Waterjetting 22a - Mining horizontal coal

Over the last few posts I have discussed some of the problems that arise in dealing with the use of waterjets in mining coal, when the material mined has to be collected and transported away from the face where the coal is extracted. I thought I would follow on that thread in a few more posts, ending up, hopefully, where I began back in the process of removing thin layers of material (such as rust) from flat surfaces.

But to get there I am first going to go back to coal mining. One of the problems with adapting what we might call conventional hydraulic mining to coal is that many of the coal seams around the world are relatively flat – it is, after all, the way in which the vegetation that became coal was laid down. Thus the gravity that can be used in a steeply dipping seam as a way of carrying away the coal and the water together, is not initially that helpful.

There are several different ways that have been suggested over the years to solve the problem. Initially these were based on existing mining machines, and methods for mining the coal, but with the teeth of a conventional machine replaced with high-pressure waterjets. One such, as I have written earlier was the MS&T Hydrominer, where the cutting teeth along the edge of a coal plow were replaced with oscillating dual-orifice waterjets to cut a kerf around the coal being mined.

Figure 1. Artist’s impression of the initial Hydrominer, with jets cutting a slot one foot deep ahead of the wedge shape of the plow.

The water used was less than that conventionally used on a mining machine to suppress the dust generated as coal is mined from the solid, and the coal loads onto the armored face conveyor on which it rides down the face.

That particular design was based on an earlier mechanical machine, the Meco-Moore, which I had previously seen working on a longwall in the United Kingdom.

Figure 2. Meco-Moore mining machine set up to mine coal. The cutter jibs cut slots and the coal then collapses onto the transverse conveyor.

However this concept required a considerable investment in the supporting longwall equipment both to hold up the roof and to remove the coal. An alternative approach was to continue to conventional roof-and-pillar mining which is the most popular method of underground coal mining in the United States, but again replacing the cutting teeth with waterjets. The first of these was conceived by IIT Research Institute in Chicago, under Dr. Madan Singh.

Figure 3. A high-pressure waterjet continuous miner.

Unfortunately in this configuration the system did not work well. The jet pressures used were too high, and in consequence the volumes of the jets too low to achieve a deep penetration into the coal.

When the jets were replaced with a combination similar to that of the Hydrominer, and in a device we called RAPIERS, a slightly better performance was achieved, but the demand for innovation had, by that time passed for a spell, even though this particular machine was developed with considerable technical input and financial assistance from the Jet Propulsion Laboratory in Pasadena.

Figure 4. Progression of the RAPIERS machine in room-and-pillar mining.

Both of these machines required that a second set of machines sit behind the excavator and carry away the coal that had been mined, again at significant cost, and they also required machines to support the roof.

There is a different type of machine that is often used at the edge of the productive limit of surface mining. As seams near the surface get deeper so the cost of removing the overlying material becomes too expensive to justify continued mining. At that point companies may bring in an auger which can drill long holes into the coal, and remove the material as with conventional smaller augers that might be used for drilling in dirt (or even drilling holes in wood).

Figure 5. Conventional auger mining (Rosamine )

Because the auger drills a hole to the size of the following scroll, it is relatively easy to carry the coal back out of the horizontal hole, which might exceed 300 ft in depth. But there is a problem with the machine, in that the cutting force to push the auger teeth into the coal at the face of the machine has to be carried through the entire string of augers.

Because of the string of segments this becomes more difficult to control with longer depths, and in addition there is a friction loss due to the continual rubbing of the scrolls against the floor and sides of the hole. Together these act to limit the machine range, since there is little to steer the machine other than the direction of the hole, as it deepens.

Figure 6. Picks on the face of the auger, with early jets mounted in the center of the head to cut a central hole.

If, however, the picks on the face of the auger are largely replaced with waterjet nozzles, particularly at the outer edge of the auger, and with the flow directed there, rather than, as shown in Figure 6, towards the center, then an outer free face – up to a foot deep, can be cut ahead of the cutting head. With larger auger heads the nozzles can be placed across the face, to break the rib of coal, should it start to get too large – especially since the coal needs to be fragmented somewhat to feed down the auger.

Figure 7. Waterjets across the face of an auger (courtesy W.A. Summers)

The reduction in the amount of force that this allows on moving the auger into the coal can be illustrated by example. In developing a version of the machine we built an artificial coal face, made up of coal pieces and cement. It is a little more resistive than conventional coal, however the student, Chris Cannon, had little difficulty pulling the machine into the face with a come-along, even though he only had one uninjured arm at the time of the test.

Figure 9. Chris pulling the 2-ft diameter auger into the artificial coal seam.

By confining the coal and water it was possible to recover both, so that the water could, if needed be recycled.

I’ll continue the thread next post.

ASPO Conference- last day

One of the helpful aspects of the ASPO-USA organization is that they post the videos and presentations that were given at their conferences. Obviously these need to be tweaked after being recorded, and so do not go up immediately but, for example, they have just posted the video of the Jeff Rubin talk on their site. I am going to conclude my summary of the conference itself with this report. I was not able to stay for the final afternoon, and so Gail has kindly furnished a summary that I will add to cover that section of the Conference. As usual I will then give a short summary of what I felt were the highlights, but which is more opinion that content – the goal of these initial posts.

Turning therefore to the Saturday morning meetings, these began with a slight change, since Terry Backer the scheduled speaker was, unfortunately, ill. Paul, one of his advisors, spoke on his behalf, noting that Connecticut – where they are from – has no indigenous coal, oil or natural gas. They had a plan for moving forward that had received support for a significant effort to insulate houses, but unfortunately even though it would have provided a number of jobs, it fell victim to the recession. They are now looking to see the potential for micro-hydro in the state.

The first session was chaired by Ted Patzek and was focused on the Gulf oil spill and the likely consequences.
I led off with a chronological review of the events that occurred through the course of the spill until the time that the well was declared dead. This covered the initial completion of the well, the kick and explosion on the rig, and the sinking of the well. I then went through the stages of the capture of oil, and the capping of the well. This also covered the assumptions that led to the location of the relief well and what was found when it hit the well. Very largely it was a summary of the posts that were written at the time, with the aid of some photos that others had posted.

After my talk, Art Berman spoke of some of the errors that culminated in the failure of the well and the consequent disaster. He began by pointing out that the energy resource of the Gulf is much larger than that of shale gas, and in the deep water is likely the last great hope of American production. From that point of view the shut down (which has nominally now been lifted. He described the number of wells in the gulf and pointed out that the Macondo well was not an exception.

In reviewing the causes of the disaster he started with the problems that arose when the initial float collar, used in the injection of the cement to hold the production casing in place, did not properly function. To get to work the crew used a pulse of high pressure down the well, and then only cemented part of the lowest section, rather than injecting sufficient cement to fill the annulus up to the level of the previous casing. Because there was a considerable washout of the reservoir, the crew then chose to use a foam cement. Tests have shown that this takes some 24 – 48 hours for this cement to set, and yet they began displacing the mud holding the oil and gas within the reservoir after only 16 hours.

Because the well was drilled with an oil-based mud (rather than the more conventional water-based) natural gas will not come out of suspension at the same depth, but rather remained in suspension in the oil until very close to the surface. At that point it would expand, so that one cu ft of gas at depth would occupy some 800 cu ft and so the onset of disaster came very suddenly.

A problem that continues to face drilling and production companies has to do with experience. There is not a large cadre of well-qualified managers, since the highly cyclic nature of the industry means that many of those who would occupy such ranks were let go in the bad years, and are now otherwise employed. Thus the onus of management is falling to people that do not have the necessary experience and knowledge.

Rick Munroe brought the debate into the larger picture of the Peak fuel debate. Ho pointed out the considerable difference between the military view of the coming crisis, in contrast with the more complacent civilian government point of view. The Energy Bulletin lists over 40 papers from military groups that have highlighted the coming problems of fuel availability. In contrast it was only in 2008 that the IEA began to express similar concerns. Yet, as a paper in 2009 from the war college noted, while these strategic shocks are predictable, they are either not prepared for, or inadequately addressed. The plans that do exist are over 30 years old, dating from the last time we had such a event.

On July 25th the Energy Bulletin carried a review of the Peak Oil situation by the German military. The response to the crisis, because of this lack of preparation, will not be stable, but chaotic. This instability will increase with time as economies shrink. The result will be unprecedented in its severity.

He pointed out that, by and large, these reviews are not individual opinions, but rather the consensus of qualified analysts and it defines a comprehensive domestic external threat to the point that peak oil can be seen as a weapon of mass destruction. In earlier exercises it was projected that if 4% of the world supply was removed from the market then prices would triple.

Yet with all this information available he was unable to find any significant interest in the topic either in Canada or the United States. There is no planning for the impact of oil shortage on the agricultural production of either country, and the GAO noted that planning on the topic ceased about 20 years ago. It is only, apparently, in the UK that plans for a Liquid Fuel Emergency exist. And yet a fuel crisis will, in very short time, transform into also being a food crisis. The problem is, in part, that while the response of many in government is to ration by price, but to give farmers priority, most operate on the margin and a trebling of fuel prices would put them out of business. It is a complex problem, and thus no-one wishes to address it.

In introducing the second session of the morning Ron Swenson said that one of the goals of ASPO-USA was to bring people together in such a way as to leave a world worth inheriting. The session was on the Laws of Energy, Technology and Scale.

Tad Paczek talked of scale, and that the critical metric is the rate of production. He sees peak oil in 2 – 3 years; peak coal soon and peak NG in 20 – 30 years. But while there is still lots of fuel underground it is the rate of production, and the scale of production that are constrained and that drive us into these peaks. If, for example, oil lies in a piggy bank, and we can’t break down the walls, then the rate at which we get money back out depends on the size of the slot in the top. But we should also remember that, on average, we leave 2/3 of the oil in the ground and only recover 1/3.

We use 100 times the amount of energy we have to eat to survive. The world eats roughly 1 Exajoule (EXJ) and we turn fuels into 39 ExJ of energy. One of the more promising techniques for enhanced oil recovery (EOR) is to inject CO2 into the field. This is already in use in the United States and might be able to increase production by 10%, but this comes at the end of field life. In total it might be possible to get up to 2.5 mbd of EOR oil (remember that Ghawar is producing in the 4-5 mbd range), but to get to that level will require lots of money and engineering expertise – and he is not sure we have enough of the latter. He anticipates that Canada may be able to grow tar sand production to 3 mbd by 2020.

In discussing future energy projections he said that many companies will list the prospects that they are considering drilling into – but for budget and other reasons will only actually work a fraction of those lists. Thus those who rely on the projections paint an unrealistic view of what the future will bring. We are, therefore, not in as good shape as most predict.

Ken Zweibel spoke about the Solar Grand Plan. Current development of solar has not developed under any of the pressures that will come when supply as seen as an “emergency need.” Yet overall production gas reached 10 GW and so he is optimistic of the future. Because the liquid fuels supply problem is so tied to transportation the we need to see how the use of solar energy can feed that market. This will require evolution of the Smart Grid, and means for solar forecasting and balancing of power. Unfortunately solar distribution varies – the Southwest gets 30% more photons that the DC area, for example. But, on the other hand, wind is like the measles.

We have gone from $30 a watt to $1.50 a watt, but this only covers the module cost. That is no all the costs since installation and maintenance must also be included and these will likely double the module costs. However while one can pay back the cost of the module in 1.5 years, it might take 15 years in energy savings to cover the whole cost of the installation.

He covered the current costs of some of the major systems that we will likely see grow to dominate the market. The costs have dropped 40% of the last four years, but to go lower they need (and deserve) the lowest interest rate for loans. And he moved on from there to discuss payback on the different systems., though he noted that many costs are based on out-dated methodologies. Cadmium telluride is a promising new candidate, and is not that polluting. And he noted that, in contrast to most conventional systems solar does not use significant water. (A little for cleaning). He pointed out that of the 17 Quads used in transportation only 3.4 Quads (quadrillion Btu’s) do the effective work of moving the object. Electric powered vehicles are thus a more viable alternative.

He said that only 15% of the Canadian tar sands could be recovered by surface mining, and hat the energy costs are 15 – 50% of the recovered and useful energy. For the remainder it might be possible to get 80% of it out, but at a 40% energy cost.

On the other hand vehicles will not, in significant numbers, switch from liquid fuel to solar powered in the near future. There is also not enough lithium for batteries, so realistically the answer hans to be in electrified trains. He seen the end of fossil fuels marking the beginning of a slow-down in economic growth. So the meeting slowed down for lunch.

Lunch began with a tribute to Matt Simmons. Chairman of the ASPO-USA Advisory Board and featured speaker at many of he events. A check to support the Ocean Energy Institute was presented to his daughter Abbie, on behalf of ASPO.

The noon speaker was Ralph Nader who took his quota of time, and more, to discuss Energy and Policy. He proclaimed (just having written a novel on the subject) that “only the super-rich can save us.” The main form of censorship is self-censorship. Why do we do it? It encourages a stagnant society. It builds the blocking of technological advance through the creation of mind sets. Secretary Chu advocates nuclear power and refuses to meet with opposition groups on the topic.

Mr Nader does not see a correlation between energy and economic growth. We have passed the diagnostic phase of energy future analysis, but there has been little prescription for future action and the path forward is obscure. We must mandate changes to buildings, vehicles and connect them to jobs programs. And we must make the jobs local so that they cannot be exported to China. He sees innovation as dramatically higher than it was 10 years ago. , and expects that stimulus funds will lead to innovation. But he gave the example of Evergreen Solar which had intended to stay in the US, having 800 employees here, but found that all its competition is moving to China, so they are too. Then he quoted the example of the “largest tile carpet manufacturer” in the US who has chosen to stay, and through innovation keep costs down low enough that he can remain in business.

Unfortunately as this talk drew to a close I had to leave. Gail Tverberg remained and was kind enough to supply me with her notes, which follow.

Anthony Perl, author of "Transport Revolutions: Moving People and Freight without Oil" and fellow of the Post Carbon Institute talked about ways to reduce oil used in transport. In his view, we have lots of technology, but not much time. Emphasis needs to be on proven, robust technologies.

One thing he talked about was electric motors to replace internal combustion engines, particularly for trains. Also expansion of the use of trains. One issue, though, is the fact that most rail track is privately owned. Perhaps some approach can be used that would allow double tracking with government somehow paying for/receiving ownership of the additional track.

Another possibility is "sky sails", which can reduce fuel use by ships by 50% to 80%. Water transport is already the most efficient mode of transport, and sails would improve it further.

He believes it will cost $1 trillion for passenger rail and $1 trillion for freights train needed changes / improvements. He also pointed out that GM used to build trains and busses, and asked why they couldn't again.

Dr. Charles Schlumberger, Principal Air Transport Specialist, Transport Division of the World Bank, pointed out that from the airline's point of view, it was the recession, and not the price of oil that was the problem. He felt this way, because he felt the airlines had pretty well hedged the price of oil. Its problem was a lack of passengers and cargo, because of the recession.

He pointed out that air transport is the catalyst for modern globalization. For example, he pointed out that without access by air, there is little chance of foreign direct investment in a country.

He also pointed out that at $80 a barrel, fuel cost exceeds personnel costs. He believes that above $80 a barrel, airlines cannot be profitable.

Regarding fuel efficiency, there have been improvements, but these are becoming smaller as the low-hanging fruit have already been found. Some additional changes may be difficult. For example, if changes are made that cause the size of engines to be bigger, these might necessitate completely redesigning the aircraft. One possibility is to use "Air Ships" or dirigibles for moving freight long distances.

Biofuels are being investigated, but progress is slow--perhaps 1% replacement of fuel by 2015. One issue is the huge land area that would be required. According to his calculations, algae would require the least land area, but even so algae would require an area the size of Ireland to replace existing airline fuel.

At this point, it looks like there is a possibility that airline use will need to be significantly scaled back, but if this happens, there will likely be big social and political impacts.

Next, Sharon Astyk, ASPO-USA board member and writer, talked about the world food situation. In 2008, there were 1 billion people who were seriously malnourished. The number is perhaps a bit lower in 2009, but not a lot. While oil prices have backed off a lot from their highs, some food prices are still not too far from their 2008 highs. She pointed out that high prices are a real issue for many, since almost half of the world's population spends 50% or more of its income on food.

Now China is buying land around the world, so as to be able to feed its people. This is likely to present problems for people who live in the area, and need the farmland themselves. Sharon also talked about there likely being an "Export Land" land for food, with countries cutting back on food exports, either as their own population grows, or if crops fail.

She talked about food insecurity being a problem even in the US. One in seven people is on food stamps; one in four children receives food stamps. Children who are hungry are likely not to do well in school.

There is a close tie between food and energy, so reduced food supply in the future is a concern. There are other related issues, like phosphorous supplies, which are already getting short. Lesser energy availability is likely to make the situation worse. There is also the issue of biofuels competition with food for land and water.

The last speaker was Brian Czeck, President of the Center for the Advancement of the Steady State Economy. He talked about the need for governments to scale back their expectations from everlasting growth to a steady state economy.

Moving the coal from the face to the shaft

At the surface an underground mine might appear to cover a relatively small area, but this may be quite deceptive of its actual size. Even back around 1850 the mine that James Dunn worked in extended out more than a mile from the shaft. As they extended, so the areas that were worked left pillars that might contain up to 40 – 50% of the coal in place, but had to be left to hold the roof up. The miners drove “headways” into the coal that were connected by cross passages or bords. At Houghton Colliery, for example, the pillars would be 5.5 yards deep, while the headways were 2 yards and the bords were 3.5 yards wide. The headways would advance about 20 to 40 yards before a cross drift was drive to hole through and create a new bord, along which the ponies would bring the empty tubs, and haul away the full ones.

Face layout at Houghton (A Pitmans Notebook, The Diary of Edward Smith, 1749).

The method of mining the face can be seen in the drawing, first it was undercut, then three vertical cuts were made (the nicks) and then the intervening coal could be broken out in the larger pieces that were favored by those buying the coal.

Back then the tubs of coal were moved from the working face to the shaft by teams of boys and men. But that only worked when production rates were relatively low. As the demand for coal grew with the Industrial Revolution, so the need to produce coal in greater volumes, and to move it faster to the shaft grew.

Pit ponies went underground, but would only pull a certain (small) number of tubs, and so better ways were needed. With the coming of electricity, this turned into the use of long “endless” ropes that wound their way along the centers of the rail lines into the depths of the mine.

Walking beside the haul rope (The Miners, Anthony Burton)

Hauling the tubs in either direction meant manually attaching a front shackle or chain to the moving rope, which then pulled the set of tubs down the passage in the direction required. Usually these systems were restricted to the main haulage ways or “Mains” since the ability to turn corners was limited. The main drive engine was usually by the shaft, and when the rope was not moving continuously it could be engaged by signaling the operator through a series of bells and cables. (The wires above the pitmen's heads).

Methods of attaching tubs to the rope (Colliery Deputy’s Handbook, D.G. MaGuire)

In an alternative method of haulage the rope was attached to the front of the set of tubs, while a second rope was attached to the tail end of the set. (Hence the name Main and tail). Thus as the tubs were pulled into the mine (inbye) they extended the rope that would later be used to haul them back out (outbye). But again these systems were largely kept in the main haulage parts of the mine. Once they reached the area where mining was continuing (the working “district”) they would be broken loose and could be hauled further by the pit pony. Thus on the map of the mine, the mains could be identified as the two parallel tunnels that would run out from the shaft in the four main directions (though this was oriented to the patterns of fractures in the coal, or cleat, rather than the compass points).

Underground layout at West Moor (How long did the ponies live? Roy Thompson Beacon House 1997) ) The lines that the workings run up to and then stop are faults where the coal is vertically displaced. The older workings, generally have the smaller pillars

Full sets would then be reassembled after they were brought back from the working face and hauled back to the shaft.

While the coal was mined by hand, and then loaded out by hand this system remained capable of handling the production. It is still, apparently, used in China. However, as mines grew larger, the inflexibility of the system, and its intermittent nature reduced its popularity. It was still around, however, in the early 1960’s since I spent an uncomfortable week or two of my apprenticeship working the engine on the maintenance shift, where the rope was only needed a few times in the shift to move tubs. It was there I discovered that by just cracking the engine on, the current running through the resistance bank would slowly heat it up, while the engine had not enough power to turn. This could, as long as a) you didn’t get caught and b) the rope didn’t move, keep you warm in the cold air of the downshaft flow.

A better way was needed for hauling coal from the face, and this came with the development of the conveyor belt. Initially mining belts were relatively simple. Long flat strips of reinforced rubber belting would be joined at intervals with wire clips, to form a loop. This was, in turn driven by a motor at one end, and a tensioning return drum arrangement at the other. Miners could load the coal onto the belt, and this would carry it out of the district, where it would transfer to a second conveyor belt that would carry it to the mains, where it would transfer to a much large belt, now carried on rollers, often suspended from the roof, that would carry it to the shaft, or in shallow mines out to the surface.

Transfer point to the Main Conveyor (Colliery Deputy’s Handbook)

One of the reasons for the suspension of the rollers rather than having them set in a frame resting on the ground is that it left clearance under the conveyor. Thus as small coal and dust fell off the conveyor it fell into a space where it could be seen and removed before it became a risk. If it was allowed to build up it could rub against the rollers, generating friction, heat and ultimately causing the coal to catch fire.

Dr Bronowski studying coal dust collection and ignition under a scale model belt after the Cresswell Pit fire in 1950. (The Miners, Anthony Burgess)

The fire at a transfer point at the Cresswell Pit in the UK in 1950 created clouds of carbon monoxide, which flowed into the workings and 80 men died. Fires associated with poor belt maintenance and failure to remove the coal powder that accumulates around the transfer points and similar locations, are, sadly, still occurring even within the past month. They don’t have to be underground and one of the major problems created is the smoke that is formed, which can very rapidly make it impossible to see.

Conveyor belts do, however, when properly maintained, provide a relatively rapid and simple method for getting the coal from the working area to the shaft or out of the mine. They can even (in some cases officially) provide a way for miners to ride their way out of the mine at the end of the shift.

Harvey Manrider (lithograph 1979 Tom McGuinness) Note the rope between the rails, which is still used to haul tubs of supplies in to the face. (The single rope would mean a Main and Tail haulage).

You just had to stay awake enough to get off the belt before the next transfer point.