Solar Energy zero-emissions-cement

Published on April 10th, 2012 | by Susan Kraemer


Zero Carbon Cement Production with Solar Thermal

April 10th, 2012 by  


In a study published in a recent issue of , a team of researchers from Virginia’s George Washington University explain a revolutionary way to make lime cement that releases zero CO2 emissions – and costs less too.

After coal-powered electricity, cement manufacture is the next biggest emitter of greenhouse gases, because cement is ubiquitous in modern life.

It is needed for virtually all skyscrapers, bridges and freeway overpasses and many other buildings and structures including nuclear power plants. The world consumes about 3 trillion kg of cement annually.

Pound for pound, kilogram for kilogram, ton for ton, every 10 units of cement will release 9 units of CO2. So it is a huge problem for the increasingly unstable climate we are creating for ourselves.

Of the two ways that making cement releases carbon dioxide, separating the lime from the limestone (decarbonation, or removing the carbon atom and two oxygen atoms in limestone (CaCO3) to obtain lime (CaO) with CO2)  accounts for 70% of the emissions.

The other 30% is because it takes a lot of heat to heat the kiln reactors, burning fossil fuels.

Solar thermal power would be used. And not just to heat the limestone – but also to help in electrolysis. This would produce a different chemical reaction without a carbon dioxide byproduct.

In electrolysis, a current applied to the limestone changes the chemical reaction so that instead of separating into lime and CO2, the limestone separates into lime and some other combination of carbon and oxygen atoms, depending on the temperature of the reaction.

When electrolyzed below 800°C, the molten limestone forms lime, C, and O2. When electrolyzed above 800°C, the product is lime, CO, and ½O2.

Instead of a CO2 byproduct, their reactions produce useful industrial chemicals. Their carbon monoxide byproduct (in the higher temperature reaction) can be used to make fuels, purify nickel, and form plastics and other hydrocarbons.

This makes it cheaper than current lime production which costs $70 a ton, because the CO can be sold.

The researchers’ rough analysis shows that the total cost of the limestone material, solar heat and electricity is $173 per ton of lime and 0.786 tons of carbon monoxide (0.786 tons of carbon monoxide are produced for every ton of lime).

The market value of carbon monoxide is $600 per ton, or $471 per 0.786 tons. So after selling the carbon monoxide, the cost of the lime production is actually a negative number. $173 – $471 = minus $298 per ton.

No carbon emissions. Cheap. And even better, it has wide applications.

Nearly all of the other heaviest emitters could similarly be stripped of their greenhouse gas problem with this technology, the scientists say.

(Among other industries, these industrial processes include purifying iron and aluminum, making glass, paper, sugar, and agriculture, cleaning smoke stacks, softening water, and removing phosphates from sewage.)

The next step would be is simply scaling up the fairly straightforward process for commercialization. “Although the process itself is entirely new” coauthor Stuart Licht, a chemistry professor at George Washington University, told”the individual components (solar towers, 24/7 operation storing solar energy with molten salts) are already in place. Solar energy can be used to efficiently make products without carbon dioxide, and at solar energy efficiencies higher than in photovoltaics.”

The timing is perfect: a burgeoning Asia is about to build the new mega cities of the 21st century. And super hot solar thermal heat is ready: Halotechnics Molten Glass Thermal Storage Could Mean 6 Cent Solar.

In the electrolysis process alone, even without solar power, but using fossil heat source, “worst case scenario” says Licht,  “the products are lime, graphite and oxygen; there is still no CO2 product, but CO2 would be used in the energy to drive the process.”

Stuart Licht, et al. “STEP Cement: Solar Thermal Electrochemical Production of CaO without CO2 emission.” Chem. Commun., DOI: 10.1039/C2CC31341C

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About the Author

writes at CleanTechnica, CSP-Today and Renewable Energy World.  She has also been published at Wind Energy Update, Solar Plaza, Earthtechling PV-Insider , and GreenProphet, Ecoseed, NRDC OnEarth, MatterNetwork, Celsius, EnergyNow, and Scientific American. As a former serial entrepreneur in product design, Susan brings an innovator's perspective on inventing a carbon-constrained civilization: If necessity is the mother of invention, solving climate change is the mother of all necessities! As a lover of history and sci-fi, she enjoys chronicling the strange future we are creating in these interesting times.    Follow Susan on Twitter @dotcommodity.

  • johnBas5

    STEP got even better with lithium-free solution:
    Stabilization of STEP electrolyses in lithium-free molten carbonates
    Stuart Licht*Department of Chemistry,
    George Washington University, Washington, DC 20052, USA
    This communication reports on effective electrolyses in lithium-free molten carbonates.
    Processes that utilize solar thermal energy to drive efficient electrolyses are termed Solar Thermal Electrochemical Processes (STEP).
    Lithium-free molten carbonates, such as a sodium-potassium carbonate eutectic using an iridium anode,
    or a calcium-sodium-potassium carbonate eutectic using a nickel anode, can provide an effective medium for STEP electrolyses.
    Such electrolyses are useful in STEP carbon capture, and the production of staples including STEP fuel, iron, and cement.

  • Guydauncey

    Any development like this is important, but to echo Brian:

    “After coal-powered electricity, cement manufacture is the next biggest emitter of greenhouse gases”

    Burning coal produces 12 Gigatonnes of CO2 a year
    Burning oil also produces 12 Gigatonnes of CO2 a year
    Burning natural gas produces 5.8 Gigatonnes of CO2 a year, plus a whole bunch of methane
    Deforestation produces 5.5 Gigatonnes of CO2 a year
    Cement production produces 2.7 Gigatonnes of CO2 a year

    Source: My book The Climate Challenge: 101 Solutions to Global warming, page 29. (

  • “After coal-powered electricity, cement manufacture is the next biggest emitter of greenhouse gases”
    You mean next largest industrial source or process and it is next largest after electricity production in general (Natural gas is rather large and emits CO2).

    That’s a really neat process. I am curious how this would strip the other mentioned industrial activities of CO2 production and how much CO could be produced before saturating the market.

    • I would also be concerned about worker safety with an ultra-high-temperature process and carbon monoxide (aka the silent killer) as a byproduct. Sounds like this method will need a serious infusion of start-up cash to get the engineering just right to make it safe and reliable.

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