EME 444
Global Energy Enterprise

Coal Mining

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Coal is a solid that, if we are to use it, must be extracted from the earth. This is coal mining, going into the earth to remove coal for our consumption. The basic steps of mining and processing coal are described below.

There are two general methods of coal mining: surface mining and underground mining.

Surface Mining

Generally called surface mining, the industry also calls it "opencast" or "open cut mining," while others may refer to it as "strip mining." In this type of mining, workers use explosives and heavy earth moving equipment, such as power shovels and draglines, to break up and scoop off the layers of soil and rock (overburden) covering the coal seam. Once exposed, the coal seam is systematically mined in strips. It is broken up using drills and explosives, and then smaller shovels lift the coal from the ground and load it into trucks or onto conveyors for transport to a coal preparation plant or directly to where it will be used.

Mountaintop removal is a variant of strip mining technology commonly used in West Virginia and eastern Kentucky where local topography provides adjacent valleys which can be used as repositories for overburden. In this type of mining, bulldozers are used first to remove all topsoil and vegetation from the mountaintop. Then explosives are used to break up the bedrock above the coal. Huge draglines (the bucket can hold 15-20 pickup trucks) then remove the overburden and dump the waste rock ("spoil") into the adjacent valleys. Then the coal seam is blasted and front end loaders scoop up the coal and load it into the huge dump trucks that carry the coal to the coal preparation plant. The video below provides a pretty dramatic birds-eye view of a mountaintop removal operation, including the overburden and the coal seams below it. It is also quite clear what the mountains used to look like, as evidenced by the scenery in the background. Please watch the following (3:18) video which shows the process described above.

Spruce#1 Mountaintop Removal Strip Mine: Logan County, West Virginia

Surface mining works only when the coal seam is near the surface. It is, however, usually more cost-effective than underground mining and requires fewer workers to produce the same quantity of coal. And the industry reports that 90% or more of the coal is recovered, a higher proportion than from underground mining. Recall also that from a previous lesson that the EROI of surface-mined coal is higher than underground mines.

The optional (6:43) video below from PBS provides a good sense of the scale of the largest mine in the U.S., the Black Thunder surface mine in the Powder River Basin in Wyoming. 

America Revealed: Where Does Our Coal Come From?
Click for a transcript of "America Revealed: Where Does Our Coal Come From?" video.

PRESENTER: Coal. This one critical resource supplies nearly half of America's electricity. And this is the biggest coal mining operation in the country. The Black Thunder Mine in Wyoming's Powder River basin.

Black Thunder is one of 15 mines in the basin which stretches from Northeastern Wyoming into Montana. In the last 40 years, the area has been completely transformed.

This is what the barren landscape looked like in the 1950s. And here it is now. The terrain completely altered by mines like Black Thunder. Today, Wyoming produces more coal than any state in the nation-- far more than traditional coal mining locations like Kentucky and West Virginia. So what changed?

When you think about protecting the environment, the last thing that comes to mind is digging a giant coal mine in the middle of pristine ranch land.

Yet ironically, all this came about because of a government effort to clean up our air over 40 years ago. The environmental crusader who led the charge is the last person you might expect.

RICHARD NIXON: We can no longer afford to consider air and water common property free to be abused by anyone.

PRESENTER: With pressure from the growing environmental movement, President Richard Nixon signed the Clean Air Act of 1970 into law. It restricted emissions released into the air by big polluters like coal fired power plants. You might think that would have killed coal mining, but not here in Wyoming.

This stuff has a lot less sulfur than the coal mined elsewhere. So it burns cleaner, making the Powder River basin the new king of coal.

Josh Gardner drives one of the trucks that work these pits. It's a 6:30 AM shift change. Time to go to work.

Hey, morning Josh.

JOSH GARDNER: Hey, what's up? Hey.

PRESENTER: What's with you?

Our ride is basically a dump truck on steroids. It stands over two stories tall and weighs almost 200 tons.

But it seems dwarfed by the shovel at the base of the pit.

JOSH GARDNER: That's our first bucket in.

PRESENTER: It Felt like a small earthquake.

JOSH GARDNER: This actually is telling us how much weight we have on there. The first bucket was 68 tons. And then the second one, 60.

PRESENTER: Looks like it's raining coal.

JOSH GARDNER: So we got 174.

PRESENTER: Three bucketfulls and we're on our way. One truckload like this can produce enough energy to heat a home for more than 40 years or run your television for the next 2000 years.

All day long, Josh drives in a big loop filling his truck with coal, dumping it, filling it up again. In a single shift, he can haul 8,000 tons. And there's plenty to haul.

Typically, coal seams might be 10 feet thick. But here, they're 80 feet thick or more.

JOSH GARDNER: We're about 200 feet down. And you can see the definite line where the black starts up there and all the gray above it. And once we get done taking all the coal out of this seam, this shovel is done. Then they'll take all the dirt that sits above it. They'll blast it back down into this hole. And then they'll just start again.

PRESENTER: Again and again until the whole thing is cleared of all the coal.

JOSH GARDNER: Correct.

PRESENTER: And how long can they do that for? How much coal is there?

JOSH GARDNER: They say in the whole Powder River Basin, there's enough coal to last 150 years.

PRESENTER: So this coal will be around a lot longer than you or me.

JOSH GARDNER: Oh yeah.

PRESENTER: But digging it up may be the easiest part of the job where hundreds if not thousands of miles away from the power plants that need it.

So how to get this coal where it needs to go.

Trains.

But not just any trains. Some of them are a mile and a half long.

Carlin Vigil schedules the trains of Black Thunder. She's worked here nearly 30 years-- almost as long as a mine has been in business.

CARLIN SIGIL: We shipped our first train in December of 1977. And we were probably only loading a couple of trains a week at that time. And now you're looking at anywhere from 20 to 25 trains a day.

PRESENTER: This train is headed to a power plant in Montana. This one is on its way into Minnesota, Illinois, or Missouri. This one as far east as Georgia or New York.

And they all start out on the joint line. This 103 mile long set of tracks has developed into the busiest stretch of rail in the entire country.

It links these trains to national rail lines so the coal can get wherever it needs to go. The trains don't even stop as they roll under the chutes at the base of the tower.

CARLIN SIGIL: The coal runs right up this conveyor belt here. This tube that's down below us goes into the silos themselves. We can load a train out of here in about an hour and 20 minutes.

Generally, a good month is over 10 million tons of coal.

PRESENTER: 10 million tons of coal sounds like it's a big number. But I mean, what does that mean in terms of how much energy it's actually giving to the United States.

CARLIN SIGIL: It's actually 10% of the coal generated fuel for the United States.

PRESENTER: In the middle of nowhere, we've built ourselves the Grand Canyon of coal. With our vast reserves, it's no wonder America is still so reliant on the simple black rock to power the grid. Even though coal fired power plants are among the biggest air polluters in the US.


Underground Mining

When the coal deposit lies deep below the surface of the earth, underground mining is used. Miners dig tunnels deep into the earth near the place where the coal is located. The tunnels may be vertical, horizontal, or sloping. Once deep enough, the tunnels interconnect with a network of passageways going in many directions. Entries allow fresh air into the mine and give miners and equipment access to reach the ore and carry it out. The coal extraction is done by either a room-and-pillar method or longwall mining.

When the room-and-pillar method is used, miners cutting a network of 'rooms' into the coal seam and leaving behind 'pillars' of coal to support the roof of the mine. Working from the tunnel entrance to the edge of the mine property, they remove sections of the coal while leaving columns of coal in place to help support the ceiling. This process is then reversed, and the remainder of the ore is extracted, as the miners work their way back out.

In the case of longwall mining, the area being mined is covered with hydraulically-powered self-advancing roof supports that temporarily hold up the roof while the coal is extracted. After the coal is removed, the roof is allowed to collapse. This method requires careful planning and appropriate geological conditions. Carl Hoffman in Popular Mechanics offers this vivid description of longwall mining, 

From an elevator-like entrance shaft deep underground, continuous miners—cutting machines on wheels—bore passages on both sides of seams of coal up to a quarter mile wide and a mile or more long. At the mine face, a massive shearer on self-advancing ceiling supports known as 'shields' slides back and forth across the face like a giant cheese grater. Water sprays constantly against the coal face to dampen coal dust. After each pass, the whole apparatus, as wide as 1600 feet, lurches forward, letting the area behind the shields collapse. A conveyor belt catches the coal, moves it to another belt running along the side passages, and takes it to the surface, often several miles away. When a panel of coal is mined out, the longwall machine is moved to the next one. Over time, mines become enormous labyrinths of passages, and it can take miners a half hour or more to travel miles to the mine face in low-slung vehicles called mantrips.

To Watch Now

Please watch the following (3:30) video:

Coal Story, The Mine
Click for a transcript of "Coal Story, The Mine" video.

This song tells a story of a region, of a rugged landscape that challenges the eye, and a friendly people. It's all part of the legend of Virginia's great southwest. This is the most economically depressed area in the state. For decades, the best and practically only way to make a living in these rugged hills was beneath them in the darkness of a coal mine.

Well, I guess it just gets in your blood once you try it. It's just a daily routine.

A routine Emory Hess and thousands of other miners go through every day.

And over the last few years, you just had to continually move deeper and deeper.

This is Pittston Coal's Laurel Mountain Mine, one of about 290 licensed mines in a 10 county area.

How much longer will you be mining this particular mine?

Hopefully we can get another eight years in here. 8 to 10, anyway.

Every day, around the clock, miners make this journey underground and inside Virginia's hills and mountains. Mining is basically hit or miss. You've got to go where the coal is, and here's where it is. We're about 3 and a half miles underground, and there's about 700 feet of mountain right above us.

They've had to move a lot of rock to get this deep. Powerful machines help the miners chew and claw their way inside, and some places the shaft is less than 4 feet high. You practically have to crawl. They follow the vein, taking only the coal. This one is called the Jawbone Seam. It's hundreds of thousands of years old.

Once miners gather the coal, a conveyor belt takes it outside to be processed. Three a half miles underground means a 20 minute ride on the belt before coal sees the light of day.

Once the prize industry of southwest, coal mining is quickly losing its steam. Coal demand is down. Mines are closing, and that means layoffs. In some coal counties, the unemployment rate is 50%.

If you were looking at a crystal ball, you would see that coal mining wouldn't exactly be the thing to be trying to start into right now.

Uh, right, that's a pretty good assumption, pretty good-- [UNINTELLIGIBLE] with a crystal ball, yes.

Some coal companies are trying to mine coal a cheaper way. This is the White Stallion surface mine, also owned by Pittston, where miners literally rip off the top of the mountain to take out the coal. They're mining the Dorchester Seam here, more than 1,000 feet above the Jawbone below.

Today, the remnants of a hurricane hundreds of miles away have turned this site into a mountain of mud. But the work continues. Day and night, it never stops.

There have been better times here in southwest Virginia. Coal mining was once an old, reliable way to make a living. It isn't so reliable anymore. The people here realize that, but there's not a whole lot of other ways for them to make a dollar.


Coal Preparation ("Washing")

Once the coal is removed from the mine, it is taken to a coal preparation plant where the raw "run-of-mine" coal is processed to separate the coal from undesirable waste rock and minerals. The finer waste from this process (including silt, dust, water, bits of coal, and clay) is discharged as a thick slurry into a man-made impoundment. This structure is used to confine refuse or slurry, along with any chemicals used to wash and treat the coal at the coal preparation plant. Coarser waste from the preparation process, rock, is dumped back into the pit once mining has ceased or is used in the construction of an impoundment dam.

To Watch Now

Please watch the following (5:43) video:

How They Do It - Coal Mining Video
Click for a transcript of "How They Do It - Coal Mining Video" video.

Man has used coal as a fuel for over 3,000 years, and it remains one of the world's most vital natural resources. It generates more than 40% of the world's electricity and every year we go through 6 billion tons. Somehow, mines must ensure a constant supply, or our cities would be plunged into darkness and industries would grind to a halt. So how do they do it?

Pittsburgh, Pennsylvania. This industrial east coast city is famous for steel production and shipbuilding. But Pittsburgh is also surrounded by rich coal reserves. And here, just 30 miles from the city, are the Bailey and Enlow Fork mines. This is the largest underground mining complex in North America. And every year it produces more than 20 million tons of coal.

There are millions of dollars invested in this vast complex, and with more than 200 men working underground at any one time, keeping it running is a major logistical challenge.

At 4:00 in the afternoon, the day shift clocks off after eight hours of hard work, while the next shift makes its way into one of the lift cages to begin the 650 foot descent into the mine. Mining is one of the toughest jobs imaginable, and there's an unspoken bond between these men who spend every working day deep underground.

Once they arrive at the bottom of the shaft, they still face a long journey to the coal face. After almost 20 years of continuous mining, a vast network of underground tunnels now extends for an extraordinary 35 square miles. The miners face a five-mile journey to get to the section currently being mined. It's a cramped and uncomfortable ride aboard one of the mine's small trains, as the cars rattle their way through the maze of dark tunnels, following a network of rails that are now so busy they require traffic lights.

First up is a monster machine, known as a continuous miner. Armed with a 16-foot cutting drum, this ferocious beast chomps away at the scene, carving out a series of access tunnels. As it bores its way forward, it feeds the cold behind it to a crab-like loader and shuttle car. The continuous miner produces up to five tons of coal every minute-- more than a miner in the 1920s produced in a whole day. But its job is actually to prepare the way for the real monster-- the longwall shearer.

Armed with a set of teeth to put a Tyrannosaurus to shame, its cutting edge is over 1,000 feet long, and it can smash an amazing 50 tons of coal out of this seam every minute. Think about it. That's almost one ton of coal every second, enough to meet all the energy needs of an average household for 78 days. But there are 3 million tons of coal in this 13-foot-high seam. Despite its ferocious appetite, it will still take six months of shuttling back and forth before it has finished digging it all out.

Before the coal is fit for shipping, they first need to remove rock, soil, and contaminants, which account for up to 30% of the raw feed. So the material is fed via conveyor into the processing plant. To ensure it's all properly processed, it's first graded according to size. Next, to separate the coal from the waste rock, it's fed into this giant floatation tank. Because the rock is heavier than the coal, it sinks to the bottom where it can be removed, while the coal floats to the surface.

It's now soaking wet. So just like your home laundry, they load it into a spin dryer.

This industrial dryer spins the coal at high speed until excess water is removed. This water is then fed into vast tanks where the contaminants are removed before being disposed of as waste slurry.

Meanwhile, the different sized pieces of coal are recombined, crushed into a uniform mix, and fed into a giant hopper. Incredibly, just 15 minutes after entering the plant, it's ready for transport by rail. As they park beneath the hopper, a controller opens a chute to allow 6 tons of coal to fill each car. Once full, every train is able to transport over 10,000 tons of coal to power stations across North America.

Thanks to some extraordinary coal crunching machines and the guys who labor 24/7 to keep them working, this essential resource keeps flowing to the world's power stations, and there's enough electricity to power the wheels of the modern world.