Application of mining technology by the combination of ANSH equipment to longwall in Seam 6 of Mao Khe coal mine, Viet Nam

Currently, in the Quang Ninh coalfield, exploiting the seams with medium thickness and dip angle of over 50 degrees is often difficult, so labor productivity and safety are low. It is necessary to research and apply advanced mining technology to medium thickness seams with dip angle of over 50 degrees in order to improve efficiency and safety. Studying the actual production in the Mao Khe coal mine shows that the mining technology for the condition of the seam with medium thickness, and dip angle over 50 degrees is mainly mining technology by drilling and blasting. This technology has the disadvantage of low labor productivity and unsafety. In this paper, the authors have researched and proposed mining technology by the combination of ANSH equipment to exploit the longwall in Seam 6 of Mao Khe coal mine. This is a fully mechanized mining technology, coal cutting by plow, combined with shield. Analysis of economic and technical indicators shows that this technology has been more effective and productive than the mining technology currently applied in other coal mines. This application will benefit not only Mao Khe coal mine, but also to other coal mines of Quang Ninh coalfield with similar coal seam conditions.


Introduction
Fully mechanized mining technology is a type of technology that uses shearer or plow with mechanized shield to extract coal seams [1][2][3].This technology has been used in many countries, especially in China and European countries [4], where mechanized mining techniques applied to coal seams are also relatively effective.
In recent years, mechanized mining technology that uses shearer has been applied to a number of underground mines in the Quang Ninh coalfield, Vietnam and it has achieved certain initial effects [5][6][7][8][9].However, the fully mechanized mining technology that uses a plow is still a new technology and has not been adequately researched and invested in underground mines in the Quang Ninh coalfield.This is a mechanized mining technology that is applied to the seams with medium thickness and dip angle of over 50 degrees.
Currently, in Quang Ninh coalfield, there are many underground mines managed by Vietnam national Coal -Mineral industries Corporation.In which, the reserves of coal seams of medium thickness and dip angle of over 50 degrees account for a relatively large proportion [10].The condition of these seams belongs to most coal mines such as: Mao Khe, Nam Mau, Vang Danh, Uong Bi, Ha Lam, Nui Beo, Hon Gai, Duong Huy, Thong Nhat, Ha Long, Quang Hanh, Mong Duong and Khe Cham.Due to the geological conditions of the seams at different coal mines, the Vietnam national Coal -Mineral industries Corporation has also selected and applied many different types of mining technologies and methods, but it has not yet brought about the expected efficiency [11].Mining technology by drilling and blasting is the main technology that has been applied to coal seams of medium thickness, dip angle of over 50 degrees, this is a manual mining technology.The disadvantages of this technology are low safety, interruption in the technological chain, releasing harmful gases, and low productivity.
To eliminate the disadvantages of the drilling and blasting mining method, along with the determination to modernize technology in underground mining.For many years, the Vietnam national Coal -Mineral industries Corporation has coordinated and directed coal mines in Quang Ninh coalfield to actively research and select suitable and effective mining technologies for coal seams of medium thickness, dip angle of over 50 degrees.From the above practical issues, the article has researched and proposed a mining technology by the combination of ANSH equipment for longwall in Seam 6 of Mao Khe coal mine.Mining technology using a combination of ANSH equipment has been applied in some Eastern European countries and has brought good results when exploiting coal seams of medium thickness, dip angle of over 50 degrees.This is a fully mechanized mining technology, coal cutting by plow, combined with shield and it is applied to the seams of medium thickness, dip angle of over of 50 degrees.On the basis of the research results of the article, Mao Khe coal mine can apply and deploy these proposal designs in actual production to improve working efficiency in the longwall face, thereby increasing mining efficiency and productivity.

Geological features of the longwall in Seam 6 of Mao Khe coal mine
The thickness of the seam varies from 0.8 to 3.75 m, with an average of 1.82 m, belonging to the medium thickness and very unstable type.The dip angle of the seam varies from 57 • to 70 • , with an average of 61 • .
Roof: located directly on the seam, there is a claystone layer interspersed with coal-clay and thin layers of coal forming a layer with a thickness of 0.2 . . .2.2 m, which is easy to collapse and separate during mining, followed by layered siltstone with a total thickness of 8 . . . 25 m of medium stable hard rock.Many interstitial places in the siltstone are thin layers of sandstone.Next, the siltstone is a thick and stable layer of sandstone.
Floor: located directly below the seam, it is a soft rock layer consisting of: claystone interlaced with coal-clay lenses with a total thickness of 0.21 . . .1.8 m.The weak rock layer is followed by a thin to medium layered siltstone layer with a total thickness of 14 . . .20 m.The distribution under the siltstone is a layer of fine to medium grained sandstone with a total thickness of 5 . . .30 m. Rocks are sustainable.
Table 1.Some average physical and mechanical parameters of the roof and floor [12].The length of the complex m 45 60 60 Based on the geological conditions of the mine, on the basis of the technical characteristics of the mining equipment combinations, select the 2ANSH combination or the type with equivalent technical characteristics for the application of coal seam mining of medium thickness, dip angle of over 50 degrees at Mao Khe coal mine.Through analysis and field survey, it is shown that this equipment combination is suitable for the conditions of the longwall in Seam 6 of Mao Khe coal mine.

Shield
The shield used in this equipment complex is the 2ANSH shield combination (figure 1) and the technical characteristics are shown in table 2.

Coal cutting
To extract coal in the longwall in Seam 6, the Mao Khe coal mine has chosen the plow 1ASHM (figure 2) with specifications shown in table 3.

Technological process of mining in the longwall face
The process of this mining technology is carried out in 3 stages as follows: 3.2.1.Stage 1: exploiting to install the shields Exploiting to create space to install the shields is done by manual drilling and blasting method, supporting the longwall face by wood.When cutting and supporting in the strike direction of 4 web cuts, install the first shield, then exploit in the strike direction of one web cut to continue installing the next shield.The work of cutting and installation of shields is carried out sequentially until the number of installed shields is completed in the longwall.During the process of cutting and installing the shield, the distance from the longwall face to the shield position must not exceed 3 meters.Next, install the plow system, pumping station, communication signal equipment, automatic control device and other auxiliary equipment.
3.2.2.Stage 2: exploiting the longwall using a combination of shield Coal cutting in the longwall follows in dip direction of the seam, the cutting of coal in the longwall face by the plow system.The plow moves along the longwall face and cuts coal from the floor to the roof of the longwall.After cutting the entire length of the longwall face, the plow is returned to its original position before moving the shield.
3.2.3.Stage 3: dismantling the shield complex, moving to the next mining lift When the longwall is exploited to about 8 to 12 meters from the transport level, proceed to create a space for the longwall face to dismantle the shield system.The work of dismantling the shield is carried out in turn from the ventilation brake incline to the transport brake incline.The recovery shields are transported to the ventilation level to be installed in service of mining for the new lift.
The diagram of mining technology by the 2ANSH shield system is shown in figure 3 and the process of coal cutting in the longwall face using a plow is shown in figure 4.
3.3.Support plan for the longwall face in Seam 6 of Mao Khe coal mine 3.3.1.Arrangement of shield (figure 5) Based on the mine pressure of the longwall face, the load capacity of the shield (the load capacity of the rig for 1 m 2 is greater than 240 kN/m 2 and the load capacity of the shield is not less than 800 kN).At the same time, based on the experience of exploiting the longwall using a combination of shield equipment from a number of Eastern European countries and Ukraine, the design of the support plan for the longwall face is as follows: • The length of the longwall (a lift): 60 m.
• Distance between shields in the complex: 1.0 m. • Number of shields in the complex: 60 shields.

Moving the shield in the longwall
Moving process of the hydraulic shield is as follows: Two adjacent auxiliary shields on each vertical segment are depressurized by hydraulic control series.Auxiliary shields are pushed toward the face by stretching of the hydraulic jacks.Then, the main shield groups are depressurized by hydraulic control panels and the main shields are pulled toward the face by the shrink of the hydraulic jacks.Main and auxiliary shields are set in a straight line by hydraulic jacks.The process of moving the shield is shown in figure 6.   four meters per day (figure 7).A web cut includes the following stages: cutting face and shield shifting with an advance rate of 0.63 m, strengthen the longwall and preparing for a new web cut.The inspection and maintenance of equipment complex are carried out at the end of shift III, including maintenance, repair, and replacement of spare parts if necessary for the plow, roof supports, conveyors, electrical equipment and emulsifier pump systems, dust filter system, power supply system, water supply system, methane warning system, and pressure test of roof supports.The number of workers in the longwall face is arranged depending on the specific work of each shift.According to calculations, the required number of workers is 48 people, in which, each shift is arranged for 16 people (figure 8).(ii) In the condition that the coal seam has an average thickness of 1.8 to 2.5 m, the dip angle of the seam is from 45 • to 90 • , some countries such as Ukraine have applied the mining technology diagram in the slope direction, mining technology uses a combination of mechanization with a plow, and support for longwall face by the shield.In fact, the advantage of this mining technology is to reduce the unsafety risks from the collapse of roof during the exploitation of thin to medium-thick seams, dip angle of over 45 • .This complex has a small cutting step and the movement of the combination is due to the self-sliding mechanism on the slope due to the impact of the collapsed rock mass above the shield and the self-weight of the equipment combinations.Based on the geological conditions of the mine and the technical characteristics of the mining equipment combinations, this study proposed and selected a combination of 2ANSH equipment or a type with equivalent technical characteristics to exploit coal seam of medium thickness, dip angle of over 45

Figure 4 .Figure 5 .
Figure 4. Process of coal cutting in the longwall face using a plow [15].

Figure 7 .
Figure 7.The operation scheme in the longwall in Seam 6 of Mao Khe coal mine.

Figure 8 .
Figure 8. Chart of human resource arrangement in the longwall in Seam 6 of Mao Khe coal mine.

3. 5 .
Economic and technical indicesAfter researching and application of mining technology by the combination of ANSH equipment to longwall in Seam 6 of Mao Khe coal mine, which is exploited by fully mechanized technology, with the above equipment combination, the calculated main economic-technical indices are shown in table5.

Table 2 .
[13]ng technology by the combination of ANSH equipment 3.1.Mechanized equipment in the longwall 3.1.1.Combination of equipment type ANSH Currently, in Eastern European countries, two types of mechanized mining equipment combinations have been manufactured and applied for coal seams with medium thickness, dip angle of over 50 degrees.Combinations include: 1ASHMG, 1ANSH and 2ANSH.The basic technical characteristics of the above equipment combinations are shown in table2.Technical characteristics of ANSH mining equipment combinations[13].

Table 3 .
Technical characteristics of coal plow 1ASHM.

Table 5 .
Economic and technical indices of the longwall face in Seam 6 of Mao Khe coal mine.According to the general assessment of geological and technical conditions, reserves in Quang Ninh coalfield are about 3 billion tons, of which coal reserves of steep seams account for more than 30%.At the Mao Khe coal mine, the steep seams account for about 47.5%, of which the thick seams are 51% and the remaining 49% are the medium thick ones.Therefore, it is very necessary to research and select mining technology to ensure the economic and technical requirements to exploit the seams of medium thickness and dip angle of over 50 degrees at Mao Khe coal mine.
• at 1254 (2023) 012048 IOP Publishing doi:10.1088/1755-1315/1254/1/01204810 Mao Khe coal mine.(iii) The application of mining technology using a combination of 2ANSH equipment to the condition of the longwall in Seam 6 of Mao Khe coal mine, according to calculations, it has met the requirements of economic and technical indices when mining.Labor productivity 16 tons/worker-shift, low coal loss, high safety level (table 5).