GEOL 115: The Earth’s Energy Resources

The February issue of the American Scientist had a short note about the Toshiba 4S reactor. The 4S is a small reactor (about 10 megawatts) that is designed for operation by a small crew in remote settings. Such a device could be used in remote communities at high latitudes such as mining camps, research stations. The idea behind the 4S is that it is installed, operates for about 30 years, and is then removed. The reactor core is small (about 2 m long by 0.6 m in diameter) and operates in a concrete vault buried to a depth of 30 m.

A small reactor would have real value and might well be a sound environmental choice. Remote communities at high latitudes typically can’t use solar power and wind power may be difficult to harness (it should be noted that there are important exceptions). Power is typically generated using diesel generators. Enivronmental degradation occurs with fuel transfers and use.

The 4S concept is over 10 years old and was presented publically by Toshiba at least as far back as 1998. This reactor has gotten a fair amount of press over the last 5 years. Toshiba has apparently offered to install one in Galena, Alaska if they can get all necessary approvals for such an installation.

Its hard to say when a 4S will actually get installed. Back in 2007 the DOE projected that the earliest that one could be installed in Galena, AK would be 2013. It will be interesting to see where this goes. It seems clear that nothing will happen soon.

Wind farms are everywhere these days. This one is located in the area where I grew up in Wisconsin. DOE recently published their Annual Energy Review. It appears that renewable energy satisfied 7.35% of US energy demand in 2008. That is up from 6.7% in 2007. We will be living in a very different world when renewables are providing a significant portion of our energy needs. Students should consider this when thinking about careers.

I just got back from an NSF Cutting Edge Workshop on Teaching about Energy in Geoscience Courses.  The workshop was well-organized and quite enlightening.  Everyone takes different things from a meeting like this one.  It became clear to me that our nation’s energy paradigm will change significantly over the next fifty years.  

Electricity is generated in centralized facilities capable of gigawatt outputs using coal as the predominant fuel.  Efforts to reduce carbon dioxide emissions will probably succeed.  Solar photovoltaic and wind power are getting cheaper.  Utilities will have to operate in a world where many residences generate a portion of their own power from solar photovoltaic and where wind energy comprises a significant portion of the electrical power grid.  Thus the utilities will have to provide base level power (sufficient to meet the needs of industry and a portion of residential use) combined sufficient peaking capacity to meet demand when wind supply is poor, it is overcast, or other factors increase demand.

That is a far more challenging environment than exists today and was one of the messages that I took from Nic Woodward’s talk.  As Dr. Woodward pointed, out similar transformations have occurred previously.  This transformation in our electrical power system will be accompanied by increased competition for petroleum as a transportation fuel.  Plug-in hybrid cars might serve as electrical storage capacity and be used to help “buffer” the system.  The next fifty years are going to be interesting.

The New York Times has an interesting article about lithium earlier this month.  Lithium is a necessary component of lightweight batteries.  Leaving aside the bizarre tone of the article, it makes the point that world lithium reserves are relatively small.  The reasons for this are cosmochemical, geological, and economic.

Elemental abundance generally decreases with increasing atomic number in the solar system.  There are, however, three light elements that are much less abundant than one would expect.  These elements are Lithium, Beryllium and Boron.  These elements tend to be completely consumed in stars as rapidly as they are synthesized: our earthly endowment results largely from the interaction of cosmic rays with other light elements.

Lithium was once retrieved from the giant spodumene pegmatite deposits of the Black Hills and other localities.  Now Lithium is retrieved almost exclusively from brines in salt lakes or deposits, sediment altered by geothermal waters, or geothermal waters.  For a more complete discussion of Li and Li deposits see the Lithium Blog!

There has been some concern expressed that Li resources will not be sufficient to meet demand.  My opinion is that Li-battery technology is too immature to make a precise determination.  It is unlikely that Li will be in short supply for the forseeable future, however.  Does this contradict the second sentence of this post?  Not at all.  Lithium has not been traded on the scale that will be required if all cars carry Li batteries.  In a situation like this the resource base could be quite large but the reserves would be insufficent to meet the increased demand.

Sam Bradford has decided to return to OU for another year.  Perhaps because he loves college and perhaps because he doesn’t want to play for the Detroit Lions.  I got a chance to see the Lions play the Packers when I was back in Wisconsin over the holidays.  The Pack defeated the Lions condemning them to an 0-16 season. Calvin Johnson (a Lions’ WR) is quite impressive.  The rest of the pride doesn’t look so hot, however.  The consensus is that the Lions have been assembled through a series of horrid drafts.

The NFL draft is an interesting animal; the worst team gets the first pick.  But football isn’t a game that lends itself to a single player completely changing a team’s fortunes and the draft prevents any team from accumulating more than two or three of the very best players in any year’s draft class.  A team like the Lions has to look at itself and realize that they have a history of making bad decisions (I recognize that they fired Matt Millen; the former GM).  The last thing they need is the opportunity to spend a great deal of money on a single player.

Oil companies almost never take the top-heavy approach inherent in exercises like the NFL draft.  They spread their risk.  When very large structures are available, and when large amounts of money are required to drill a prospect, they form exploration partnerships to spread their risk (Actually to minimize the fraction of the exploration budget exposed on any particular venture).  For example, here is the original lease agreement for one of the blocks on the Jack prospect in the Gulf of Mexico.  Note that this lease was originally a 50-50 partnership between Chevron and Texaco.  Even though the bid on that individual lease was chump change ($215,000) neither company wanted to be in a position where exploration of that lease would require an inordinate amount of their exploration budget.

The application of the famous Nebraska Cornhusker Football walk-on program to these issues is left as an exercise for the reader.

I’ll be getting the blog going again this week.

I read an interesting article over the break in the American Scientist.  A paper by Casten and Schewe titled Getting the Most From Energy (link should work for UNL library subscribers) discusses recycling waste heat.  US power plants waste an exceptional amount of heat.  The electrical utilities are not being profligate intentionally.  People generally don’t want to live or work near large power plants and therefore we build power plants away from homes and manufacturing sites.  As a result, little can be done with heat remaining in the spent steam after it goes through the turbine and generates electricity.  These authors point out that in the US about 8% of all energy used is recycled energy (typically cogeneration, although not generally in conjunction with oil production).  In Denmark, on the other hand, over 50% of the energy used is recycled energy.  There is considerable room for improvement on this side of the pond.  This obviously has all sorts of interesting implications for things like greenhouse gas emissions, energy efficiency, cap and trade policies, and so on.  It is a fascinating article that discusses some nifty ideas for energy recycling and I recommend it highly.

One of the most important things to understand is that hydrogen is not a source of energy but rather is a chemical species that will be used for the transfer of energy.

A significant incentive for using hydrogen is the ability to use fuel cells. These are electron wranglers that herd the electrons transferred in chemical reactions in particular directions. We can then use those electrons to run a motor or to power a light. Batteries will also push electrons transfered in specific chemical reactions in specific directions but fuel cells are different in that we can refuel them. We just add more hydrogen (or whatever fuel is being used). A battery must be recharged (the reactants must be refreshed by pushing the electrons in the opposite direction). By using the electrons directly we can potentially use the energy in the hydrogen oxidation reaction more efficiently.

The downside is that we have to make the hydrogen. We would do this using natural gas and the partial oxidation reaction in tandem with the gas-water shift reaction. (See the comment on the partial oxidation reactions and the water gas shift reactions in the XTL comment)

There are potential geological sources of hydrogen. These include chemical reactions involving the reduced iron in rocks. We might also be able to isolate strain of microbes that perform these reactions and recover hydrogen (I’m not kidding). Finally, any hydrogen technology will likely require some geologically obtained element or compound to use for storage. The example that we considered in class considered the conversion of magnesium hydride to brucite in the presence of water following the reaction
MgH₂ + H₂O = Mg(OH)₂ + H₂
Remember that the reason to store hydrogen as a solid is that gases take up a lot of space (the molecules want to stay far apart) whereas the atoms in solids are quite comfortable sitting quite close together.

The point of this lecture was to discuss a way to convert solid fuels (or stranded gas) into fuels that society values more highly. The fuel that society values most is gasoline. We can convert reduced carbon compounds into gasoline by using several sets of reactions

For our purposes we will consider the partial oxidation process and the water gas shift reaction.
Here a fuel is burned under controlled conditions. Because a limited amount of oxygen is allowed into the system, some of the other material will be converted to carbon monoxide and hydrogen. The partial oxidation reaction is typically presented as
CH₄+1/2O₂ = CO + 2H₂
The reaction of organic material with steam will also produce carbon monoxide and hydrogen
C + H₂O = CO + H₂
We can optimize hydrogen production by using what is called the water-gas shift reaction
CO + H₂O = H₂ + CO₂
The mixture of carbon monoxide and hydrogen is referred to as “synthesis gas.” You should understand what these reactions do.

But back to producing liquid fuels.

If we are going to produce liquid fuels we need to convert the synthesis gas (CO and H₂) to liquid hydrocarbons. Fortunately carbon monoxide and hydrogen are not happy when placed together and they do want to react. The problem is to get them to make the right thing. This problem is addressed by using catalysts. Catalysts are substances that help reactions to happen. They are neither consumed nor produced in reactions so in theory can be re-used. In the presence of the proper catalyst the Fischer-Tropsch synthesis will proceed from left to right and release heat
(2n+1)H₂ + nCO = C_nH_2n+2+ nH₂O
In this reaction the species in synthesis gas, that is the mixture of hydrogen (H₂) and carbon monoxide (CO), are on the left whereas the hydrocarbons ( C_nH_2n+2) and water are on the right. In this way we can convert any carbon-based substance into gasoline.

Do we have sufficient reserves of coal to support the conversion of coal to liquid fuels? Although the US has sufficient coal to support more than 100 years of use at current rates, there is no evidence (yet) that we have sufficient supplies for 250 years. If we began to consume coal at rates to support our current transportation needs we would begin to draw down our coal reserves much more rapidly (in decades rather than centuries).

Because coal is a solid we can’t extract it from the ground through a pipe, we have to go get it. Coal mines are like very large construction projects; large amounts of material must be moved, massive equipment is used, and the “footprint” of the operation is considerable. More so than conventional petroleum operations, much of the emphasis in mining operations is placed on moving material (coal, overburden rock and soil) efficiently.

The average citizen typically laments that mining companies don’t refill the mine when operations are completed. Consider the Berkeley Pit in Butte, Montana. This image of Berkeley Pit was taken from the International Space Station. Nobody’s gonna fill that hole up: it would be too expensive and the company or companies that made the pit are no longer generating any revenue from the mine to use on such reclamation. We’ll return to this thought later in the discussion on surface mining.

Underground Mining Methods
Underground mining methods generally leave a smaller surface footprint.

Longwall mining is reasonably safe and yields high coal recovery. The coal is transported out of the mine largely on conveyors eliminating the need for vehicles to transport the coal (in those small spaces only small vehicles could be used). This video from a University of Wollongong site shows a shearer removing coal from a face while the supports move toward the face from behind the miners. The back (roof or ceiling) may then collapse behind the supports as they move forward. You can see images of the equipment in the lecture notes. The disadvantage to longwall mining is that as the overlying rock collapses, the collapse may reach and disrupt the surface. Thus if there are roads, buildings (a built environment) or an important aquifer over the the coal deposit, longwall mining is not the preferred method.

Room and pillar mining allows one to retrieve the coal without any subsidence or surface collapse. It is a straightforward process in concept; you leave pillars of coal to support the overlying rocks.

The main problem with the room and pillar technique is that the pillars may be very large (about 40% of the coal in the area mined). Reducing pillar size or removing pillars ( called retreat mining when the miners are working back toward the “exit”) yields greater financial return but at the cost of greater risk to the miners (from unstable ground conditions within the mine). Its worth noting that every action that you take (using a seat belt, studying for an exam) involves some consideration of risks and rewards. This consideration is particularly stark when considering retreat mining: probably the most hazardous mining activity in the United States. On July 31, 2007 Assistant Secretary of Labor Richard Strickler opened a scientific conference on ground control (the science of preventing big rocks from falling on you in a mine) with a statement that included the following words

Roof and rib (the wall of the mine RMK) fatalities and injuries appear to be disproportionately high during retreat mining. For example, since 2000, fourteen of 49 fatalities (29 percent) occurred during room-and-pillar retreat mining operations. This percentage is high when you consider that mines which use this mining method employ only around 19 percent of underground coal miners and account for about 18 percent of the underground coal production. In addition, the actual retreat process accounts for only a portion of the production.

This doesn’t mean that companies that engage in retreat mining are run by bad people. It does mean that this activity is one that needs to be undertaken carefully and with appropriate recognition of the risks involved.

Surface Mining Methods
Surface mining has many advantages over underground mining. Many of the the ground control, dust control, and ventilation problems that are faced underground disappear. It is somewhat unfortunate that the most environmentally benign and safest surface mining technique has gotten a bad rap.

This brings us to strip mining.

View Larger Map

Strip mining is a technique by which you mine a near-horizontal coal seam in a series of strips. The example above is from Beulah North Dakota. 1)A trench is dug from one end of the property to the other from the surface to the top of the coal seam. The overburden removed is placed along side the trench. 2)As the trench is dug equipment follows removing the coal from bottom of the trench. 3)Upon completion of the initial strip, a second trench is dug adjacent to the first exposing more coal. The overburden (spoils) is placed in the first trench. 4)The coal is removed from the bottom of the new trench. 5)Steps 3 and 4 repeat until the coal is completely mined. The equipment used for overburden removal quite large and may be a walking dragline (these guys can hook you up if you’re in the market). The equipment used to remove the coal is a bit smaller (although still massive by our standards). The gigantic bucket-wheel excavator that we looked at in class was the Tenova TAKRAF RB293 (the largest vehicle in human history).

One great advantage to true strip mining is that the company doing the mining can regrade the spoils piles while they are earning money from the mine. Thus the environmental impact is minimized: you fill the hole as part of the mining process and have revenue from the mining operation to use to perform the reclamation.

Strip mining got a bad rap for two reasons. 1)Early strip mines weren’t reclaimed.

View Larger Map
This example is from Illinois. You’ll get a better picture if you move the map around and enlage portions of it. You will easily see which areas have been disturbed by mining. The spoils piles are unsightly. Because they contained significant amounts of pyrite the piles were also an environmental hazard.
2)The term strip mine has been applied to all surface mines many of which are not as easy to reclaim as strip mines. Examples include contour mines (where a coal seam is mined along the contour of a hill) and mountaintop removal. In the last method large amounts of rock are graded off the top of a topographic high, deposited in a low area and a coal seam is removed. The effects of both contour and mountaintop removal are visually jarring. Both methods are hard to reclaim. It is impossible to regrade the land to its original contours and relatively little reclamation can take place until much of the mining has been completed. At this point the operation generates no more revenue. Thus strip mining, which typically allows much of the heavy work in reclamation to take place at the same time as mining, is a superior operation. Reclamation occurs when the mining operation is generating a positive cash flow. Because the lease holders will want to continue operations they will be more willing to heed the suggestions of a environmental regulator that represents the citizens.

hen we were dealing with oil, heavy oil, or oil shale we were discussing fossil fuels that are derived largely from lipid-rich organisms that lived in water. Coal on the other hand is derived almost exclusively from ancient land plants. Thus oil, oil shale, heavy oil (and much gas) form when carbon dioxide is photosynthetically reduced to make aquatic plants that are preserved as kerogen. Coal forms when carbon dioxide is photosynthetically reduced to form land plants.

As thick accumulations of land plants are buried to progressively greater depths and exposed to greater thermal stress the organic matter is converted to coal through loss of volatiles such as carbon dioxide and light hydrocarbons (water will also be lost during this process). It is important to remember that it is the increasing temperature that drives the coalification process rather than increasing pressure. As volatiles and water are lost, carbon content increases (slightly). Although carbon content doesn’t increase much, the H:C and O:C ratios of the organic matter (on an atomic basis) decrease dramatically.  This process is also called an increase in coal rank.

We also discussed macerals. Macerals are to coal as minerals are to rocks. Macerals are the building blocks of coal. John Crelling of Southern Illinois University has an excellent website devoted to coal macerals. One of the macerals that he has pictured is called vitrinite (The bar scale with the 25µ label is 25 microns long; 40 of those bar scales end to end would make a millimeter). Vitrinite consists of the woody material of a plant and fossil cell walls can be recognized this maceral. Other macerals comprise spores, resins, or even old charcoal.

In general the heat content of coal will increase as its rank increases. All else being equal, therefore, coal with a higher rank should be more valuable than coal with a lower rank. Of course all else will not be equal. We can get some indication of that by looking at the table of coal production.  If you look at the very bottom of that table you will note that there are many more mines in the eastern US.  This is because the complex geology in many eastern coalfields lends itself to numerous smaller mines.   Yet the relatively few mines in the western US produce significantly more coal.  The coal ranks in the Appalachians and Eastern Interior are higher than those in the western states yet the western states produce significantly more coal.

The variables that control the value of coal are rank, coal seam thickness, ash content, the depth and dip of the seam, and the sulfur content of the coal.

Seam thickness, depth and dip all control the mining method and therefore the cost of recovering the coal. Obviously thick coal seams are more attractive than thin coal seams. The issues of depth and dip (combined with surface topography) control whether the coal can be recovered using surface mining methods (safer, cheaper) or will require underground techniques. We’ll consider these in greater detail later.

Ash content and sulfur content are related somewhat to the depositional environment of the coal. Lets consider the depositional environments of coal. A reasonable modern analog for the environments that formed coal in the past is the Orinoco Delta of Venezuela. The Orinoco delta is the area circled on the map shown here where the Orinoco River system empties into the Atlantic Ocean.

This is a large feature and it is difficult for a few images to convey the scope of the delta system. But if you look at these images you should think about three things. 1)Woody vegetation is abundant. 2.)The streams that flow through the delta will flood periodically and deposit the clay and silt that they are transporting among that vegetation. That silt and clay becomes ash in coal that forms later. 3)Finally note the delta has very low relief (low elevation and little difference from the highest elevation to the lowest) and is close to sea level.  A small rise in sea level would flood the delta with sea water.  Much of this delta is influenced by tidal activity and small changes in sea level over geologic time can cause complete inundation  of the delta.

The seawater influence is important because it contains significant sulfate whereas freshwater does not. Microbes (similar to those that eat oil) eat the organic matter in the swamp sediment and the sulfate converting the organic matter to carbon dioxide (CO₂) and the sulfur to hydrogen sulfide (H₂S). The H₂S would then combine with iron bearing minerals to make pyrite (FeS₂; fool’s gold). The reduced sulfur is converted to sulfur dioxide (SO₂) when pyrite-bearing coal is burned. Once in the atmosphere the SO₂ is converted to sulfuric acid.and produces acid rain. Acid rain is an significant environmental issue that can be addressed by treating the smokestack exhaust and (more easily) by purchasing coal that contains small amounts of sulfur. Most western coal has never seen seawater, contains very little sulfur, and is, therefore more valuable than much Eastern and Interior States coal.