Emissions from the Cement Industry

A single industry accounts for around 5% of global carbon dioxide (CO2) emissions. It produces a material so ubiquitous it is nearly invisible: cement. Cement is the primary ingredient in concrete, which in turn forms the foundations and structures of the buildings we live and work in, and the roads and bridges we drive on. Concrete is the second most consumed substance on Earth after water.  On average, each year, three tons of concrete are consumed by every person on the planet.

Concrete is used globally to build buildings, bridges, roads, runways, sidewalks, and dams. Cement is indispensable for construction activity, so it is tightly linked to the global economy. Cement production is growing by 2.5% annually, and is expected to rise from 2.55 billion tons in 2006 to 3.7-4.4 billion tons by 2050.

Manufacture of Cement

Though “cement” and “concrete” are often used interchangeably, concrete is actually the final product made from cement. The primary component of cement is limestone. To produce cement, limestone and other clay-like materials are heated in a kiln at 1400°C and then ground to form a lumpy, solid substance called clinker; clinker is then combined with gypsum to form cement.

Cement manufacturing is highly energy – and – emissions intensive because of the extreme heat required to produce it.  Producing a ton of cement requires 4.7 million BTU of energy, equivalent to about 400 pounds of coal, and generates nearly a ton of CO2. Given its high emissions and critical importance to society, cement is an obvious place to look to reduce greenhouse gas emissions.

Cement Emissions

The production of cement releases greenhouse gas emissions both directly and indirectly: the heating of limestone releases CO2 directly, while the burning of fossil fuels to heat the kiln indirectly results in CO2 emissions.

The direct emissions of cement occur through a chemical process called calcination. Calcination occurs when limestone, which is made of calcium carbonate, is heated, breaking down into calcium oxide and CO2. This process accounts for ~50% of all emissions from cement production.

Indirect emissions are produced by burning fossil fuels to heat the kiln. Kilns are usually heated by coal, natural gas, or oil, and the combustion of these fuels produces additional CO2 emissions, just as they would in producing electricity. This represents around 40% of cement emissions. Finally, the electricity used to power additional plant machinery, and the final transportation of cement, represents another source of indirect emissions and account for 5-10% of the industry’s emissions.

Opportunities to Mitigate

Indirect emissions from burning fossil fuels to heat the kiln can be reduced by switching to alternative fuels, including natural gas, biomass and waste-derived fuels such as tires, sewage sludge and municipal solid wastes. These less carbon-intensive fuels could reduce overall cement emissions by 18-24% from 2006 levels by 2050.

Alternatively, efficiency measures can reduce the demand for fuel by addressing the production process itself (such as switching from inefficient wet kilns to dry ones) or through technical and mechanical improvements (such as preventative maintenance to repair kiln leaks). While some estimate that energy efficiency improvements could achieve emission reductions of up to 40%, some industry analyses suggest that producers may have already exhausted this potential. Without additional financial incentives (such as subsidies or a tax on carbon), further breakthroughs could be difficult.

Reducing emissions from the calcination process means looking to a material other than limestone. Blended cement replaces some of the limestone-based clinker with other materials, primarily coal fly ash and blast furnace slag. Blended cement could reduce CO2 emissions by as much as 20%, but widespread use of blended cement is limited by other environmental regulations (these substitutes can contain toxic heavy metals); the limited availability of substitute material; and some building code restrictions (blended cement can take longer to set).

Finally, CO2 emissions can be captured after they are produced through carbon capture and storage (CCS). In addition to traditional CCS methods, which are already employed in some power plants, concrete producers can actually use their own product as a sink for CO2. Through the process of accelerated carbonation, CO2 penetrates concrete and reacts with calcium hydroxide in the presence of water to form calcium carbonate; the result is stable, long-term CO2 storage. As a mitigation technology, accelerated carbonation can be achieved by exposing freshly mixed concrete to flue gases with high CO2 concentrations.

Adapted from a factsheet on cement published in the GNCS Factsheet Series, available here.


5 thoughts on “Emissions from the Cement Industry

  1. Francine says:

    I am assisting a waste to energy technology company to enter into the cement industry.

    The plant requires waste input such as municipal garbage, including construction waste of a large volume. It outputs heat and electricity that can be used in the production of cement.

    Any input you have to offer would be appreciated!

  2. chad says:

    http://climatecolab.org/web/guest/plans/-/plans/contestId/1300403/planId/1305704

    how bout this instead. We can actually absorb more CO2 than we create by producing HEMPCRETE rather than concrete. plus, it;s a better material, in every way. Look into it mates,

    Chad

  3. Hoy Hawkins says:

    The automotive industry produces cars/trucks. The primary final assembly plant, and all the sub-supportive facilities, belch polluting emissions in response to ad driven demand (usually television). From there, the final product begins a new layer of pollution that is far more devastating than the birthing plant emissions from whence it originated. One can only begin to list coughing tail pipe emissions, spent tires piling up, windshield glass/dashboard plastic/seating foam/doors, body, and frame steel/ electronics copper wiring, and floor carpets- all insisting upon recycling attention. The same is true of the cement/concrete industry where the real pollution begins AFTER the slab concrete parking lot is no longer in use, AFTER the grain storage structure becomes obsolete, AFTER the cement bags are sent to the batch plant. Belching implosions, removals, and recycles are, many times, more in need of environmental consideration than originating production. And the real defeat is when the cement bags are sent to the batch plant for concrete slab end use. Please, not another earth smothering/heat generating parking lot. Madeleine’s stage one is a very alerting and informative article- we just need an equally alerting stage two article, because concrete is very hard to remove and very earth smothering. When there is high CO2 at the onset, and the end use stifles natures ability to make adjustments, a losing situation prevails.

  4. Treasured Homes says:

    Unfortunately, going from my own experience in the construction industry, very few firms would even consider spending extra money on these alternative solutions. I’ve worked with both great firms and shady cowboys and one thing they share is the desire to maximise profit, going green is normally the last thing on their mind.

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