Responsible Mining & 3D Machine Control

A 1.246Mb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE

When you hear the words surface mining several things may come to mind. You may think about the important role mining plays in manufacturing consumer and industrial goods. You may think how mining provides affordable energy to over 40% of the world. You may have concerns about potential risks mining can bring to the environment including air quality and ground water. Whatever your thoughts, mining impacts the health of global economies and can be polarizing. For the purpose of this article, I will focus on the evolution of surface mining in coal and the industry's pursuit of responsible mining. 3D machine control and positioning along with fleet management can play a significant role in this pursuit.

The Industrial Revolution, which began in Britain in the 18th century, and later spread to continental Europe and North America, was driven by the availability of coal. Coal was burned to power steam engines. These coal-fed steam engines powered the railways and steamships, exponentially expanding international trade.

New coal mines were established to meet new demands, and in those early days mining was dependent on men using a pick and shovel, primitive by today's standards. Coal-cutting machines were invented in the late 1880's and by 1912, surface mining was conducted with steam shovels specifically designed for coal mining.

Modern surface mining
Surface mining and deep underground mining are the two primary methods of mining. The choice of method depends on depth of the coal seam, density of the overburden, and the thickness of the coal seam. Seams relatively close to the surface, at depths less than approximately 180 ft (50 m), are usually surface mined.

Coal that occurs at depths of 180 to 300 ft (50 to 100 m) is usually deep mined, but in some cases surface mining techniques can be used. For example, some western U.S. coal that occurs at depths in excess of 200 ft (60 m) is mined by the open pit methods, due to thickness of the seam 60­90 feet (20­30 m). Coal occurring below 300 ft (100 m) is almost always deep mined, although there are open pit mining operations working on coal seams up to 1000­1500 feet (300­450 m) below ground level.

Open cast coal mining recovers a greater proportion of the coal deposit than underground methods, as more of the coal seams in the strata may be exploited. Large open cast mines can cover an area of many square kilometers and use very large pieces of equipment. This equipment can include the following: Draglines which operate by removing the overburden, power shovels, large trucks in which transport overburden and coal, bucket wheel excavators, and conveyors. (Bucket Wheel Excavators, 3D Machine Control on a Large Scale, In this mining method, explosives are first used in order to break through the overburden of the mining area. The overburden is then removed by draglines or by shovel and truck. Once the coal seam is exposed, it is drilled, fractured and thoroughly mined in strips. The coal is then loaded on to large trucks or conveyors for transport to either the coal preparation plant or directly to where it will be used.

Most open cast mines in the United States extract bituminous coal. In Australia and South Africa open cast mining is used for both thermal and metallurgical coals. In New South Wales open casting for steam coal and anthracite is practiced. Surface mining accounts for around 80 percent of production in Australia, while in the US it is used for about 67 percent of production. Globally, about 40 percent of coal production involves surface mining.

3D machine control benefits mining processes
Surface mining operations are process intensive. You might say they manufacture coal. Like any manufacturing system, there are many procedures that make up systems and subsystems. Some of these procedures include geology analysis, drill samples, design, managing the overburden, extracting the coal, transporting the coal, storing the coal and much more. The processes are refined to achieve the best production. Small gains in productivity equal big numbers working on such a large scale.

Removing overburden as described above is one of the early steps in getting to the coal seam. The drill samples and subsequent strata analysis can be saved and represented as part of the digital design. These design files are loaded into the machine doing the primary cutting. These include scrapers that remove topsoil, and draglines and shovels that remove the bulk of the overburden. By assisting the operator with visual guidance, the blade maximizes the cut. For example, if the blade is continually pushed deep into the cut, machine wear and failure can result. So not only is production maximized by cutting properly, production is maximized by reducing machine downtime.

Positioning systems are also added to the haul truck fleet. Tasks such as load, material type (grade of coal), distance traveled, dump location, volume material type and dispatch enhance material management. Material management assists in locating stock piles for blending coal and top soil for later reclamation. If high accuracy GNSS is installed on both a wheel loader and a haul truck, fields of data can all be populated by geolocation. Valuable information such as which coal seam was the coal cut from, quality, which machine loaded the coal, etc. can all be populated automatically. This eliminates human error, enhancing data integrity. Safety is also improved, keeping the operator focused on operation and less on logistics.

Once the machines are deployed with positioning systems, site connectivity and remote fleet management offers another level of benefits. The ability to populate all machines with new design change files via wireless connectivity not only saves a lot of time, but also ensures that all machines have the latest data. Compare this automated system to taking a USB drive to each machine. Manual file updates not only halts production but also increases risk by placing personnel on the working face in harm's way.

As the machines cut the surface, be it overburden or coal, the grids are updated in near real-time. Updated grids are communicated back to the database via the wireless infrastructure. Progress is monitored as all grids from all machines are combined, updating the entire work area. This offers managers a great view of the work, and corrective measures, if required, can be quickly implemented.

Another benefit of stored fleet data is historical play back. This allows a replay of one or more machines from any time period stored in the database. For example, a high performer can be analyzed, sharing those productive techniques with other operators and new hires. Historical playback also benefits incident investigation. I have learned that it is better to store as much data as possible. This way it is available for future reports and analysis even if those uses are not obvious during initial implementation.

Mine reclamation is the process of restoring land that has been mined to a natural or economically usable state. Mine reclamation creates useful landscapes that meet a variety of goals ranging from the restoration of productive ecosystems to the creation of industrial and municipal resources. In the United States, mine reclamation is a regular part of modern mining practices. Modern mine reclamation minimizes and mitigates the environmental effects of mining and are part of the overall design strategy.

Show me the coal
It has been estimated that there are over 847 billion ton of proven coal reserves worldwide. This means that there is enough coal to last us around 118 years at current rates of production. In contrast, proven oil and gas reserves are equivalent to around 46 and 59 years at current production levels. These statistics certainly change over time as new reserves and recovery methods are developed. Coal also can be easily stored to stockpile to meet spontaneous increasing demands. This is logistically less possible with natural gas. In 2011, coal was the fastest growing form of energy outside renewables. Its share in global primary energy consumption increased to 30.3%--the highest since 1969.

Coal reserves are available in almost every country worldwide, with recoverable reserves in around 70 countries. The biggest reserves are in the USA, Russia, China and India. After centuries of mineral exploration, the location, size and characteristics of most countries' coal resources are quite well known.

What tends to vary much more than the assessed level of the resource--the potentially accessible coal in the ground--is the level classified as proven recoverable reserves. Proven recoverable reserves is the tonnage of coal that has been identified by drilling etc., and is economically and technically extractable.

Below are the Top Ten Coal Producers (2011). I have also included other production and consumption statistics that put the importance of coal into perspective. (see PDF for charts)

Total world coal production reached a record level of 7,678Mt in 2011, increasing by 6.6% over 2010. The average annual growth rate of coal since 1999 has been 4.4%.

Responsible mining
Electricity literally powers our world. Coal is the major fuel used for generating electricity worldwide, and generates more than 40% of the total. Methods of coal extraction in today's mining operations are designed responsibly. Modern mining companies continually invest in technology that increases productivity while lessening the carbon footprint. This helps meet our energy needs affordably while harmonizing with the environment.

Randy Noland is the Managing Editor and Co-founder of Machine Control Magazine.

External Links and References
Methods of mining
Glossary of Mining Terms
World Coal Institute
World Coal Association

A 1.246Mb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE

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