Wednesday, April 16, 2014

Tech Talk - Of production stability, peaks and the future

Jeffrey Brown (Westexas from TOD) is quoted extensively in Kurt Cobb’s recent piece that points out that global crude production has pretty reasonably stayed constant at between 64 and 67 mbd since 2005. (H/t Nate Hagens). While there has been a total increase in the total refined products side of the house (with the total number floating around 90 mbd) this includes a number of different sources that, within generally defined standards, are not considered crude. The four main culprits that he lists are biofuels, natural gas plant liquids (NGLs), lease condensate and refinery gains. He makes a good point.

Figure 1. Crude oil production alone over the past decade (Kurt Cobb)

I can remember that it was some years ago, when looking at the OPEC reports on production, that I suddenly realized that the projected increases in NGL production made a significant difference in the overall volumes that they were producing. (It is anticipated to average 5.95 mbd in 2014). Back in 2001 OPEC just defined the fluid as natural gas liquids, but went through significant revisions of numbers in 2002 and in March 2004 redefined the volume counted as “OPEC natural gas liquids and non-conventional oils”.

Figure 2. NGL and unconventional oil production by OPEC (OPEC MOMR )

Over the past decade volumes have almost doubled. In the United States, with the increased development of the shale gases, production has also increased.

Figure 3. Increase in production of NGL in the United States (EIA )

The price obtained for these fluids, however, falls below that of conventional gasoline. For example:

Figure 4. Relative prices of NGL fuels relative to crude and gasoline. (EIA)

The EIA is reporting a continued growth in US production:
Altogether, in the Bakken, Niobrara, Permian, and Eagle Ford, oil production is expected to increase by 70,000 bbl/d in May 2014. The monthly growth rate is 3,000 bbl/d more than in April 2014 due to solid gains in Permian rig count and continuous rig productivity gains across the regions. While the DPR does not forecast weather impact, the spring thaw season has officially started in the Bakken region and may disrupt some drilling activity between now and June.
These additional resources take on an increasing importance as world demand is anticipated to increase another 1.14 mbd this year, slightly up on this year’s figure. This gain in demand was largely offset by increased production from the Americas, though OPEC note that overall global suppliy decreased last month to average 90.63 mbd but is expected to reach peak demand in the fall, at 92.24 mbd.

Looking at the supply side for this year, and bearing in mind that gains must more than offset lost production if the total increase in supply OPEC are projecting an overall gain in supply of 1.34 mbd, largely to come from outside of OPEC. This is expected to come from the OECD Americas (the USA, Canada and Mexico) group, while the increased production from countries such as those of the Former Soviet Union is expected, to rise by 150 kbd or less.

There has been relatively little change in the estimates of where the increases in North American production are anticipated to come. By the end of the year US production is expected to reach 12.45 mbd by the last quarter of the year. As OPEC noted:
Based on the US Energy Information Administration (EIA)’s monthly oil production report for January, regular crude oil output registered at 4.93 mb/d, tight oil production increased to 3 mb/d, NGLs output reached 2.64 mb/d and biofuels and other non- conventional oils recorded the highest output at 1.22 mb/d. The use of energy from biomass resources in the United States grew by more than 60% over the decade between 2002 and 2013 — primarily through increased use of biofuels like ethanol and biodiesel which are produced from biomass. According to the EIA, biomass accounted for about half of all renewable energy consumed in 2013 and 5% of total US energy consumed.
This month the OPEC MOMR focused on increased production from the Gulf of Mexico, with anticipated gains from the Olympus project at Mars B.

The total gain in production from the Gulf is currently anticipated to increase, this year alone, to perhaps 1.55 mbd, and to pass the previous record Gulf production of 1.8 mbd by 2016. In addition the Cardamom project is expected to add 50 kbd to the Olympus figure, and the start of oil production from Phase 3 of the Na Kika field is expected to add an additional 40 kbd to the 130 kbd which Na Kika is currently producing. However Gulf wells have a habit of going south a little earlier than predicted and I have borrowed the following graph from Ron Patterson which illustrates the cumulative fate of the combined Atlantis, Thunder Horse, Tahiti and Blind Faith fields.

Figure 5. Changes in production from major Gulf of Mexico fields over time (Ron Patterson )

When this is combined with Dennis Coyle’s prediction that the Eagle Ford field will peak in 2015, at 1.4 mbd, with a declining rate of production increase as one reaches that peak. Similarly the number of wells that can continue to be drilled in North Dakota in the sweeter counties of the state are limited, and beyond that there is a concern (which I have expressed before, and which others have explained much better than I) that as the estimates of production fall in the less successful regions of the state that it will become harder to raise the capital for the new wells needed to sustain and increase production.

That being said, I am beginning to suspect that this may be the year that the OPEC estimates for US production may get a bit ahead of what actually is produced. And if that is the case, then that means that the following two years will become even more interesting as the nations of the world start to realize that yes, there is a peak. Which might mean that the coal resurrection might be greater than I currently anticipate, but perhaps I will have more on that next time.

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Wednesday, April 9, 2014

Waterjetting 20a - Making holes in soil

There are two problems that often arise when applying waterjets to a soil-like material. The first of these is that the water can spread into the surrounding soil around the hole being excavated so that it loses its strength and can collapse into the hole. (This can be used to advantage in some cases.) This is a particular problem when excavating trenches, where the hole has to be as small as possible, yet the sides have to be stable so that work can be done at the bottom. The other is that, once the soil is loosened it has to be picked up and moved, and a way has to be found to be sure that the particles don’t settle out before they should.

Figure 1. Three consecutive frames from a video record of a jet firing into glass beads behind a glass wall. The framing rate was 30 fps.

In the sequence of frames shown above the jet is seen to first penetrate down through the beads (which were simulating soil, being easier to handle and see through), and then when it reaches about a nine inch depth it stops penetrating and starts to widen and fill the hole, which until the is relatively open. Note that at this stage there is no ejected material from the hole and very little penetration of the water outside the line of the hole. The penetration stops when the water no longer has the energy to push the particles aside, and continue to penetrate. (The test was at relatively low pressure to keep the penetration small enough to remain inside the box). Note also that the hole is largely hollow at this time.

If the jet is allowed to continue to play on the surface, the water will now penetrate into the material on either side. This can be better seen if the fluid color is changed to black by adding fine carbon particles to the water. The pressure was further lowered (to 100 psi) to keep the jet penetration down to below three inches, and in this case the jet was a fan shape to encourage the spread, rather than being projected through a round orifice.

Figure 2. Video frame taken as a waterjet laced with fine carbon penetrates into glass beads, note that the carbon starts to be carried into the surrounding material, and that again, in this short time interval there is very little material being ejected from around the hole.

In passing it might be noted that this is a relatively effective and simple way to inject remedial chemicals into layers of clay and soil that could contain undesirable chemicals (such as PCBs) but where going in to remove the contaminant might be difficult and cause other problems. This could occur if the contaminated layer is now covered with more material, and trying to dig the contaminated material out would cause it to disperse into a stream, river or bay where the problem has been found to lie.

But if we want to remove the soil, then the process, as it stands with using a single jet, is fairly inefficient. The water, at this pressure, is cutting into the soil, making a hole, penetrating into the soil around the hole, but not much is being moved. Again that could be an advantage.

Those who play golf know that good maintenance requires that golf greens need to be aerated at regular intervals to keep the grass healthy. At the same time, pulling plugs of material out of the green is disruptive, and conventional mechanical tools will still make a bit of a mess, and take some time. On the other hand Toro has developed and improved a tool – the Toro Hydroject – which has a series of jets that are spaced at adjustable intervals (but typically around 3 inches) along a distribution manifold, so that when the jets pulse they drive holes down into the soil, with no surface spillage of soil. And this can be done at walking speed – between foursomes, and without disrupting play.

Figure 3. Toro aerator at work. (After Toro )

The tool is also effective in poking holes under pools of water to speed drainage. The most effective pressures vary for different soil types and conditions, but are typically in the low thousands of psi, with penetration depths of up to eight inches. (They are also a potential tool for finding land mines, but that is another story).

Figure 4. Cut through a hole jetted into soil (turned on its side for convenience) (Toro)

Yet these applications again illustrate that the tool might be more difficult to use, where the main purpose is to remove the soil, and where a sequence of passes of a jet over the surface won’t potentially move much material.

The answer to this problem is to use more than one jet at once, and to place them at some distance apart, depending on the soil and jet parameters this might be more than an inch or two. What now happens is that the resistance of the soil is removed when it the jets pass along either side of the intervening rib at the same time. This very rapidly liquefies the rib in the middle, and it is removed as the jets cut past.

This can be seen where, for example, two jets simultaneously traverse over a clay bed. When only one jet was used it cut only a thin slice into the clay, with little material removed.

Figure 5. Single consecutive cuts into clay with a water jet that also contains kaolin so as to show where the cuts were made. (Note that even where the cuts are close together there is no removal of the ribs between cuts.)

Figure 6. Material removed when two jets cut side-by-side into clay. Note that all the intervening clay between the jets has been removed, to a depth of four inches.

The contrast between the two figures shows that by changing the way in which the jets cut into the material (concurrently rather than consecutively) up to ten times or more material can be removed from the surface for the same amount of input energy.

Figure 7. Slot cut in the ground by a combination of jets acting together as a head was moved through the ground (Halliburton - the Soil Saw)

This also works with some rock types, and I will discuss how we used it to design a machine for mining coal in a later post, but it is not the end of the story in developing the soil cutting aspect. The problem that can then arise comes from the type of soil that is being cut, and the distance between the jets. As the soil becomes more coherent (clay laden) the jets need to be brought a little further together (and the more sandy the soil, the further apart they can be.) But if the jets don’t have enough time to totally break up the rib of material into particles (controlled by how fast the jets are being moved over the surface and the relative depth of cut) then the pieces may come out in lumps of varying size and shape. These are more difficult to break up, once they break away from the solid.

The alternative is to move the jets relatively rapidly over the surface. This shortens the depth of the soil that is being moved at one time, but if, for example, the jets are being spun around an axis inside a shroud connected to a vacuum system, then the particle sizes can be controlled to fit within the vacuum line, and the depth of cut is small enough to hold the partial vacuum around the edge of the shroud to make sure that all the particles and water are removed and the walls are kept dry enough to remain stable. But, again that brings us into hydro-demolition and I’ll cover more of this in a later post.

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Monday, April 7, 2014

Tech Talk - from 1491 to China, coal, smog and CCS

I have written about my curiosity about the condition of Native Americans at the time that Europeans arrived in the Americas in the past, and so, when I came across Charles Mann’s “1491” at the Brookline Booksmith the other day, I bought a copy. It tells a fascinating story of the developments of agriculture and civilization, largely in South and Central America perhaps pre-dating the time around 10,000 years ago that the first cities were developing in Mesopotamia. He tells, with reference to considerable evidence, of the changing understanding of the state of society, and how it developed pre-Columbus. And if you thought the debate over climate change was rough, apparently that over the changing understanding of such civilizations is at least as intense, although confined to a smaller group.

Conventional theories are that Native Americans crossed over the Bering Straits from Siberia while the land was above water some ten to fifteen thousand years ago. However the discovery of remains at Monte Verde in Chile, with a site that dates back over 13,000 years and with other sites that may date to considerably earlier has thrown this all into debate and controversy – which the book explains in some detail. (It was published in a second edition in 2011, since when DNA tests of skull parts from the Botocudo peoples of Brazil have shown some Polynesian markers suggesting a possible sea route for the first Americans.) I am looking forward to reading the chapter that covers Cahokia.

This is a long introduction to explaining why I was drawn to the cover story in the April Wired that the book's author, Charles Mann, has written on the Future of Coal. It is a fairly rational review of ongoing developments in China to find ways of easing their air pollution problems, while continuing to rely on coal to power the ongoing industrial changes in their society. For as he notes,
Nowhere is the preeminence of coal more apparent than in the planet’s fastest-growing, most populous region: Asia, especially China. In the past few decades, China has lifted several hundred million people out of destitution—arguably history’s biggest, fastest rise in human well-being. That advance couldn’t have happened without industrialization, and that industrialization couldn’t have happened without coal. More than three-quarters of China’s electricity comes from coal, including the power for the giant electronic plants where iPhones are assembled. More coal goes to heating millions of homes, to smelting steel (China produces nearly half the world’s steel), and to baking limestone to make cement (China provides almost half the world’s cement). In its frantic quest to develop, China burns almost as much coal as the rest of the world put together—a fact that makes climatologists shudder.

. . . . . . “Coal is too low-cost, too plentiful, and too available from reliable sources to be replaced,” says fuel analyst John Dean, president of the JD Energy consulting firm. “China is putting in solar and wind power at a tremendous pace, but it will have to use more and more coal just to keep up with rising demand.”

The article then goes on to discuss the facility at Tianjin, where GreenGen is developing a Carbon Capture and Sequestration (CCS) plant. The first phase of the plant was inaugurated in December 2012, and the site is now in Phase 3 construction to develop a 400 MW demonstration IGCC power station.

In the WIRED article, however, lies the sentence “Conceptually speaking, CCS is simple: Industries burn just as much coal as before but remove all the pollutants. “ However, later in the piece this is qualified since one of the problems with the technology is that there is a significant (up to 40%) increase in the amount of power that the station must generate to provide that now needed to capture, liquefy and dispose of the carbon dioxide (by underground injection). Thus the plant burns significantly more coal, for the same effective power supply into the grid. This is one of the reasons that the DOE has concluded that the costs of such a plant will increase electricity costs by 70-80%, making it potentially too expensive. Interestingly that considerable increase in cost is, in part, because power generation using coal is currently relatively inexpensive.

Reading the story in WIRED made me realize that I must be quite a bit older than Charles Mann. Being raised in the North of England in the years after the Second World War I can remember when the UK was in much the same state as China is now, with the need for as much coal as possible to rebuild the nation’s industry and power the restoration of the economy. As a result the UK had vicious smogs when the air pollution mixed with a fog to create a condition when I can remember not being able to see the hand at the end of my arm, in the middle of the day in Leeds in 1962. The Great London Smog of 1952 was reported to have killed more than 4,000 people and severely affected the health of many others. The 1962 smog killed over 750 Londoners and the pollution from burning coal had long since turned most of the buildings in the cities of Britain into black edifices, with the original stone crusted with soot. I can remember that in the mining villages of the North the windows and steps were washed and “holystoned” every week to minimize the soot, and curtains and windows were constantly washed to remove the residue.

Two major acts were passed by the British Government, the Clean Air Acts of 1956 and 1968. While the advent of North Sea oil and gas removed the need for homes to burn coal in open fires (which I did until I left the UK in 1968) coal has continued to power the island (31% of power is still generated by coal) but the air pollution that contributed to those smogs is gone. The buildings in the major cities have been cleaned and brought back to the golden sandstone, or white limestone finishes that they had when initially built and the dark clouds that are shown issuing from power stations only occur when the photographer puts the steam emission between his camera and the sun.

The same change has occurred across Europe and in the United States (see photographs of Pittsburgh in 1940) - laws were passed, natural gas played a larger part in domestic energy supply, and the air cleared away.

It is likely that China will be able to achieve the same changes, as they increasingly import natural gas (perhaps from Russia, certainly from Turkmenistan) and provided they impose the same standards for air quality as are found in our power plants, then the air can be cleaned up. In this way the more than a million premature deaths that air pollution is currently causing (according to the article) can be ameliorated, perhaps at a lesser cost than the CCS technology, which is still struggling to provide meaningful demonstrations of its effectiveness. And China has to do something for, as the article continues to emphasize:
More important from China’s perspective, more than one-quarter of its citizens still live on less than $2 a day. These people—more than 350 million men, women, and children, an entire United States of destitution—want schools and sewers, warm homes and paved highways, things that people elsewhere enjoy without reflection. China can’t provide enough energy to make and maintain these things with oil or natural gas: The nation has little of either and not much incentive to import them at great cost. (Asian natural gas prices are roughly five times higher than US prices.) Nor can solar, wind, or nuclear fill China’s needs, even though it is deploying all three faster than any other country. Meanwhile, it has the third-biggest coal reserves in the world.

China, like most of the rest of the world, “pretty much has to use coal,” says Dean, the fuel analyst. “Or, I guess, leave people in the dark.”
And in this view of the future, China is not alone.

Good article (and good book)!

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Sunday, April 6, 2014

Waterjetting 19d - waterjets and material removal

When miners first began to use water as a means of moving soil and ore from valuable deposits at, or near the surface, stream flow, or the energy from stored volumes of water was the main source of the power used. However, at these low pressures it was necessary to use large volumes of water (often in flows of over a thousand gallons a minute) to move the material. At the same time, even at these large flow volumes, the flow has to be confined in order to ensure that there is enough water around the particles to keep them in suspension. There is also a certain amount of turbulence required in this flow to retain the suspension and to stop the particles from settling out before the riffles where the gold or other valuable minerals can be collected.

As pressure is increased these jets can be increasingly productive, and can be used for a variety of functions, including the rapid removal of soil. Raising the pressure allows the tool to be used in mining soft rock. As an example there is a layer of relatively soft sandstone that lies in a roughly horizontal layer and appears along the banks of the Mississippi river and can be found, for example, under Minneapolis. There is a sand mine that lies along the banks of the river, that has a high-grade sand that can be used for making glass, but which also has a vein within it that has larger grains that can be used in the fracking stage of increasing oilwell production. However, with conventional mining (using blasting) it was not economic to screen the sand after it had been mixed during mining. The Bureau of Mines of the time (since closed) tried some experiments to see if a waterjet could be used to “high-grade” the sand, mining the larger layer first, and then that surrounding it to let machines and men progress further (and also to produce the sand for glass making).

Figure 1. Bureau of Mines experiment washing out sandstone, with 4,000 psi water and cutting about 9 ft. deep. Note the yellow color of the water as the sand settles out but the clay contaminant is suspended in the water and washed away.

The experiment, carried out by Dr. George Savanick’s team, was successful, and had the unexpected advantage, since the grains were all separated, of stripping the small amount of clay contained in the sandstone and carrying it away with the water, while leaving the sand on the floor, where it had to be picked up mechanically.

The use of pressurized water is used both to mine sand, and also, in Cornwall, for example, in the mining of clay, although the pressure and volumes needed are a function of the quality and amount of weathering that the clay has seen.

Figure 2. Mining clay in Cornwall (Pathe video here)

Engineers have even accelerated the movement of landslides, using clay mine pumps, in order to move the soil away faster and allow the slide to be remediated. At Dawlish in the UK, for example, railway engineers have added water under pressure to remove the sliding soil as a slurry, making clean-up faster, safer and less costly.

Figure 3. Moving soil in a landslide that has covered the railway line at the bottom of the slope, Dawlish UK March 2014. (The Packet)

A jet was also used from the bottom of the slide to liquefy the soil, which then flowed through the railway path and into the sea.

Figure 4. Removing the soil from the landslide from above the railway. (From a video at The Packet)

As a comment, for those who watch the video that the above picture was taken from, the jet cuts much more effectively closer to the nozzle, and had they used it to undercut the bank they could slurry the soil lower down, and have removed the material a bit faster than dispersing most of the jet energy in the air as they tried to reach the back of the slope. (If they had undercut the bank then the soil would have slid down towards them shortening the reach and speeding the process).

During the Second World War engineers also used water jets to uncover land mines that had been planted on beaches along the coast. (video from Pathe here ).

However the control of the water, and debris, can quite quickly become a problem, and containing the water and keeping the soil/sand particles suspended in it requires more preparation. As an illustration the civil engineers who work under Minneapolis are aware of the benefits of using higher pressure waterjet streams in driving tunnels (and occasionally rooms) under the city. For example, in driving a sewer tunnel (the St Anthony Park Storm Sewer extension) the engineers set up an extensive train behind the tunnel face, so that the resulting slurry could be pumped out of the tunnel.

Figure 5. Train behind the tunnel face, required to supply the jets and to pump the slurry from the excavation (after Nelson*)

The tunnels can be driven by two main jet operators at speeds of up to 120 ft per day () with a third jet being used to break the larger pieces down to slurry so that it can be pumped down the tunnel to the river, where it is barged and sold as glass-making sand.

Figure 6. Driving the storm sewer tunnel under Minneapolis. Two operators are carving the face into small pieces and the third is slurrying the sand (after Nelson*)

By feeding the sand and water into a channel cut into the floor of the tunnel it was possible to confine it, so that the blocks could be broken up more easily, and this also then provided a catchment for the intake to the slurry pumps.

The tunnels were pre-cut along the profile, so that the arch girders that provided support could be slid into place with the central core of rock still there to support them. This made the support easier to install, and provided immediate support of the working area ahead of the place where the miners were working.

(That ability to use waterjets to penetrate ahead of the tunnel and allow a support to be installed before the main core of the tunnel rock is removed has since been improved, and in the Advanced Austrian Tunneling Method high pressure jets drill out cylindrical bores along the profile ahead of the tunnel, which are filled with a grout that can be generated partially using the surrounding material as the holes are drilled. But I will talk about the use of cement mixed with the jets in a later post).

*Nelson C. Tunneling under Minneapolis, Water jet Workshop, Rolla, MO 1975.

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Friday, April 4, 2014

Iceland becomes a little more active

So I just glanced at the Iceland Earthquake map again tonight, and it has become a little more active than in recent times.

Recent quakes in Iceland (Iceland Met Office)

As a reminder:The colors of the circles show the time since the earthquakes occured (the numbers below the color palette represent hours). The latest earthquakes are shown in red and the dark blue ones occurred over 24 hours ago. The earthquakes stay blue until 48 hours have elapsed since their occurrence, then they disappear. Earthquakes bigger than M3 (on the Richter scale) are represented with green stars that turn yellow after 24 hours.

No more - as yet!

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Tuesday, April 1, 2014

Tech Talk - of Wheat and Coal

The release of the latest assessment of the IPCC on the future of the planet, failing their push to cut greenhouse gas emissions, has brought forth headlines and supportive editorials in papers around the world. Yet I could not help but note a couple of things that form the basis for this tech talk. The first was that the report discussed the impacts of climate change (for which I suspect in this case they mean global warming) on agricultural production. They stress the negative impacts on crops such as wheat, and so, being curious, I went to the Wikipedia page that provides a table of wheat production over the past eighteen years, and plotted the data.

Figure 1. Global wheat production in millions of metric tons (after the Food and Agricultural Organization via Wikipedia)

Clearly wheat production is growing rather than, as the IPCC report implies, declining with the increase in carbon dioxide levels and longer growing seasons in parts of the world. More to the point – which is providing more food – (h/t Joules Burn) the two staple crops wheat and corn, have both seen growing production, but it is the slower pace of growth of wheat (at about 0.9%) over corn (at about 1.6%) that is of current concern, and which is to be addressed with new investments in the International Wheat Yield Partnership that plan to more than double yields in the next 20 years. This is needed in large part to match the continued growth in world population, which is likely to continue to rely on wheat to provide roughly 20% of the calories that this population will consume. Gains come both from increased land acreage being used, but also from the yields of that land. In the UK, for example, yields now average 7.8 tonnes per hectare up from 2.5 tonnes in 1940, the current target is to reach 20 tonnes per hectare in the next 20 years. Given that the global average is still down around 3 tonnes per hectare, the ability to bring this productivity to the broader community will give significant help to feeding the world.

I mention this because of the clear disparity between this information and the way that material is presented by the IPCC. Further the real needs of the world and its nations are now increasingly being addressed with less attention to the strident demand of the more alarmist of those who push the climate change agenda, in part perhaps because of the overhyping of the message. The latest illustration of this comes from Japan.

Following the devastation of the tsunami following the Great East Japan Earthquake on March 11, 2011 the Japanese public has been very nervous about the use of nuclear power, banning the restart of 48 nuclear power stations until after a new series of safety checks. This has had two short-term consequences, the financial melt-down of the power companies, which is now being addressed through government bailout and the need to switch to alternate fossil fuels to replace the power that the country obtained from the reactors. The switch was largely to natural gas, and to oil but this has proved to be an expensive undertaking with companies feeling that they could only raise power prices to a limited degree, hence their need now for government funding.

Figure 2. The changing face of electricity supply in Japan following the Earthquake, (MIT technology review )

But the sustained high cost of the gas and oil is estimated to be costing the companies over $30 billion a year and even with the government bailouts this is not an acceptable long term solution, given that it is likely to be years before the safety changes are made in the reactors, and also given the continued public opposition to restarting the reactors. As a result the companies have sought permission to switch back to coal-fired power plants. Concurrently the Japanese Coal Energy Center has been looking for coal resources around the world ranging from Mongolia to Mozambique.

in 2012 Japan was the second largest of the coal-importing nations at 189 million tons (behind China at 289 million) and current plans are to increase the amount of power that the fuel will provide by roughly 20% through construction of new power stations. (Some of these will be needed since, while some nuclear power stations may come back on line others are proving to be too expensive to restart under the new codes, and thus will be permanently closed).

It is this clear benefit of cost that is driving the change, and that benefit is unlikely to disappear over the next couple of decades. The renewable energy industry has not been able to overcome the advantages of coal’s ubiquitous presence and low cost of production. In the case of Japan supplies are anticipated to come from Canada and the United States easing their dependence on Australia and perhaps helping reduce their costs as they develop more international suppliers. Glencore, for example, their Australian supplier, has now reduced costs to $88 a ton, from the $95 being paid last year. It is estimated that there is currently a glut of about 5% of the coal market, and the reduced demands for thermal coal in the United States and Europe is unlikely to change that picture in the short term.

The longer term remains more cloudy, since the potential for the United States to enter, in a significant way, the LNG market and potentially to change those supply costs is not yet clear. It seems, however, unlikely that the volumes that will become available will not have much impact on price, and if that remains the case then coal will continue to grow as the price differential continues to add pressure for the its use in generating cheaper electricity.

Whether this will change the recently better-defined coal resources off the British Isles into a reserve remains, in the short term, unlikely, but even in the UK power costs can only rise so far before the public complaints begin to have an effect.

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Thursday, March 27, 2014

Waterjetting 19c - Of soil removal by water

The tragedy in Washington state, where a hillside slid down, across a river and destroyed and covered the small community of Oso on the other side is a reminder of the ways in which natural ground saturation can help dislodge large volumes of material. While it is unlikely that the exact trigger for the slide will be identified the underlying cause is well known. As water from the heavy persistent rains permeated down through the hillside it penetrated deeply into the sand, silt and clays that made up the cliff, filling the voids in the material and reducing the friction that held the slope together.

Once the water is between the grains there is a second stage, where the overlying water adds hydrostatic pressure to the water below it. This pressure starts to push the grains apart, further reducing the friction holding the grains together and, since water has no shear resistance, lowering the overall resistance to the gravity that is pulling the overlying material down a potential failure plane. Once the resistance falls below that pull the slope starts to fail. It happens very quickly and large volumes can move almost as fast as though it were just water. In this case the water moved roughly 15 million cubic yards of material off the mountain. and across the valley.

The power of water to move material once dislodged was an early part of the mining process, and an earlier post referred to “hushing” where water was first trapped, and then released to erode away overlying soil, and then ore, before carrying it down to a flume where the valuable mineral could be trapped and recovered. But it does not take much pressure to dislodge weak material. Russian studies* have shown that light soil can be moved with a pressure of only about 10 psi (which would be generated in the water at the bottom of a slope only 20-ft high), while medium soil would require perhaps 30 psi, and firm clay would need a pressure of about 100 psi before the jet would mine and erode it.

That ability to move soil using a monitor was further developed in Russia, where tests showed that it would take water flows of between 3 and 10 times the amount of soil being removed depending on the strength of the material. In the gold mining regions around Lake Bykal it lowered mining costs to 40% of that for conventional mining, and gradually the tool found wider application in general soil removal, being used in the construction of several dams, and also for soil removal during construction of the Moscow Canal.

An interesting example of the speed and effectiveness with which waterjets can remove relatively soft soil formations arose during the Yom Kippur War (10th of Ramadan War, October 1973) between Egypt and Israel. The Israeli Army had built defensive positions along the edge of the Suez Canal and these were mounted behind an earthen and sand barrier known as the Bar-Lev line.

Egyptian intelligence had determined** that the Israeli Army had assumed it would take 24 hours for this barrier to be breached, and a total of 48 hours for the Egyptian tank forces to successfully penetrate the line. The response time of the military units was planned accordingly. This time estimate was based upon the time that it was expected to take to make a hole 22-ft wide through the barrier, since this had, for each breech, to move 60 cu yards of material, and a total of 60 such holes were needed to get enough troops through to be effective. Conventional methods involving explosives, artillery, and bulldozers would taken over ten to twelve hours, and required nearly ideal working conditions. For example, sixty men, 600 pounds of explosives, and one bulldozer would have needed five to six hours, uninterrupted by Israeli fire, to clear 2,000 cubic yards of largely sand from the wall. Employing a bulldozer on the east bank while protecting the congested landing site from Israeli artillery would be nearly impossible during the initial hours of the assault phase. Construction of much-needed bridges for the main army would consequently begin much too late.

Figure 1. Using waterjets to breech the Bar-Lev line during the 1973 war (Mashpedia)

To deal with these 70-ft high sand and earth barriers, the Egyptians instead used water cannons fashioned from hoses attached to dredging pumps that were floated on platforms in the canal. A study was made of the speed with which different pumps could move the sand:soil mix and the initial tests with British pumps showed that it would take around 3 hours. But by combining them with larger German pumps into six pumps per breech the army was able to get the time down to about two hours, although it took a little time after that to deal with the residual mud on the floor of the breech and give an adequate road for the tanks and other vehicles. A total of 81 holes were made, moving over 3 million cubic yards of material.

Figure 2. Egyptian forces crossing the Suez Canal, showing the size of the breech created (Wikipedia)

The bridges were then put in place, and the Egyptian Army moved on into the Sinai, well ahead of the time that they had been anticipated to be there.

The combination of high-pressure water to dislodge and separate the particles of a soil/sand layer can be combined with the active suction from a modern vacuum truck, in what is now being called hydro-excavation. By removing the soil and water as the excavation is made this stops water from entering the walls of the excavation and leaves them relatively dry – thus resolving one of the problems that the Egyptian army encountered after their holes had been made. At the same time, by using smaller jets at higher pressures and moving them much faster the excavation rates can also be increased, with lower water volumes, so that narrow trenches can be excavated without the need for support, where rapid access is needed. But I will talk about those applications in a separate post.

*Okrimenko, V.A., "Hydro-Monitor Operator in Coal Mines and Pits", State Scientific Technical Press of Literature on Mining, Moscow, 1962, pp. 264 (Translation U.S. Army Foreign Science and Technology Center, Document AD 820634, 1967).
**London Sunday Times, December 16, 1973, p. 33

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