Greener Cement

One of the challenges in attempting to reduce emissions of greenhouse gases (such as carbon dioxide and methane) is the considerable variety of emission sources.  Some, like the burning of fossil fuels for power generation and transportation, are reasonably obvious, but there are others that aren’t.   For example, it has been estimated that, in some California counties, cattle flatulence produces more greenhouse gas than motor vehicles.

Another source that might not spring immediately to mind is the production of cement, which is estimated to account for 5-6% of man-made greenhouse gas emissions.  Conventionally, cement is made by heating crushed limestone (which is basically calcium carbonate, CaCO₃) to a temperature of about 1500°C, where it breaks down to give calcium oxide (CaO, also called quicklime), the key ingredient of cement, and carbon dioxide.

CaCO₃ -> CaO + CO₂

About 60% of the carbon dioxide produced in the production of cement comes from this reaction; the balance comes from the fossil fuel burned to heat the limestone.

According to an article at Technology Review, a team at George Washington University has developed a new process that produces calcium oxide from limestone without the emission of carbon dioxide.

The new process changes the chemistry. Rather than emitting carbon dioxide, it converts the gas, using a combination of heat and electrolysis to produce oxygen and either carbon or carbon monoxide, depending on the temperatures employed.

In this process, the crushed limestone is mixed with lithium carbonate and heated to about 900°C.  The application of a relatively small electric current causes calcium oxide to form as a precipitate.

The research team believes that the heating required for the process could be provided by solar energy, and has constructed a proof-of-concept apparatus to demonstrate this.  The device uses two large Fresnel lenses to concentrate sunlight on the mixture of limestone and lithium carbonate, and a third to focus sunlight on a solar cell, which provides the electricity required.   The device makes use of about 50% of the available solar energy, which compares favorably with the ~15% efficiency of solar cells.

The technique is still at a very early stage of development, and considerable work remains to check that the process can be scaled up to industrial size.  Nonetheless, it is an intriguing idea, and another example of the value of encouraging research into alternative technologies.  Cement is not very exciting or sexy, after all; but I suspect that progress in reducing greenhouse gases will, in the end, involve a number of changes like this.

Slightly Less Rare Earths

Toward the end of 2010, we saw several items in the news about a potential shortage of the chemical elements known collectively as rare earths.  (The rare earths are the elements that lie in the periodic table from Lanthanum [La], atomic number 57, to Lutetium [Lu], atomic number 71, plus Scandium [Sc], atomic number 21, and Yttrium [Y], atomic number 39. )   These are used, typically in relatively small quantities, in a variety of technologies, including wind turbines, DC electric motors, and solar cells.

Up until the 1980s, there were a number of places where rare earths were mined, with the United States and South Africa being the largest suppliers.  China then commenced a major push into the market, offering lower prices because of its lower labor costs, and its lax-to-nonexistent environmental regulations — producing rare earths is a a dirty business.  The Chinese eventually came to supply 95+% of the market.

There was a certain amount of alarmist talk at the time about the strategic threat posed by China’s control of the supply of these elements.  I wrote at the time that I thought these fears were a bit overblown, since there were other sources, which had fallen out of favor only because of China’s cheap prices.

…  it seems likely that the main risk is a short-to-medium term run-up in prices, until alternative sources are fully operational.

As it happens, there also some alternative technologies, some quite mature, that can be used as substitutes for newer tech requiring rare earths.

An article posted on the “Wired Science” blog at Wired provides an update on the situation with the rare earths supply at present.  The US, the EU, and Japan have filed a joint complaint with the World Trade Organization against China, alleging manipulation of mineral prices.

Foreign companies buying rare earths from China must now pay more than twice the rate paid by companies inside China. The tiered pricing encourages companies to move factories and jobs to China, where they can be sure of supply and lower prices. Beyond the extra economic boost for China, this has made it easier for Chinese companies to steal foreign intellectual property.

As expected, there has also been some considerable progress in developing alternative sources of supply.  Molycorp Minerals has re-opened its mine in Mountain Pass, California, once the largest source of rare earths in the world; another new mine is being opened in Malaysia.  So it seems likely that, within a few years, we will return to a world of competing suppliers, in which no one can completely control the market.

“In five years there will be rare earths produced all over the world and China will lose its edge,” said mining analyst John Kaiser, editor of Kaiser Research Online. “Molycorp is part of that equation. They’re putting back into production what was once the largest rare-earth mine in the world.”

It is also heartening that, at least in the US, the revitalized facilities seem to be making progress in addressing some of their nastier environmental side effects.

Another Look at DC Power

Back in December, I posted a note about the resurgence of interest in DC power distribution systems, especially within data centers.  Although large scale electricity distribution systems (such as regional or national grids) have used AC for years, since the resolution of the “War of the Currents“,and obviously constitute a workable solution — I am, after all, writing this at about 10:00 PM — the data center environment differs in some significant ways from that of the average utility customer.  The electronic devices themselves almost all work on DC power  (converted from the AC supplied by the grid; backup power supplies for emergencies almost always use batteries, which supply DC.   As I noted in that earlier post, the use of DC distribution in large data centers could potentially produce significant increases in energy efficiency.

Technology Review has a new article that discusses the possible use of DC power distribution on a larger scale.   According to Greg Reed, director of the Power & Energy Initiative at the University of Pittsburgh, the growth in the use of electronic devices, especially consumer electronic devices, has meant that a larger amount of the total demand for power is, ultimately, for DC.  Currently, this DC power is supplied by the battery chargers, power supplies, and “wall warts” of our PCs, smart phones, flat-screen TVs, and other gadgets.  Reed thinks that this trend will continue.

“Within the next 20 years we could definitely see as much as 50 percent of our total loads be made up of DC consumption,” he [Reed] says. “It’s accelerating even more than we’d expected.”

He goes on to argue that a “DC takeover” of the grid is “inevitable”, due to improvements in efficiency, from eliminating AC/DC conversions, and to the increased use of consumer electronics, solar panels, and LED lighting, all of which are more “at home” in a DC-powered world.

It is certainly true that there is technology today, unavailable in Edison’s time, that makes high-voltage DC transmission over significant distances feasible.  I expect this type of distribution will be used more in the future for installations where it makes sense.  I also think that the use of DC power distribution in data centers will increase; moreover, this kind of local grid installation probably makes sense in a number of other contexts, like large commercial buildings.  Electric vehicles, too, use batteries that are recharged with DC power, so there is probably a role for local DC grids there.

Dragan Maksimovic, an expert in power electronics at the University of Colorado in Boulder, estimates that solar-powered vehicle chargers his group is developing should cut power losses from 10 percent of what the panels produce to just 2 percent.

So, I think there is a pretty good case for deployment of DC power distribution on the local scale.  In a data center, it makes little sense to have a large number of servers, each with its own power supply, taking AC from the local utility and turning it into, say, 24 volt DC.  However, I very much doubt that we will see any wholesale switch to DC power distribution on a large scale.  The US power grid represents a huge capital investment, and it does work.

IBM’s Breathing Battery

I’ve written here several times before about the importance of better battery technology to the effort to use more energy from renewable sources (such as wind or solar power), and to the development of better electric vehicles.  While autos like the Toyota Prius, which have hybrid gasoline-electric power, have been reasonably successful (helped, of course, by tax and other incentives), the development of all-electric vehicles has been held back by the relatively low power to weight ratio of current batteries.  Gasoline’s big advantage as a vehicle fuel is that it has a high energy density, the amount of power that can be generated per kilogram of fuel.

Back in 2009, IBM launched a research project, called Battery 500, aimed at developing new battery technology that would allow an electric vehicle to travel 500 miles on a single charge.   The project cites consumer surveys that indicate that “range anxiety”, the fear of being stranded without power, is a significant obstacle to consumer acceptance of all-electric vehicles.

Electric cars today typically can travel only about 100 miles on current battery technology, called lithium-ion (LIB). LIB technology stands little chance of being light enough to travel 500 miles on a single charge and cheap enough to be practical for a typical family car.

Now, according to an article at Wired, IBM has demonstrated a prototype lithium-air battery that the company believes has the potential to power a car for 500 miles.   (The ExtremeTech site also has an article on this development.)  The idea of a lithium air battery is not new; one of its key attractions is that, because one of the reactants, air, is taken in from the outside rather than having to be built into the battery, weight and size are reduced.  In the approach developed by IBM, oxygen from the air is taken into tiny openings in the battery cell, about 1 angstrom (10^-10 meter) across.  The oxygen then reacts with lithium ions on the battery cathode, producing lithium peroxide and electrons, and thus electric current.  Charging the battery reverses the chemical reaction, releasing oxygen back into the air.  Theoretically, this technology should be able to achieve an energy density of about 12 kWh/kg, roughly 15 times that of lithium-ion batteries.

There is considerable work still to be done to turn this development into a practical product; some of that will probably decrease the energy density somewhat.  Nonetheless, this is a significant step forward, because it has the potential of achieving an energy density at least roughly comparable to gasoline.

Sodium Ion Batteries, Revisited

Back in December, 2009, I wrote about a new sodium-ion battery technology being developed by a start-up company, 44 Tech, founded by Jay Whitacre, a professor of materials science and engineering at Carnegie Mellon University.   Compared to the lithium-ion batteries commonly used in everything from cell phones to electric vehicles, these new batteries have the advantage that their sodium-based chemistry uses cheaper materials and a non-toxic water-based electrolyte.

Technology Review is now reporting that the venture, now called Aquion Energy, has announced that it will open a new factory, at a site near Pittsburgh that formerly housed a Sony television factory.

The site for Aquion’s factory is a sprawling former Sony television factory near Pittsburgh. The initial production capacity will be “hundreds” of megawatt-hours of batteries per year—the company doesn’t want to be specific yet.

The initial target market for Aquion’s batteries will be in areas of the world where there is no existing electricity infrastructure.

The first applications are expected to be in countries like India, where hundreds of millions of people in communities outside major cities don’t have a connection to the electrical grid or any other reliable source of electricity.

Although people in these areas may get power from diesel generators, the rising price of fuel and the falling price of solar panels makes adding solar an attractive option, if there is a way to store the generated electricity.   Suitable battery systems could provide reliable power without the cost of building a grid, just as cell phones have made telephone service possible in places that have little or no wired telephone infrastructure.

Initially, Aquion expects its batteries to be very cost-competitive with lithium-ion technology, and  to be more attractive than lead-acid batteries because the sodium-ion cells can be recharged thousands of times, giving a significantly longer service life.

The company has said that it initially hopes to make batteries for under $300 per kilowatt-hour, far cheaper than conventional lithium-ion batteries. Lead-acid batteries can be cheaper than Aquion’s, but they last only two or three years. Aquion’s batteries, which can be recharged 5,000 times, could last for over a decade in situations in which they’re charged once a day.

The company hopes that, in time, the cost of its batteries will drop below $200 per kilowatt-hour, which it says would make them competitive for electricity storage for the US power grid.

Really Green Solar Cells

The search for practical and economically feasible ways to make better use of renewable energy sources, such as solar or wind power, continues to attract a lot of attention, for a couple of reasons.  The first, obvious consideration is that developed economies use a lot of energy, much of which currently comes from fossil fuels.  That fuel dependence comes with a number of disadvantages attached: the production of greenhouse gases and other pollutants, environmental damage from extraction, and reliance on suppliers that may not be paragons of social and political stability.  The second issue is the provision of energy for the developing world.  If that follows current practice, the problems associated with fossil fuels will only get worse; furthermore, the logistics of supplying fuel to remote regions are difficult.

The MIT News service  has a report on some new research that may help in finding solutions for these problems.  A team of MIT researchers has developed a method of constructing solar cells using materials from plants.  Plants, of course, extract energy from sunlight all the time, in the process of photosynthesis.   The new technique uses the chemicals involved in photosynthesis, coated on a high-tech substrate, to produce electricity.

Within a few years, people in remote villages in the developing world may be able to make their own solar panels, at low cost, using otherwise worthless agricultural waste as their raw material.

The work builds on research done several years ago by Shuguang Zhang of MIT, which demonstrated the basic feasibility of generating electricity from the reactions of photosynthesis.

n his original work, Zhang was able to enlist a complex of molecules known as photosystem-I (PS-I), the tiny structures within plant cells that carry out photosynthesis. Zhang and colleagues derived the PS-I from plants, stabilized it chemically and formed a layer on a glass substrate that could — like a conventional photovoltaic cell — produce an electric current when exposed to light.

Although the original work demonstrated that the idea of generating electricity in this way was valid, it was far too inefficient to be of practical use. The new work [PDF], published in the open-access journal Scientific Reports, uses a substrate composed of nanostructured titanium dioxide [TiO₂] and zinc oxide [ZnO].  This produces something like a tiny “forest” of projections from the underlying surface.  (Andreas  Mershin, one of the lead researchers, says that looking at a pine forest was one of his inspirations.)   This structure, and the properties of the substrate, allow much more efficient use of the incident light.

Turning that insight into a practical device took years of work, but in the end Mershin was able to create a tiny forest of zinc oxide (ZnO) nanowires as well as a sponge-like titanium dioxide (TiO2) nanostructure coated with the light-collecting material derived from bacteria. The nanowires not only served as a supporting structure for the material, but also as wires to carry the flow of electrons generated by the molecules down to the supporting layer of material, from which it could be connected to a circuit.

The resulting system is not quite ready to go on the market.  Although it is much more effective in converting sunlight to electricity than the original experimental technique, it still only converts about 0.1% of the incident light energy to electricity.  Still, Mershin hopes that, by making the approach much more accessible — he thinks a high school science lab could do the work — further experiments will be able to improve the efficiency of the devices enough to be practical; and a great advantage of the approach is that is potentially can be useful without a lot of supporting infrastructure.

He hopes the instructions for making a solar cell will be simple enough to be reduced to “one sheet of cartoon instructions, with no words.” The only ingredient to be purchased would be chemicals to stabilize the PS-I molecules, which could be packaged inexpensively in a plastic bag.

Mersin also points out that nature’s approach is known to work even in dirty environments; after all, nature is used to them.  Even hyper-hygienic Americans might benefit; after all, the dirt is optional.