J. Shanghai Jiaotong Univ. (Sci.), 2012, 17(3): 341-344 DOI: 10.1007/s12204-012-1283-z

CO2 Emissions from Typical Cement Plants in China LI Chen1∗ ( ), CUI Su-ping1 (), WANG Zhi-hong1 () GONG Xian-zheng1 (), MENG Xian-ce1,2 (), LIU Yu1 ( ) (1. School of Materials Science and Engineering, Beijing University of Technology, Beijing 100124, China; 2. China Development Strategy Institute for Building Materials Industry, Beijing 100035, China)

© Shanghai Jiaotong University and Springer-Verlag Berlin Heidelberg 2012 Abstract: The objective is to know how the CO2 emits and how much the CO2 emits due to the cement manufacture in both direct and indirect ways with the increasing concerns about the global warming and the cement plants emitting huge CO2 . A precise method to calculate CO2 emissions including three processes was established in this paper and a case study was provided. From the case of 23 typical plants in China, we can see the amount of CO2 emissions at the right level. The summary of CO2 emissions consists of emissions from raw materials, fuels and electricity. The average result of the 23 typical plants is 0.74 t CO2 per ton clinker in this study. Therefore, CO2 emissions from these typical cement plants were pictured and then measured. The creative point is that an approach provides a basic framework to identify various situations in different cement plants in China and other in the rest of the world. The framework would be useful in quantitatively evaluating CO2 emissions for government to know precisely CO2 emissions in the cement plants. Key words: carbon dioxide emissions, greenhouse gas, cement manufacture, coal combustion CLC number: TQ 170.1, X 501 Document code: A

0 Introduction Carbon dioxide is one of the most important contributors to the greenhouse effect, and its amount in the atmosphere is rising at a frightening rate with no sign of slowing. The Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report issued in late 2007 clearly stated the “very likely” relation between human-induced greenhouse gas concentrations and most of the observed increase in the global average temperature since the mid-20th century (IPCC, 2007)[1]. A post-Kyoto agreement period comes. China, ratified the Kyoto protocol, is not obligated to reduce greenhouse gas production at the moment as a developing country. The APP (Asia-Pacific Partnership on Clean Development and Climate), in the Sino-US cooperation project, estimated that CO2 emissions from 1 t clinker production were about 0.87 t (APP, 2010). The ISO 14067 referred to carbon footprint of product (Part 1: quantification, Part 2: communication). IPCC issued CO2 emission factors due to cement production, includReceived date: 2011-11-21 Foundation item: the National Key Technology Research and Development Program of the Ministry of Science and Technology of China (Nos. 2011BAE29B00, 2011BAC04B06 and 2011BAJ04B06) ∗E-mail: [email protected]

ing limestone decomposition by heat process (IPCC, 1996). Besides that, IPCC also published the methods and data necessary to estimate emissions from stationary combustion. Methods are provided for the sectored approach in three tiers based on: fuel combustion from the national energy statistics and the default emission factors, together with the country-specific emission factors, fuel statistics and data on the combustion technologies applied together with the technology-specific emission factors[2-4] . This includes the use of models and facility level emission data where available. However, in 2006 IPCC did not issue CO2 emission factors from cement production, it only issued coal combustion. The latest CO2 emission factors from cement production were given by APP of “comprehensive program to improve energy efficiency, increase the use of alternative fuels and raw materials, and reduce emissions in the cement sector in China” project[5] . The project estimated CO2 emissions factors through the investigation with 42 cement plants over the whole China in 2008. The CO2 emission factors calculated by APP were considered by two parts: raw material component and fuel component. APP did not consider the indirect CO2 emission factors from electricity and the factors were served for the macro circumstance not for the independent plant. In this paper, the methodology was established to calculate the CO2 emission factors precisely, and the factors were served for the independent

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J. Shanghai Jiaotong Univ. (Sci.), 2012, 17(3): 341-344

plant. A detailed analysis about CO2 emissions due to typical cement plants was taken and the factors in this paper were not the average factors but the representative factors.

1 Goal Definition and Scope The primary goals of this paper are to calculate the CO2 emissions due to cement manufacture, not the av-

erage factors for the whole China but the representative factors for the independent plant. The scope includes raw materials and fuels grinding, clinker incineration, clinker and other mixtures grinding. As shown in Fig. 1, the system that is considered for this research consists of three processes. In this paper, the quarrying process, the raw materials and fuels transportation process, and the cement transportation are not considered.

CO2

Raw materials and fuels grinding

Clinker and mixture grinding

Clinker incineration

CO2

CO2

Electricity

CO2

Electricity Fig. 1

Electricity

Cement manufacture processes

2 Methodology Details 2.1 CO2 Emissions Cement manufacture is divided into three processes in this paper as shown in Fig. 1. The first process is raw materials and fuels grinding, which consumes electricity. Thus, the first process has the indirect CO2 emissions. The second process is clinker incineration, in which the fuels would have CO2 emissions in the combustion and the limestone would have CO2 emissions by heat mainly in the pre-calciner kiln. Especially in China, the fuel mainly is the coal. Carbon dioxide emissions from the second process are the main direct source. Finally, the last process is clinker and other mixtures grinding, which also consumes electricity. 2.2 Emissions Due to Raw Materials Raw materials for the Portland cement are mainly limestone and clay. Decomposition of limestone is an essential process in the Portland cement production which takes place in the cement kiln. The chemical reaction for this process is CaCO3 → CaO + CO2 . The environmental impacts associated with cement production have been investigated thoroughly in recent periods. These researches were focused CO2 emission factors on average. The independent cement plant may not use the factors because the plant has its own situation. The existing international standard methods to measure CO2 are: ISO 12039:2001 of stationary source emissions. However, the amount of CO2 emissions due to cement manufacture is large and the cost is too high, so the methods above may not be used in the real world. The only way to calculate the amount of CO2 emissions

from raw materials is to calculate the amount of limestone according to the chemical reaction above. Certainly, the amount of CO2 emissions from magnesium carbonate (MgCO3 ) is also considered in this paper. The chemical reaction magnesium carbonate decomposition is MgCO3 → MgO + CO2 . The contents in clinker of this plant are analyzed through X-ray diffraction (XRD). The reason of the clinker analyzed instead of the raw material is that the clinker does not include the loss content. The result of clinker analyzed would be more precisely than that of raw material. The contents in clinker are shown in Table 1. From Table 1, the amount of CO2 emissions due to raw materials is able to obtain from the amount of CaO and MgO. It is assumed that CaCO3 and MgCO3 should decompose completely in this paper. The calculation is illustrated as 44 44 mCaO + mMgO = Frw = FCaO + FMgO = 56  40  44 44 wCaO + wMgO mcl , (1) 56 40 where, Frw is the amount of CO2 emissions due to raw materials in the incineration process; FCaO is the amount of CO2 emissions due to CaCO3 decomposition in the incineration process; FMgO is the amount of CO2 emissions due to MgCO3 decomposition in the incineration process; mCaO is the mass of CaO in clinker; mMgO is the mass of MgO in clinker; mcl is the mass of clinker; wCaO is the mass fraction of CaO to clinker; wMgO is the mass fraction of MgO to clinker.

J. Shanghai Jiaotong Univ. (Sci.), 2012, 17(3): 341-344 Table 1

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Data collection and calculation details of the 23 typical cement plants

No.

Eelec /(kW · h)

wCaO /%

wMgO /%

Fcoal /t

1

85.81

65.55

2.75

0.275

2

89.59

66.40

1.46

0.269

3

86.08

66.04

1.73

0.266

4

88.77

64.48

2.77

0.285

5

91.67

66.24

0.86

0.287

6

76.12

64.92

1.54

0.313

7

89.13

64.58

3.54

0.275

8

78.34

66.37

0.95

0.276

9

88.13

64.62

2.91

0.293

10

90.66

65.52

2.70

0.301

11

98.39

65.11

3.34

0.300

12

94.68

66.97

1.08

0.276

13

80.48

64.88

2.93

0.261

14

73.23

64.87

2.28

0.273

15

63.54

67.15

0.60

0.301

16

88.19

64.78

3.69

0.289

17

75.19

65.75

1.01

0.273

18

80.46

66.23

0.99

0.282

19

73.71

66.21

1.39

0.264

20

78.89

66.85

1.39

0.300

21

88.46

67.11

0.91

0.291

22

81.12

67.17

1.23

0.329

23

80.46

64.50

2.47

0.308

2.3 Emissions Due to Fuels In China, fuel for cement production is mainly coal, especially bituminous coal. The coal combustion gives heat in the incineration process of cement production. The fixed carbon in coal contributes the calorific value[6] , and also it reacts with oxygen in the kiln to produce CO2 . The amount of fixed carbon in coal cannot be measured directly. Usually, the mass of the received coal sample minus the amount of total moisture, ash and volatile matter equals to the amount of fixed carbon. Thus, the amount of CO2 emissions due to fuels is able to obtain from the amount of fixed carbon. It is assumed that the fixed carbon of coal should completely react with oxygen in the kiln to produce CO2 in this paper. In fact, some CO and CH4 emit if there is not enough oxygen and some fixed carbon does not react in the end. However, many researches stated that CO and CH4 would transfer into CO2 finally in 50 years or more[7-8] . Also, there is a little CO, CH4 and un-reacted fixed carbon. Therefore, the assumption is reasonable that the fixed carbon of coal should completely react with oxygen to produce CO2 . The calculation is illustrated as Fcoal =

44 44 m(FC)ad = w(FC)ad mcoal , 12 12

(2)

where, Fcoal is the amount of CO2 emissions due to coal of cement manufacture in the incineration process; m(FC)ad is the mass of fixed carbon in coal; w(FC)ad is the mass percentage of fixed carbon to coal; mcoal is the mass of coal. 2.4 Emissions Due to Electricity China is the second largest electricity power production and consumption country in the world. By the end of 2006, the total national installation capacity had reached 624 GW with electricity generation of 28 344 TW · h per year, in which the thermal power generation is 23 573 TW · h, hydropower generation is 4 167 TW · h and nuclear power generation is 543 TW · h. Nowadays, the electricity grid system of China mainly is constituted by seven trans-regional grids: China North Grid, China Northeast Grid, China East Grid, China Central Grid, China Northwest Grid, China South Grid and Hainan Province Grid (China National Development and Reform Commission, CNDRC, 2010). According to the development of hydropower being slower than thermal power, and nuclear power being in its initial step, the thermal power takes 82% more share in the China power. Besides that, thermal power generation consumes coal hugely which is the major emission source of carbon dioxides of electricity industry: Felec = αEelec ,

(3)

where, Felec is the indirect CO2 emissions due to electricity in the first and third processes; α is the combined margin factor of power; Eelec is the amount of electricity in the three processes used.

3 Results and Discussion Table 1 shows details of the 23 typical cement plants in China from Shandong province, Zhejiang province, Jiangxi province and Jiangsu province. Production scale of the 23 typical plants is from 2 500 t clinker per day to 10 000 t clinker per day, which can present Chinese cement industry in some degree. According to the methodology above, the calculations with Eqs. (1)—(3) are illustrated as follows. The amount of clinker is 1 t in the calculation. That is to say, the value of mcl is 1 t. Therefore, the result of Frw is the amount of CO2 emissions per ton clinker due to raw materials, the result of Fcoal is the amount of CO2 emissions per ton clinker due to coal of cement manufacture, and the result of Felec is the amount of indirect CO2 emissions per ton clinker due to electricity generation. Thus, the average result of CO2 emissions from the 23 typical cement plants is 0.74 t CO2 per ton clinker. Notice that the unit is “clinker” not the cement, because CO2 emissions mostly are from the clinker production process.

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4 Conclusion In this work, a precise method to calculate CO2 emissions due to cement manufacture was established and a case study was provided. The feasibility of the method in this paper was examined by employing a case study approach. From the case, the amount of CO2 emissions is at the right level. A cement producer can calculate CO2 emissions easily in this method by his own. Therefore, CO2 emissions from the typical cement plants in China were pictured and then measured. The study shows that CO2 emissions have the potential to achieve reductions if fewer raw materials, fuels and electricity are used. Then the green house gas effect of alternative raw materials and fuels will be discussed in the future. In addition, the un-reacted carbon in the cement kiln dust (CKD) would be considered in the future. In this paper, the approach provides a basic framework to identify various situations in different cement plants in China and other in the rest of the world. The framework would be useful in quantitatively evaluating CO2 emissions for government to know precisely CO2 emissions in the cement plants; therefore, the decision of making best use of local resources would be done. In addition, reducing CO2 emissions with AFRs would be probable. Finally, this paper could serve in the development of a low carbon society.

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