MIT: Concentrating emissions—using a pressurized combustion system to capture carbon dioxide

[OKIsItJustMe]

http://web.mit.edu/newsoffice/2009/oxyfuel-coal.html

Concentrating emissions

Ahmed Ghoniem of mechanical engineering leads an MIT effort to make coal plants cleaner by using a pressurized combustion system to capture carbon dioxide.

David L. Chandler, MIT News Office

Researchers at MIT have shown the benefits of a new approach toward eliminating carbon-dioxide (CO2) emissions at coal-burning power plants.

Their system, called pressurized oxy-fuel combustion, provides a way of separating all of the carbon-dioxide emissions produced by the burning of coal, in the form of a concentrated, pressurized liquid stream. This allows for carbon dioxide sequestration: the liquid CO2 stream can be injected into geological formations deep enough to prevent their escape into the atmosphere.

Finding a practical way to sequester carbon emissions is considered critical to the mitigation of climate change while continuing to use fossil fuels, which currently account for more than 80 percent of energy production in the United States and more than 90 percent worldwide. CO2 emissions from fossil fuels are projected to rise by more than 50 percent worldwide by 2030.

It might seem paradoxical to reduce the carbon footprint of a coal plant by making its emissions into a more concentrated stream of carbon dioxide. But Ahmed Ghoniem, the Ronald C. Crane (1972) Professor of Mechanical Engineering and leader of the MIT team analyzing this new technology, explains: "this is the first step. Before you sequester, you have to concentrate and pressurize" the greenhouse gases. "You have to redesign the power plant so that it produces a pure stream of pressurized liquid carbon dioxide, to make it sequestration ready."

…

[pscot]

1. And the pilot project is being built Where?

n/t

[hunter]

2. Swedish submarines use this system.

A mixture of fuel oil and liquid oxygen is burned at high pressure in a Stirling engine. The waste carbon dioxide is dissolved in water and expelled.

Disposing of carbon dioxide from coal power plants in deep ocean water would be a really, really bad idea, and disposal in geological formations probably isn't much wiser -- you can easily imagine some kind of rupture that would smother every breathing creature across a large area.

[OKIsItJustMe]

3. The key is to stabilize the carbon chemically

Don’t imagine a giant pressure vessel (yeah, that one bothers me too.) Instead, think about locking it up http://en.wikipedia.org/wiki/Carbon_capture_and_storage#Mineral_storage">chemically in http://en.wikipedia.org/wiki/Carbonate_minerals">carbonate minerals.

[Nihil]

4. Do you have any details on that please?

Whilst I agree that the theory of locking CO2 in "carbonate minerals"
is far better than simply pumping the damn stuff underground and hoping
that it stays there, the practice is a bit more problematical.

For example, the minerals on the wiki page you linked to are all naturally
occurring as carbonates. I trust that this isn't another "let's bake the
carbonate to produce an oxide then add the 'captured' CO2 to make a
carbonate" plan? (i.e., as was suggested for the "CO2-capturing artificial
trees" ... very nice way of getting the CO2 out of the atmosphere but a
trifle lacking in thought for what to do with it next.)

What naturally occuring oxides/hydroxides were they thinking of using
to produce stable carbonates?

:shrug:

[OKIsItJustMe]

5. Geologists Map Rocks to Soak CO2 From Air

http://www.earth.columbia.edu/news/2003/story06-25-03b.html

…

Lackner presents a more permanent method of CO₂ disposal through neutralization in carbonate form. This could be accomplished by injecting CO₂ into alkaline mineral rich layers of the Earth. When exposed to alkaline minerals, CO₂ gas reacts with the alkaline mineral to form carbonates or bicarbonates. Another option is to mine, crush, and react rock that is rich in magnesium silicates with CO₂ to form insoluble carbonates. Although this latter method is still more costly, it “would enable above-ground mineral sequestration that has the capacity of binding all CO₂ that could ever be generated and limiting the environmental impact, including terrain changes, to relatively confined areas.”

…

http://www.earth.columbia.edu/articles/view/2393

posted: 2009-03-05

Geologists Map Rocks to Soak CO2 From Air

6,000 Square Miles in U.S. Might Turn Emissions to Harmless Solids

To slow global warming, scientists are exploring ways to pull carbon dioxide from the air and safely lock it away. Trees already do this naturally through photosynthesis; now, http://pubs.usgs.gov/ds/414">in a new report, geologists have mapped large rock formations in the United States that can also absorb CO2, which they say might be artificially harnessed to do the task at a vastly increased pace.

The report, by scientists at Columbia University’s Earth Institute and the U.S. Geological Survey, shows 6,000 square miles of ultramafic rocks at or near the surface. Originating deep in the earth, these rocks contain minerals that react naturally with carbon dioxide to form solid minerals. Earth Institute scientists are experimenting with ways to speed this natural process, called mineral carbonation. If the technology takes off, geologic formations around the world could provide a vast sink for heat-trapping carbon dioxide released by humans.

Lead author Sam Krevor, a graduate student working through the Earth Institute’s Lenfest Center for Sustainable Energy, says the United States’ ultramafic rocks could be enough to stash more than 500 years of U.S. CO2 production. Conveniently, most of them are clustered in strips along the east and west coasts--some near major cities including New York, Baltimore and San Francisco. "We're trying to show that anyone within a reasonable distance of these rock formations could use this process to sequester as much carbon dioxide as possible," said Krevor.

…

Ultramafic rocks generally form in earth’s mantle, starting some 12 miles under the surface and extending down hundreds of miles. Bits of these rocks—peridotite, dunite, lherzholite and others-- may be squeezed to the surface when continental plates collide with oceanic plates, or, less often, when the interiors of continents thin and develop rifts. Because of their chemical makeup, when the rocks are exposed to carbon dioxide, they react to form common limestone and chalk. http://pubs.usgs.gov/ds/414/downloads/DS414_map.pdf">A map accompanying the report shows that most such rocks are found in and around coastal mountain ranges, with the greatest concentrations in California, Oregon and Washington, and along the Appalachians from New England to Alabama. Some also occur in the interior, including Montana. Worldwide, other formations are scattered across Eurasia and Australia.

…

http://www.energy.columbia.edu/mineral-carbon

Mineral Carbon Sequestration

Mineral carbon dioxide sequestration refers to a technology whereby carbon dioxide is reacted with metal cations in silicate minerals to form solid carbonate minerals. This technology provides permanent removal of carbon dioxide from the atmosphere, while eliminating the need for monitoring for CO2 leakage. It is also appealing in the potential for its storage capacity to exceed what would be required for the sequestration of 100% of U.S. CO2 emissions at current levels for centuries. Carbonates are overwhelmingly the most abundant natural storage mechanism for carbon on the surface of the Earth. This is a simple result of the fact that at the temperatures and pressures experienced by the Earth's crust, carbonate minerals are the thermodynamic ground state of carbon. Carbon dioxide is not the unavoidable end product of the oxidation of fossil fuels. Instead, at least in principle, it is possible to extract additional energy from a carbon atom by letting the carbon dioxide react with a base to form carbonates or bicarbonates (exemplified in Fig 1).


Figure 1. Free energy of carbon compounds relative to carbon.

The economic and technical challenges in above-ground mineral sequestration do not so much lie in the mining effort, which is well understood, but in the complications of accelerating the carbonation reaction to the point that they are economically attractive. These weathering reactions occur spontaneously in nature, albeit with extremely slow reaction kinetics. For sequestration, these reactions must be accelerated. For common magnesium silicates, the net reactions are:

    ½ Mg2SiO4 + CO₂ → MgCO₃ + ½ SiO₂ + 88 kJ
     (olivine) (CO₂) (magnesite) (silica)

    1/3 Mg₃Si₂O₅(OH)₄ + CO₂ → MgCO₃ + 2/3 SiO₂ + 2/3 H₂O + 35 kJ
        (serpentine)  (CO₂)(magnesite) (silica)    (water)

Currently, all processes involve the carbonation of the mineral in an aqueous medium or salt melt. It has been shown that serpentine minerals can be carbonated with reaction rates that are sufficiently fast when activated with pretreatment. Roasting serpentine at temperatures between 600 and 700°C makes it highly reactive. Similarly, grinding olivine to ultra-fine grain sizes (< 35 mm) increases the reactivity of the mineral. However, the cost of activating the serpentine material in order to raise the reaction rates is still too high. We are exploring pathways that avoid such energy-intensive treatment steps. Research is being performed to determine how varying the composition of the medium may enhance the kinetics of the reaction. Specifically, we are studying aqueous processes of mineral dissolution of Mg-bearing and Ca-bearing silicate minerals (see Fig 2). After the dissolution step, which is the rate-limiting step at present, the carbonate and solid byproducts from the dissolved mineral-bearing rock are precipitated by controlling the pH.

…

[Nihil]

6. Thanks for those links ...

From the first article, the first part of the statement is the hopeful bit:
> This could be accomplished by injecting CO₂ into alkaline mineral rich layers
> of the Earth. When exposed to alkaline minerals, CO₂ gas reacts with the
> alkaline mineral to form carbonates or bicarbonates.

Deliberate chemical alteration of minerals in situ is the bit that I haven't
found as anything other than a theoretical wish-list item. Unfortunately,
it appears that this is still largely the case although the second link
talks about a study starting "soon" in Iceland using the geothermal steam/water
already available there as a carrier fluid.

(FYI: http://www.or.is/English/Projects/CarbFix/AbouttheProject/)

Mind you, even they admit that it is more of a Hail Mary pass:
>> It shall be kept in mind that the amount of pores in the basaltic rock is
>> limited. Therefore, the results from the Hellisheidi experiment will not
>> safe (sic) the world’s climate. However, the experiment might demonstrate
>> that a “near zero CO2 emission” geothermal power plant is a possibility and
>> even the option to store the main part of Iceland’s CO2 emission in a safe
>> way.

This will be a project to try to monitor (in Spring of next year). :thumbsup:


The rest of the first link is the same old crap: dig up more stuff, burn up
more CO2 to process it and then "do something with it":

> Another option is to mine, crush, and react rock that is rich in magnesium
> silicates with CO₂ to form insoluble carbonates. Although this latter method
> is still more costly, it “would enable above-ground mineral sequestration
> that has the capacity of binding all CO₂ that could ever be generated and
> limiting the environmental impact, including terrain changes, to relatively
> confined areas.”

Note how they gloss over the *actual* impact of a near infinite process
(the "capacity of binding all CO₂ that could ever be generated") with a
hand-wave and nice weasel words ("relatively confined areas" that are
obviously finite and being used for something at the moment).


The second article also has a link to a project in its early stages
that will attempt to drill a 3-4000' hole then "apply for a state permit
to inject 1,000 tons of carbon dioxide" into it. After this, there will
be an 18-24 month delay before being able to sample the rock to determine
how the practice relates to the theory. Might be worth tracking.


The third article brings home a couple of important points (my italics below):

> The economic and technical challenges in above-ground mineral sequestration
> do not so much lie in the mining effort, which is well understood, but in
> the complications of accelerating the carbonation reaction to the point that
> they are economically attractive.

...

> Roasting serpentine at temperatures between 600 and 700°C makes it highly
> reactive. Similarly, grinding olivine to ultra-fine grain sizes (< 35 mm)
> increases the reactivity of the mineral. However, the cost of activating
> the serpentine material in order to raise the reaction rates is still
> too high. We are exploring pathways that avoid such energy-intensive
> treatment steps.

...

> Even though in the near future, injection underground is certain to
> be cheaper, the cost of assuring long-term integrity of the underground
> storage may in the end render mineral carbonation competitive.

(Not that any of today's problems have been driven by cost of course ...)

... and not forgetting the real reason for all of this "concern" ...

> By developing mineral sequestration to the point of demonstrated feasibility,
> one can guarantee long-term availability of fossil energy, which should be an
> important policy consideration.

Busted. So much for the happy clappy PR releases about "capturing CO2 from
the atmosphere" and fluff about assisting the iron & steel industry.

This is simply pro-coal feel-good activity to lull people into the belief
that "someone is doing something about it". Unfortunately, the "someone" is
mainly the coal industry and the "something" is mainly profits as usual.

:-(