• The Superior Highwall Mining System can mine coal seams ranging from 30” to 16’.
• Penetration depths over 1000 feet are possible.
• Rigid pushbeam design with PLC controlled sump forces allows for more consistent and accurate cutting depths.
• Modular design allows the system to be moved easily from pit to pit.
• Current systems are successfully mining 40,000 to 100,000 plus tons per month depending on the coal seam height.
• Three to four man crews keep labor costs low.
• Up to 70% of in place coal can be recovered using the Terex SHM System.
• Enclosed pushbeam conveyor eliminates external ash dilution from the roof.
• Ability to operate on contour benches as narrow as 42 feet.
• Technical support assuring Terex SHM availability is provided.
• Assistance in designing mine plans for highwall mining can be provided.

• What thickness of coal seams can your miner accommodate and to what depths?

• When it comes to safety, how does highwall mining compare with other coal extraction methods?

Methane can also pose a threat if its presence is not recognized and appropriate action taken. In this respect, highwalling has more in common with underground coal mining, so we use a similar approach. A sudden increase in methane concentrations will result in power to the cutterhead automatically being switched off, and if the coal seam being mined is known to be particularly gassy, then the umbilical cable that provides power, water, methane monitoring and control to the cutterhead can also be equipped with an air-blowing pipe that will ensure that any methane that is produced during coal mining is safely diluted.

 

• What are some key inovations on the Terex SHM Miner that increase coal recovery efficienty?

We have always adopted the philosophy that automation needs to be used in situations where it can help to improve the productivity of the highwall miner. On one level, this applies to the use of PLC technology at the heart of the machine-control system. Through the use of touch-screen technology, the highwall miner operator not only has simple, immediate-response control over the highwall miner’s functions but can also adjust these functions in response to changing mining conditions within the entry. Allowing the operator to respond to changing conditions in this way means that – although it cannot be seen directly– the coal mining operation can be optimized, resulting in a cleaner coal product that will command a higher price.

 

Moreover, our team developed a Pushbeam Transfer Mechanism in order to speed up the installation and recovery of individual pushbeams during and after each coal mining entry. In this sense, automation has helped to reduce the time taken for a repetitive, wholly mechanical function within the mining and coal recovery cycle, which at the end of the shift translates into more cutting time, more tones mined, and higher shipments through the mine gate.

 

• What are some key considerations when considering and area for Highwall Mining?

A number of parameters need to be evaluated when designing a highwall mining layout. The depth of cover above the coal seam is obviously one, as are the seam thickness, the thickness recovered, the cutterhead width, and the in-situ strength of the coal. Another factor that may come into play is whether, in some cases, the coal seam has already been mined by augering, in which case the effects of the holes and of in-situ weathering have to be taken into consideration.

 

A paper presented  at the 24th International Conference on Ground Control in Mining by David Newman of Appalachian Mining and Engineering Inc and Karl Zipf of NIOSH in Pittsburgh addressed this topic in some detail. Using rock-mechanics principles, they derived graphical guideline sets that can be used as a starting point for detailed engineering evaluations for appropriate pillar widths between entries. In their conclusions, they noted that: “Highwall mining requires a thorough knowledge of the strength and physical properties of the immediate roof, coal, and immediate floor strata.”

“Engineering design and surveying the orientation of each highwall miner cut is necessary to avoid ground control problems.” In this context, our highwall miner design helps to ensure that sequential entries lie parallel to each other. The four corner-mounted tracks permit tight maneuverability along the highwall as well as allowing the operator to orientate the highwall miner precisely in situations where the highwall is curved or follows hillside contours.

 

• What means of power source does The Terex SHM highwall system use?

Our machines can be powered either from a coal mine’s main grid or from a dedicated mobile generator. Both systems have specific advantages. Supplying the miner from the main grid can mean lower energy costs, depending on the location and the individual mine’s power-supply agreement. However, there is a trade-off in terms of operational flexibility, since power cables will have to be moved regularly. In addition, the mobile generator approach allows the highwall miner to move from site to site on its own, without having to disconnect and reconnect to fixed power sources. The mobile unit that we supply for use with its machines features a 2,000 hp, V-16 Cummins diesel engine that drives a 995 V, 1,500 kW generator to power all of the principal miner functions. In addition, the unit contains a separate 50 kW generator that provides power to the highwall miner’s computers, air conditioning, lights, and accessories. Power from the generator is transformed to the correct voltage in an Electric Control Module onboard the highwall miner.

Track-mounted for high mine-site maneuverability and wholly self-contained, the gen-sets are housed in a super-silenced container body. With a length of just 6 m, this is small enough to be transported on a standard trailer without the need for any additional permitting. It is also flexible enough to travel with the highwall miner from site to site, providing continuous power during highwall miner moves.

 

• How does a mine’s condition and the operating company’s aspirations affect the highwall system that should be chosen?

The fundamental aspiration behind any highwall mining operation is to produce low-cost coal from resources that mght otherwise be abandoned. In today’s coal market, that makes even more sense that it did just a few years ago, especially if metallurgical coal can be recovered. The available bench space is a key factor in deciding on the most appropriate highwall mining system to use. If highwalling is considered to be an integral part of a contour- or trench-mining operation, then the probability is that benches will be laid out to accommodate the highwall miner during a second production phase. By contrast, if highwalling is planned for old bench areas, where coal mining perhaps took place some time ago, the narrower benches used then will dictate the use of a highwall miner that can operate under these conditions.

 

Our highwall miners have a big advantage in this context. Where thin-seam, narrow bench mining is planned, a vertical-discharge system may still be the most effective option. Then again, a combination of a narrow bench and a thicker coal seam may mean that a rear-discharge highwall miner equipped with a right-angle discharge conveyor will be more productive and cost-effective.

 

There is also the question of accessibility for trucks to transport out the mined coal, and for the storage of critical components such as pushbeams. Good road maintenance and the ability to minimize pushbeam-transport distances are both important considerations in this context. In terms of the coal seam itself, there needs to be an appraisal of the roof and floor conditions. A soft floor can present problems if the cutterhead unit and power-transmission system do not have adequate flotation: in our case, the pushbeams have a low ground-bearing pressure, with a Hardox steel base, so soft floors offer less of a challenge. In addition, the fact that in one of our highwall mining systems, the cut coal is transported completely within the pushbeam train means that any roof-fall that does occur cannot contaminate the product: what you mine is what you get.

 

• How does the Terex SHM highwall miner accommodate high production rates and how much can it convey per hour?

One of the major developments that we have introduced with our second generation highwall miners has been its rear-discharge concept. The original highwall miner design featured the vertical discharge system that was more than adequate for narrow benches and thin-to-medium height seams, with the cut coal being stockpiled alongside the miner.

 

As we increased the seam-thickness capability of our highwall minerss, the coal-transport demands rose as well, so the rear-discharge system, in which the cut coal flows right through the miner’s base frame unit, was the obvious solution. When equipped with a right-angle conveyor, the highwall miner can still work on a 12 m bench, so the coal mining system’s capacity has been increased without compromising its narrow bench capabilities.

 

In terms of sheer hourly tonnage, that obviously has a relationship to the thickness of the seam and the hardness of the coal, but suffice it to say that our pushbeam transport and discharge systems can handle anything that the cutterhead will produce.

 

• How does your The Terex SHM highwall system differ from it's competitors?

We let the operational success of our highwall miners speak for themselves. The company has now shipped more than 60 units, all are still reliably producing low-cost coal. Another key consideration is that we have proved that it can provide support to its highwall miners anywhere in the world. Three units have been operating overseas since 2004, and the company has now established a facility in Europe to handle its foreign business. Closer to home, it has a satellite parts depot in Appalachia, providing its customers with faster, more cost-effective service in the area in which it has the largest machine population.

 

Major factors in the company’s success to date have included the flexibility of its highwall miners and the ease with which their performance can be optimized. To provide an example of the former, one Terex SHM customer, Stollings Mining, initially used a vertical-discharge machine to selectively mine one particular coal seam. By doing so in two separate cuts with two different qualities, Stollings successfully marketed all its coal on an as-mined basis, and later bought a second, rear-discharge machine for additional flexibility.

 

In terms of optimization, the PLC control systems used on our machines are a big benefit, not only for direct control of the highwall miner but also for maintenance and fault awareness. Using these systems means that coal operators can be as productive at the end of a shift as they were at the beginning.

 

Most importantly, the financing community is now comfortable with highwall mining’s track record as a profitable method of coal extraction, which has made machine purchase easier to fund. We are now making a major move into the international market, with the aim to build on the success the company has achieved so far by helping coal mining companies make better use of highwall resources around the world.