Cement manufacture is a significant source of Global CO2 emissions. About 3.4% to 5% of anthropogenic CO2 is emitted from the Cement manufacturing process. The process of manufacturing portland cement requires the burning of large amounts of fossil fuels. In addition the cement manufacturing process triggers the emission of even larger amounts of CO2 as a byproduct of heating raw materials. Lisa J. Hanle, Kamala R. Jayaraman and Joshua S. Smith point out, Cement is often considered a key industry for a number of reasons. To begin with, cement is an essential input into the production of concrete, a primary building material for the construction industry. Due to the importance of cement for various construction-related activities such as highways, residential and commercial buildings, tunnels and dams, production trends tend to reflect general economic activity.
In addition to the emission of CO2 by burning fossil fuels during the production of cement and the the discharge of CO2 from raw materials during cement processing, the burning of fossil fuels to produce electricity used while grinding cement clinkers also contributes to the atmospheric CO2 burden. Burning fossil fuels in cement manufacturing also releases a significant amount of NOX and SO2 gases, creating further environmental problems. There has as of yet been no environmentally satisfactory solution to the cement manufacturing issues, involving the substitution of renewable energy for fossil fuels.
The relation between cement and CO2 is actually complex. Cement in concrete actually goes through prolonged chemical curing processes, during which over half of the CO2 emitted during the manufacturing process is reabsorbed. Thus the CO2 produced by burning fossil fuels during cement manufacture constitutes a separate issue from the CO2 emitted by raw materials, because much of the latter CO2 will later be recaptured later on.
CO2 emissions from materials can be controlled by using a low carbon emissions cement manufacturing process, that might begin with different materials, or inclusion of alternative materials in the raw materials mix. Alternatively carbon recapture could be facilitated during the curing process.
Carbon emissions from burning fossil fuels while processing cement materials, can be eliminated use of nuclear power in the heat production process. One approach would be the production a carbon neutral flsmable gas using process heat from a reactor. The gas would then be burned to provide sufficient heat to process cement raw materials. There are decarbonization objections to this approach, Even if the gas manufacturing process is carbon neutral, we may not be assured of carbon neutrality during all stages of handling and use. For example methane has a far more serious greenhouse implications than CO2 does. Methane lossed inadvertantly to leaks is not carbon neutral, as is methane loses due to imperfect combustion. Thus the introduction of carbon based gases into the cement manufacturing process, presents significant challenges if carbon neutrality is the goal.
There would be no such problem if the gas were hydrogen. My well informed readers will recognize that there are problems with the handling and storage of hydrogen, but those probles relate more to the storage of hydrogen than its production. The hydrogen problems can be minimalized if hydrogen is burned immediately after its production.
Nuclear power can contribute to cement manufacture, both by serving as the indirect source of the required heat input, and as a carbon free source of electricity.
Both gas cooled and liquid salt cooled reactors could be useful in cement manufacturer, but LFTRs have the potential to perform the heat production role with the lowest potential cost. The LIFT would be the energy source that is most compatible with high energy post-carbon future. It has the greatest potential to produce industrial heat and electricity at a low cost, while for all practical purposes, energy produced by LFTRs would not be limited by natural forces or supply problems.
If decarbonization is imagined to be adressed on a sector by sector basis. In terms of electrical generation decarbonization can take place by substituting nuclear power for fossel fuel generating systems. In surface transportation, decarbonization can be accomplished by electrification. Space heating can also be electrified, especially through use of heat pumps. Finally energy for the industrial sector can be provided by greater electrification or by nuclear heat inputs.
This vision would assign to nuclear power a predominate role in the production of post carbon energy. It is quite evident that this role could not be fulfilled by conventional light water nuclear technology. First because of the limited avaliability of U-235. By a switich to Generation IV nuclear technology, energy avaliability of current supplies of nuclear fuel would be increased by a factor of 500 or more.
The program endorced by Nuclear Green is highly ambitious. I advocate the use of nuclear powered energy sources in the creation of a globalized high energy industrialized economy. My view is that this program is not incompatible with environmental values, infact it is more consistent with environmental protection than a low energy renewables powered post-carbon future. In addition, a post carbon high energy future would be less likely to produce the political and economic conditions that would lead to war.
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I don't know much about them, but there are also unconventional cements which require much lower temperatures than portland cement to produce. E.g. magnesium oxide can be produced from magnesium carbonate at temperatures as low as ~700 degrees C.
Soylent I pointed out that "CO2 emissions from materials can be controlled by using a low carbon emissions cement manufacturing process, that might begin with different materials, or inclusion of alternative materials in the raw materials mix." These pose complex issues. While alternatives are possibility, the global abundance of limestone, and the ease of cement manufacture from limestone, makes its continued use likely, We simply need to make the best of the situation.
Barry Brook wrote a similar post for steel production
http://bravenewclimate.com/2009/06/16/steel-yourself-a-clear-role-for-hydrogen/
Alex P, I find that Barry and I often think in parallel, and that of my peers with the exception of Kirk, Barry most frequently comes to similar conclusions. I must admit that Barry often makes a better case for the conclusions than I do. I just need to convince Barry that putting liquid sodium inside a reactor core is not a good idea.
Deassemblaging the circle data, I'd like to understand which fraction of the energy use in US (or in any industrialized country) is for electricity generation, transportation (both air and surface one) and both low temp heat and high temp heat applications - I don't expect that the energy use for high temp heat applications is more than 10% of the total
Alex, your question has no easy answer, because some of the industries that require high heat inout have moved off shore. While their operations are no longer carried out in the United States, their products are still sold here. Industries that require heat input include steel and other metals manufacturing, oil refining, cement manufacture, and other chemical manufacture.
I expect that some of these industrial operation nay return to the United States during the next 40 years, because local and international economic developments will be transforming the global economy.
in particular among current growing industrial powers, China and India will develop high level consumer economies that will increase their industrial labor costs. Secondly, decarbonization will lead inevitably to some global redistribution of industry. The united Stats is likely to received continuing waves of latin American immigrants, that could be employed in heavy industry.
If the only major carbon burden from cement manufacturing was from the calcination itself, we wouldn't be having this conversation.
I find the Greens obsession with this source just a red herring that they are trying to drag through this debate.
Charles, I think you missed the point of my reply. Calcining magnesium carbonate or silicates is easily within reach of high temperature reactors, but calcining lime will require a circuitous route via hydrogen.
If a significant premium is placed on high temperatures by current limits of reactor materials, this makes alternative cements more viable(which may or may not be enough to reach significant market share). This is true EVEN if hydrogen gas from high temperature reactors is as cheap as coal, because direct production of heat is even cheaper.
Soylent, I understood your point. I am not however convinced that alternative materials that require lower manufacturing temperatures are consistent with what builders want from cement. Time will tell, I suppose. in the mean time it is not a bad idea to keep the options open.
Soylent wrote:
If a significant premium is placed on high temperatures by current limits of reactor materials, this makes alternative cements more viable(which may or may not be enough to reach significant market share). This is true EVEN if hydrogen gas from high temperature reactors is as cheap as coal, because direct production of heat is even cheaper.
While the direct use of heat from a reactor would be most desirable, indirect use via hydrogen is not a show-stopper. Even if the reactor is just hot enough only to produce some hydrogen, the rest of the heat is still available to produce electricity, which is also a valuable commodity. A system approach that balances the production of two useful commodities against the increased cost of higher temperature materials will produce an optimized solution.
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