sectoral economic costs and benefits of ghg mitigation - IPCC

Energy Intensive Industries
(D) Alternate Raw Materials
The industry has actively pursued the economic use of alternate materials in the manufacturing
process that would have a positive effect on greenhouse gases. There is a possibility of reducing
CO 2 from calcination by using previously calcined, by-product materials as raw mix components;
but the availability of such materials is limited.
Cement companies have worked with other industries to see if there are by-products that might
be used in cement manufacturing that will reduce overall emissions. An example of this is the
work that has been done with the steel industry to develop the use of slag as a raw material
additive for cement. Another option is to reduce the proportion of limestone in the raw mix.
Some research and development has been done in this area, however, the achievable reduction in
CO 2 emissions would be relatively small.
(E) Product Modifications
Research continues on several new methods that will increase the quantity of finished cement
produced without increasing the amount of kiln-produced clinker. Among the materials that can
be interground with clinker and continue to meet the high quality standards for portland cement
are: steel industry blast furnace slag, fly ash, limestone, and, in some cases, cement kiln dust. For
example, if ten percent alternative materials can be interground with clinker then the kiln
production can be reduced by ten percent, with a concomitant reduction in combustion and decarbonation
emissions.
Limestone Addition - Replacement of up to five percent of clinker with limestone at the finish
milling step does not impair, but may even improve, the performance of portland cement.
Addition of limestone in this way reduces the CO 2 emissions from calcination and fuel
combustion, and for each one percent of clinker replaced by limestone, CO 2 emissions per tonne
of cement drop by approximately one percent. The projections indicate that CO 2 emissions could
be 22 percent above the target in 2010 in the moderate growth scenario. The addition of five
percent limestone by itself would not reach the target level but would bring emissions within 10.9
million tonnes per year of that target.
Addition of Pozzolans and Other Cementitious Materials - Pozzolans are materials, which by
themselves have weak or no cementitious properties, but when mixed with portland cement can
contribute to the performance of the mixture. Pozzolans may be naturally occurring, but the best
known example is fly ash from coal-fired electric utilities. Certain types of blast furnace slag
have cementitious properties and can also be used to replace some of the clinker in portland
cement without affecting the performance of the blended product. The proportion of pozzolan
that can be used to replace clinker in blended cement depends on the nature of the pozzolan and
the performance required from the blended cement. The level of replacement that can be
achieved with slag is generally higher than that achievable with fly ash.
As with limestone, introducing a pozzolan or cementitious material at the finish-milling step
reduces CO 2 emissions by about one percent for each one percent of clinker replaced. To reach
the emission target in the moderate growth scenario, the average tonne of cement produced in the
United States would have to contain about 17 percent of limestone and/or pozzolan. The issues
regarding the use of pozzolans are:
• the economic availability of suitable materials,
• the performance of portland cement containing pozzolans, particularly higher
percentages of pozzolans,
• appropriate allocation of credit for the CO 2 reduction achieved by the use of
pozzolans in cements,
• market acceptance of blended cements.
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