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On the future of Chinese cement industry
Cement and Concrete Research 78 (2015) 2–13
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Cement and Concrete Research journal homepage: http://ees.elsevier.com/CEMCON/default.asp
On the future of Chinese cement industry Delong Xu a,⁎, Yuansheng Cui b, Hui Li b, Kang Yang b, Wen Xu b, Yanxin Chen b a b
Chinese Academy of Engineering, Beijing 100088, China College of Materials and Mineral Resources, Xi'an University of Architecture and Technology, Xi'an 710055, China
a r t i c l e
i n f o
Article history: Received 2 June 2015 Accepted 4 June 2015 Available online 5 August 2015 Keywords: Cement industry Green degree Low CO2 emission degree Cycling degree Smart development
a b s t r a c t The Chinese cement industry is now facing several problems, including increasing environment pressure and serious overcapacity. In this paper, the Chinese cement and cement industry are re-examined in the light of aiming for low CO2 emissions in cement manufacturing, development of recycling and integration with related industries. Progress towards a smart cement industry is advocated for the manufacturing of environmentally friendly cement products. The green degree (GD), low CO2 emission degree (LCD) cycling degree (CD) and smart degree (SD) of different industries are quantitatively characterized based on material flow, energy flow and information flow. Moreover, comparisons are made among industries of cement, steel, nonferrous metallurgy, glass, and ceramics in different historical periods and this shows that cement and steel, traditional still modern as building materials, are not replaceable. It is demonstrated that ecology, lowering CO2 emissions, recycling and integration, and smart development are the four requisites for transformation in the Chinese cement industry, and the main path of transformation is presented as well. It is stressed that success of the transformation will largely depend on innovation in science and technology. Originality: In this paper, the cement and cement industry are re-examined by combining “oriental philosophy” and “western philosophy”. Based on the in-depth analysis of material flow, energy flow and information flow during cement manufacture and usage processes, the green degree (GD), low CO2 emission degree (LCD), cycling degree (CD) and smart degree (SD) were creatively put forward, accordingly, the ecological performance, low carton, cycling and intelligence degree were quantitatively characterized. The future direction of development of the cement industry was presented from the technical innovation point. © 2015 Elsevier Ltd. All rights reserved.
Contents 1. 2.
3.
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Transformation in Chinese cement industry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1. Green cement products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2. Lowing CO2 emissions in cement manufacturing . . . . . . . . . . . . . . . . . . . . . . . 2.2.1. The main approaches to achieve low CO2 emissions in cement manufacturing process . . 2.2.2. Low CO2 emission degree of cement manufacturing process . . . . . . . . . . . . . . 2.3. Recycling development and integration with related industries . . . . . . . . . . . . . . . . . 2.3.1. Assumption of producing high calcium fly ash in power plants . . . . . . . . . . . . . 2.3.2. Idea of enhancing quality of blast furnace slag in steel production process . . . . . . . . 2.3.3. Integrated utilization of municipal solid wastes . . . . . . . . . . . . . . . . . . . . 2.3.4. The cycling degree of cement industry and its related industries . . . . . . . . . . . . 2.4. Smart cement industry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.1. Smart manufacturing process . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.2. Smart marketing and management . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.3. Smart development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Suggestions for the transformation in Chinese cement industry . . . . . . . . . . . . . . . . . . . . 3.1. Re-examination of cement and cement industry . . . . . . . . . . . . . . . . . . . . . . . 3.2. Recycling development and in-depth integration with related industries: key to the transformation
⁎ Corresponding author. Tel.: +86 29 82202762, fax: +86 29 85535724. E-mail address: [email protected] (D. Xu).
http://dx.doi.org/10.1016/j.cemconres.2015.06.012 0008-8846/© 2015 Elsevier Ltd. All rights reserved.
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3.3. Taking concrete for the final products, increasing cement categories and extending the industrial chain 3.4. Realization of smart development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1. Introduction The basic needs for human survival are clothing, food, shelter and transportation, among which “shelter” and “transportation” greatly rely upon construction and building materials. Among the many building materials, cement is seen as the “food” for building and plays an irreplaceable role in the process of human civilization. Modern cement was born [1,2] in 1824 with the patent awarded to the British engineer J. Aspdin, for “Portland cement”. Modern cement is a kind of traditional and yet modern building material based on ancient cementitious materials. As is shown in Fig. 1, cement and steel, with a brief history of 190 years, represent some of the greatest achievements of human endeavor and the milestones of civilization in the history. The Chinese cement industry has been playing a vital role for the rise of China over the past 100 years since its initial growth. Fig. 2 shows the Chinese cement output and its share in the total world cement output over the last 30 years. It can be seen that with the rapid development of the economy and increasing demand for cement, China's cement output has grown rapidly. It has become the world's largest cement production country since 1985, and its output has accounted for over half of the total in the world since 2006. Cement has been the bulk indispensable building material after the foundation of new China. It has been widely used in civil construction, water management, national defense and traffic engineering and plays a very important role in the construction of the national infrastructure. By the end of 2014, the proportion of Chinese living in urban areas had reached 55%, highway is up to 112,000 km, high-speed railway reaches 16,000 km, and the number of water conservancy dams has increased to nearly 90,000 with a total length of dikes of more than 250,000 km. As a result of the unremitting efforts of several generations of cement workers, Chinese cement manufacturing technology and equipment have reached the world leading level. Based on the new dry cement production technology, the Chinese cement industry is striving for the aims of large scale, high efficiency equipment, high performance, clean process and comprehensive utilization of wastes. The technology and equipment have so far not only satisfied the domestic needs, but have also been exported to overseas.
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In the development of cement industry, there are several problems to solve. First, growing pressure on the environment which is unsustainable, and the substantial increase in management cost of enterprises. In July 2013, the Chinese Ministry of Environmental Protection issued new standards with stricter limits on emission of dust particles, SO2 and NOx. A considerable number of cement plants cannot meet these limits with existing technology. Second, there is serious overcapacity. Profitability is greatly threatened. In 2014, Chinese cement output was 2.476 billion tons, while the actual capacity is 3.315 billion tons, the capacity utilization rate was only 75%, which is far below the internationally recognized rate of 85%. Third, the rate of development is slowing down. The theoretical thermal consumption of cement per kg is 1800– 2165 kJ (including raw material drying, 5–8% water is included). Since the pre-calcination technology has been developed, thermal consumption per unit of cement clinker has decreased from 3100 kJ/kg clinker to 2250 kJ/kg, however, it is difficult to further reduce the calcination thermal consumption further given that there is now a thermal loss of only 200 kJ/kg clinker in the manufacturing process. What is the future for Chinese cement industry? What are the essentials to the future cement research? We urge researchers to ponder these questions and seek answers. 2. Transformation in Chinese cement industry There is no other new material that can completely take the place of cement. With the growing pressure on environment, consumption of resources, and the increasing demand of environment protection, significant transformations will continue to take place in cement industry, including more environmentally friendly products, low CO2 emissions in manufacturing, recycling development and integration with related industries, and smart cement industry. 2.1. Green cement products The production of materials comes along with material flow and energy flow. Ecological products result from the minimum use of raw materials and energy during the process of manufacturing with minimum
Fig. 1. History of materials [3].
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Fig. 2. Output of Chinese cement and ratio between Chinese and world cement output in the last 30 years (Source: Chinese Cement Association [4]).
negative impact on the environment. An objective should be the use of wastes as raw materials or semi-finished products for production, in order to reduce the need to extract more raw materials from the environment. Ecological degree of products can be measured by the green degree (GD): Theoretical usage of nature resources for unit qualified product Actual usage of materials for unit qualified product Mts þ M tl þ Mtg þ M te ¼ M s þ M l þ M g þ M e −Mw
GD ¼
ð1Þ where: Ms—the actual usage of the solid materials (mineral raw materials), kg/kg products; Ml—the actual usage of liquid raw materials (water), kg/kg products; Mg—the actual usage of raw gas (air), kg/kg products; Me—the actual usage of energy (converted into standard coal), kg/kg products; Mw—the actual usage of wastes, kg/kg products;
Mts—the theoretical usage of the solid materials (mineral raw materials) rate, kg/kg products; Mtl—the theoretical usage of liquid raw materials (water), kg/kg products; Mtg—the theoretical usage of raw gas (air), kg/kg products; Mte—the theoretical usage of energy (converted into standard coal), kg/kg products; Mt—total raw materials required for the production of per unit product, kg/kg products. GD b 1, the manufacturing process is pollutants emissions process; GD = 1, the manufacturing process is almost a theoretical process, with no excessive damage on the environment; GD N 1, the manufacturing process is eco friendly, and the products can be defined as ecological products. The larger GD is, the higher the green degree of the process. In accordance with the above definition about the green degree, on the basis of the actual production situation of various industrial products, we have calculated green degree for magnesium alloy, aluminum alloy, crude steel, cement, glass and building ceramics and other industrial products, as is shown in Fig. 3. Accordingly, Chinese cement green degree can be calculated in terms of technology progress level over the years, as is shown in Fig. 4.
Fig. 3. Comparison of GD of different industries in China.
D. Xu et al. / Cement and Concrete Research 78 (2015) 2–13
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Fig. 4. GD of Chinese cement industries from 2002 to 2011.
Global warming has become a focus of international community, especially the huge amount of greenhouse gas CO2 emissions is the main factor of climate warming. Controlling CO2 emissions is the urgent task faced by human society. The total amount of global CO2 emissions in 2013 was 36 billion tons, of which industrial CO2 emissions accounted for about 29% (as is shown in Fig. 5), and cement industry was one of the major industrial sectors that generated CO2 emission [6]. The global cement output is about
4.2 billion tons in 2013. The Chinese clinker coefficient in cement is 0.560 and the average clinker coefficient in other parts of the world was 0.780. If one assumes 0.815 tons of CO2 release per ton clinker, it is calculated that the global cement production is about 2.2 billion tons of CO2, accounting for 6% of the global CO2 emissions, and accounting for 21% of global industrial CO2 emissions. Based on the above data, lowering CO2 emissions in cement manufacturing has an important significance for the global CO2 emissions reduction. China is the world's largest country in energy consumption and its CO2 emissions accounted for about 27% of global emissions and ranked the first in the world (as is shown in Fig. 6). As the world's largest developing country, China has the responsibility and obligation to make contributions to the reduction of global greenhouse gases emissions (especially CO2). The cement industry, coming after the power industry with coal, is the second largest emitter of Chinese industrial CO2 emissions [9]. Lowering CO2 emission of the manufacturing process in the cement industry is an important objective (Fig. 7). Almost 0.930 ton of CO2 is produced with every ton of cement clinker, in which direct CO2 emission due to the consumption of fossil fuels by cement clinker calcinations is 0.393 t/t cement clinker, and direct CO2 emission produced by decomposition of carbonate in the raw material is about 0.500 t/t clinker, indirect CO2 produced by power consumption during clinker calcinations is 0.035 t/t clinker (assuming energy consumption of per ton clinker calcinations is 3200 MJ and power consumption is 24 kWh/t clinker. Calorific value of standard coal is 29.300 MJ/kg standard coal, fixed carbon content of standard coal is 0.733, effective oxidation fraction of coal is 0.982, the coefficient of carbon being converted into carbon dioxide is 3.670, and conversion coefficient of coal to electricity is 0.404 kg standard coal/kWh). CO2
Fig. 5. Basic composition of global CO2 emissions [7].
Fig. 6. Individual country's CO2 contributions to global CO2 emissions [8].
It is seen from Fig. 3 that compared with other structural materials, cement is the material with highest utilization ratio of raw materials and good ecological performance. With the development of science and technology, the cement industry will play a more and more important role in municipal garbage disposal, sludge disposal and hazardous waste treatment, so the green degree of cement products will be higher. Fig. 4 shows that the green degree of Chinese cement industry has been increasing year by year, which is mainly due to the major breakthrough in energy saving and emission reduction technology especially the dust control technology applied in Chinese cement industry recently. The manufacturing process of cement and cement products is becoming more and more ecological. It took over 1000 years [5] for lime and volcano ash from ancient Rome to switch to Portland cement invented by British engineer J. Aspdin. With the limited reserves of high quality natural resources, it is the inevitable choice to manufacture high performance cement today using industrial wastes rich in calcium silicate or aluminosilicate minerals. 2.2. Lowing CO2 emissions in cement manufacturing
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Fig. 7. Chinese industrial components of CO2 emission.
generated by limestone decomposition accounts for about 53% of the total CO2 emissions during clinker production process. Fig. 8 shows changes in CO2 emissions of unit cement product in Chinese cement industry from 2000 to 2013. It can be seen that the CO2 emissions of unit cement product in China decreased significantly, with the rapid progress of cement manufacturing technology due to progress in calcination technology, which enables energy consumption per unit of cement product to decrease gradually, moreover, direct CO2 emissions produced by clinker calcinations decline accordingly. At the same time, slag, fly ash and other industrial solid wastes used as active admixtures by the cement industry greatly reduce direct CO2 emissions produced by decomposition of carbonate. Indirect emissions caused by electricity consumption are decreased year by year, but the progress is not so obvious (the slope of the line is very small), which indicates that the innovation of the mechanical equipment is slow. 2.2.1. The main approaches to achieve low CO2 emissions in cement manufacturing process Cement production technology has gone through the development of shaft kiln, wet process rotary kiln, rotary kiln, Lepol kiln and suspension preheating technology since Portland cement was invented [11–13]. Since Japanese Ishikawajima Harima Heavy Industries Company invented new suspension preheater (New Suspension Preheater, referred to as NSP kiln) based on Humboldt kiln (four stage cyclone suspension preheater kilns) in 1971, the cement industry production has benefited from the new dry cement production technology— suspension preheating and precalcining technology [14]. Since cement
production is a high energy consuming process, energy consumption has been the subject of technical progress. After 100 years of development, the new XDL (named after Prof XU Delong) cement clinker calcining technology invented in China in 2003 has successfully reduced heat consumption of unit cement clinker from 7942 kJ/kg clinker to 2839 kJ/kg clinker (as is shown in Fig. 9). So the use of new technology to decrease heat consumption of clinker calcinations is one of the important ways to realize low CO2 emission cement manufacturing process. Compared with the ordinary dry suspension preheating and precalcining cement clinker technology, XDL new technology has the following technical advantages[15,16]: first, the clinker calcination, raw meal preparation and mineral powder production are combined together to make full use of the system waste heat. Moreover, the comprehensive heat consumption of unit cement clinker production is reduced to 2366 kJ/kg clinker (as is shown in Table 1); second, due to use of high solid gas ratio preheater and external circulation, high solid gas ratio decomposing furnace, the contact area of gas and solid, times of heat exchange and heating time is doubled, so that heat efficiency and decomposition rate of kiln material are both significantly increased, the clinker output is increased by 40%, the unit volume output of rotary kiln can be as high as 5.890 t/m3 d (see Fig. 10); third, the emission of SO2 and NOx is low; fourth, the strength of cement clinker is increased by 10% and there is better flexibility to use inferior raw materials. Various technical indicators are shown in Table 1 [15,16]. The cement production process can be summarized as “two grindings and one calcination”. The so-called “two grindings” refer to the two grinding processes including cement raw meal preparation and cement preparation. It is estimated that power consumption of the two grinding processes accounts for 62% of overall power consumption in traditional cement manufacturing process (as is shown in Table 2). So the grinding energy conservation is another important way to realize lower CO2 emissions in cement production. Powder processing has a long history. In ancient China, powder processing technology evolved from pestle to roller and millstone, and the contact between grinding equipment and ground materials developed from “point contact” to “line contact” and then “plane contact”. As a result, the grinding efficiency is significantly improved and the grinding energy consumption is reduced. Modern grinding technology, nurtured by ancient wisdom, has also experienced the progress from “point contact” of ball mill to “line contact” of roller mill and high pressure roller mill (Table 3). Table 4 and Table 5 show the comparison between effects
Fig. 8. CO2 emissions produced by every unit cement products in China from 2000 to 2013.
D. Xu et al. / Cement and Concrete Research 78 (2015) 2–13
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Fig. 9. The waste heat utilization chart of the XDL cement clinker calcination technology.
of grinding raw material, slag and clinker using different techniques. It is concluded that progress of grinding techniques should be sort to further reduce CO2 emissions in the cement manufacturing process. The results indicate that non ball milling is the future trend in cement industry (Fig. 11). In addition, to replace clinker by preparing ecological cement with other industrial solid waste residue that is rich in silicate and aluminosilicate substitution, is the third approach to realize low CO2 emission manufacturing process. With the increase in clinker substitution rate, CO2 emissions per unit cement product are significantly reduced [10].
non ferrous metallurgy, iron and steel and energy industries, Chinese cement industry shows lower CO2 emission degree and it keeps abreast with the global advanced level in general. Moreover, the innovative XDL process represents the leading level globally, where LCD = 1. XDL cement clinker calcining technology together with non-ball milling can reduce unit CO2 emissions by 6%. In the future, lowering CO2 emissions in the cement manufacturing process is likely to be achieved via collecting and reusing CO2 on one hand, and utilizing heat source under 80 °C on the other.
2.2.2. Low CO2 emission degree of cement manufacturing process The low CO2 emission degree (LCD) can be used to measure the level CO2 emissions in the manufacturing process. The definition formula is as follows,
The Chinese philosophy stresses “Round tao”. “Round” means recycling interlinkage while “tao” is related to yin–yang alternation. “Round tao” is used to explain the rules governing relations between phenomena including contradiction, interaction and reciprocal development, namely, integration and harmony between things. Metal, wood, water, fire, earth, the five basic elements in the universe, are closely related to each other. In particular, earth as the nonorganic material is related more closely with fire and gold (as is shown in Fig. 13). In real life, metallurgists employ pyrogenic process and use CaO as slagging constituent to extract metal with high purity while producing huge amounts of slag rich in silicate and aluminosilicate, e.g., iron making, steel making, melting magnesium and copper smelting. There are such significant issues as how to innovate metallurgical and calcinating process to extract pure metal and generate electricity while producing
LCD ¼
world leading level of CO2 emissions of unit qualified product : total amount of CO2 emissions of unit qualified product ð2Þ
0 b LCD ≤ 1. The closer LCD is to 1, the closer is to the leading contemporary level. In accordance with the above definition about low CO2 emission degree, on the basis of actual production situation of various industries in China, LCD of magnesium alloy, aluminum alloy, crude steel, cement, glass and building ceramics and other industrial products can be calculated separately, as is shown in Fig. 12. It is shown that compared with
2.3. Recycling development and integration with related industries
Table 1 Comparisons of technical indicators between XDL cement calcining new process and the traditional NSP technology. Item
XDL process
NSP process
Change ratio (%)
Solid–gas ratio (kg solid/kg gas) Kiln output (t/d) Heat consumption (kJ/kg cl) System heat consumption (kJ/kg cl) Temp. of waste gas (°C) Volume of waste gas (Nm3/kg cl) Electricity consumption (kWh/kg cl) SO2 emission (kg/t cl) NOx emission (kg/t cl) Strength of clinker (MPa) Calcining efficiency (%)
2.00 3592 2839 2366 260 1.23 24.22 0.075 0.164 57.78 N99
0.90 2500 3350 3078 320–360 1.52 26–30 0.305 0.392 51.75 90–95
+122.00 +43.68 −15.25 −23.13 −21.21 −19.08 −13.50 −75.41 −58.28 +11.65 +7.03
Fig. 10. The technical progress of cement industry since 1887.
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Table 2 Power consumption of unit product of cement plant [17]. Consumer name
Power consumption per unit clinker (kW·h/t)
Ratio (%)
Reclaiming and homogenizing Raw material grinding Raw meal homogenizing Clinker manufacture Cement grinding Transportation, packing, shipment Total
5.5 26.4 6.6 24.2 41.8 5.5 110
5 24 6 22 38 5 100
Table 3 Progress of grinding process.
slag as good as cement clinker, and how to intensively develop metallurgical and power industries while effectively reducing the environmental burden and realizing harmonious coexistence between human society and nature, and recycling development and integration with related industries.
2.3.1. Assumption of producing high calcium fly ash in power plants In 2013, Chinese coal (including coal gangue) power generation was 3947.400 billion kWh, accounting for 94% of the total amount of thermal power generation, producing about 0.300 billion tons of fly ash. Since a large amount of coal will produce a lot of fly ash, CO2, SO2 and NOx, related technologies must be applied to control relevant emissions. Fig. 14 shows the production process in Chinese thermal power plants, where selective catalytic reduction denitration process (SCR) and limestone-gypsum wet flue gas desulfurization (FGD) are mainly
used. Due to the use of NH3 as reducing agent and catalyst which needs to be replaced every 3–4 years, the denitration cost is quite high for SCR process (10,000 yuan per ton of NOx). Besides, it is easy for NH3 to escape in the process, which causes second pollution. In addition, there are other disadvantages as well, for instance, in the FGD process low temperature electrostatic precipitator (ESP) and wet electrostatic precipitator (WESP) are required respectively in front of and behind the desulfurization tower, hence, a large complex system and a high initial investment. A point-to-point treatment is taken in both SCR and FGD processes, which results in a longer production process. What's more, a failure of one individual link may break down the entire production line and the operating rate will be affected accordingly. In order to get rid of air pollution caused by coal-fired boiler, wisdom in traditional Chinese medicine is brought into full play. Every symptom has its essential cause, which should be tracked and treated. Likewise, the fundamental solution to the problem lies in the likelihood to grind coal and desulfurized limestone together, which enables desulfurization in combustion reaction, hence production of super high calcium fly ash as a result. In experiments, high efficiency desulfurization in combustion is realized, in the process of which the ratio of desulfurizer is adjusted in accordance with the Ca/S ratio. Meanwhile, accurate, real-time and on-line high sensitivity detection of sulfur content in coal is achieved through ECA element analyzer and the signal is fed back to the feed bag in time (as is shown in Fig. 15). It is proved that by mixing and grinding limestone and coal fuel together strictly according to Ca/S (calcium sulfur ratio) and going through the temperature reaction in the furnace, the furnace temperature does not drop but rise slightly. In addition, sulfur in coal is trapped during combustion of pulverized coal. Moreover, the desulfurization rate is high, and sulfur minerals are transformed into calcium sulfate, dicalcium silicate, sulphoaluminate, sulphoferrite and other useful cementitious minerals by solid state reaction, so that the quality of fly ash is greatly improved. High calcium fly ash high performance can partially replace cement clinker for cement manufacturing.
2.3.2. Idea of enhancing quality of blast furnace slag in steel production process China is the largest producer of steel. Chinese pig iron production was 0.712 billion tons in 2014 and produced 0.200 billion tons of blast furnaces slag, accounting for about 60% of global production. The main ironmaking method used in current iron and steel enterprises is the
Table 4 Comparisons of techniques for raw material grinding. Standard
Vertical mill
Ball grinder
Rolling machine
Maximum feeding water
Up to 25%
Energy consumption per unit Production flexibility Compared with construction cost of ball mill
60%–70% Satisfied 110%–120%
Without drying bin, up to 3% With drying bin, up to 6% With drying bin and outer drying, up to 12% 100% None 100%
6%–10% In powder selecting machine or outer drying 40%–50% Satisfied 110%–120%
Table 5 Contrasts between grinding of slag and clinker.
Energy consumption (kWh/t) Investment (10 K RMB) Operation and maintenance
Ball mill (host) Vertical mill Ball mill Vertical mill Ball mill Vertical mill
Slag
Clinker
65–75 26–29 850 2000 High energy consumption, dry classification is needed, poor environment coordination Low energy consumption, drying, grinding and grading in one set, good environmental coordination
35–40 21–25 850 2000 High energy consumption, dry classification is needed, poor environment coordination Low energy consumption, drying, grinding and grading in one set, good environmental coordination
D. Xu et al. / Cement and Concrete Research 78 (2015) 2–13
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Fig. 11. Market share of different kinds of grinding processes in cement industry.
blast furnace reduction process. The traditional production process needs to preheat cold limestone to 800–950 °C to ensure that the limestone is decomposed as CaO, and the decomposed CaO then will be cooled down to room temperature and used as binder and powdered iron raw material for mixing and granulating, and then go through high temperature sintering in the sintering equipment. In the process of preheating and decomposing + cooling + high temperature sintering, there will be a lot of waste heat wasted. Besides, only iron making is considered in the process, little attention is paid to the composition and properties of the resulting slag. The production of every 1 ton of pig iron produces 0.300 ton of slag. It is estimated that Chinese steel industry produced at least 0.200 billion tons of blast furnace slag in 2014. If the existing process is improved, not only to ensure the quality of the iron but also the quality of the produced slag, high quality cement clinker can be made, maximum benefit can be realized by iron and steel
and building materials enterprises, and the integration of material production can be effectively achieved. Based on the ideas above, the idea of producing high calcium cement clinker while producing iron is proposed as is shown in Fig. 17: in contrast to the traditional process, the early stage of limestone calcination and subsequent adding lime stone into blast furnace processes are both eliminated, while enough limestone powder is added one-time according to the later reaction needs during granulation process to make them fully decomposed in the sintering process and participate in slagging reaction in blast furnace. As a result, the calcination times of calcareous raw materials are reduced (once is sufficient), slagging needs are considered in the ingredients (high calcium). This process is energysaving and effective in producing high quality cement clinker, and it verifies the likelihood in recycling and establishing integration between steel industry and that of building materials. (See Fig. 16.)
Fig. 12. Contrast between low CO2 emission degree (LCD) of different industrial products in China.
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of cement industry and its related industries can be calculated by reciprocal of clinker coefficient and expressed as: CD ¼
1 −1 k
ð3Þ
CD—cycling degree, dimensionless; k—clinker coefficient, the ratio of cement clinker usage per unit cement products, dimensionless. The range of k is [0–1], while the range of CD is [0–∞]. When CD is 0, it means that there is no recycling, with the increase of CD, the degree of recycling is increased to infinity. Fig. 19 shows CD of Chinese cement industry over the years. It is shown that CD of Chinese cement industry and its related industries increase year by year, by the end of 2014, Chinese cement output is 2.476 billion tons, while clinker is only 1.417 billion tons, the CD is as high as 0.750 accordingly. 2.4. Smart cement industry
Fig. 13. The five elements.
2.3.3. Integrated utilization of municipal solid wastes With the acceleration of Chinese urbanization, a large amount of construction waste has appeared in China (some 1.500 billion tons of construction waste being produced annually), causing severe environmental problems. It is urgent to utilize this construction waste. In the early days, it was difficult to separate powder waste bricks from concrete in the construction garbage, so the use of construction wastes was limited to landfill, excluding steel and timber. With the breakthroughs of pre separation technology (as is shown in Fig. 18), the powder, steel, brick and concrete can be completely separated from construction wastes, which lays the solid foundation for high valueadded fine utilization of construction wastes. In the future, waste steel bar can be recycled for steel making; concrete can be recycled as aggregate used in construction; brick after crushing and grinding can be made into lightweight aggregate. The performance of powder made by waste bricks is close to slag, which can be used as concrete mineral admixture. Construction powder wastes can be used as plaster or mortar. Recycled and intensive development of various industries is an important way to realize ecological civilization, and will also create new ecological benefit. 2.3.4. The cycling degree of cement industry and its related industries The purpose of recycling of cement industry and its related industries is to completely use their solid wastes which are rich in silicate and aluminosilicate to replace cement clinker and produce high quality cementing materials, e.g., cement or concrete. The cycling degree (CD)
With the popularization of information technology and information communication technology such as internet, mobile internet, cloud computing, big data, the fourth industrial revolution led by intelligence is coming. In the new generation of information technology and acceleration of industrial integration, the Chinese cement industry needs to keep up with the trend of the times, with a realization of the significance of smart industry. There are three key aspects in smart cement industry, (1) smart manufacturing process; (2) smart marketing and management; and (3) smart development. SD can be used to measure intelligence degree in the process of manufacture of cement. The equation is:
SD ¼
Annual output of cement enterprise : The total staff number
ð4Þ
The larger SD is, the higher the per capita GDP of cement manufacturing enterprises. The intelligence degree, marketing and management informatization can be reflected by SD. The smart degree of Chinese cement enterprises in 2014 is summarized in Fig. 19 according to the annual output and staff number. 2.4.1. Smart manufacturing process Currently, DCS automation control system has been used in almost all Chinese cement enterprises, however, compared with the world advanced level, the capability of optimization and integration of process and timely automatic optimization control level all lag behind. It is urgent to upgrade the automation knowledge and improve the management personnel skills. With the establishment of physical information system (CPS), ubiquitous sensors and embedded terminal system, intelligent control system and communication facilities will be formed
Fig. 14. Current thermal power plant production process.
D. Xu et al. / Cement and Concrete Research 78 (2015) 2–13
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Fig. 15. Schematic process of manufacturing high performance fly ash by adding calcium and desulfurization in accurate furnace.
Fig. 16. The process of ironmaking along with production of high calcium cement clinker.
into an intelligent network in hopes to gradually realize the seamless link of information and human–machine interaction, reduce the interference level difference, reduce the waste of resources and equipment caused by the fluctuation of production line damage, and improve equipment operating efficiency, and eventually to improve the product quality, reduce production costs, reduce pollutant emissions, and promote green development of cement enterprises.
2.4.2. Smart marketing and management With the continuous development of modern cement manufacturing enterprises, and their interaction with financial, logistics, e-commerce and other related industries, its management becomes more and more complex. At the same time, in the ever-changing market economy environment, smart marketing and management of cement enterprises is becoming more and more important. In the future, cloud technology
Fig. 17. Scheme of construction waste recycling process.
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Fig. 18. Cycling degree of Chinese cement industry from 1990 to 2013.
will be applied in cement enterprises and will bring them into closer ties with related enterprises. With the guide of big data, a new overall management and service system will be materialized covering all the major phases from the design of the products, their manufacturing, their delivery, to their application and maintenance, and new values will be established as well. 2.4.3. Smart development In light of the current problems Chinese cement industry is facing, namely, overcapacity and throat-cutting competition, we must take overall control over the industry. Industry association is taken as leader to foster coordination and cooperation between cement enterprises, and to promote comprehensive set of production and marketing. Peak production is applied to reduce pressure on environment, thus human being and nature can coexist in harmony. The formation of a highly flexible, personalized, smart production and service mode will be realized.
3. Suggestions for the transformation in Chinese cement industry The development mode of cement industry has to change since we are facing severe environmental, resources and overcapacity problems. The transformation has to be taken from the conventions which mainly depend on investment and resources consumption to innovationdriven development which means green development, low carbon development and recycling development. The transformation could be painful since it entails breaking away from old fashioned practices and will require great adjustment in both our minds and our practices.
3.1. Re-examination of cement and cement industry In the teaching and research of material engineering, there are different disciplinary areas and subjects. People mainly focus on the study of components, structure and performance of cement since it was found and used while its essence of being cementing material is neglected. Furthermore, people seem to fail to realize that the final product is nothing but high quality concrete and that all kinds of solid wastes can be modified into high quality cementing materials. We need to trace back to the essence of cementing materials and to understand what cement is and what cement industry is all about. The new thinking and new orientation will define the future development.
3.2. Recycling development and in-depth integration with related industries: key to the transformation
Fig. 19. Comparison of SD between main Chinese cement enterprises.
Recycling development and in-depth integration with related industries including construction materials, metallurgy engineering, energy resources, chemical engineering and municipal construction are the most important ways for green and low carbon development in cement industry. The R&D of chain connection technology and initiative of intensive development will decide the depth of integration between these industries. R&D of recycling engineering and its technology should be the main research area of innovation-driven development. Moreover, utilization of CO2 emitted during cement calcinations is vital to the recycling development.
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3.3. Taking concrete for the final products, increasing cement categories and extending the industrial chain On one hand, as a kind of cementing material, cement is just the middle product while concrete is the end product for construction. Nowadays, the profit margins for normal cement products are small since they are oversupplied. On the other hand, the performance of special cements such as the expansive cement for dam construction, the high abrasion resistant cement for the express ways and heavyloaded road and corrosion resistant cement for marine construction fails to live up to the expectations. Therefore, the only way out is to keep a close eye on the ultimate demand in the market and integrate cement industry with concrete production. 3.4. Realization of smart development In the face of the fourth industrial revolution, we must accelerate the in-depth integration of cement industry with information technology and promote an all-round transformation to achieve the smart development. 4. Conclusion Cement is a kind of traditional yet young building material, which cannot be replaced in a fairly long period of time. The vitality in the cement industry lies in the incessant transformation and development. Green, low carbon, integration and smart development are the inevitable trends in the transformation. The success of the transformation largely depends on science and technology innovation.
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References [1] C.R. Gagg, Cement and concrete as an engineering material: an historic appraisal and case study analysis, Eng. Fail. Anal. 40 (2014) 114–140. [2] Y. Jani, W. Hogland, Waste glass in the production of cement and concrete—a review, J. Environ. Chem. Eng. 2 (2014) 1767–1775. [3] K. Dan, L. Ward, The History of Glass, Orbis, London, 1984. [4] China Cement Association. China cement almanac, 2001-2013. [5] J. Davidovits, The history of concrete and the nabataeans, http://nabatate.net/ cement.html. [6] K. Vatopoulos, E. Tzimas, Assessment of CO2 capture technologies in cement manufacturing process, J. Clean. Prod. 32 (2012) 251–261. [7] P. Nejat, F. Jomehzadeh, M.M. Taheri, etc, A global review of energy consumption, CO2 emissions and policy in the residential sector (with an overview of the top ten CO2 emitting countries), Renew. Sust. Energ. Rev. 43 (2015) 843–862. [8] E. Benhelal, G. Zahedi, E. Shamsaei, etc., Global strategies and potentials to curb CO2 emissions in cement industry, J. Clean. Prod. 51 (2013) 142–161. [9] J.H. Xu, T. Fleiter, Y. Fan, W. Eichhammer, CO2 emissions reduction potential in China's cement industry compared to IEA's cement technology roadmap up to 2050, Appl. Energy 130 (2014) 592–602. [10] M.B. Ali, R. Saidur, M.S. Hossain, A review on emission analysis in cement industries, Renew. Sust. Energ. Rev. 15 (2011) 2252–2261. [11] H.D. Walter, Cement-data-Book, Bauverlay Gmbh, Berlin, 1996. [12] C.D. Lawrence, The production of low-energy cements, in: HewlettPC (Ed.), Lea's Chemistry of Cement and Concrete, 4th EdArnold, London 1998, pp. 421–470. [13] C.D. Popescu, M. Muntean, J.H. Sharp, Industrial trial production of low energy belite cement, Cem. Concr. Compos. 25 (2003) 689–693. [14] V. Johansen, T.V. Koouznetsova, Clinker Formation and New Process, The 9th Int. Cong. Chem. Cement, New Delhi1992. 125–152. [15] D.L. Xu, H. Li, Y.X. Chen, et al., Theory and practice of cement suspension preheating and precalcining technology with high solid–gas mass ratio, Proc.6th Int. Conf. on Cement and Concrete, Xi'an2006. 15–20. [16] D.L. Xu, H. Li, Y.X. Chen, etc., XDL cement manufacture technology of high solid–gas mass ratio, Cem. Int. 3 (2014) 82–87. [17] A. Bosoga, O. Masek, J.E. Oakey, CO2 capture technology for cement industry, Energy Procedia 1 (2009) 133–140.
Contents lists available at ScienceDirect
Cement and Concrete Research journal homepage: http://ees.elsevier.com/CEMCON/default.asp
On the future of Chinese cement industry Delong Xu a,⁎, Yuansheng Cui b, Hui Li b, Kang Yang b, Wen Xu b, Yanxin Chen b a b
Chinese Academy of Engineering, Beijing 100088, China College of Materials and Mineral Resources, Xi'an University of Architecture and Technology, Xi'an 710055, China
a r t i c l e
i n f o
Article history: Received 2 June 2015 Accepted 4 June 2015 Available online 5 August 2015 Keywords: Cement industry Green degree Low CO2 emission degree Cycling degree Smart development
a b s t r a c t The Chinese cement industry is now facing several problems, including increasing environment pressure and serious overcapacity. In this paper, the Chinese cement and cement industry are re-examined in the light of aiming for low CO2 emissions in cement manufacturing, development of recycling and integration with related industries. Progress towards a smart cement industry is advocated for the manufacturing of environmentally friendly cement products. The green degree (GD), low CO2 emission degree (LCD) cycling degree (CD) and smart degree (SD) of different industries are quantitatively characterized based on material flow, energy flow and information flow. Moreover, comparisons are made among industries of cement, steel, nonferrous metallurgy, glass, and ceramics in different historical periods and this shows that cement and steel, traditional still modern as building materials, are not replaceable. It is demonstrated that ecology, lowering CO2 emissions, recycling and integration, and smart development are the four requisites for transformation in the Chinese cement industry, and the main path of transformation is presented as well. It is stressed that success of the transformation will largely depend on innovation in science and technology. Originality: In this paper, the cement and cement industry are re-examined by combining “oriental philosophy” and “western philosophy”. Based on the in-depth analysis of material flow, energy flow and information flow during cement manufacture and usage processes, the green degree (GD), low CO2 emission degree (LCD), cycling degree (CD) and smart degree (SD) were creatively put forward, accordingly, the ecological performance, low carton, cycling and intelligence degree were quantitatively characterized. The future direction of development of the cement industry was presented from the technical innovation point. © 2015 Elsevier Ltd. All rights reserved.
Contents 1. 2.
3.
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Transformation in Chinese cement industry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1. Green cement products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2. Lowing CO2 emissions in cement manufacturing . . . . . . . . . . . . . . . . . . . . . . . 2.2.1. The main approaches to achieve low CO2 emissions in cement manufacturing process . . 2.2.2. Low CO2 emission degree of cement manufacturing process . . . . . . . . . . . . . . 2.3. Recycling development and integration with related industries . . . . . . . . . . . . . . . . . 2.3.1. Assumption of producing high calcium fly ash in power plants . . . . . . . . . . . . . 2.3.2. Idea of enhancing quality of blast furnace slag in steel production process . . . . . . . . 2.3.3. Integrated utilization of municipal solid wastes . . . . . . . . . . . . . . . . . . . . 2.3.4. The cycling degree of cement industry and its related industries . . . . . . . . . . . . 2.4. Smart cement industry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.1. Smart manufacturing process . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.2. Smart marketing and management . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.3. Smart development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Suggestions for the transformation in Chinese cement industry . . . . . . . . . . . . . . . . . . . . 3.1. Re-examination of cement and cement industry . . . . . . . . . . . . . . . . . . . . . . . 3.2. Recycling development and in-depth integration with related industries: key to the transformation
⁎ Corresponding author. Tel.: +86 29 82202762, fax: +86 29 85535724. E-mail address: [email protected] (D. Xu).
http://dx.doi.org/10.1016/j.cemconres.2015.06.012 0008-8846/© 2015 Elsevier Ltd. All rights reserved.
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3.3. Taking concrete for the final products, increasing cement categories and extending the industrial chain 3.4. Realization of smart development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1. Introduction The basic needs for human survival are clothing, food, shelter and transportation, among which “shelter” and “transportation” greatly rely upon construction and building materials. Among the many building materials, cement is seen as the “food” for building and plays an irreplaceable role in the process of human civilization. Modern cement was born [1,2] in 1824 with the patent awarded to the British engineer J. Aspdin, for “Portland cement”. Modern cement is a kind of traditional and yet modern building material based on ancient cementitious materials. As is shown in Fig. 1, cement and steel, with a brief history of 190 years, represent some of the greatest achievements of human endeavor and the milestones of civilization in the history. The Chinese cement industry has been playing a vital role for the rise of China over the past 100 years since its initial growth. Fig. 2 shows the Chinese cement output and its share in the total world cement output over the last 30 years. It can be seen that with the rapid development of the economy and increasing demand for cement, China's cement output has grown rapidly. It has become the world's largest cement production country since 1985, and its output has accounted for over half of the total in the world since 2006. Cement has been the bulk indispensable building material after the foundation of new China. It has been widely used in civil construction, water management, national defense and traffic engineering and plays a very important role in the construction of the national infrastructure. By the end of 2014, the proportion of Chinese living in urban areas had reached 55%, highway is up to 112,000 km, high-speed railway reaches 16,000 km, and the number of water conservancy dams has increased to nearly 90,000 with a total length of dikes of more than 250,000 km. As a result of the unremitting efforts of several generations of cement workers, Chinese cement manufacturing technology and equipment have reached the world leading level. Based on the new dry cement production technology, the Chinese cement industry is striving for the aims of large scale, high efficiency equipment, high performance, clean process and comprehensive utilization of wastes. The technology and equipment have so far not only satisfied the domestic needs, but have also been exported to overseas.
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In the development of cement industry, there are several problems to solve. First, growing pressure on the environment which is unsustainable, and the substantial increase in management cost of enterprises. In July 2013, the Chinese Ministry of Environmental Protection issued new standards with stricter limits on emission of dust particles, SO2 and NOx. A considerable number of cement plants cannot meet these limits with existing technology. Second, there is serious overcapacity. Profitability is greatly threatened. In 2014, Chinese cement output was 2.476 billion tons, while the actual capacity is 3.315 billion tons, the capacity utilization rate was only 75%, which is far below the internationally recognized rate of 85%. Third, the rate of development is slowing down. The theoretical thermal consumption of cement per kg is 1800– 2165 kJ (including raw material drying, 5–8% water is included). Since the pre-calcination technology has been developed, thermal consumption per unit of cement clinker has decreased from 3100 kJ/kg clinker to 2250 kJ/kg, however, it is difficult to further reduce the calcination thermal consumption further given that there is now a thermal loss of only 200 kJ/kg clinker in the manufacturing process. What is the future for Chinese cement industry? What are the essentials to the future cement research? We urge researchers to ponder these questions and seek answers. 2. Transformation in Chinese cement industry There is no other new material that can completely take the place of cement. With the growing pressure on environment, consumption of resources, and the increasing demand of environment protection, significant transformations will continue to take place in cement industry, including more environmentally friendly products, low CO2 emissions in manufacturing, recycling development and integration with related industries, and smart cement industry. 2.1. Green cement products The production of materials comes along with material flow and energy flow. Ecological products result from the minimum use of raw materials and energy during the process of manufacturing with minimum
Fig. 1. History of materials [3].
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Fig. 2. Output of Chinese cement and ratio between Chinese and world cement output in the last 30 years (Source: Chinese Cement Association [4]).
negative impact on the environment. An objective should be the use of wastes as raw materials or semi-finished products for production, in order to reduce the need to extract more raw materials from the environment. Ecological degree of products can be measured by the green degree (GD): Theoretical usage of nature resources for unit qualified product Actual usage of materials for unit qualified product Mts þ M tl þ Mtg þ M te ¼ M s þ M l þ M g þ M e −Mw
GD ¼
ð1Þ where: Ms—the actual usage of the solid materials (mineral raw materials), kg/kg products; Ml—the actual usage of liquid raw materials (water), kg/kg products; Mg—the actual usage of raw gas (air), kg/kg products; Me—the actual usage of energy (converted into standard coal), kg/kg products; Mw—the actual usage of wastes, kg/kg products;
Mts—the theoretical usage of the solid materials (mineral raw materials) rate, kg/kg products; Mtl—the theoretical usage of liquid raw materials (water), kg/kg products; Mtg—the theoretical usage of raw gas (air), kg/kg products; Mte—the theoretical usage of energy (converted into standard coal), kg/kg products; Mt—total raw materials required for the production of per unit product, kg/kg products. GD b 1, the manufacturing process is pollutants emissions process; GD = 1, the manufacturing process is almost a theoretical process, with no excessive damage on the environment; GD N 1, the manufacturing process is eco friendly, and the products can be defined as ecological products. The larger GD is, the higher the green degree of the process. In accordance with the above definition about the green degree, on the basis of the actual production situation of various industrial products, we have calculated green degree for magnesium alloy, aluminum alloy, crude steel, cement, glass and building ceramics and other industrial products, as is shown in Fig. 3. Accordingly, Chinese cement green degree can be calculated in terms of technology progress level over the years, as is shown in Fig. 4.
Fig. 3. Comparison of GD of different industries in China.
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Fig. 4. GD of Chinese cement industries from 2002 to 2011.
Global warming has become a focus of international community, especially the huge amount of greenhouse gas CO2 emissions is the main factor of climate warming. Controlling CO2 emissions is the urgent task faced by human society. The total amount of global CO2 emissions in 2013 was 36 billion tons, of which industrial CO2 emissions accounted for about 29% (as is shown in Fig. 5), and cement industry was one of the major industrial sectors that generated CO2 emission [6]. The global cement output is about
4.2 billion tons in 2013. The Chinese clinker coefficient in cement is 0.560 and the average clinker coefficient in other parts of the world was 0.780. If one assumes 0.815 tons of CO2 release per ton clinker, it is calculated that the global cement production is about 2.2 billion tons of CO2, accounting for 6% of the global CO2 emissions, and accounting for 21% of global industrial CO2 emissions. Based on the above data, lowering CO2 emissions in cement manufacturing has an important significance for the global CO2 emissions reduction. China is the world's largest country in energy consumption and its CO2 emissions accounted for about 27% of global emissions and ranked the first in the world (as is shown in Fig. 6). As the world's largest developing country, China has the responsibility and obligation to make contributions to the reduction of global greenhouse gases emissions (especially CO2). The cement industry, coming after the power industry with coal, is the second largest emitter of Chinese industrial CO2 emissions [9]. Lowering CO2 emission of the manufacturing process in the cement industry is an important objective (Fig. 7). Almost 0.930 ton of CO2 is produced with every ton of cement clinker, in which direct CO2 emission due to the consumption of fossil fuels by cement clinker calcinations is 0.393 t/t cement clinker, and direct CO2 emission produced by decomposition of carbonate in the raw material is about 0.500 t/t clinker, indirect CO2 produced by power consumption during clinker calcinations is 0.035 t/t clinker (assuming energy consumption of per ton clinker calcinations is 3200 MJ and power consumption is 24 kWh/t clinker. Calorific value of standard coal is 29.300 MJ/kg standard coal, fixed carbon content of standard coal is 0.733, effective oxidation fraction of coal is 0.982, the coefficient of carbon being converted into carbon dioxide is 3.670, and conversion coefficient of coal to electricity is 0.404 kg standard coal/kWh). CO2
Fig. 5. Basic composition of global CO2 emissions [7].
Fig. 6. Individual country's CO2 contributions to global CO2 emissions [8].
It is seen from Fig. 3 that compared with other structural materials, cement is the material with highest utilization ratio of raw materials and good ecological performance. With the development of science and technology, the cement industry will play a more and more important role in municipal garbage disposal, sludge disposal and hazardous waste treatment, so the green degree of cement products will be higher. Fig. 4 shows that the green degree of Chinese cement industry has been increasing year by year, which is mainly due to the major breakthrough in energy saving and emission reduction technology especially the dust control technology applied in Chinese cement industry recently. The manufacturing process of cement and cement products is becoming more and more ecological. It took over 1000 years [5] for lime and volcano ash from ancient Rome to switch to Portland cement invented by British engineer J. Aspdin. With the limited reserves of high quality natural resources, it is the inevitable choice to manufacture high performance cement today using industrial wastes rich in calcium silicate or aluminosilicate minerals. 2.2. Lowing CO2 emissions in cement manufacturing
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Fig. 7. Chinese industrial components of CO2 emission.
generated by limestone decomposition accounts for about 53% of the total CO2 emissions during clinker production process. Fig. 8 shows changes in CO2 emissions of unit cement product in Chinese cement industry from 2000 to 2013. It can be seen that the CO2 emissions of unit cement product in China decreased significantly, with the rapid progress of cement manufacturing technology due to progress in calcination technology, which enables energy consumption per unit of cement product to decrease gradually, moreover, direct CO2 emissions produced by clinker calcinations decline accordingly. At the same time, slag, fly ash and other industrial solid wastes used as active admixtures by the cement industry greatly reduce direct CO2 emissions produced by decomposition of carbonate. Indirect emissions caused by electricity consumption are decreased year by year, but the progress is not so obvious (the slope of the line is very small), which indicates that the innovation of the mechanical equipment is slow. 2.2.1. The main approaches to achieve low CO2 emissions in cement manufacturing process Cement production technology has gone through the development of shaft kiln, wet process rotary kiln, rotary kiln, Lepol kiln and suspension preheating technology since Portland cement was invented [11–13]. Since Japanese Ishikawajima Harima Heavy Industries Company invented new suspension preheater (New Suspension Preheater, referred to as NSP kiln) based on Humboldt kiln (four stage cyclone suspension preheater kilns) in 1971, the cement industry production has benefited from the new dry cement production technology— suspension preheating and precalcining technology [14]. Since cement
production is a high energy consuming process, energy consumption has been the subject of technical progress. After 100 years of development, the new XDL (named after Prof XU Delong) cement clinker calcining technology invented in China in 2003 has successfully reduced heat consumption of unit cement clinker from 7942 kJ/kg clinker to 2839 kJ/kg clinker (as is shown in Fig. 9). So the use of new technology to decrease heat consumption of clinker calcinations is one of the important ways to realize low CO2 emission cement manufacturing process. Compared with the ordinary dry suspension preheating and precalcining cement clinker technology, XDL new technology has the following technical advantages[15,16]: first, the clinker calcination, raw meal preparation and mineral powder production are combined together to make full use of the system waste heat. Moreover, the comprehensive heat consumption of unit cement clinker production is reduced to 2366 kJ/kg clinker (as is shown in Table 1); second, due to use of high solid gas ratio preheater and external circulation, high solid gas ratio decomposing furnace, the contact area of gas and solid, times of heat exchange and heating time is doubled, so that heat efficiency and decomposition rate of kiln material are both significantly increased, the clinker output is increased by 40%, the unit volume output of rotary kiln can be as high as 5.890 t/m3 d (see Fig. 10); third, the emission of SO2 and NOx is low; fourth, the strength of cement clinker is increased by 10% and there is better flexibility to use inferior raw materials. Various technical indicators are shown in Table 1 [15,16]. The cement production process can be summarized as “two grindings and one calcination”. The so-called “two grindings” refer to the two grinding processes including cement raw meal preparation and cement preparation. It is estimated that power consumption of the two grinding processes accounts for 62% of overall power consumption in traditional cement manufacturing process (as is shown in Table 2). So the grinding energy conservation is another important way to realize lower CO2 emissions in cement production. Powder processing has a long history. In ancient China, powder processing technology evolved from pestle to roller and millstone, and the contact between grinding equipment and ground materials developed from “point contact” to “line contact” and then “plane contact”. As a result, the grinding efficiency is significantly improved and the grinding energy consumption is reduced. Modern grinding technology, nurtured by ancient wisdom, has also experienced the progress from “point contact” of ball mill to “line contact” of roller mill and high pressure roller mill (Table 3). Table 4 and Table 5 show the comparison between effects
Fig. 8. CO2 emissions produced by every unit cement products in China from 2000 to 2013.
D. Xu et al. / Cement and Concrete Research 78 (2015) 2–13
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Fig. 9. The waste heat utilization chart of the XDL cement clinker calcination technology.
of grinding raw material, slag and clinker using different techniques. It is concluded that progress of grinding techniques should be sort to further reduce CO2 emissions in the cement manufacturing process. The results indicate that non ball milling is the future trend in cement industry (Fig. 11). In addition, to replace clinker by preparing ecological cement with other industrial solid waste residue that is rich in silicate and aluminosilicate substitution, is the third approach to realize low CO2 emission manufacturing process. With the increase in clinker substitution rate, CO2 emissions per unit cement product are significantly reduced [10].
non ferrous metallurgy, iron and steel and energy industries, Chinese cement industry shows lower CO2 emission degree and it keeps abreast with the global advanced level in general. Moreover, the innovative XDL process represents the leading level globally, where LCD = 1. XDL cement clinker calcining technology together with non-ball milling can reduce unit CO2 emissions by 6%. In the future, lowering CO2 emissions in the cement manufacturing process is likely to be achieved via collecting and reusing CO2 on one hand, and utilizing heat source under 80 °C on the other.
2.2.2. Low CO2 emission degree of cement manufacturing process The low CO2 emission degree (LCD) can be used to measure the level CO2 emissions in the manufacturing process. The definition formula is as follows,
The Chinese philosophy stresses “Round tao”. “Round” means recycling interlinkage while “tao” is related to yin–yang alternation. “Round tao” is used to explain the rules governing relations between phenomena including contradiction, interaction and reciprocal development, namely, integration and harmony between things. Metal, wood, water, fire, earth, the five basic elements in the universe, are closely related to each other. In particular, earth as the nonorganic material is related more closely with fire and gold (as is shown in Fig. 13). In real life, metallurgists employ pyrogenic process and use CaO as slagging constituent to extract metal with high purity while producing huge amounts of slag rich in silicate and aluminosilicate, e.g., iron making, steel making, melting magnesium and copper smelting. There are such significant issues as how to innovate metallurgical and calcinating process to extract pure metal and generate electricity while producing
LCD ¼
world leading level of CO2 emissions of unit qualified product : total amount of CO2 emissions of unit qualified product ð2Þ
0 b LCD ≤ 1. The closer LCD is to 1, the closer is to the leading contemporary level. In accordance with the above definition about low CO2 emission degree, on the basis of actual production situation of various industries in China, LCD of magnesium alloy, aluminum alloy, crude steel, cement, glass and building ceramics and other industrial products can be calculated separately, as is shown in Fig. 12. It is shown that compared with
2.3. Recycling development and integration with related industries
Table 1 Comparisons of technical indicators between XDL cement calcining new process and the traditional NSP technology. Item
XDL process
NSP process
Change ratio (%)
Solid–gas ratio (kg solid/kg gas) Kiln output (t/d) Heat consumption (kJ/kg cl) System heat consumption (kJ/kg cl) Temp. of waste gas (°C) Volume of waste gas (Nm3/kg cl) Electricity consumption (kWh/kg cl) SO2 emission (kg/t cl) NOx emission (kg/t cl) Strength of clinker (MPa) Calcining efficiency (%)
2.00 3592 2839 2366 260 1.23 24.22 0.075 0.164 57.78 N99
0.90 2500 3350 3078 320–360 1.52 26–30 0.305 0.392 51.75 90–95
+122.00 +43.68 −15.25 −23.13 −21.21 −19.08 −13.50 −75.41 −58.28 +11.65 +7.03
Fig. 10. The technical progress of cement industry since 1887.
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Table 2 Power consumption of unit product of cement plant [17]. Consumer name
Power consumption per unit clinker (kW·h/t)
Ratio (%)
Reclaiming and homogenizing Raw material grinding Raw meal homogenizing Clinker manufacture Cement grinding Transportation, packing, shipment Total
5.5 26.4 6.6 24.2 41.8 5.5 110
5 24 6 22 38 5 100
Table 3 Progress of grinding process.
slag as good as cement clinker, and how to intensively develop metallurgical and power industries while effectively reducing the environmental burden and realizing harmonious coexistence between human society and nature, and recycling development and integration with related industries.
2.3.1. Assumption of producing high calcium fly ash in power plants In 2013, Chinese coal (including coal gangue) power generation was 3947.400 billion kWh, accounting for 94% of the total amount of thermal power generation, producing about 0.300 billion tons of fly ash. Since a large amount of coal will produce a lot of fly ash, CO2, SO2 and NOx, related technologies must be applied to control relevant emissions. Fig. 14 shows the production process in Chinese thermal power plants, where selective catalytic reduction denitration process (SCR) and limestone-gypsum wet flue gas desulfurization (FGD) are mainly
used. Due to the use of NH3 as reducing agent and catalyst which needs to be replaced every 3–4 years, the denitration cost is quite high for SCR process (10,000 yuan per ton of NOx). Besides, it is easy for NH3 to escape in the process, which causes second pollution. In addition, there are other disadvantages as well, for instance, in the FGD process low temperature electrostatic precipitator (ESP) and wet electrostatic precipitator (WESP) are required respectively in front of and behind the desulfurization tower, hence, a large complex system and a high initial investment. A point-to-point treatment is taken in both SCR and FGD processes, which results in a longer production process. What's more, a failure of one individual link may break down the entire production line and the operating rate will be affected accordingly. In order to get rid of air pollution caused by coal-fired boiler, wisdom in traditional Chinese medicine is brought into full play. Every symptom has its essential cause, which should be tracked and treated. Likewise, the fundamental solution to the problem lies in the likelihood to grind coal and desulfurized limestone together, which enables desulfurization in combustion reaction, hence production of super high calcium fly ash as a result. In experiments, high efficiency desulfurization in combustion is realized, in the process of which the ratio of desulfurizer is adjusted in accordance with the Ca/S ratio. Meanwhile, accurate, real-time and on-line high sensitivity detection of sulfur content in coal is achieved through ECA element analyzer and the signal is fed back to the feed bag in time (as is shown in Fig. 15). It is proved that by mixing and grinding limestone and coal fuel together strictly according to Ca/S (calcium sulfur ratio) and going through the temperature reaction in the furnace, the furnace temperature does not drop but rise slightly. In addition, sulfur in coal is trapped during combustion of pulverized coal. Moreover, the desulfurization rate is high, and sulfur minerals are transformed into calcium sulfate, dicalcium silicate, sulphoaluminate, sulphoferrite and other useful cementitious minerals by solid state reaction, so that the quality of fly ash is greatly improved. High calcium fly ash high performance can partially replace cement clinker for cement manufacturing.
2.3.2. Idea of enhancing quality of blast furnace slag in steel production process China is the largest producer of steel. Chinese pig iron production was 0.712 billion tons in 2014 and produced 0.200 billion tons of blast furnaces slag, accounting for about 60% of global production. The main ironmaking method used in current iron and steel enterprises is the
Table 4 Comparisons of techniques for raw material grinding. Standard
Vertical mill
Ball grinder
Rolling machine
Maximum feeding water
Up to 25%
Energy consumption per unit Production flexibility Compared with construction cost of ball mill
60%–70% Satisfied 110%–120%
Without drying bin, up to 3% With drying bin, up to 6% With drying bin and outer drying, up to 12% 100% None 100%
6%–10% In powder selecting machine or outer drying 40%–50% Satisfied 110%–120%
Table 5 Contrasts between grinding of slag and clinker.
Energy consumption (kWh/t) Investment (10 K RMB) Operation and maintenance
Ball mill (host) Vertical mill Ball mill Vertical mill Ball mill Vertical mill
Slag
Clinker
65–75 26–29 850 2000 High energy consumption, dry classification is needed, poor environment coordination Low energy consumption, drying, grinding and grading in one set, good environmental coordination
35–40 21–25 850 2000 High energy consumption, dry classification is needed, poor environment coordination Low energy consumption, drying, grinding and grading in one set, good environmental coordination
D. Xu et al. / Cement and Concrete Research 78 (2015) 2–13
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Fig. 11. Market share of different kinds of grinding processes in cement industry.
blast furnace reduction process. The traditional production process needs to preheat cold limestone to 800–950 °C to ensure that the limestone is decomposed as CaO, and the decomposed CaO then will be cooled down to room temperature and used as binder and powdered iron raw material for mixing and granulating, and then go through high temperature sintering in the sintering equipment. In the process of preheating and decomposing + cooling + high temperature sintering, there will be a lot of waste heat wasted. Besides, only iron making is considered in the process, little attention is paid to the composition and properties of the resulting slag. The production of every 1 ton of pig iron produces 0.300 ton of slag. It is estimated that Chinese steel industry produced at least 0.200 billion tons of blast furnace slag in 2014. If the existing process is improved, not only to ensure the quality of the iron but also the quality of the produced slag, high quality cement clinker can be made, maximum benefit can be realized by iron and steel
and building materials enterprises, and the integration of material production can be effectively achieved. Based on the ideas above, the idea of producing high calcium cement clinker while producing iron is proposed as is shown in Fig. 17: in contrast to the traditional process, the early stage of limestone calcination and subsequent adding lime stone into blast furnace processes are both eliminated, while enough limestone powder is added one-time according to the later reaction needs during granulation process to make them fully decomposed in the sintering process and participate in slagging reaction in blast furnace. As a result, the calcination times of calcareous raw materials are reduced (once is sufficient), slagging needs are considered in the ingredients (high calcium). This process is energysaving and effective in producing high quality cement clinker, and it verifies the likelihood in recycling and establishing integration between steel industry and that of building materials. (See Fig. 16.)
Fig. 12. Contrast between low CO2 emission degree (LCD) of different industrial products in China.
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of cement industry and its related industries can be calculated by reciprocal of clinker coefficient and expressed as: CD ¼
1 −1 k
ð3Þ
CD—cycling degree, dimensionless; k—clinker coefficient, the ratio of cement clinker usage per unit cement products, dimensionless. The range of k is [0–1], while the range of CD is [0–∞]. When CD is 0, it means that there is no recycling, with the increase of CD, the degree of recycling is increased to infinity. Fig. 19 shows CD of Chinese cement industry over the years. It is shown that CD of Chinese cement industry and its related industries increase year by year, by the end of 2014, Chinese cement output is 2.476 billion tons, while clinker is only 1.417 billion tons, the CD is as high as 0.750 accordingly. 2.4. Smart cement industry
Fig. 13. The five elements.
2.3.3. Integrated utilization of municipal solid wastes With the acceleration of Chinese urbanization, a large amount of construction waste has appeared in China (some 1.500 billion tons of construction waste being produced annually), causing severe environmental problems. It is urgent to utilize this construction waste. In the early days, it was difficult to separate powder waste bricks from concrete in the construction garbage, so the use of construction wastes was limited to landfill, excluding steel and timber. With the breakthroughs of pre separation technology (as is shown in Fig. 18), the powder, steel, brick and concrete can be completely separated from construction wastes, which lays the solid foundation for high valueadded fine utilization of construction wastes. In the future, waste steel bar can be recycled for steel making; concrete can be recycled as aggregate used in construction; brick after crushing and grinding can be made into lightweight aggregate. The performance of powder made by waste bricks is close to slag, which can be used as concrete mineral admixture. Construction powder wastes can be used as plaster or mortar. Recycled and intensive development of various industries is an important way to realize ecological civilization, and will also create new ecological benefit. 2.3.4. The cycling degree of cement industry and its related industries The purpose of recycling of cement industry and its related industries is to completely use their solid wastes which are rich in silicate and aluminosilicate to replace cement clinker and produce high quality cementing materials, e.g., cement or concrete. The cycling degree (CD)
With the popularization of information technology and information communication technology such as internet, mobile internet, cloud computing, big data, the fourth industrial revolution led by intelligence is coming. In the new generation of information technology and acceleration of industrial integration, the Chinese cement industry needs to keep up with the trend of the times, with a realization of the significance of smart industry. There are three key aspects in smart cement industry, (1) smart manufacturing process; (2) smart marketing and management; and (3) smart development. SD can be used to measure intelligence degree in the process of manufacture of cement. The equation is:
SD ¼
Annual output of cement enterprise : The total staff number
ð4Þ
The larger SD is, the higher the per capita GDP of cement manufacturing enterprises. The intelligence degree, marketing and management informatization can be reflected by SD. The smart degree of Chinese cement enterprises in 2014 is summarized in Fig. 19 according to the annual output and staff number. 2.4.1. Smart manufacturing process Currently, DCS automation control system has been used in almost all Chinese cement enterprises, however, compared with the world advanced level, the capability of optimization and integration of process and timely automatic optimization control level all lag behind. It is urgent to upgrade the automation knowledge and improve the management personnel skills. With the establishment of physical information system (CPS), ubiquitous sensors and embedded terminal system, intelligent control system and communication facilities will be formed
Fig. 14. Current thermal power plant production process.
D. Xu et al. / Cement and Concrete Research 78 (2015) 2–13
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Fig. 15. Schematic process of manufacturing high performance fly ash by adding calcium and desulfurization in accurate furnace.
Fig. 16. The process of ironmaking along with production of high calcium cement clinker.
into an intelligent network in hopes to gradually realize the seamless link of information and human–machine interaction, reduce the interference level difference, reduce the waste of resources and equipment caused by the fluctuation of production line damage, and improve equipment operating efficiency, and eventually to improve the product quality, reduce production costs, reduce pollutant emissions, and promote green development of cement enterprises.
2.4.2. Smart marketing and management With the continuous development of modern cement manufacturing enterprises, and their interaction with financial, logistics, e-commerce and other related industries, its management becomes more and more complex. At the same time, in the ever-changing market economy environment, smart marketing and management of cement enterprises is becoming more and more important. In the future, cloud technology
Fig. 17. Scheme of construction waste recycling process.
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Fig. 18. Cycling degree of Chinese cement industry from 1990 to 2013.
will be applied in cement enterprises and will bring them into closer ties with related enterprises. With the guide of big data, a new overall management and service system will be materialized covering all the major phases from the design of the products, their manufacturing, their delivery, to their application and maintenance, and new values will be established as well. 2.4.3. Smart development In light of the current problems Chinese cement industry is facing, namely, overcapacity and throat-cutting competition, we must take overall control over the industry. Industry association is taken as leader to foster coordination and cooperation between cement enterprises, and to promote comprehensive set of production and marketing. Peak production is applied to reduce pressure on environment, thus human being and nature can coexist in harmony. The formation of a highly flexible, personalized, smart production and service mode will be realized.
3. Suggestions for the transformation in Chinese cement industry The development mode of cement industry has to change since we are facing severe environmental, resources and overcapacity problems. The transformation has to be taken from the conventions which mainly depend on investment and resources consumption to innovationdriven development which means green development, low carbon development and recycling development. The transformation could be painful since it entails breaking away from old fashioned practices and will require great adjustment in both our minds and our practices.
3.1. Re-examination of cement and cement industry In the teaching and research of material engineering, there are different disciplinary areas and subjects. People mainly focus on the study of components, structure and performance of cement since it was found and used while its essence of being cementing material is neglected. Furthermore, people seem to fail to realize that the final product is nothing but high quality concrete and that all kinds of solid wastes can be modified into high quality cementing materials. We need to trace back to the essence of cementing materials and to understand what cement is and what cement industry is all about. The new thinking and new orientation will define the future development.
3.2. Recycling development and in-depth integration with related industries: key to the transformation
Fig. 19. Comparison of SD between main Chinese cement enterprises.
Recycling development and in-depth integration with related industries including construction materials, metallurgy engineering, energy resources, chemical engineering and municipal construction are the most important ways for green and low carbon development in cement industry. The R&D of chain connection technology and initiative of intensive development will decide the depth of integration between these industries. R&D of recycling engineering and its technology should be the main research area of innovation-driven development. Moreover, utilization of CO2 emitted during cement calcinations is vital to the recycling development.
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3.3. Taking concrete for the final products, increasing cement categories and extending the industrial chain On one hand, as a kind of cementing material, cement is just the middle product while concrete is the end product for construction. Nowadays, the profit margins for normal cement products are small since they are oversupplied. On the other hand, the performance of special cements such as the expansive cement for dam construction, the high abrasion resistant cement for the express ways and heavyloaded road and corrosion resistant cement for marine construction fails to live up to the expectations. Therefore, the only way out is to keep a close eye on the ultimate demand in the market and integrate cement industry with concrete production. 3.4. Realization of smart development In the face of the fourth industrial revolution, we must accelerate the in-depth integration of cement industry with information technology and promote an all-round transformation to achieve the smart development. 4. Conclusion Cement is a kind of traditional yet young building material, which cannot be replaced in a fairly long period of time. The vitality in the cement industry lies in the incessant transformation and development. Green, low carbon, integration and smart development are the inevitable trends in the transformation. The success of the transformation largely depends on science and technology innovation.
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