan semakin banyak luasan permukaan batubara yang bersentuhan langsung dengan material pengotor di bagian roof dan floor dibandingkan dengan penggalian batubara. Kondisi tersebut diperparah dengan adanya losses saat menggunakan alat gali yang berukuran besar. Dilusi dan losses ini akan berdampak kepada menurunnya kuantitas, kualitas dan recovery pengolahan batubara. Dalam paper ini akan dibahas mengenai upaya konservasi batubara dari PT. Arutmin Indonesia Site Senakin di Pit A dengan melakukan kajian tentang optimasi penambangan lapisan batubara tipis (thin coal seam) dengan tebal minimum 20 cm. Batas ketebalan minimum ini merupakan batas optimal dari kemampuan peralatan yang digunakan di Senakin. Karakteristik Pit A yang memiliki beberapa sisipan di dalam batubara juga menjadi faktor kunci apakah batubara tipis tersebut layak untuk ditambang. Semakin tebal material sisipan maka kadar abu akan semakin tinggi dan ini akan menjadi acuan terkait keekonomisan batubara tersebut. Secara operasional penentuan ketebalan batubara ini dilakukan oleh Geologist secara aktual di lapangan. Selanjutnya dilakukan analisa sampel batubara tersebut dan jika secara kualitas layak untuk ditambang maka akan dilanjutkan ke dalam tahap operasional penambangan dengan menggunakan alat kelas 20 ton dan 30 ton serta dengan pengawasan khusus selama proses pembersihan, pengumpulan, pemuatan sampai dengan pengangkutan. Batubara tipis tersebut kemudian diolah oleh Washplant yang ada di Senakin dengan recovery pengolahan sekitar 79,3%. Dengan optimasi ini maka akan didapatkan tambahan batubara dengan range 20 – 30 cm sekitar 1,49% dari jumlah cadangan sebelumnya. Berdasarkan hasil dari metode penambangan dan pengolahan tersebut, batubara tipis di Pit A dapat dioptimalkan dalam rangka memenuhi konservasi batubara serta meningkatkan revenue perusahaan dan pemerintah. Kata Kunci : Batubara tipis, Recovery penambangan, Recovery pengolahan, Konservasi batubara, Kadar Abu ABSTRACT Coal reserve conservation is an effort to optimize the management, utilization and data collection of coal in a measured, efficient, responsible and sustainable manner. This Management is applied by carrying out the mining process in accordance with the plan to obtain optimal mining recovery with controlled coal dilution and losses.According to Ministerial Decree No. 1827 K / 30 / MM / 2018 in appendix VII stated that the minimum coal cut-off thickness is 30 cm. Coal thickness minimum limit is applied in order to optimize mining recovery and minimize dilution during the mining process. The risk of coal extraction with thickness less than 30 cm has extra potency for dilution because more of coal surface area directly contact with impurity materials on the roof and floor rather than coal excavation. That condition is exacerbated by the lost when using a large digging tool. Dilution and loss will have an impact to the decline of the quantity, quality and recovery of coal processing. This paper will discussed about coal conservation efforts from PT. Arutmin Indonesia Site Senakin at Pit A. PT. Arutmin Indonesia conducting a study on optimizing thin coal seam mining with a minimum thickness of 20 cm. Regarding to the coal thickness minimum limit is the optimal limit of the equipment capabilities used at Senakin. The characteristic of Pit A which has several parting material in coal is also a key factor whether the thin coal is feasible to be mined or not. Parting material thickness will be impacted to the ash content and related to the coal economical. Coal thickness is measured by geologist in the field. Furthermore, the coal sample is analyzed and if it is qualified to be mined it will be proceed to the mining operation stage using 20 tons and 30 tons grade tools also with special supervision during the cleaning, collecting loading and hauling processes. Thin coal is processed using Washplant in Senakin with processing recovery around 79.3%. This optimization method will be resulted an additional coal with a range about 20-30cm around 1.49% of the amount of reserves. The result is thin coal in Pit A can be optimized in order to achieve coal conservation and increase company and government revenue. Keywords: Thin coal, mining recovery, recovery processing, coal conservation, ash content