Longwall mining

Longwall mining is a mountain architectural decomposition method in mining, which comes in flözartigen deposits apply. Other names for the longwall are Streichendbau or Streckbau. However, these names are hardly common today. In English it refers to the process as Longwall Mining. Of the occurring in underground mining method of longwall mining is the safest method and the method with the highest productivity. In the German coal industry excluding the longwall mining is applied to coal mining.

• 7.1 Longwall mining with wide view
• 7.2 Bogenstrebbau
• 7.3 Geradstrebbau with Schälschrapper

History

Longwall mining is from the Mansfeld Kuferschieferbergbau and was from the 19th century, used as a decomposition method, mainly in coal mines. First, the method was limited to flat mounted to slightly inclined seams with a maximum thickness of 2 meters. The longwall length was limited to 8-12 meters due to the difficult transportation. This one was forced to divide the respective construction site by a corresponding number of Flözstrecken. In addition, had to stop so-called security pillar. The extraction of coal was carried out with the wedge hoe, then later with the Hammers. The removal of the incoming recovered mineral resources was carried out by car transport with Hunten. With emerging mechanization, particularly in the transportation of coal, the coal face lengths could be substantially increased. Longwall face lengths from 100 to 300 meters prevailed more and more.

Basics

Longwall mining is a rectangular Flözabschnitt Spanking is progressing normally. By means of longwall coal seams are mined and Kupferschieferflöze. The working face, which hosts the collection, is referred to as mining front. Characteristic of this is that several are pushed forward. Depending on the working direction is made between streichendem, floating or falling longwall mining. The working space in which the longwall is taking place referred to as knuckle. The aspirant is accompanied on each side by a degradation route. The degradation leadership takes place when longwall fact that the aspirant is led from a Aufhauen, between the two drifts to the field. A distinction is the stem and decommissioning. The excavated area behind the longwall face, which was already thrown off is referred to as Old Man. This area is filled with offset. There are different offset method. The offset method is used the most is the fractional offset. Longwall mining is a mining methods in coal seams with low cardinality and with minimum latch. Manageable during longwall widths are up to four meters and dip of around 40 Gon. For larger seam applications for specific measures such as Dividing the seam into two banks required. For larger incidence than 40 Gon other degradation processes are used. A particular problem is the degradation of steeply dipping seams. Here the miner must take special care that the offset does not slip into the routes. This can and must be prevented by careful interception of the offset. The reduction in steeply dipping coal seams is used worldwide only very rarely. As the longwall mining are exposed more Hangendflächen the same time, the host rock must have sufficient strength in longwall mining. This is required so that the hill is not breaks prematurely. If the hanging wall thrown behind the longwall targeted to break, so it's called method as Strebbruchbau.

Procedures and direction

Longwall mining is one of the long front -like construction. Indicator of this is that the extraction of the mineral takes place on a long front. Depending on whether the working face in the strike direction, the direction of fall or advances diagonally between the two direction of the seam, a distinction is made between streichendem, floating and diagonal longwall mining.

Prowling longwall

The trending Longwall mining is a process in which the degradation direction is the direction of the string line of the deposit. A characteristic of this method is that the working face is machined on each extraction layer on both the total as well as on the half- length. The incident is of no serious role in trending longwall mining. The method is suitable for both shallow, moderately sloping and steep storage. A greater impact on the execution of the procedure, the position of the wicked in connection with the case angle. The method is applied when the dip of the seam is about 20-40 Gon or when the wicked are mainly floating in the coal. Especially in coal seams with a thickness of three to four meters, it is the most widely used method. However, the method is also suitable for seams with less thickness, with a strong attack or mountains caving.

In preparation for the dismantling the seam is called by two parallel Flözstrecken, also String routes, prepared. The lower tailgate serves as conveying, the upper head section as Abwetterstrecke. These two are connected by a Flözstrecken Aufhauen. This Aufhauen forms in reducing the longwall. In the face ridges is supported by stamp and caps. The weather be steered with the help of weather doors by the longwall area. Running is when stroking Verhiebrichtung longwall mining in the same direction as the working direction, this is called trending longwall with streichendem Verhieb. In the Ruhr the trending longwall face construction method is the most commonly used.

Floating longwall

In this form of longwall mining the whole front is advanced floating. Prerequisite for the floating longwall coal seams are, who have no Methane and therefore do not release resounding weather. The dip of the seam must not exceed 33 Gon. For larger incident when floating Longwall mining is a greater danger of coal case. In addition, it is more difficult with a larger dip to move the longwall conveyor. With manual promoting the dip must not exceed 5.5 Gon. Particularly important is the floating longwall good ventilation. In order to achieve good ventilation, a weather punch to the upper sole is created first. About this, a sculpting is created as a connecting building. About this sculpting then the floating mining operations are connected. The weather connection is via Weather florets. The Abwetter can, where necessary, be derived by means of a weather bridge.

When floating longwall can, for the same field size, more strut set up and operated. In order to operate more mining operations, which serves for driving experiences and promoting route is kept open and not mixed with mountains. Once the first longwall has moved to the field, the second operation is applied. Then follow the same pattern the other strut. The method even allows the reduction of streichendem with longwall mineable coal seams not. Each mining operation two Aufhauen form the face boundaries, the reduction is chosen with regard to the recovery of the lighter carbon perpendicular to the strike direction, contrary to the traps. If the mountain misalignment applied in this method, the mountains must be supplied from other operating points or above ground often. In steeper storage, the foreign mountains can be collapsed for all mining operations together on the Weather sculpting [ NOTE 1].

Diagonal longwall

When diagonal longwall mining the direction is as diagonal as the direction of the tracked conveyor lines. The diagonal degradation has the advantage that you can break down a mining area of considerable length with a lot of attack points. This achieves a conveyor Quantum, which was easily the striking reduction not possible and was only better by optimizing production techniques. For ventilation of struts, which are operated in coal seams with high methane content, a weather crispness must be built to weather current feedback. The incident must not be greater than 17 Gon For the diagonal longwall and it can be used only where no firedamp hazard. Since these conditions are hardly observed yet, the diagonal Longwall mining is no longer used today.

Working face course

Depending on the mutual position of the mining impacts to each other speaks of Bergmann of longwall mining with wide views and longwall mining with remote shocks. Longwall mining with wide view is the actual longwall mining. Here, the working face is broken down in an unbroken straight line. This re-entrant corners are avoided. This has great advantages in terms of mechanical ventilation. The collections of beating bettors are by the straight coal face, especially in mines with firedamp hazard is avoided. Longwall mining with wide view is used in particular in pursuit in which cutting machines are used for the extraction. Especially in the fully mechanized mining working face as straight as possible is essential. Through the steady advance of the working face is also breaking through the hanging wall, especially avoided in the range of striking edges. Thus, the risk of the hazard is reduced by rock and coal case. In addition, the rock pressure can this spread evenly on the offset. Furthermore, can better monitor the operations in the face by the leadership of the working face as straight as possible. Longwall mining with wide view is suitable for reservoirs with low incidence.

Longwall mining with contrasting impacts the working face is not a straight line, but similarly to the Firstenbau, an inverted stair-like shape. This form of longwall mining also has great similarities with the shortwall and is therefore often referred to as. This form of longwall mining is particularly applicable to steep bearing seams. In the application of this method is allowed to proceed, the lower shocks. This is necessary so that one does not have to traverse through the cavity between mountain misalignment and the coal face of the lower strut in the drifts. The rock pressure is negatively affecting the longwall with offset shocks in the preceding corners.

Mechanization

Mechanization is a key component of the performance of the longwall. The first partial mechanization was achieved by introduction of the jig at the beginning of the 20th century. Further improvements were the use of cutting machines, the scraper chain conveyor and the mechanized removal.

Extraction

The extraction longwall runs almost exclusively mechanized. The manual extraction by means of hammers is limited only to small portions and become largely meaningless. During mechanical extraction, a distinction between the ramming extraction, peeled and recovery of cut mining. Since the measures necessary for the ramming extraction piling rigs did not find any dissemination, this method could not prevail at the longwall. When cut mining different cutting machines ( Shearer, Rahmenschrämlader ) are used. These run on the conveyor (usually a tank conveyor), cut with their tools, the coal from the network and transport it on the conveyor. The cut extraction has at moderately inclined seams from 40 Gon dip advantages over the peeling recovery. The peeling extraction is done with a goaf side drawn coal plow. These mining machines can be used in pursuit with an incidence of up to 60 gon. Due to the universal applicability and the simple structure of the coal plow the shelling recovery of all method is most widely used. When obtaining the planer is pressed by means of cylinders back to the coalface. This allows the chisel plow to penetrate into the coal seam and virtually tear the cabbage chest. The dissolved carbon is simultaneously loaded sideways on the face conveyor.

Copper mining

Longwall mining with wide view

Longwall mining with wide eyes grew to about 1908, on the upper soles, used in the Mansfeld copper mining. The working direction was Underlining also led the Verhiebsrichtung stroking. The aspirant was formed either straight or diagonally. The ausgererzte cavity was hand- mixed with the " roof mountains ". In offset lanes were cut out as conveyor lines ( " conveyor ride " ) and zuznehmender longwall length, auxiliary brake mountains punctuating.

Bogenstrebbau

With the advance of the degradation in ever greater depths of longwall mining with wide views prepared by the higher rock pressure increasing problems in the control of the hanging wall. Therefore, the Bogenstrebbau was developed that allowed for floating degradation direction and arched Verhieb, advantageously exploit the rock pressure for the recovery of copper slate with the Hammers. A bow longwall consists of a large number of different individual sheets. From the Sohlstrecke starting up the face is ( "float " ) is cut. An approximately circular arc is extended to an ellipse until it eventually grows together with the neighboring arcs. Conveyor drives and Bremsberg be recessed in the offset. Is a flat distance of approximately 80 meters reaches the Sohlstrecke, a degradation route is parallel to this cut out, which connects the conveyor rides trending direction. Again 80 m Spanking, the next degradation route is created. Conveyor drives, drifts and brake mountains are in the hanging wall nachgerissen at least 1.1 m distance to reach altitude, during which the strut is only 80 cm high. The width of a face sheet is about 25 m.

Geradstrebbau with Schälschrapper

In the Mansfeld copper mining was up to its setting beside the traditional Bogenstrebbau developed in the 1970s called Schälschrapperstrebbau, a variant of peeling extraction with floating degradation direction and streichendem Verhieb used. Due to the geological features of the Kupferschieferflözes ( to no dip, low thickness of only 40 cm, compared to coal greater hardness of the copper shale little ) you use to prepare the ground pressure to obtain the seam. First, a plurality of struts from existing mining area is pre- aligned by the head and tailgate, which are connected by boundary surfaces. Parallel to these driven drifts of the mining sector in 15 to 20 m wide single strut is divided. In the next step stroking horizontal relief wells are introduced with 160 mm diameter at a distance of about 40 cm in the struts. This relief cavities are created, so that the rock pressure can loosen the seam. Then only, the actual recovery with the Schälschrapper. In contrast to the coal plow the Schälschrapper is simultaneously acquisition and funding. By further Scraper in the drifts, the copper ore obtained is promoted to the handover point in the tailgate. The ausgeerzte range will be expanded with support bodies.