By Dai Jianjun, Department of Techno-Economic Research of DRC
Research Report No 123, 2010
The cement industry is a basic industry consuming large amounts of energy resources and discharging oceans of pollutants. By developing the circular economy, the world advanced cement manufacturing countries have gradually realized energy conservation and environmental protection. China's cement output has ranked first in the world, yet there is still a difference between China's overall level and the world advanced level. Developing the circular economy to facilitate the energy conservation and emission reduction for the cement industry and to boost the upgrading of the industry is of vital importance to transforming the mode of the Chinese economic development.
I. Development of the World Cement Industry: To Realize Energy Conservation and Environmental Protection through Technical Innovation
By consolidating the technical research and development of the circular economy of the cement industry, developed countries are constantly striding forward towards energy conservation and environmental protection and have realized the transformation and upgrading of the industry.
1．Energy resources conservaton by using industrial wastes and trash to produce cement
The cement industry can use the majority of toxic and harmful wastes as blended material in cement1, as substitute cement raw material or as the alternative fuels for the cement kiln without causing secondary pollution, without using special equipment to treat exhaust gases and without consuming extra energy resources. Firstly, use deeply processed blended material to produce blended cement. During 2000～2007, the average amount of the material blended into cement went up from 7% to 12.3% in Japan, 11% to 14.1% in Germany and 4% to 6% in the United States. The proportion of the blended cement is daily on the increase on the whole. The deep-going research and processing focused on the potential properties of the blended material has enabled the material to replace cement clinker without degrading the quality and has improved the utilization of wastes. Secondly, use industrial wastes and urban trash as fuel and .raw material. From mid-1990s to 2006, the proportion of heat provided by alternative fuels of the cement industry in aggregate heat consumed by cement clinker throughout the country went up from 15% or so to 40%～50% (80% in Holland, ranking top) in countries of West and North Europe and from 5% to 15% in the United States. It is predicted that in 2010 such a proportion will reach 70%～90% in countries of West Europe and 30% in the United States. What merits special attention is that Japan originally burned all flammable wastes, incurring the leakage of the burned ashes causing secondary pollution, therefore, Japan used cement kilns to absorb flammable wastes. In 2007, the coal substitution rate presented by the alternative fuels of the cement industry came to approximately 30% according to the average heat consumption by cement clinker.
2. Cogeneration and energy recuperation by using exhaust gas from cement kiln
The heat from exhaust gas discharged from cement production accounts for more than 30% of all heat from cement burning. The low-temperature cogeneration technology uses moderate- and low-temperature exhaust gas discharged from the cement kiln to generate electricity for cement production or other purposes. The research and development of this technology was started early in Japan and achieved a high level of technology maturity. In 2003, nearly 80% of the 64 cement kilns invested by Japan were installed with low-temperature cogeneration equipment, recycling 48% of the electric energy consumed during cement production. In 1995, the US Cement Association claimed that the new dry-process cement plants could meet their own power consumption with cogeneration by 2015.
3. Bulk cement carriers could reduce resource consumption and environmental pollution
Bulk cement carriers are favorable for resource conservation, protection of environment and constant improvement of carrier efficiency. Compared with sacked cement, bulk cement can be loaded, transported, stored and used in a sealed-off way directly with special equipment (tank-bodied vehicles, vessels and warehouses), reducing resource consumption on the packaging chain and decreasing dust emission and occurrence of broken cement bags. During 1955～1975, the bulk cement carrier rate rose in Japan from 17.6% to 90.5%，and to 97.5% in 1985. The bulk cement carrier rate in the United States reached 70% in mid-1950s and 90% in 1970s and now remains at 95% or so. The bulk cement carrier rate in Germany, Britain and North European countries all remains around 70%. In recent years, handling, transportation and storage of cement packed in bulk have been also required in Asian and Southeast Asian countries (such as South Korea and Singapore).
II. A Period for the Transformation of the Mode of Development of the Chinese Cement Industry through Technical Innovation
The cement industry is a key field for China to transform its mode of economic development. In 2009, there were more than 5,000 cement manufacturing enterprises in China, generating an output of 1.63 billion tons, making up about half of the world total. The coal consumption by the cement industry has made up about 6% of the national total, with large amounts of mineral resources, such as limestone, clay and gypsum, being also consumed. And the amount of CO₂ emissions has accounted for over 10% of the national total, the amount of dust (smoke) has constituted more than 30% of the national total and the amount of sulfur dioxide and nitric oxide emissions has also ranked high among all industries.
1. Boosting industrial upgrading through technical innovation
Before 2000，the Chinese cement industry was focused on expansion of output. When building cement plants during the planned economy period， the enterprises directly under the central government adopted advanced rotary-kiln technologies, while local enterprises mainly used backward shaft-kiln technologies. With the rapid development of the national economy, the cement output generated by rotary-kiln plants was far from being able to meet the market demand. Nevertheless, thanks to the less construction investment and short construction period, the shaft-kiln plants grew rapidly. During 1971～2000, when cement production technology structure experienced some changes in China, the ratio of cement produced with such advanced technologies as rotary kiln was constantly decreasing, while the ratio of cement produced with such small-scale backward technologies as shaft kiln was increasing, making up 80% in 2000. The cement produced with backward technologies, with its quality being poor yet with a high consumption of resources, a serious environmental pollution and a low labor productivity, was eliminated early in developed countries and has been rejected by rising industrial countries as well.
After entry into the 21st century, efforts have been stepped up to accelerate the adjustment of the industrial structure of the cement industry through technical innovation. Since 1970s, by integrating technology introduction, technology assimilation and independent development, China started the research and development of the new dry process as advanced cement production technology. Around the year of 2000, the late-model dry-process cement production equipment was developed to suit the Chinese national conditions. After 2000, China began to nurture and develop the dry-process cement. In 2009, the proportion of the dry-process cement accounted for 70% of the total cement output, winning initial success in the structural adjustment of the production technologies. At the same time, the Chinese cement enterprises also pushed the lump-sum contracting including China-made complete equipment onto the international market, making up 37% of the kind on the international market in 2007.
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1The major raw materials for cement manufacturing are limestone and clay, which are made into cement raw meal through breaking, burdening and fine grinding and then placed in the kiln to be burnt into clinker. Clinker, gypsum, and other process additions are ground together in ball mills to form the final cement products