Steeply Inclined Seam Longwall Mining Projects

HOT Mining has get many achievements in the study of longwall mining technology and equipment of large inclination coal seam in recent years. HOT Mining’s strategic partner, Sichuan Coal Group, and other units to solve the problem of large inclinatio


Steeply Inclined Seam Longwall Mining Projects


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Ground commissioning of longwall shearer for steeply inclined working face


       According to the angle size, Chinese coal industry could be divided into the following stype: nearly-horizontal coal seam if the dip angle <12°, gentally-inclined coal seam if the dip angle is between 12°~25°, inclined coal seam if the dip angle is between 25°~45°, steeply-inclined coal seam if the dip angle >45°(among which if the dip angle is between 35°~55°, it’s called large inclination coal seam). Large inclination coal seam and steeply-inclined coal seam are widely scattered in many coal mines in China, which takes about 21% among the explored reserve, and many of the coal seams are scarce and protectively-developed coal resources. The large inclination coal seams are complicated and hard to exploit coal seam recognized all over the world. Improving the standard of safety assurance and recovery rate is the most important strategical issue for Chinese coal resources and energy.

 

The big angle and steep inclination of the longwall mining working face and the condition of roof and floor makes it hard to ensure the stability of the equipment. Except for some studies about this field in Former Soviet Union and Poland in 1970s~1980s, there’s few study, and no achievement in recent years, thus, no breakthrough has been made about the equipment of large inclination coal seam mechanization mining.

HOT Mining has get many achievements in the study of longwall mining technology and equipment of large inclination coal seam in recent years. HOT Mining’s strategic partner, Sichuan Coal Group, and other units to solve the problem of large inclination coal seam mechanization mining, and conducted mechanization mining successfully in the working face with average coal seam angle 38°. After more than 10 years research, it has developed the hydraulic support applied in the steeply-inclined coal seam, with maximum dip angle of 50°.

At present, the standard of large inclination longwall mining technology of Sichuan Coal Group could represent the most advanced technology in the world. But according to recent years’ practice, it has the best performance when the longwall mining equipment is applied in the coal seam angle which is small than the coal gangue angle around 40°, and the annual outcome could reach 0.6MT. However, when the working face coal seam dip angle is larger than the coal gangue angle, the coal shearer couldn’t cut coal in two ways, and there’ll be more breakdown, the output decreases and the safety couldn’t be ensured. 

1. The nececissity of the large inclination longwall mining projects

The steeply-inclined coal seam is common in Chinese coal mines, which takes about 21% among the explored reserve, and many of the coal seams are scarce and protectively-developed coal resources. How to exploit it safely and high efficiently has become a series strategic problem for state resource sustainable.

There’re 3 critical defects if the steeply-inclined coal seam is exploited with non-mechanized method by tool pillar, stage, flexible shield support and manual blasting: 

The first one is frequent security incidents, the MT death rate is more than 6.0;

The second one is low recovery ratio, only about 30%~40%, which leads to waste of great coal resources;

The third one is bad working environment and high working intensity, and the average working face output is 60,000-150,000ton/year.

 

        To overcome the problems above, the only solution is mechanization mining method.There’s still no important breakthrough in the world in the field of large inclination and steeply-inclined coal seam mechanization mining, the coal shearer is the critical equipment, however, the biggest applied angle of coal shearer is only about 45°in the world.

 

 

                               Figure 1.1                                                                                                    Figure 1.2  

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2. Introduction of Large Inclination Longwall Mining Support

        According to the investigation of Chinese main coal mines, many coal mines of the provinces and cities that produce coal have coal seams not less than 40°large dip angle, most of them are between 40°~60°, such as Chongqing Nantong Coal Mine, Chongqing Tianfu Coal Mine, Xinjiang Urumchi Coal Mine, Xinnjiang Construction Crops Coal Mine, Xinjiang Ewirgol Coal Mine, Gansu huating Coal Mine, Gansu Jingyuan Coal Mine, most of the coal mines in Guizhou Province, Heilongjiang Shuangyashan Coal Mine, Heilongjiang Qitaihe Coal Mine, Heilongjiang Hegang Coal Mine and etc. Generally speaking, these coal mines don’t use longwall mining method for the coal mines with dip angle is more than 40°, some of the coal mines don’t exploit coal seam with this kind of angle, and some of the coal mines use conventional mining method to exploit, which leads to the result of low productivity, high labor working intensity and bad safety. Some of the coal mines use large inclination longwall mining method to exploit coal seams with dip angle below 40°, and they don’t exploit the coal seams with dip angle above 45°with longwall mining method. According to information research, there’s no report about medium-thick coal seam with dip angle above 45°using one-way longwall mining method. It indicates that many Chinese coal mines need to use the one-way longwall mining method which could adapt to the coal seam dip angle >45°.

 

At present, with the decurrence of exploiting standard, some coal mines of Sihuan Coal Group Guangneng Company such as Lvshuidong Coal Mine, Liziya South Coal Mine have the coal seam dip angle>40°in the recoverable reserve, and most of them are between 45°~60°. These coal resources need a suitable longwall mining equipment which could adapts to the large inclination well.

According to the analysis, it suggests that it’s hard to exploit coal seam with dip angle>60°by longwall mining method, and there’s mature technology by using pseudo inclined flexible shield support; and there’s no mature mining method for exploiting coal seam with dip angle between 45°~60°, in order to extend the working life of the coal mine and ensure the safety and efficiency, many coal mines need to make achievement in this field. Among the longwall mining equipment applied in the large inclination coal mines, the existing conveyor could meet the demands, the first critical problem for large inclination coal seam longwall mining is the working face hydraulic support couldn’t meet the requirements, and the second critical problem is to invent the face-end supports which could meet the safety protection requirement.

Longwall mining equipment consists of hydraulic support, coal shearer and conveyor. As the main equipment for mechanization mining, the one-time investment of hydraulic support holds more than 70% of the whole longwall mining equipment investment budget, which is the key of realizing longwall working face safety and high efficient production. The roof and floor of the hydraulic support must fit the underground coal mining environment, and could provide power source for mining and conveying equipment. After decades of years research and development, we have made great achievement in design and manufacture of hydraulic support, and developed many kinds of hydraulic supports which could adapt to various geological condition and different coal seam thickness.

2.1 Coal Shearer

Four technical problems of large dip angle seam coal shearer as follow: 1.it is difficult to move for hauling the shearer when up going cutting. 2.the coal shearer will slide down and runaway. 3.tube cables will damage the equipment and hurt people. 4. operating staff will be easily injured by the flying gangue. Coal shearer is composed of hauling moving unit, cutting unit, electric control box and attached tube cables etc.

(1)The maximum seam inclination of coal shearer is smaller than 45° in the world. No drum shearer’s seam inclination is bigger than 45°.

(2)The stress of coal shearer will be changed along with the coal seam dip angle start to change. When the coal seam dip angle is bigger than 40°,many faults of traction walking system come out like the walking gear is broken down of coal shearer, guide foot is breakdown and traction box internal gear is fractured. Failure rate of airborne inverter is high because of the cutting vibrating.

(3)Now coal shearers domestic and overseas only have one stage braking that is hydraulic brake. Coal shearer will be runaway when the hydraulic system is broken down or the moving gear is raptured or the axis of motor is raptured. It will cause serious effect.

(4)When the shearer is operating, the cables, dustproof pipes and cold water pipes are moving closed behind shearer in the cable groove from side to side. It will cause tube cables broken off, endanger men's safety, even cause gas explosion if tube cables overlap and sharp decline suddenly when the coal shearer goes down.

(5)The men working space and the operation space of the coal shearer is completely closed and isolated. The display of original coal shearer is designed in shearer’s body. In the process of coal mining, in order to observe the working condition and parameters of coal shearer workers need to open the Isolated protection device. Shearer drivers and workers are easily hurt by gangue because of the large dig angle and flying gangue.

(6)When the coal shearer is working in coal seam angle >40°, it could only go down cutting and go up operate the reamers in vain, which can not play the ability of mechanized equipment enough. Because the problems of no enough up traction and antiskid are not resolved.

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Figure 2.1Coal Shearer

2.2 Hydraulic Support

(1)Suitable seam inclination is smaller than 60°.

(2)The push jacks of hydraulic support are easily hurt without shell.

(3)The hydraulic control of gangue plates might be elevated up to the support beam to damage the tube cables.

(4)The automatic moving function should be improved of hydraulic support.

(5)The automatic tilting prevention and antiskid function of hydraulic support should be improved.

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Figure 2.2.1 Support stress of two pillar type hydraulic support diagram 

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Figure 2.2.2 The support of large dip angle screen type hydraulic support structure

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Figure 2.2.3 Large angle horizontal end hydraulic support structure


2.3 Scraper Conveyor 

Selection of face scraper conveyor in fully-mechanized coal mining should be suited to production capacity of face coal shearer .Most of us choose the heavy scraper conveyor, to meet the requirements of the coal shearer’s production capacity etc; The structural form and the components of the working face scraper conveyor must be able to match the structure of the coal shearer. For example, selecting the width of the scraper conveyor trough according to the width of the coal shearer’s travel unit to ,selecting the length of the scraper conveyor according to the length of the working face, meanwhile, it should also be support matched with support advancing ram ,connection unit spacing and structure.

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Figure2.3 Scraper conveyor head figure

 

1——head frame    2——reducer    3——chain tightener  4——connection coupling 

5——motor    6——head spillplate 

 

2.4 Face-end support

Face-end support, especially for steeply inclined coal seams, is an important part of full-mechanized coal mining. The face-end support for the lower party of steeply inclined coal seams' working face controls the roof of connection part between working faces and wood roadways, it is also a pusher jack of stage loaders. The support for the upper side of face-ends can use single hydraulic props with steel I-beams' framed timber supporting, because of the conveyor, which the sample working face is using, has a overhead drive head and a transverse motor. So we are going to mainly analyze the support for the lower part of working face.

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Figure 2.4 Longitudinally face-end support layout plan

1- Canopy  2- Base   3- Pillar

 

3.Large Dip Angle Fully Mechanized Coal Mining Project

3.1 General Situation of Working Face

 

Chart 1 The Position of Working Face and Relationship between Ground and Underground

 

Name of Mining Level

+530m Mining Level

Name of Mining Area

561 Mining Area

Ground Elevation

+825m+925m

Underground Elevation

+450m+585m

 

Parameters of working face & Conditions of coal seam

 

Relative Position of Ground

The ground corresponding to working face is from Thatch Hill to Tea Taipa. The ground is slope topography, southeast is high and northwest is low. There is no building and water, the ground surface is covered by bamboo forest, natural grassland and firs.  

The Influence of Mining On the Ground Facilities

There is two Northwest trending subsidiary fold because the working face is squeezed by the Northeast. This will affect layout and mining of working face directly.

Underground Location and Adjacent Relations

This working face is a monocline, it is located the West Wing of the Daluowan Anticline 561 mining area. There is a small fold which is skew with the mechanical roadway of working face. East of the working face is 5634 goaf of working face. South of the working face is 5614 goaf of working face. North is 5654 working face, its mining is coming to an end, following is 321 mining area. Southeast of the working face across the 528 main adit, and there is security coal pillar 50m.

Length of Strike (m)

700

Length of Incline (m)

78160

Area(m2)

74873.72

 

 

Parameters of working face: the length of coal seam strike is 700m, the length of inclined is about 88-160m, dip angle of coal seam is 0°- 49°, average dip angle is 34°, inclined area is 74873.72m2.

 

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Figure 3.1.1 Fully Mechanized Working Face and Roadway Layout

 

Geological Structure

 

This working face is a monocline, it is located the West Wing of the Daluowan Anticline 561 mining area. There is a oblique working face formed by anticline and syncline of two axial N31 ~ E because the working face is affected by the tectonic stress of N59°W. Ventilating roadway of working face is less affected by the fold, dip angle is between 36°38°, the affected part is the north of ventilating roadway. Mechanical roadway is affected greatly by the fold, the dip angle varies between 0°49°. Geological profile of working face is shown in Figure 1.1.

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Figure 3.1.2 Geological Profile of Working Face

The working face mainly formed by reverse fault (number 01, 03, 11) of N50°W inclination because of the effect of fold, the throw is 0.7m3.5m, it is in parallel with the fold. Specific location is: 561601# strike reverse fault, H=0.7m, 27.8m away from the south of mechanical roadway 61872 point; 561603# strike reverse fault, H=3.5m, 16m away from the south of mechanical roadway 61878 point; 561611# strike reverse fault, H=1.1m, located 3# exploration entry 61877 point of working face. Ventilating roadway developed fault without the effect of fold, there is a strike reverse fault at the point of ventilating roadway 61770, H=0.90m.

 Chart 2 Geological Conditions

 

Number of Fault

Property of Fault

Fault Occurrence   (°)∠°

 

Fault Throw(m)

F561601

Reverse Fault

310°∠65°

0.7

F561603

Reverse Fault

310°∠6070°

3.5

F561605

Reverse Fault

125°∠05°

3.0

F561607

Reverse Fault

125°∠10°

1.1

F561609

Reverse Fault

135°∠20°

2.53.0

F561611

Reverse Fault

333°∠78°

1.1

F561602

Reverse Fault

12°∠50°

0.9

F561604

Reverse Fault