IPCC Fourth Assessment Report: Climate Change 2007
Climate Change 2007: Working Group III: Mitigation of Climate Change

7.4.5 Minerals Cement

Cement is produced in nearly all countries. Cement consumption is closely related to construction activity and to general economic activity. Global cement production grew from 594 Mt in 1970 to 2200 Mt in 2005, with the vast majority of the growth occurring in developing countries. In 2004 developed countries produced 570 Mt (27% of world production) and developing countries 1560 Mt (73%) (USGS, 2005). China has almost half the world’s cement capacity, manufacturing an estimated 1000 Mt in 2005 (47% of global production), followed by India with a production of 130 Mt in 2005 (USGS, 2006). Global cement consumption is growing at about 2.5%/yr.

The production of clinker, the principal component of cement, emits CO2 from the calcination of limestone. Cement production is also highly energy-intensive. The major energy uses are fuel for the production of clinker and electricity for grinding raw materials and the finished cement. Coal dominates in clinker making. Based on average emission intensities, total emissions in 2003 are estimated at 1587 MtCO2 (432 MtC) to 1697 MtCO2 (462 MtC), or about 5% of global CO2 emissions, half from process emissions and half from direct energy use. Global average CO2 emission per tonne cement production is estimated by Worrell et al. (2001b) at 814 kg (222 kg C), while Humphreys and Mahasenan (2002) estimated 870 kg (264 kg C). CO2 emission/t cement vary by region from a low of 700 kg (190 kg C) in Western Europe and 730 kg (200 kg C) in Japan and South Korea, to a high of 900, 930, and 935 kg (245, 253 and 255 kg C) in China, India and the United States (Humphreys and Mahasenan, 2002; Worrell et al., 2001b). The differences in emission intensity are due (in order of contribution) to differences in the clinker content of the cement produced, energy efficiency, carbon intensity of the clinker fuel and carbon intensity of power generation (Kim and Worrell, 2002b).

Emission intensities have decreased by approximately 0.9%/yr since 1990 in Canada, 0.3%/yr (1970–1999) in the USA, and 1%/yr in Mexico (Nyboer and Tu, 2003; Worrell and Galitsky, 2004; Sheinbaum and Ozawa, 1998). A reduction in energy intensity in India since 1995–1996 has led to a reduction in emissions from the industry despite the increase in output (Dasgupta and Roy, 2001). Analysis of CO2 emission trends in four major cement-producing countries showed that energy efficiency improvement and reduction of clinker content in cement were the main factors contributing to emission reduction, while the carbon intensity of fuel mix in all countries increased slightly.

Both energy-related and process CO2 emissions can be reduced. The combined technical potential of these opportunities is estimated at 30% globally, varying between 20 and 50% for different regions (Humphreys and Mahasenan, 2002; Kim and Worrell, 2002b). Energy efficiency improvement has historically been the main contributor to emission reduction. Benchmarking and other studies have demonstrated a technical potential for up to 40% improvement in energy efficiency (Kim and Worrell, 2002b; Worrell et al., 1995). Countries with a high potential still use outdated technologies, like the wet process clinker kiln. Studies for the USA identified 30 opportunities in every production step in the cement-making process and estimated the economic potential for energy efficiency improvement in the US cement industry at 11%, reducing emissions by 5% (Worrell et al., 2000b; Worrell and Galitsky, 2004). The cement industry is capital intensive and equipment has a long lifetime, limiting the economic potential in the short term. The clinker kiln is an ideal candidate for the use of a wide variety of fuels, including waste-derived fuels, such as tyres, plastics, biomass, municipal solid wastes and sewage sludge (see Section 7.3.2). Section 7.3.7 discusses the potential for applying CCS in the cement industry.

Standard Portland cement contains 95% clinker. Clinker production is responsible for the process emissions and most of the energy-related emissions. The use of blended cement, in which clinker is replaced by alternative cementitious materials, for example blast furnace slag, fly ash from coal-fired power stations, and natural pozzolanes, results in lower CO2 emissions (Josa et al., 2004). Humphreys and Mahasenan (2002) and Worrell et al. (1995) estimate the potential for reduction of CO2 emissions at more than 7%. Current use of blended cement is relatively high in continental Europe and low in the USA and UK. Alternatives for limestone-based cement are also being investigated (Gartner, 2004; Humphreys and Mahasenan, 2002). Geopolymers have been applied in niche markets, but have yet to be proven economical for large-scale application.