Tech Talk - Coal mining continues to produce

Sadly I was away from home last week to attend a family funeral in Northumberland where, for the past nine generations including mine, our family have been miners. The funeral was for my father’s sister, Linda, who had documented early life in the mining village of Ashington in her books “A Tune for Bears to Dance To,” and “The Pit Village and the Store.” The latter was made into a docu-drama for British Channel Four television. The hotel at which we stayed was next to the Woodhorn Mining Museum which has been built around the colliery offices from the old mine. The rest of the property has been turned into a nature park – with a little twist.

Figure 1. Part of the old mine site, now the Queen Elizabeth II Country Park, with a 40 acre lake. Note the wind turbines in the background – all but one of the 14 were turning during my stay. (Hotel on the right)

The site is also now home to considerable bird life – including over three dozen swans that I counted as I meandered around the lake.

Figure 2. Some of the birds on the lake at Woodhorn

Much of this part of Northumberland has changed considerably since the time – over 50 years ago – that I was an Indentured Apprentice in the National Coal Board working at Seghill Colliery, though on day release once a week to Ashington Technical College. One of the greater changes is illustrated in the background to a painting of my father that my aunt painted.

Figure 3. My Dad as Undermanager at Ashington (note the yard stick, the safety lamp is hidden by the coat). (Linda McCullough-Thew)

The large mounds are the pit heaps which were scattered all around the road as the bus carried me from Newcastle to the pit. They are all gone now, and the land is restored and, as the pictures above testify, now visually contaminated by the latest form of energy generation, though that doesn’t seem to worry the red squirrels and the geese.

Figure 4. Pit heap dominating the miners houses (Sunderland Public Library)

I thought of that as the recent reports on the devastation that mining creates are once again headlining the problems as new and enlarged lignite mines are developing in Europe. The transition to mining lignite, which contains considerable quantities of water and is a geological precursor to the black bituminous and anthracite coals that are preferred, is coming because it is considerably cheaper than alternate sources and nations have it at hand, instead of having to spend currency on importing alternate and increasingly expensive fuels from elsewhere. The reason that lignite is attractive is that the black coal seams that used to be mined in much of Europe have been mined out at currently economic depths, and lignite – even though less energy intense – has become an economically viable alternative.

To mine the surface deposits Europeans rely on the Bucketwheel Excavator (video here) with one machine replacing 40,000 men with picks and shovels (the way I was initially taught to mine). The overlying rock and soil (overburden) is first removed and stored, and then, once the coal has been removed, the land is restored with very stringent requirements for the condition of that restoration, so that in many cases the stone walls around the fields are replaced and the appearance of the land is similar to what was there before.

At present surface mining is becoming the dominant method for coal production. The thick seams in Wyoming and Montana have huge reserves, and the coal is very simple to mine and remove. Once mined it is trucked away from the machines and loaded into rail cars which then carry the coal around the nation. Because this coal has a low sulfur content it has proved competitive even against the more local coals of the East, which must often now be expensively mined from the underground. As the Wall Street Journal recently noted two counties in Wyoming now account for 40% of the US coal mined, while underground mines are closing in Appalachia.

After seeing a drop in coal production of around 9% as coal fired power plants were replaced by natural gas in the 2011 to 2013 time frame, the EIA is now projecting that US coal demand will increase by 3.6% this year, as natural gas prices rise. This will be followed by a 2.5% decline in 2015 as the new EPA regulations bite harder in driving the closure/transition of power plants. However US natural gas prices continue to be much lower than those in most of the rest of the world, and thus, as the WSJ notes , overall coal production in the USA is likely to stabilize around current levels for the next three decades, while domestic demand reduction is offset by increasing demands for coal from other countries which will continue to find it a cheaper alternative.

Much of the alternative replacement fuels for coal (and in some cases nuclear) are presumed to be from the increased levels of shale gas that are being produced in the United States, and which are projected to become domestic sources of fuel in many other countries around the world , including Europe. However while the plans and actions to close coal fired power plants proceed apace the rate and scale at which alternate sources of energy, particularly European shale gas, will appear are much less certain.

And in the interim, as coal mines have found better ways of processing the coal to meet power station demands, the potential for growth still exists, as the recent example in the Illinois Basin shows, where Sunrise Coal are planning to open a new underground mine in Vermillion IL this year, producing around 3 million tons of coal a year. The mine will use room and pillar mining to ensure that there is no surface ground subsidence, which can be a problem in the Illinois Basin.

And those who anticipate that China and India will reduce coal demand in order to overcome the problems that they have with air pollution, should remember that air pollution in the UK was at least as bad in the early 1060’s but by changing the way in which coal was burned the air was cleaned, and Britain continues to rely on coal for a significant portion of its electrical power.

Tech Talk - The evil in the hearts of men.

It was Edmund Burke who said "The only thing necessary for the triumph [of evil] is for good men to do nothing," and with a hat-tip to Bishop Hill who drew my attention to the testimony, I think I had better say something.

Back in the days when I left school the United Kingdom, and most of Europe, was finally emerging from the brutal impacts of the Second World War. That recovery was helped immeasurably by the coal mining industry where thousands of men labored underground across Europe to ensure that adequate power was available to supply the needs of their various countries as industrial capacity was restored. As an eighteen-year old indentured Apprentice I laid on my back in 20-inch high coal to shovel the 15-tons of my ordained shift onto the conveyor, and braced the roof over my head with hand-sawn timber props to hold it for the following week, as we moved the longwall face forward. I was paid just over four pounds a week, but they did allow me, on Wednesdays, to go to the local Technical College in Ashington where I studied from 8 am until 8 pm. In the good weeks I could then go home, but in the alternate weeks I was either on foreshift, which meant that I went to college directly from the mine, or nightshift, when I went from the college to the mine and worked the following shift. I was woken more than once from an exhausted sleep having fallen into the corridor on the bus. Men died in those mines that I worked in to ensure that Britain had the power that it needed to recover and rebuild.

I thus find myself seriously affronted when this industry (and myself), are called evil by some academic from Oxford, no matter how illustrious his qualifications. In his testimony before the House of Lords Committee on “The Economic Impact on UK Energy Policy of Shale Gas and Oil “ last week, Professor Dieter Helm said

Of course one would want to make sure that regulators are on top of any environmental consequences that might flow from drilling, but I find it truly extraordinary that people want to ban fracking in a context where they are not prepared to ban coal mining, and indeed across Europe actually promote coal mining. When one thinks about the relative environmental impacts of the alternatives, coal mining is truly evil in comparison. I find it extraordinary that people are legally allowed to mine coal if you want at the same time to have a blanket ban on shale gas extraction.

It is almost a throw-away line, a necessary genuflection to the politically correct views of the day, a glib reference to transient effects long recognized and ameliorated by the coal industry over the past decades.

In those days of my youth, back in 1962, I walked into Newcastle to take the first bus of the morning from the terminal to the mine some 11 miles away at Seghill. It drove past pit heap after pit heap, and the impacts that Professor Helm is I believe referring to were real, and evident. The mine I worked in was over a hundred years old, and my father had been manager there when my brother was born. You walked stooped for part of the way to the face, since the roof of the passage was low, though the temperatures were pleasant, year round. Coal moved by conveyor and mine car, once hand-loaded from the blasted face, and supplies came in on carts hauled by pit ponies – another unforgettable memory. Hundreds of men worked at each mine, with a typical stint being a 10-yard length along the 200-yard measure of each longwall. We were not evil, the industry was not evil – it was vital and necessary. And it has changed.

Instead of walking there are now mine cars that haul workers to the face, electric trams have replaced ponies, and machines now do the work that muscle did back in those days. Where then is the evil? Is it that we are removing material from the ground? But unless you wish to go back to human densities of 70 people per hundred square miles of the hunter:gatherer era this must happen, for if they aren't grown resources must still be mined from the earth.

Yes there are transient effects, but if instead of dwelling on the ugliness of the excavation on some cold wet day when the shadows are right to emulate some hellish landscape, one were to go back five years after the mine has moved on (presuming that this is some surface site) then those wounds from current mines have gone. Laws require, and company self-interest demands, that land be restored. In parts of the world that can realize unexpected benefits as the land becomes more productive than it was before. You can no longer find much negative evidence of the underground mines in the area I worked in.

But the intent of this post is not to pat myself on the back, nor to run off on a rising rant, but rather to point out a problem which this broadly prevalent and stridently negative attitude is generating. Early this morning I received a call soliciting funds for the Footsteps Program at the University of Leeds, where I was awarded my degrees. But I had to gently break it to the young student calling that I could not participate because the University had done away with the Mining Engineering program through which I obtained my degrees. Further they have turned over the building, donated to the University by the industry and its workers for such studies, to the Art Department.

Leeds is not alone, the Royal School of Mines, merged now into Imperial College, London no longer offers mining courses.. The Welsh School of Mines, now the University of South Wales, no longer offers mining courses – there is but one place in the UK, at what was Cambourne School of Mines but is now the Penryn campus of the University of Exeter, where such a course still exists.

This image of the industry as an evil entity is ironic given, as Professor Helm pointed out:

Practically now, in Europe and the UK, we are switching from gas to coal. We have gone from about 28% of our electricity generated by coal a couple of years ago to about 40% today. Germany is bringing 7 to 8 gigawatts of new coal on to its system. Coal stations are being built across eastern Europe. The coal burn generally has gone up across Europe. Germany has gone from nuclear to coal and from gas to coal. This is a really serious environmental development across Europe.

For many years the rational pursuit of energy policy in many parts of the world was hindered by the demonization of nuclear power. It has taken that industry many years to work through the opprobrium that hindered realistic discussions of costs and benefits, and it is only now that some of the green community are beginning to recognize the irrationality of some of their earlier arguments. Yet the vilification of that industry cost it an entire generation of management and engineers who were persuaded to avoid such a career and who starved the industry of a strong supply of graduates. Now that engineers are needed there not that many with long experience, since the generation running the industry is retiring.

And here we are seeing a growth in the demand for coal, and yet – in part because of the demonization of the industry – there are but limited places where qualified engineers can be found, and at a time when advanced levels of technology will be called for as deposits get leaner, deeper and more difficult to extract there are even fewer places that can carry out the needed research into excavation technology.

Sadly academia and government seem to be unwilling to face the reality of the future that these circumstances will bring. Because the situation cannot be reversed in a year or two, as the knowledge base fades (as it now rapidly is) so it will become harder and harder to meet global needs. But no doubt academia will find a way to blame that on us miners, the few of them that will remain.

Someone told me once – “if you want to find gratitude, you’ll find it in the dictionary, between chump and sucker*.” But, one might have thought that for those who claim to predict the future, perhaps the occasional thought of self-interest might burble its way through, but not, I suppose, at Oxford.

*the statement has been modified for a general audience.“

Highwall Mining of coal

There is an aspect of coal mining that gets relatively little attention, even though it is growing in popularity, It is with this method that I will conclude this series on mining, and its precursor on oilwell production. Most mining can be divided clearly into either surface mining, where the rock over the coal is removed, and the coal taken away before the land is restored, or underground mining, where some of the coal has to be left in place to hold the roof up. But what happens in the middle?

There is an intermediate between the two main methods of mining, when the surface mine has produced coal from a seam that is steadily getting deeper, it reaches a point where stripping the rock from above it is no longer economical. So what to do? And the answer is what is known as Highwall Mining. When the last economic cut has been made with a surface mining operation, the coal seam is still exposed, lying under the rock and overburden in what is known as the Highwall of the mine. So, before the land is reclaimed and that final cut along the face filled back in, sometimes it is economic to look at using different mining machines to mine into that exposed coal face in the Highwall – hence the name.

Coal seams that might be mined this way are not going to be worked to that great a distance into the coal that a full underground operation will develop, rather a machine is mounted at the surface face of the coal, and advances into the coal mining and feeding it back out, so that it can be collected and hauled away.

The early machines that were used for this were often Augers, and in this picture the highwall had three seams of coal in it, (at the current bottom of the wall, and along the two sets of higher augered holes).

Augered seams in a highwall (Bundy Auger)

The coal auger is not dissimilar in shape to the auger used in making large holes in wood, or which might be used to drill large vertical surface holes, except that in this case the holes are drilled horizontally forward into the seam, and the auger might be more than 2-ft in diameter. Once the picks on the cutting head have mined the coal from the solid, then the broken coal is fed back along the scroll of the auger as it rotates, to the surface, where it is loaded, via the conveyor you can see in the above picture, into trucks. The scrolls are clearer in the picture below:

Auger working in Australia

The friction generated as the scroll rubs against the walls of the hole drilled require that it be pushed with increasing force, as the auger head mines deeper into the seam. This ultimately limits production from a single hole, since there is only a certain amount of force that can be applied through the auger string before it starts to deviate from drilling straight and, as a result, the head may begin to penetrate either the floor or roof rock around the coal, which is not to be desired. Back when I did some analysis of these some decades ago that limit was less than a couple of hundred yards.

However as the top picture shows, the holes can be placed fairly close together, though again care has to be maintained that the auger doesn’t punch through into a previous hole, since it is the hole walls that help get the coal back out.

Augered holes showing the narrow pillars between them (Bundy Auger )

The holes, once augered, can be backfilled with mine waste if that is thought viable.

The difficulty in steering the auger head, and thus the limitation on mining depth that this gives, has lead to the development of different pieces of mining equipment that can do the same job, though hopefully more effectively. One of these is the Highwall Miner (2:44 minute video here – the vertical auger is used for bracing posts, before mining begins)

This is a much more sophisticated machine and replaces the simple auger scroll with a miniature version of a continuous miner, which I have previously described being used underground. The resulting support machinery is significantly larger, although the basic functions, mining the coal, and feeding it back out to a cross-conveyor that then loads into trucks, remains the same.

Overview of Mining Machine (Bucyrus )

The mining head can oscillate up and down as it moves forward into the coal, thus mining seams that are larger in size than the machine itself (something that the auger does not do as well).

Highwall mining cutter head (Bucyrus )

The box conveyor sections provide a more robust platform for pushing the head forward into the coal, and contain two screw conveyor segments that carry the coal itself back to the cross conveyor.

Conveyor/push elements for the miner (the scroll feed conveyor segments can be seen inside the central box) (Bucyrus )

A machine of this type can produce between 40,000 and 120,000 tons of coal a month, depending on the conditions in which it is operating. It needs a crew of 3 or 4 folk, and averages 30 – 40 tons per man-hour. Remember that it must reposition at intervals.

Highwall miners of this type can advance much further into the highwall than augers, and machines are available that can mine in as far as 1,600 ft, achieving production levels (in Appalachia) of 300,000 tons a month. There is a video of the Addcarsystem, which is slightly different from the two described above, here).

The Addcar system, which uses an open conveyor concept to bring the coal out.

As I mentioned in an earlier post, this is the last segment of the coal mining series that I have been posting on Sundays. After a short break for Thanksgiving, I hope to begin a new series of Tech Talks, but more focused on nations from which we get our fuel, rather than on just the wells and mines that it comes from.

Breaking rock in a surface coal mine

There is a growing concern, as fossil fuels are recovered from the ground, that the cost of the energy required to extract and process them is rising, and that a point may be reached where it is no longer energy-cost effective to continue with production. One of the big questions that I have in that debate relates to the use of explosives in extracting the mineral. Mining tends to use significantly more explosive than other industries (and that includes the military). I was reminded of this when, in the course of demilitarizing unused ammunition, we looked for civilian uses for the explosive that we had removed. To begin with the explosives tend to be of different types, so the best of one is not necessarily that much use in the other, but more to the point the quantities that would be generated were trivial, relative to those of industrial need.

Why do we use the explosive in the first place? Well coal seams are generally found under a certain amount of rock and soil, the overburden, and while the soil can be relatively easily removed by scrapers, and similar equipment, the rock must be broken into easily handleable pieces before it can be moved. The soil is removed and stored, so that, after the coal is gone, the land can be restored – there are, in most countries now, strong regulations regarding reclamation, and a significant effort is made to achieve land recovery after mining.

Acorn Bank open cast site, just after reclamation.


I have put this picture up in part, because it is rare for those who debate the issues of mining to show what the mine looks like after reclamation. To achieve this level of restoration, however, the site must be catalogued before mining, and the soil and overburden segregated so that it can be restored, and the conditions re-established, after the mine has passed.

Scraper that could be used to remove and replace soil (Source Caterpillar).

After the soil has been removed, then there are usually several tens of feet of rock that will lie over the coal. Before the coal can be mined this rock must be broken first, before it can be moved. The fracturing is usually done by drilling large (say 8-inch) diameter holes down through the rock, and then filling them about two-thirds full of an explosive. As a general rule you don't want to fill them all the way, since if you did, then when the explosive went off it would just shoot back out of the hole. The large columns of black smoke you see shooting from such blasts in movies are for effect. A skilled blaster will fire the entire round, and if you were to watch a slow-motion movie, the ground level would rise in a pattern, as the individual rows of charges went off, but there would be almost no gas vented from the holes. To confine the charge, the top part of each hole is filled with what is known as stemming, usually some of the rock particles that were removed from the hole during the drilling operation. Generally this fills the top third of the hole, after the explosive has been placed in the hole.

The explosive that is used is no longer gunpowder – though to get back to the EROI question that I started the post with – how do you count the amount of energy used by the explosive? Is it that required to make the powder – gathering the ingredients for gunpowder (as a number of novels will be glad to inform you) is not that energy intensive, and while milling the particles to achieve a better burn requires some effort, it is nowhere near the amount of energy released when the gunpowder is set off.

Modern blasting typically uses a mixture of ammonium nitrate and fuel oil, known as ANFO. (There are a number of videos on Youtube showing ANFO charges going off, you might start here ). A single blasting operation might use between 2 million and 5 million lbs of explosive. In conventional blasting the rock over the coal. (One of the largest disasters in Texas occurred when a ship loaded with ammonium nitrate blew up in 1947). In the simplified sketch below, the rock over the coal is first drilled and broken using the explosive charges, and then it is moved from over the coal to the spoil bank on the other side of the active mining section, so that the underlying coal can be taken out and away.


The typical picture of large, uncontrolled blasts that make the popular press are actually quite far from the truth as to what usually happens in this stage. And the fireball from firing a shot in coal is very unusual. (It could come from igniting any gas in the coal, or from burning some of the very fine coal particles that are formed in firing the shot). Where the ground just heaves a little and then settles back is the sign of a good shot, since all the energy has gone into breaking the rock, so that it is then easier to move.

The explosive is fired in rows, and this is to make the explosive work more efficiently. When you "fire" an explosive you are causing the chemicals in the charge to very rapidly turn to gas. At the same time the blast wave from the start of the reaction will have cracked the rock immediately around the drilled hole. Thus as the explosive turns to gas, that gas can penetrate into the cracks around the hole, causing them to grow out into the solid. The gas follows the cracks, and helps them to grow, while, at the same time "lifting" the rock away from the solid as the gas penetrates. At the same time, firing the explosive in a sequence lowers the overall vibration directed into the ground.

However there is a fair amount of wasted energy in just lifting the rock with the explosive gases, and then allowing it to fall back into place. Thus there is a growing practice to use that energy more effectively by having it not only break the rock, but also to “cast” it into the open space beside it, where it would otherwise be loaded by machine.

To cast the coal the blast holes are angled so that as this gas penetrates under pressure, (video ) it will also throw the rock some distance towards the area of the mine that has previously been worked. This is known as blast-casting and is not always needed. However by firing the rows of charges in sequence (using small delays set into the detonators that are connected together to set-off the individual charges) the rock nearest the edge of the last layer of rock removed is broken first. This removes some of the confinement of the next layer. In this fashion and with only millisecond level delays in each row, the entire rock in a strip overlying the coal can be fragmented and a significant portion of it moved into the open space beside the coal seam, where the last strip of coal had been removed. (Note that in the videos I referenced, the dust is usually from the rock impact, not the blast.)

The need is, therefore to use the explosive energy more efficiently, and I rather suspect that since, until recently this hasn’t been much of a concern, there is still considerable progress to be made in improving the efficiency of the process. For example, by switching to an emulsion explosive the hole is filled more completely than with the granules of ANFO.

But once the rock is broken and displaced it is still very simple to use shovels (albeit the rock is often moved with a dragline, and the coal then removed with the more precise control of an electric shovel).

Changing times and mining shovels

I have been discussing the technologies for oil well drilling and coal mining for quite some time, and am thinking that with that review available and just about complete, it might be time to switch the focus of these Sunday information topics. While I could give a more detailed discussion of the different topics that I have covered in the past, I suspect that this would be of decreasing interest to most and so I thought to change the subject matter. What I am planning on doing is to shift focus, and start to write about the different countries that have oil reserves (or had) and what we know about them. The idea, in much the same way as with the technical talks, will be to provide an informative set of background notes, so that, for example, if the topic of the Yamal gas fields comes up, you would know a little about where they are (a peninsula in Russia), and how much gas (maybe 30 trillion cubic meters) is there, as well as how soon they will be developed (not this year).

That is the plan for the future, but before moving there, I would like to revisit coal mining to wrap up the discussion with a small number of posts about surface mining. The first use of coal came from finding outcrops where the coal could easily be picked out of the seam, or where, in the North of England, the sea would do the mining and wash the coal up on the beach, where it could be collected.

Even today there are still areas around the world where there is coal very close to the surface, which can easily be uncovered and removed. Some years ago a farmer came to my office to discuss what he needed to do to mine a layer of coal he had found in his farm (in central Missouri) just below the surface. All that was needed, he thought, was a blade for his tractor to push the soil away, and then a loader to scoop up the coal and take it to market. I had to explain that those simple times had passed, and that there was a considerable body of regulation that he had to comply with before he could do that. And also he had to restore the land to the way it was, after he was done. The profit he had anticipated, faded as he went through some of the costs that he would have to face.

However, and this was part of my first talk at the ASPO-USA meeting in Washington earlier in the month) the technology for mining that coal on the surface remains at about the level of simplicity that he anticipated. Coal supplies, whether in Africa, Asia, Europe (though to a more limited extent) and America are still available that can be extracted with nothing more than a shovel. Now, having said that, the size of the shovel has undergone a significant change since the time that I manually wielded one, to move 15 yards of coal from the face to the conveyor (as I recounted in the video). And as an aside, the shape of mining shovels differs a bit from those usually seen at the surface.

Mining shovels and a pick (with the Engineer at an early age) at the Beamish Museum in the UK

The heart-shape allowed you to get under the coal and pry in a way that the square and molded shovels more common on the surface did not, though most of them came without the cross piece at the top end. Today’s shovels are electrically powered and have bucket sizes that can pick up between 7 and 36 cubic yards of material in a single scoop. They routinely fill 400-ton haul trucks in two to three scoops in operations at the tar sands, and in mines around the world.

Modern shovel loading a haul truck (P&H )

Shovel schematic to give an idea of size – the bucket can hold 170 tons, some 60 cu yds. of material.

With that relatively large-volume, simple approach it is difficult to envisage something that can be simpler or more economic, in the mining of minerals. And as long as this technology can be applied, the need for more advanced mining means does not exist. (And this was part of the talk that I gave at the ASPO meeting).

Mining shovels such as that shown above, which are generally powered by electricity – you can see the cable if you look closely – are used for the more precise removal of material that is needed when mining the valuable material, whether tar sand, coal or a metal ore. To remove the rock and dirt that lie on top of this valuable material, where there is not quite the same need for precision, it is quite common to use a machine known as a dragline. (There is a video of one working here ) Here the bucket is not rigidly connected to the boom as with the shovel shown above, but is instead connected through ropes. This, historically, made the bucket more difficult to control. However the arrival of the computer to both monitor and control rope position, now makes it much easier to "spot" and unload the bucket than in the past.

Working dimensions for a dragline (P&H )

A bucket might move 150 cu. yds at one time with an operating radius of some 350 ft, digging down to a depth of 180 ft and dropping the spoil in a height of up to 160 ft. That doesn't mean that they don't get stuck, or collapse on occasion.

The size of the shovels thus make it possible to mine very large quantities of material at one time, and make the economics of large-scale mining practical. The critical dimension is typically the relative depth of the soil and rock over the coal seam, in relation to the thickness of the coal. It is known as the stripping ratio, so that a coal seam that is 5 ft thick, for example, at a depth of 100 ft, would have a stripping ratio of 20. Depending on the costs of mining, and the quality of the coal, that may or may not be worth going after at this time.

There are other machines that are used in different parts of the world, the largest being the bucketwheel excavator, which usually only get into the news when they are on the move.



These machines work extremely well in a controlled environment, but are extremely expensive, and when they are down, so is production. (One of the main reasons that they are no longer used in mining tar sand in Canada). Mind it is not wise to get one irritated, since they have been know to eat uppity other equipment.



That aside, the nature of the rock and other material overlying the seam will also influence how that material (which is called overburden) is removed, and I’ll discuss that process in more detail next time.

Coal reserve considerations

I am still travelling but have found a book that will help me with the discussion of historic mining that is the usual current fare on Sundays (an autobiography from 1910 that is illustrated). Wanting to include some of this in the next post, I am going to step a little away from the topic this weekend and instead post again an earlier comment on coal reserves. It is also a topic that I will expand on in the future, but here is some background.

So you want to start a coal mine – where to begin? The first thing that you need is some coal, and in most cases today the coal seams that are exposed at the surface are known and owned by somebody else. So you will need to drill some exploratory boreholes down into the earth to find some suitable seams. For the sake of example I am going to use a project in South Africa. Other than having found it on the Web I know nothing about the coal, or the company so please don’t think of this as any endorsement or otherwise of the property.

Quite often new developments are based on where folk have found coal before. If there is a mine then, with deposits such as coal there may well be more coal, out beyond the boundaries of that original property. This is because of the way that coal was formed as vegetation spread over a large swampy area that ran for many miles. Unlike oil, once the vegetation was put in place, and slowly buried, it changed composition in place, and so coal seams may well run for many miles, although they may get different names in different places. Thus, for example the Pittsburgh seam extends over perhaps 8,000 sq. miles, while the Herrin seam in Southern Illinois has about the same range (And this does not include cannel coal, some of which is found in Kentucky, which was moved from the original site by the actions of water).

Because these quasi-horizontal seams were formed over such a large area, and because the stratigraphy (order of the rocks as you take a core down through them) will remain relatively constant, in many cases, it is not necessary to make the exploration holes that close together. Thus in the example above, the boreholes were placed some 4 km apart and the volume of coal inferred from the thickness of the beds found, and assuming that they ran continuously from borehole to borehole.


This is referred to as:

Reconnaissance Resource: is quantified as a minimum one cored borehole with coal quality data per 400 ha (approximately 2km spacing) for multiple seam deposit types, while for thick interbedded seam deposit types a reconnaissance coal deposit is quantified by a minimum one cored borehole with coal quality data per 1,600 ha (approximately 4km spacing).

In this case the property was drilled over an area that required 402 boreholes, and it identified 5 seams of coal that could be produced. However it brings me to the point of this post, which is how much of the coal can be counted and as what type of reserve. This is quite an important distinction, since in the debate that I have had with others in the past, including David Rutledge, the confusions of what has been counted and how it is defined is often overlooked. This is how the information was reported:


So what are the different definitions of the reserves? Isn’t this coal all a reserve, well no, the coal seam is divided into different quality of reserve, depending on how far it is from one of the proving wells. Let’s consider the official definitions:

Points of Observation This is the point where the coal presence has been physically seen either at an outcrop or in the recovered core from a borehole.

Inferred coal reserves are those that can be extrapolated from a Point of Observation but to a distance of no more than 2 km.

Indicated coal reserves are those that can be extrapolated from a Point of Observation, but to a distance of no more than 1 km.

Measured coal reserves are those that can be extrapolated from a Point of Observation, but to a distance of more than 500 m.

So that, when we are assessing the amount of coal that we consider available at a site, if we are conservative, we are only reporting the measured coal reserves as that within 500 m of each of the boreholes, even though the consistency of the seam has seemingly been proven over many kilometers. It is a very conservative system, note that only 17% of the likely coal is considered a measured resource. To make this post more comprehensive, and to include some definitions that I will come back to in later posts, let me now go on to include the ranges of economically recoverable coal (in terms of thickness and depth) that are currently accepted.

In terms of international definition of resource the US Geological Survey has set up some definitions, that have also been adopted by the Federal Government, in their Code of Federal Regulations, which were just revised. The new regulations are a little more inclusive than the older ones (at the USGS site).

(5) Coal reserve base shall be determined using existing published or unpublished information, or any combination thereof, and means the estimated tons of Federal coal in place contained in beds of:
(i) Metallurgical or metallurgical-blend coal 12 inches or more thick; anthracite, semi-anthracite, bituminous, and sub-bituminous coal 28 inches or more thick; and lignite 60 inches or more thick to a depth of 500 feet below the lowest surface elevation on the Federal lease.
(ii) Metallurgical and metallurgical-blend coal 24 inches or more thick; anthracite, semi-anthracite, bituminous and sub-bituminous coal 48 inches or more thick; and lignite 84 inches or more thick occurring from 500 to 3,000 feet below the lowest surface elevation on the Federal lease.
(iii) Any thinner bed of metallurgical, anthracite, semi-anthracite, bituminous, and sub-bituminous coal and lignite at any horizon above 3,000 feet below the lowest surface elevation on the Federal lease, which is currently being mined or for which there is evidence that such coal bed could be mined commercially at this time.
(iv) Any coal at a depth greater than 3,000 feet where mining actually is to occur.
(6) Commercial quantities means 1 percent of the recoverable coal reserves or LMU recoverable coal reserves. . . . .
(19) Logical mining unit (LMU) means an area of land in which the recoverable coal reserves can be developed in an efficient, economical, and orderly manner as a unit with due regard to conservation of recoverable coal reserves and other resources. An LMU may consist of one or more Federal leases and may include intervening or adjacent lands in which the United States does not own the coal. All lands in an LMU shall be under the effective control of a single operator/lessee, be able to be developed and operated as a single operation, and be contiguous.
(20) Logical mining unit (LMU) recoverable coal reserves means the sum of estimated Federal and non-Federal recoverable coal reserves in the LMU.
(21) Maximum economic recovery (MER) means that, based on standard industry operating practices, all profitable portions of a leased Federal coal deposit must be mined. At the times of MER determinations, consideration will be given to: existing proven technology; commercially available and economically feasible equipment; coal quality, quantity, and marketability; safety, exploration, operating, processing, and transportation costs; and compliance with applicable laws and regulations. The requirement of MER does not restrict the authority of the authorized officer to ensure the conservation of the recoverable coal reserves and other resources and to prevent the wasting of coal. . . . . .
(23) Minable reserve base means that portion of the coal reserve base which is commercially minable and includes all coal that will be left, such as in pillars, fenders, or property barriers. Other areas where mining is not permissible (including, but not limited to, areas classified as unsuitable for coal mining operations) shall be excluded from the minable reserve base.
(24) Mine means an underground or surface excavation or series of excavations and the surface or underground support facilities that contribute directly or indirectly to mining, production, preparation, and handling of coal.

It is important to note item 23, since no underground method of mining will remove all the coal from a seam, but will leave significant quantities of the coal in place as pillars to hold the roof up, and thus protect the miners and their equipment from the roof falling in. (In the African example the percentage of coal that might be recovered is about 50% of the reserve volume).

I should be back with some quotes from the book, and discussion of the considerable progress that has been made in mining since the early days, starting back next week

Looking back at 2009

This has been an interesting year to look back on. The change in the Administration and the difference in outlook that they bring to many of the concerns that I write about have altered the way in which the future will evolve. That evolution is still continuing, but there can be no doubt that the key committees in the Congress are now led by folk that do not look particularly kindly on the historic producers of fossil fuels. Yet the path forward for the alternatives, power from renewable energy, is not necessarily going to be that certain either. That was brought home just recently with the move by Senator Feinstein to protect portions of the Mohave Desert from future construction. This limits some of the areas in which solar farms had been planned, though clearing some of the legislative hurdles for others. But the legislation (which would apparently affect some 19 applications) is a sign of the debates to come, as the land needed for renewable energy is discovered to have other potential uses or benefits, that will make the search for available space that much more difficult.

And it is not just in California, there are debates in other states, including Wyoming.

As a result, 23 percent of Wyoming's winds that are class 4 or higher -- and about half or more of developable class 6 and 7 winds -- are in core areas. And in July, the state put those winds off-limits by essentially banning big wind farms in core areas. Many in the wind industry see it as devastating. The Interwest Energy Alliance -- a trade group -- said the ban could have "a deleterious effect on renewable energy development" across the West, and that it could kill the development of 10,000 megawatts of wind in Wyoming.

Though there are some sites that appear less controversial than others.

He takes me on a tour in a big white truck, making me wear a hardhat because turbine blades can throw chunks of ice. From the top of a hill, as a bunch of antelope amble nearby, Anderson points southward through the forest of windmills to a huge plume of steam that marks the Dave Johnston power plant. Then he motions to the earth all around where we stand. The wind farm sits on the reclaimed remnants of an old, giant coal mine; all this land was once torn up, gouged by draglines, its carboniferous bounty burned in the plant down below. "We wanted to take a coal mine," says Anderson. "And make it useful."

Yet as these debates continue, there seems to be little recognition of the needs that the future will bring, that are not being prepared for. Nor is there much recognition of the problems in getting power from where wind can generate electricity to the places where it is needed (particularly those states that have mandated high levels of renewable energy into their mix in the nearer future). For while wind turbines can generate money for the landowner, there is much less for the farmer who lets a transmission line across his land, who only gets a single payment.

The cap-and-trade legislation may not, in the end, make it through the Senate, and thus may die for this Congress, but it has made it difficult to justify investment in coal-fired power stations, when the rules that will govern their use are not clear. And while the EPA has adjudged carbon dioxide to be a pollutant , it has yet to write the rules under which plants that produce carbon dioxide will operate. (Remembering of course that each of us is also a generator). As a consequence some 100 or more power plants have been put on hold until the situation becomes clearer. But given the challenges that will likely come to the legislation (there is some question, for example as to whether they can limit the application of legislation to plants that produce more than 25,000 tons for example), the delays in planning for construction of future power plants are likely to continue, and perhaps grow worse.

The new Administration does not see much in the short-term that will cause energy supply, whether crude oil or electricity, to be a problem. The Secretary of Energy, through the research and funding that they have produced over the past year, is looking at more distant options for generating power than meeting any proximate needs. Unfortunately, coming from California, where it was easy to mandate a reduction in coal-burning in the state when the power could be generated alternately from coal-burning plants in Utah, does not work as well when the entire country becomes subject to the legislation, and such an alternative no longer exists.

Among other news of the past year that make my list of major stories I would count two more. They don’t seem to have caught as much attention of folks such as Robert Rapier who has a different list, but one of them is listed in the page that Platts had for their survey. The first (and that listed by Platts) is the continued collapse of the oil production in Mexico. While this has significant impact to the United States (which is now going to have to find alternate sources for the Mexican oil it was importing from fields that are now running dry, particularly Cantarell) the impact on Mexico’s deficit has been to drop the deficit off a cliff. For the USA it is going to be increasingly difficult to find that alternate supplier. China has increased their purchases from Saudi Arabia by more than 12% this year (to 800,000bd) and has signed agreements to take this over 1 mbd next year. With non-OPEC production having peaked, it is only the surplus production in the OPEC countries that keeps the world in balance, and the size of that “cushion” is something that we debate. (I am less optimistic than some others).

The other event was the opening of the gas pipeline from Turkmenistan to China. Again it is feeding fuels that were, at one stage, available to the West, to a new customer, itself growing in demand, and with a considerable scope to increase market purchases in the years to come. The glut in natural gas that we currently see will not I suspect, last as long as it is currently projected, and that will open a different can of worms.

But all these stories from the past aside, I do wish you all a Successful and Prosperous Year, that brings you Happiness and Joy, and not too many snow storms.

T9. Surface Mining of Coal

Coal, as most of you know, is found as a layer in the ground. It can be found at a variety of depths and in a wide range of thicknesses. Some of the thickest coal in the United States, for example, lies in Wyoming, where the Black Thunder Mine alone produces the equivalent of 750,000 bd of oil every day. The first mine to produce over a billion tons of coal, it is now actually second in size to the nearby North Antelope Rochelle Mine, which can fill up to 5,900 railcars a day, and ship the coal all around the United States to provide the raw fuel for about 10% of the U.S. demand for electricity. Here, where the coal seams are more than 100 ft. thick, Arch Coal which owns the Black Thunder has just agreed to acquire the adjacent Jacobs Ranch Mine and when the two are combined as part of an enlarged Black Thunder, it will rise to being the largest mine again.

The coal is not always found as a single layer, or seam, in fact in most mines there are a number of different layers. At Jacobs Ranch, for example, the coal is found in three mined seams, collectively known as Wyodak. The upper Wyodak is 11 ft thick on average, the Middle Wyodak is 42 ft thick and the Lower Wyodak is 5 ft thick. However you can get some idea of the amount of coal available from this map, produced by the USGS.

Coal Thicknesses in the Powder River Basin (Source USGS)


When the coal lies near the surface, it is this thickness of the coal, relative to the thickness of the rock that lies between the coal and the ground surface, that decides whether it is going to be economic to mine at all, and if it is economic whether to remove the rock from over the coal to get it out (hence the strip of strip mining) or whether the coal is better mined from underground. (The name also comes because you work on one strip of land at a time, as you remove the coal sequentially across the property).

This ratio between the thickness of the coal, and that of the overlying rock is known as the stripping ratio, and the economic limit varies with the quality of the coal, and other operational costs. For example a coal seam that was 100 ft underground, and some 6 ft thick, would have a stripping ratio of around 16.7, and there was a time that that would have been about the economic limit. But as the price of coal increases, and earth-moving equipment gets more efficient, that ratio changes.

So what is involved in strip mining (apart from all the permits, surveys etc that make the whole process of installing a mine take a number of years)? The first step is to remove the top soil, and that which lies under it, as either one or two separate lifts. Generally these are scrapped from the surface using specially designed equipment that can remove the more fertile, and underlying layers separately and move them to areas where they can be stored, until the mine has removed the coal, and replaced the overlying rock. At that time the soil is replaced in the same order as it was found. Because a mine is a continuous operation, after the first set of soil is removed and the coal in that segment is also taken out, so the mine will be replacing rock and soil in one part of the mine, as it is removing it in another, so that the storage over time only holds true for a small portion of the overlying material.

Scraper that could be used to remove and replace soil (Source Caterpillar).

After the soil has been removed, then there are usually several tens of feet of rock that will lie over the coal. Before the coal can be mined this rock must be broken first, before it can be moved. The fracturing is usually done by drilling large (say 8-inch) diameter holes down through the rock, and then filling them about two-thirds full of an explosive. As a general rule you don't want to fill them all the way, since if you did, then when the explosive went off it would just shoot back out of the hole. The large columns of black smoke you see shooting from such blasts in movies are for effect. A skilled blaster will fire the entire round, and if you were to watch a slow-motion movie, the ground level would rise in a pattern, as the individual rows of charges went off, but there would be almost no gas vented from the holes. To confine the charge, the top part of each hole is filled with what is known as stemming, usually some of the rock particles that were removed from the hole during the drilling operation.

The typical picture of large, uncontrolled blasts that make the popular press are actually quite far from the truth as to what usually happens in this stage. And the fireball from firing a shot in coal is very unusual. (It could come from igniting any gas in the coal, or from burning some of the very fine coal particles that are formed in firing the shot). Where the ground just heaves a little and then settles back is the sign of a good shot, since all the energy has gone into breaking the rock, so that it is then easier to move.

The explosive is fired in rows, and this is to make the explosive work more efficiently. When you "fire" an explosive you are causing the chemicals in the charge to very rapidly turn to gas. At the same time the blast wave from the start of the reaction will have cracked the rock immediately around the drilled hole. Thus as the explosive turns to gas, that gas can penetrate into the cracks around the hole, causing them to grow out into the solid. The gas follows the cracks, and helps them to grow, while, at the same time "lifting" the rock away from the solid as the gas penetrates. At the same time, firing the explosive in a sequence lowers the overall vibration directed into the ground.

If the mine so chooses it may angle the holes that were drilled so that as this gas penetrates under pressure, it will also throw the rock some distance towards the area of the mine that has previously been worked. This is known as blast-casting and is not always needed. However by firing the rows of charges in sequence (using small delays set into the detonators that are connected together to set-off the individual charges) the rock nearest the edge of the last layer of rock removed is broken first. This removes some of the confinement of the next layer. In this fashion and with only millisecond level delays in each row, the entire rock in a strip overlying the coal can be fragmented. (Note that in the video I referenced, the dust is from the rock impact, not the blast.

After the rock is broken in this way, then a dragline bucket will be used to pick up the rock from over the coal, and move it into the space left when the last row of coal was removed. These draglines are the largest of the pieces of mining equipment and drag the bucket up over the rock pile, filling it, so that it can then be moved over.

With a dragline, the machine usually sits on top of the rock, and will lower a bucket that is dragged up the free surface of the blasted rock, until it is full. The dragline then swings its boom, until it is over the strip of land where the last pass of the process had removed the coal, and dumps the rock into that space. By steadily working across the face and back down the area that was blasted, all the coal seam is exposed, and is ready for removal. At the same time, the previous strip of ground is filled back up to about the starting level of the ground.

After the bulk of the rock has been moved off the coal, then the final clearing off is done with smaller shovels that expose the coal. Depending on the coal thickness and strength it can also then either be blasted to break it into smaller pieces, or just shovel loaded into trucks. Typically a shovel can pick up around 100 tons of coal in a single stroke, and can take 3 loads to fill one of the coal trucks, that then carry the coal out of the mine to the surface plant. As with the excavator, the shovel scoops up the broken rock, swings around and dumps it in the cut behind the machine. Note that it is more economic for the rock to be moved only once, and so the width of the strip will be governed by the size of the machine that is used. And a shovel will often only remove rock layers of around 15 - 45 ft high, depending on machine size.

After the coal has been exposed, then, depending on the strength and thickness, it can either be removed without any further process, or it may require some additional explosive fracturing to make it easier to pick up. It depends on the coal. In either case, when it is loose enough, the coal can be picked up by a smaller shovel, and this will usually load the coal into trucks, that will carry it away to the plant where it will be cleaned. At which point you may say, wait a minute, you have just dug a hole 100 ft deep, and have trucks being loaded with coal, but how do they get out? Good point! Generally during the creation of the spoil banks behind the working area, bulldozers will create a ramp that slopes down, from the surface, to the coal level, and this will be kept moving forward as the strip of ground that is being mined moves across the property.

The rock than has been placed into the space where the last strip of coal was removed is initially laid out in ridges, since it was dropped in place by the dragline, which works from fixed positions, and this is generally the view that the general public is presented with, since it leaves the impression of desolation that many of those opposed to mining wish to convey. In fact the operation is quite a bit from being over.

First the ground is leveled, and then the soil is restored, and by law the conditions of this restoration are quite rigorous, so that it follows to as great a degree as possible, to contours that were originally in place. Where necessary additional fertilizer is added to the ground, to re-establish crops and farming conditions. Cattle can then be reintroduced, and wild life return.

This is part of a series of technical posts that I am making to try and explain some of the background to mining of coal, and drilling for oil and natural gas, so that in the debates on some of the issues those discussing the issues have a better understanding of what is going on. A version of this was posted when I was doing the same sort of thing after helping found The Oil Drum, and can be found in the post that I made there on January 29,2006. As with the posts there, this has been simplified to make it fit, so if anyone wants to correct or refine these posts please comment.

T7. On Augering, coal reserves and EROI.

Today I thought I would digress a little from the more methodical passage through history that I was taking in regard to coal mining to talk a little about coal reserves, coal resources and technology. It is a little focused towards some of the work that we developed some years ago, and so I give you that warning up front. I am going to try and keep it simple, and so those who know about what I write should bear that in mind.

When you find a seam of coal, if it is near the surface then the soil and rock can be removed from over the coal, the coal removed, and then the rock and soil are replaced. This is surface mining and I will cover that in a specific post later. At the same time there is a point where the coal is too deep for that process to be economical, and so underground mining takes place. There are two main methods of mining coal, room and pillar mining and longwall mining, and I’ll talk about them in separate posts also. Today however I want to cover that point where the seam has just become too deep to make it profitable to take any more of the cover from the coal. One method of mining at this point has been to send a small mining machine known as an auger in to mine out the coal, that is exposed at the edge of the mine.

The auger works in the same way as a wood bit that chews into a piece of wood, when you want to drill a large hole through it. There is a cutting head on the front of the machine that cuts into the coal, and then behind the head is a scroll feed that carries the coal out of the hole, to a point where it can be collected and taken away.

Auger cutting head (Cutting head. (Source BryDet Augers Note the head is shown without the picks that would be placed in the sockets on the face of the two perimeters.

Auger scroll

There is a small video of the process here

Typically the auger holes are placed relatively close together, and they are drilled on the order of 100 ft deep.

Auger holes (Source Lukhele )

One of the major reasons for the limitation that the auger will drill into the coal is related to the way in which the auger works. In just the same way as when you drill a hole with a wood auger, you have to push hard to get the bit to cut into the coal. But the push has to be transmitted down the flights of the spiral sections of the auger assembly. These are not very strong, and they rub against the walls of the hole that has been drilled, so that as the drill goes further into the coal, more of the push is used up in the rubbing friction between the scrolls and the wall of the hole. Also, if you push too hard after the auger is in the coal some distance then the scroll shafts can slightly buckle and this can thrust the auger head out of alignment so that it drills into either the roof or the floor.

The auger is thus a tool with a relatively limited role, though in that role it can be quite effective. Now here is the change that we made. If you take two or three small (0.04 inch diameter) nozzles and attach them to the front of the auger head, so that two cut on the outer edge of the hole, and one is on the inner diameter, then the jets of water that come out of the nozzles will cut into the coal. The jets should operate at around 7 – 10,000 psi, depending on what other rock is found to be in the coal. Typically these jets will cut into the coal about 6 – 9 inches ahead of the auger body as the head rotates. This breaks the central core of the coal free from the confinement of the surrounding coal, and when the head contacts the coal, it will break outwards in tension, in handle-able sized pieces. The push now required to move the machine into the coal is much lower (we had a student with one arm in a cast use a come-along to pull a 2-ft diameter machine into the face). Because the coal breaks so easily, and the force is so much lower, the scroll sections do not have to be so large, and without the need for the high thrust a smaller scroll, that does not contact the walls all the way around the hole, can be used. With this combination, since there is now no frictional limitation to the push, and the force required to pull the auger head into the coal is so much lower, the range of the machine can be extended from under a hundred feet, to several hundred feet.

The small blocks across the auger face show where the nozzles are mounted. (The sawdust is because we cut plywood to see the cutting pattern).

However there is an additional advantage to this change in design, and that comes about because the coal is now being cut with a water stream instead of with a mechanical tool. The pressure and cutting pattern of the stream can be adjusted so that the jet cannot continuously cut into the rock that overlies and underlies the coal. When the cutting pattern is controlled in that way, and with the lowered push being applied to move the auger head forward, the head cannot cut into the rock, but is held to follow the coal seam. The machine becomes inherently self-steering, and thus can drill further into the coal than its predecessor.

I have described this machine (which we only tested in the lab before the energy crisis of the 80’s went away) to make a relatively simple point. With very little change in the design of the auger – using existing pumps and other parts, we built a machine that could extend the range of mining from the highwall of the surface mine into coal that would otherwise be uneconomic to mine, for a distance of probably more than half-a-mile. (That is based on other research I’ll talk about another day). The innovation is but one of many that could be made to transition equipment being used today to allow it to mine coal that is only counted today as a resource and which people are quite quick to discount as being un-minable.

The economic need for coal is going to be such, however, remembering that all the solar and wind energy being currently used in the country adds up to the power output of only one medium sized coal mine, that we will be mining for a long time. As we do, and the easily recoverable coal goes, then in exactly the same way as innovation has made more difficult gas and oil resources into reserves, so we will see the same change occur with coal resources. And of those we have enough to see us through until new sources of power come along in the right scale and from that they will replace coal.

Jets on the auger face cutting into artificial coal

(Please note I have originally used photos and sketches from the internet for this piece, as I get more skilled in modeling I will replace them with my own. I will also more jet pictures later).