Depth of cover is a significant issue, as mines in the Northern and Central Rocky Mountain region often exceed 2000 feet. McCallum said the increased overburden does affect the design of equipment, which he said results in “beefier” machines and greater horsepower.
These design alterations also work well with the faces of western mines: “Generally, they are thicker seams,” he said.
With the extreme overburden, one would think that shaft mines are the norm in the west – not so. Drift design is prominent, with varying levels of grading into and out of the mine.
Grading in itself leads to intrinsic issues, but transportation into and out of active sections is not one of them. Mantrips so common in the east are replaced with diesel trucks that easily navigate the often unpredictable terrain.
Diesel use for personnel transport lends a hand to these operations: ease in travel as well as a more rapid time to reach an active section. This results in more face time by workers and more production time by the mine as a whole.
Most operations have one true uniqueness compared to all other regions of the US: it is not unusual to see a mine with two gate entries, or even more. This can be attributed to the unique ventilation issues faced by western operations.
One can also check all gate entries of a western mine and note one very vital missing component: tracks. According to McCallum, the increased horsepower of belt systems and mobile equipment combined with the use of diesel for haulage and transportation have rendered them mostly obsolete.
At the face
Thanks to the natural topography of the seam, he added, it is rare to see a face that is perfectly horizontal. Therefore, shields often lean and are installed in somewhat of a staircase pattern so that the face equipment can “run strike”, or run straight and remain in seam.
While head and tail shield design and installation are taken into account in all areas of the US, this is especially true with western mines. Across the board, shields are built for the different heights and cover of the region, McCallum said.
Some of the highest coal seams in the country and in this part of the world are found in the west, with seam height more often measured in feet than in inches. It is a rarity for an average-height person to not be able to stand at a longwall face; in fact, the average seam height for Utah, Colorado, New Mexico and Wyoming (where the majority of these faces are found) is approximately 7-8ft.
Also taken into much consideration by operators is the type of coal some western mines are working with, which can possibly be much harder than in other regions of the country. “The design of a cutting drum will come into play with harder coal,” McCallum said, which is obviously true of both longwall and CM development in these operations.
The hard coal is a consumables manufacturer’s dream come true, with items such as bits kept in check much more often. While moisture is also used to aid in the dust suppression process, too much of a good thing can lead to bigger problems with water inundation; grading often compounds that issue even further.
While not every western US mine suffers from it, bouncing is a problem that results from all of the above issues. A bounce, or blow-out, is usually over before those present realize it has occurred and leaves the mine with blown-out coal rubble that, if not prepared for with safety measures, could easily leave a mine with equipment damage.
The worker safety procedures taken so seriously at all mining operations become a matter of armor – literally. Armor-coated boot shields and vests cover western miners’ bodies, while heavy-duty chains or belts carefully hung the entire width of the face protect from sudden outbursts.
Just as diesel trucks are a staple of western mine transportation, the same is true with diesel and battery-powered equipment underground. “Diesel will probably never go away. In [most] minds, we will always use diesel,” McCallum said, and noted that there is a movement in some areas from diesel to battery. That shift, he agreed, will never be completed and the use of the two technologies will be used in tandem.
The natural progression from coal extraction to preparation, in this case, is not present – one looking for a prep plant in the west will look for some time, because they are very rare. Coal is virtually always taken in-seam, and all tonnage is generally measured in raw tons.
The issues the east faces with preparation, the west tackles with regards to transportation. Most mining areas of the Rocky Mountains are dealt a triple whammy: they are in a remote area of an arid region that is nowhere near a port, they are at a higher elevation and incorporated areas are often hours apart.
Enter the double-length truck, the most common form of transportation to get output from the mine to one of many rail line loadouts strewn throughout the west. Union Pacific and Burlington Northern Santa Fe are the most often-used carriers that aid in getting the coal from operations to customers.
McCallum said one problem western mines are facing is a dilemma found throughout the US: the availability of rebuildable equipment. “Any good core has already been consumed,” he said, and added that with the coal boom, the option to go new is not always there because of the wait time and capital cost.
As a result, he said, DBT has noted a significant shift by mines to a “mini” or partial rebuild. When time and expense are of the essence, sending small sections of equipment out for rebuild at a time is a workable option for most operations.
To aid in this area of the industry across the country, he said, DBT is currently in the process of completing a multimillion dollar expansion of its Huntington, Utah facilities. The staff at its Price office will be transferred by year’s end to its new Huntington location, a 110-workforce complex with a field services office and warehouse.
The OEM’s new home will also have plenty of space to set up complete longwalls; have the compatibilities to service new equipment; and conduct rebuilds. It will do just that with its first big project, a 200ft face with 30 shields, AFC and shearer to be delivered to a large western mine in 2007, “to ensure there are no problems,” McCallum said.