Have you ever considered how a continuous miner works? Coal mining operations use these large machines to remove coal reserves from underground coal seams.
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The miner consists of a rotating steel drum fitted with tungsten carbide picks that scrape coal from seams.
An optimized continuous miner system moves smoothly from location to location without requiring workers to dismantle parts.
Other elements of a high-quality continuous miner include:
The continuous miner should also have a roof and bolter attached. However, these elements should not prevent construction personnel from placing support pattern rows.
For the most part, continuous miners offer companies high advance rates. However, longwall retreat rates and longwall continuity issues remain a concern for mines that utilize continuous miners.
Developing longwall continuity can strain other service functions, such as personnel, material handling, dust ventilation, water and power supplies, and gas drainage.
Despite these issues, continuous miner systems make coal mining faster while minimizing blasting. In addition, these machines make it possible to meet the increasing demand for underground coal production.
Read on for more information about how companies can use continuous miners to streamline their mining processes while ensuring a safer working environment.
A continuous miner system includes several critical features that impact the system’s functionality. Generally, these machines operate based on a room-and-pillar system.
Before implementing a continuous mining system, mining companies must divide each mine into 20 to 30 coal beds. Then, workers must install support systems to prevent the mine from collapsing.
After carving work areas into the coal beds, mining teams can begin setting up continuous miners to extract coal. Miners can then carry extracted coal to the surface with the help of a conveyor system.
In many cases, on-site workers operate continuous miners. However, modern continuous miner systems may also feature remote-controlled or robotic features.
Fully automated versions of the mining system make it easier to cut coal in hard-to-mine seams, lowering the risks of operating a continuous miner.
Additional features of the ideal continuous miner include:
The cutting head features a metallic rotating drum. Sharp cutter picks attach to the head and extract coal from the coal seam, working within the machine's minimum and maximum cutting height.
Some models have a dual gathering head system to increase development rates. Both single and double cutter head systems lift to reach their maximum cutting height. After doing so, internal mechanisms enable the cutters to lower back to their minimum cutting height.
Throughout the split and rendering process, the roadways leave a six-to-ten-meter fender, or coal strip, between the extracted area and the roadway. After the continuous miner reaches the block limit, the system retreats and returns to the fender.
The miner repeats this process while removing coal from the original panel each time it pulls back. The machine's traction system provides the power to extract coal, even in compact spaces.
While the split and fendering process is relatively efficient, it presents a substantial risk for on-site personnel. With that in mind, employees should avoid the unsecured roof during the room-and-pillar process.
Operators must proceed carefully while transporting coal during room-and-pillar mining.
Generally, companies use shuttle cars to carry the mined coal from the extraction point to the transfer point. Machines then tip the coal onto a conveying system connected to the surface.
Tram speed and conveyor width determine how quickly companies can collect and distribute coal to customers.
Narrow conveyor width slows down the process, a factor that companies should consider during the mine construction phase.
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Several workers take part in continuous miner operations. Depending upon the situation, you can expect to see a team consisting of:
Team members handle different tools, including the cutter, and keep an eye on the roof for safety reasons during all mining processes. Drivers then deliver each batch of coal to the conveyor.
A continuous miner offers trustworthy support at many coal production sites. Companies often select this system for use in areas where they cannot safely perform longwall mining.
The actual performance of a continuous miner machine depends upon several factors, though, including:
Each mine uses a unique haulage system and has specific dimensions. However, continuous miner equipment generally functions well, even in close quarters.
Underground hard-rock mining refers to various underground mining techniques used to excavate "hard" minerals, usually those containing metals,[1] such as ore containing gold, silver, iron, copper, zinc, nickel, tin, and lead. It also involves the same techniques used to excavate ores of gems, such as diamonds and rubies. Soft-rock mining refers to the excavation of softer minerals, such as salt, coal, and oil sands.
Accessing underground ore can be achieved via a decline (ramp), inclined vertical shaft or adit.
Declines are often started from the side of the high wall of an open cut mine when the ore body is of a payable grade sufficient to support an underground mining operation, but the strip ratio has become too great to support open cast extraction methods. They are also often built and maintained as an emergency safety access from the underground workings and a means of moving large equipment to the workings.
Levels are excavated horizontally off the decline or shaft to access the ore body. Stopes are then excavated perpendicular (or near perpendicular) to the level into the ore.
There are two principal phases of underground mining: development mining and production mining.
Development mining is composed of excavation almost entirely in (non-valuable) waste rock in order to gain access to the orebody. There are six steps in development mining: remove previously blasted material (muck out round), scaling (removing any unstable slabs of rock hanging from the roof and sidewalls to protect workers and equipment from damage), installing support or/and reinforcement using shotcrete or other supports, drill face rock, load explosives, and blast explosives. To start the mining, the first step is to make the path to go down. The path is defined as 'Decline' as describe above. Before the start of a decline, all pre-planning of the power facility, drilling arrangement, de-watering, ventilation and, muck withdrawal facilities are required.[2]
Production mining is further broken down into two methods, long hole and short hole. Short hole mining is similar to development mining, except that it occurs in ore. There are several methods of long hole mining. Typically, long hole mining requires two excavations within the ore at different elevations below surface (15 to 30 metres or 50 to 100 feet). Holes are drilled between the two excavations and loaded with explosives. The holes are blasted, and the ore is removed from the bottom excavation.[citation needed]
One of the most important aspects of underground hard rock mining is ventilation. Ventilation is the primary method of clearing hazardous gases and/or dust which are created from drilling and blasting activity (e.g., silica dust, NOx), diesel equipment (e.g., diesel particulate, carbon monoxide), or to protect against gases that are naturally emanating from the rock (e.g., radon gas). Ventilation is also used to manage underground temperatures for the workers. In deep, hot mines ventilation is used to cool the workplace; however, in very cold locations the air is heated to just above freezing before it enters the mine. Ventilation raises are typically used to transfer ventilation from surface to the workplaces, and can be modified for use as emergency escape routes. The primary sources of heat in underground hard rock mines are virgin rock temperature, machinery, auto compression, and fissure water. Other small contributing factors are human body heat and blasting.
Some means of support is required in order to maintain the stability of the openings that are excavated. This support comes in two forms; local support and area support.
Area ground support is used to prevent major ground failure. Holes are drilled into the back (ceiling) and walls and a long steel rod (or rock bolt) is installed to hold the ground together. There are three categories of rock bolt, differentiated by how they engage the host rock.[3] They are:
Local ground support is used to prevent smaller rocks from falling from the back and ribs. Not all excavations require local ground support.
Using this method, mining is planned to extract rock from the stopes without filling the voids; this allows the wall rocks to cave in to the extracted stope after all the ore has been removed. The stope is then sealed to prevent access.
Where large bulk ore bodies are to be mined at great depth, or where leaving pillars of ore is uneconomical, the open stope is filled with backfill, which can be a cement and rock mixture, a cement and sand mixture or a cement and tailings mixture. This method is popular as the refilled stopes provide support for the adjacent stopes, allowing total extraction of economic resources.
The mining method selected is determined by the size, shape, orientation and type of orebody to be mined. The orebody can be narrow vein such as a gold mine in the Witwatersrand, the orebody can be massive similar to the Olympic Dam mine, South Australia, or Cadia-Ridgeway Mine, New South Wales. The width or size of the orebody is determined by the grade as well as the distribution of the ore. The dip of the orebody also has an influence on the mining method for example a narrow horizontal vein orebody will be mined by room and pillar or a longwall method whereas a vertical narrow vein orebody will be mined by an open stoping or cut and fill method. Further consideration is needed for the strength of the ore as well as the surrounding rock. An orebody hosted in strong self-supporting rock may be mined by an open stoping method and an orebody hosted in poor rock may need to be mined by a cut and fill method where the void is continuously filled as the ore is removed.
[7]
Orebodies that do not cave readily are sometimes preconditioned by hydraulic fracturing, blasting, or by a combination of both. Hydraulic fracturing has been applied to preconditioning strong roof rock over coal longwall panels, and to inducing caving in both coal and hard rock mines.
In mines which use rubber-tired equipment for coarse ore removal, the ore (or "muck") is removed ("mucked out" or "bogged") from the stope using center articulated vehicles. These vehicles are referred to as "boggers" or LHD (Load, Haul, Dump machines). These pieces of equipment may operate using diesel engines or electric motors, and resemble a low-profile front end loader. Electrically powered LHD utilize trailing cables which are flexible and can be extended or retracted on a reel. [12]
In shallower mines the ore is then dumped into a truck to be hauled to the surface. In deeper mines, the ore is dumped down an ore pass (a vertical or near vertical excavation) where it falls to a collection level. On the collection level, it may receive primary crushing by a jaw or cone crusher, or by a rockbreaker. The ore is then moved by conveyor belts, trucks or occasionally trains to the shaft to be hoisted to the surface in buckets or skips and emptied into bins beneath the surface headframe for transport to the mill.
In some cases the underground primary crusher feeds an inclined conveyor belt which delivers ore via an incline shaft direct to the surface. The ore is fed down ore passes, with mining equipment accessing the ore body via a decline from the surface.
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