CONCRETE SOLUTION: Energy efficiency and material substitutions at cement kilns can cut greenhouse gas emissions but carbon capture and storage will be required to fully control such emissions from industry. Image:
Making cement, which requires heating to 1,450 degrees Celsius a mass of limestone and other ingredients, caused the release of nearly 46 teragrams (roughly 50.7 million tons) of greenhouse gases in the U.S. in 2005, according to the U.S. Environmental Protection Agency. It is the basic ingredient in concrete (first used by the Romans), which paves our walks, supports our walls and even is used in our furniture in some cases. It is the essential substrate of modern life—and therefore the third largest source of U.S. greenhouse gas emissions (though dwarfed by fossil fuel consumption).
Following it in the list of significant industrial sources in the U.S. are the production of iron and steel, ammonia, aluminum and petrochemicals—the building blocks of much of modern endeavor. A host of new techniques and technologies will be required to reduce emissions from these sources that includes reusing heat and power generated in manufacturing processes; recycling materials or substituting them; controlling greenhouse gases other than carbon dioxide (CO2); and, ultimately, capturing and burying the CO2 produced. "The key approach is energy efficiency, but its application has to be tailored to each specific industrial situation," says Lenny Bernstein, an environmental consultant and coordinating lead author for the Intergovernmental Panel on Climate Change (IPCC) report chapter on mitigating emissions from industry.
For example, cement manufacturers can use either blast furnace slag from steel mills or pozzolans—natural or manufactured reactive materials that increase the long-term strength of concrete—as substitutes for other, more traditional materials. Either reduce the energy needed to form the cement. Or manufacturers can use alternative fuels. "Cement kilns are great for disposing of almost anything," Bernstein says. "You can extend the fuel source with these and thus avoid the energy associated with new fossil fuels."
Already, a host of industries have voluntarily begun to cut back on their greenhouse gas emissions worldwide, primarily by controlling the gases other than CO2 that contribute to climate change, such as methane (CH4). "The cost of reducing non-CO2 emissions is cheaper relative to reducing CO2 emissions, mainly because many of the technologies used to reduce emissions [in the former] also reduce costs to the firm through conservation and reuse of the gases," explains Casey Delhotal, another IPCC lead author who contributed to the industry chapter.
For example, Dow Chemical Co. has saved approximately $4 billion in energy costs between 1994 and 2005 by cutting greenhouse gas emissions 32 percent and its chemical industry competitor DuPont saved $3 billion between 1990 and 2005 while cutting such emissions 60 percent. "These [voluntary] activities have led to significant reductions in emissions from some companies and some industries, but overall have not had a significant effect on emissions at the national or regional level," Bernstein says. "Industry has certainly applied a great number of energy-efficiency options but so far those have been only or largely things where there's a return in terms of cost savings. There's a lot more energy efficiency that could be done but it has a cost to it."
Dealing with the emissions of CO2, the most ubiquitous greenhouse gas, will require carbon capture and storage (CCS) for the ammonia, cement and iron industries—and that will cost. But it will also be easier to apply—and therefore may pave the way for this critical technology to come into widespread use. "The gas that comes off a blast furnace contains higher CO2 concentrations than a coal-fired power plant," Bernstein says. Concentrated CO2 is easier to capture, compress and inject into the ground, and ammonia plants, for example, are already typically built on or near subterranean deposits of natural gas, which might serve for geologic sequestration. "For actually doing [CCS], that would be the lowest cost and the technologically simplest way to do it," says Bill Moomaw, an international energy policy expert at The Fletcher School of Law and Diplomacy at Tufts University.