Environmental impact assessment of three coal-based electricity generation scenarios in China

Energy 45 (2012) 952e959

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Environmental impact assessment of three coal-based electricity generation scenarios in China Xiaowei Cui a, Jinglan Hong b, c, *, Mingming Gao b a

School of Environment and Resource, University of Jinan, Jinan 250022, PR China Shandong Provincial Key Laboratory of Water Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Shandong University, Shanda South Road 27, Jinan 250100, PR China c Shandong University Climate Change and Health Center, Public Health School, Shandong University, Jinan 250012, PR China b

a r t i c l e i n f o

a b s t r a c t

Article history: Received 21 March 2012 Received in revised form 14 May 2012 Accepted 24 June 2012 Available online 21 July 2012

A life cycle assessment was conducted out to estimate the environmental impact of three coal-based electricity generation scenarios commonly used or encouraged in China, namely, sub-critical technology (300 MW), supercritical technology (600 MW), and ultra-supercritical technology (1000 MW). Compared with other scenarios, the ultra-supercritical technology accounted for significantly environmental benefits in most categories, except in the natural land occupation category because of the landfill disposal of coal ash. Optimizing net coal consumption efficiency, reusing coal ash as building material, increasing desulfurization and denitrization system efficiency, and decreasing the road transport distance from coal buyer to supplier are key factors in reducing the overall environmental impact of electricity generation. Ó 2012 Elsevier Ltd. All rights reserved.

Keywords: Coal-based electricity generation Life cycle assessment Sub-critical technology Supercritical technology Ultra-supercritical technology

1. Background, aim, and scope Over the last two decades, China’s electric power industry has grown dramatically because of the vast economic development and rapid urbanization in the country. For instance, about 1.37
103 TWh and 4.21
103 TWh of electricity produced in China was reported in 2000 and 2010, respectively [1], corresponding to an average annual increase of 11.9%. Such growth will address the significant demands in the coal market because coal-based electricity generation plays an important role in national electricity production [1]. The growth also places heavy pressure on the Chinese and on meeting global carbon reduction targets. Currently, the Chinese government is turning its attention to utilizing electric power in a cleaner and more efficient manner because of the relatively low efficiency of coal-based thermal power, along with the high occurrence of environmental pollution from small-scale coal-based thermal power sites. Fig. 1 shows the electricity generation mix in China from 2000 to 2010. An increase in the

* Corresponding author. Shandong Provincial Key Laboratory of Water Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Shandong University, Shanda South Road 27, Jinan 250100, PR China. Tel./fax: þ86 (0531) 88364513. E-mail address: [email protected] (J. Hong). 0360-5442/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.energy.2012.06.063

use of hydropower, nuclear power, and other sources (e.g., biofuel and wind) has been observed over the years. China’s electricity generation has been dominated by thermal power and hydropower sources. Hydropower has exhibited a very low environmental impact compared with thermal power-based electricity generation. Hence, understanding the environmental implications of thermal power-based electricity production in China, identifying key environmental indicators, and assessing the improvement potential of thermal power-based electricity are important for China’s development strategy and the global community. Accordingly, methods that evaluate the environmental burden created by electricity production during its whole life cycle are urgently needed. Life cycle assessment (LCA) is an effective tool to evaluate the potential environmental burden associated with all the stages of a product, process, or activity life from cradle-to-grave. Nowadays, LCA applications are used as the basis for eco-design, strategic planning and management, marketing, consumer education, and process improvement throughout the world. Even in China, the environmental impact of electricity production has been extensively studied using the LCA method [2e6]. Notable differences in potential environmental impact of electricity generation can be observed because of the numerous factors, including the type of processes applied, fuel, technologies, plant size, and others. Currently, most of the LCAs in China are focused on

X. Cui et al. / Energy 45 (2012) 952e959

30.57%, 35.43%, 30.5%, and 3.5% of national coal-based electricity generating units had a capacity of 300 MW or less, 300 MWe600 MW, 600 MWe1000 MW (no 1000 MW), and 1000 MW, respectively. Also, China’s development and reform commission have clear instructions to confine the capacity of coalbased electricity generating units to 300 MW or less [15]. China has completed the 300 MW sub-critical technology and has mastered the 600 MWe1000 MW supercritical and ultra-supercritical technologies. In China’s “Twelfth Five-year Plan”, 600 MWe1000 MW supercritical and ultra-supercritical technologies are encouraged.

4500 Others Nuclear Hydraulic Power Thermal power

Electricity (TWh/yr)

4000 3500 3000

953

2500 2000 1500 1000

2. Scope definition

500 2.1. Functional unit

0

2010

2009

2008

2007

2006

2005

2004

2003

2002

2001

2000

In this study, raw coal is used for thermal power generation because it plays an important role in the national fuel consumption in thermal power plants (94.3%, Table 1). The functional unit is 1 kWh of net electricity production. All materials, waste, emissions, and energy consumption levels are based on this functional unit.

Time (yr) Fig. 1. Electricity production in China.

the environmental impact of greenhouse gas emissions and energy consumption [6e8]. However, to avoid pollutant transfer and secondary pollution caused by new technologies or processes, the environmental impact of China’s electricity generation should be better characterized. Most of the LCAs in China, including the research conducted in [9e12], were unclear as to whether or not life cycle emissions from energy inputs, direct heavy metal emissions, end-life disposal, or capital equipment were included in the calculation of results. Moreover, very few LCA studies in the country collect the life cycle inventories of electricity generation from modern and technically advanced industry sites. Thus, comparing such LCA results with those in other parts of the world to determine China’s global standing and improve its potential in managing the environmental impact of power generation will be difficult. Electricity generation plants recently accounted for 20% of the total final energy consumption in China [13]. Such rate has an important implication on global carbon reduction because China is known as one of the world’s largest energy consumers and emitters of greenhouse gases [14]. To address the abovementioned requirements, the environmental impact of thermal power-based electricity generation in China was estimated using the LCA approach. In the present study, three raw coal-based electricity generation scenarios commonly used or encouraged in China, namely, sub-critical technology (300 MW), supercritical technology (600 MW), and ultra-supercritical technology (1000 MW) was estimated. This approach was undertaken because raw coal accounts for 94.3% of the national fuel consumption in thermal power plants (Table 1). Furthermore, in 2009, approximately

2.2. System boundaries System boundaries are set using a cradle-to-gate approach. Three coal-based electricity generation scenarios were studied, namely, the sub-critical technology (300 MW) scenario, supercritical technology (600 MW) scenario, and ultra-supercritical technology (1000 MW) scenario. Each scenario involves the life cycle processes of road transportation of raw materials to the electricity generation site, infrastructure of power plants, raw material and energy production, wastewater treatment on site, hard coal ash disposal to landfill, and direct air emissions (i.e., carbon dioxide, sulfur dioxide, nitrogen oxides, carbon monoxide, methane, nonmethane volatile organic compounds, heavy metal, and particulates) of power plants. For the 300 MW and 600 MW scenarios, the additional process was the hard coal ash reused as building materials. Fig. 2 presents system boundary. 2.3. Methodology The life cycle impact assessment (LCIA) results are calculated at midpoint level using the ReCiPe method [16,17] because this model is the most recent indicator approach available in LCA analysis. This method builds on the results of Eco-indicator 99 [18] and Centrum voor Milieukunde Leiden [19] on LCA. It assumes that the potential effects of future extractions have been included in the life cycle inventory analysis. Additionally, the ReCiPe method uses impact mechanisms that have a global scope and considers a broad set of midpoint impact categories (i.e., climate change, ozone depletion,

Table 1 Chinese energy balance for thermal power generation in 2009. Amount Coal

Oil

Gas

Other energy Total

Raw coal Cleaned coal Other washed coal Crude oil Diesel Gasoline Fuel oil Other petroleum product Natural gas Coke oven gas Other gas

1.41 1.68 3.34 4.38 1.52 900 1.93 1.52 1.34 8.84 1.10 e








109 105 107 104 106








106 106 1010 109 1010

Unit

Standard quantity (TCE)

Ratio

tonne tonne tonne tonne tonne tonne tonne tonne m3 m3 m3 e

91679.81 15.17 1752.72 6.26 221.20 0.13 275.75 212.40 1785.39 543.16 315.31 378.47 97185.77

94.33% 1.56
102 % 1.80% 6.44
103 % 0.23% 1.34
104 % 0.28% 0.22% 1.84% 0.56% 0.32% 0.39%

954

X. Cui et al. / Energy 45 (2012) 952e959

from coal-based electricity production in China. The net coal consumption for electricity generation of 300, 600, and 1000 MW in 2009 was 0.34, 0.31, and 0.22 kg/kWh, respectively. Table 2 shows the characterization of three coal-based thermal power processes considered in the study. The air pollutants are calculated according to reference [22]. As information on the Chinese electricity production site is lacking, relevant background data from Europe are used [23], including data on the infrastructure of coal-based thermal power plants, chemical production, and wastewater treatment processes.

Raw materials and energy production

Mining Transport Storage Grinding

Dedust & Exhaust gas cleansing

Burning Electricity generation

Landfill

2.5. Life cycle inventory The inventory analysis is a mode of investigation in which the chemicals, energy, infrastructure, direct emissions, raw material, transport, and waste disposal are accounted for across the different steps of each process. Table 3 presents the main inventory data on the operation stage in the coal-based thermal power production site.

Solid waste reused as building materials

Fig. 2. System boundary.

3. Results

human toxicity, photochemical oxidant formation, particulate matter formation, ionizing radiation, terrestrial acidification, freshwater eutrophication, marine eutrophication, terrestrial ecotoxicity, freshwater ecotoxicity, marine ecotoxicity, agricultural land occupation, urban land occupation, natural land transformation, water depletion, metal depletion, and fossil depletion). In addition, normalization is applied in this study to compare midpoint impacts and to analyze the respective share of each midpoint impact to the overall impact. The normalized factor of midpoint impact is determined by the ratio of the impact per unit of emission divided by the per capita world impact for the year 2000 [20]. The detailed methodology and complete characterization factors for ReCiPe are available on the website of Institute of Environmental Science in Leiden University of Nederland (http:// www.cml.leiden.edu/research/industrialecology/researchprojects/ finished/recipe.html). Moreover, IMPACT2002þ [21] method which is one of the most widely used models in LCA analysis, is used as a comparison to complement ReCiPe and check the robustness of the obtained results from ReCiPe. 2.4. Data sources Annual monitoring data related to the coal-based electricity production processes (i.e., raw material, energy, chemicals, direct emissions, and waste disposal) of an electricity production company in China are used in this study. The Chinese electricity production site modeled in this study represents one of the largest and most prominent high-grade electricity production enterprises in the nation. In 2009, this site reported an annual production of electricity of around 620 TWh. The typical coal-based electricity generating units with a capacity of 300, 600, and 1000 MW are used as model samples to assess the environmental impact generated

3.1. Life cycle impact assessment results Table 4 shows the life cycle impact assessment (LCIA) midpoint scores. The 1000 MW and 600 MW scenarios represented higher environmental benefit in most categories except for natural land transformation. In the natural land transformation category, the 300 MW scenario demonstrated high environmental benefit because of the relatively high value of coal ash disposed in landfills. The higher potential effect of the 300 MW and 600 MW scenarios are attributed primarily to the direct emissions generated from electricity production and the landfill disposal of coal ash. By contrast, 1000 MW coal-based electricity production technology represented the lowest potential impact in most categories except in ozone depletion. In the ozone depletion category, 600 MW coalbased electricity production technology represented the lowest potential impact because of its lowest consumption of hydrochloric acid. In addition, to confirm and add credibility to the current research, IMPACT2002þ method was used for comparison with ReCiPe. The LCIA results of the IMPACT2002þ method tended to be similar to those of the ReCiPe analysis results for the ozone layer depletion, land occupation, and acidification categories. For the particulate matter formation, the LCIA result using the IMPACT2002þ method in all scenarios was less than the result obtained using the ReCiPe method because the particulate matter with a diameter larger than 10 mm had no effect considered by the IMPACT2002þ method. For the energy category, the ReCiPe analysis result of 300 MW, 600 MW, and 1000 MW was approximately 10.2, 9.4, and 5.1 MJ, respectively (change rate at 42.62 MJ/kg oil eq). The results obtained from ReCiPe analysis are consistent with the results obtained by the IMPACT2002þ method. For the climate change category, the IMPACT2002þ LCIA result in all scenarios was lower than that obtained using the ReCiPe method because the

Table 2 Characterization of coal-based thermal power plants.

Electricity generation in 2009 Ash content of coal Net calorific value of coal Sulfur content of coal Dedust efficiency Desulfurization efficiency Water recycle rate

Unit

300 MW sub-critical technology

600 MW supercritical technology

1000 MW ultra-supercritical technology

TWh/yr % MJ/kg % % % %

65.8 46.39 14.88 0.56 99.8 97.5 96.9

28.6 32.15 19.96 0.43 99.6 95.0 92.0

32.1 20.19 22.41 0.82 99.7 95.0 94.0

X. Cui et al. / Energy 45 (2012) 952e959

955

Table 3 Life cycle inventory. Values are presented per functional unit.

Raw material

Direct emissions

Waste disposal

Coal Fuel oil H2SO4 HCl NaOH Limestone Freshwater CO2 SO2 NOx Particulates CO CH4 NMVOC As Cd Cr Ni Pb V Zn Hg Wastewater Landfill Used for building materials production

300 MW sub-critical technology

600 MW supercritical technology

1000 MW ultra-supercritical technology

0.66 kg 0.25 g 0.23 g 62.19 mg 58.24 mg 4.96 g 84.70 g 0.80 kg 1.67 g 8.05 g 0.02 g 1.04 g 7.90 mg 0.24 g 18.62 mg 0.24 mg 1.42 mg 1.83 mg 48.08 mg 24.24 mg 65.06 mg 41.34 mg 84.70 g 263.72 g 48.96 g

0.45 kg 0.04 mg e 42.76 mg 41.95 mg 5.30 g 165.73 g 0.73 kg 0.30 g 5.49 g 0.08 g 0.95 g 7.18 mg 0.22 g 6.23 mg 0.16 mg 0.97 mg 1.23 mg 32.78 mg 16.52 mg 44.22 mg 28.16 mg 165.73 g 31.49 g 84.41 g

0.22 kg 0.62 g e 0.44 g 0.17 g 2.30 g 12.20 g 0.41 kg 1.32 g 2.47 g 0.11 g 0.53 g 4.05 mg 0.12 g 26.56 mg 0.08 mg 0.47 mg 0.65 mg 16.03 mg 8.09 mg 22.12 mg 13.87 mg 25.70 g 0g 36.20 g

IMPACT2002þ method considers a 500-year time horizon in the climate change category. If the climate change potential impact of a 100-year time horizon is used in the study, the climate change potential impact of the current research will similar to the ReCiPe analysis results. The rest of the LCIA results were difficult to compare because of the significantly different categories or label substances. Overall, IMPACT2002þ achieved results similar to those of ReCiPe, but several substances played a significant role. These results indicate that ReCiPe is reliable as far as the current research is concerned. Fig. 3 shows the normalized ReCiPe midpoint results. For all the scenarios, their effect on climate change, human toxicity, photochemical oxidant formation, particulate matter formation, terrestrial acidification, freshwater eutrophication, marine eutrophication, freshwater ecotoxicity, marine ecotoxicity, and fossil depletion had an important contribution, whereas their effect on the rest of the

categories was small. Specifically, for the 300 MW and 600 MW scenarios, the process contributing most to the overall environmental impact were the direct emission generated from electricity production and the landfill disposal of coal ash. For the 1000 MW scenario, the direct emissions from electricity production, road transport, crude oil production, coal production, and hydrochloric acid production processes played important roles in the overall environmental impact. Fig. 4 shows the contributions of the most significant substance to the abovementioned key midpoints. For all the scenarios, the substances contributing most to climate change were direct methane and carbon dioxide emission generated from the electricity production stage. Similarly, the substance contributing most to human toxicity was mercury in the air, which was also directly emitted in the electricity production stage. The direct emission of arsenic and selenium emission to water seen from the process of

Table 4 Life cycle impact assessment results. Category

Climate change Ozone depletion Human toxicity Photochemical oxidant formation Particulate matter formation Ionizing radiation Terrestrial acidification Freshwater eutrophication Marine eutrophication Terrestrial ecotoxicity Freshwater ecotoxicity Marine ecotoxicity Agricultural land occupation Urban land occupation Natural land transformation Water depletion Metal depletion Fossil depletion

Unit

kg kg kg kg

CO2 eq CFC-11 eq 1,4-DB eq NMVOC

kg PM10 eq kg U235 eq kg SO2 eq kg P eq kg N eq kg 1,4-DB eq kg 1,4-DB eq kg 1,4-DB eq m2a m2a m2 m3 kg Fe eq kg oil eq

300 MW sub-critical technology

600 MW supercritical technology

ReCiPe

IMPACT2002þ

ReCiPe

IMPACT2002þ

ReCiPe

IMPACT2002þ

0.94 2.18
109 0.24 8.82
103

0.86 2.18
109

0.86 1.08
109 4.16
102 6.03
103

0.78 1.08
109

0.48 1.76
109 1.01
102 2.86
103

0.44 1.75
109

2.2
103 4.3
103 6.4
103 2.62
104 1.09
103 1.27
105 7.30
103 6.94
103 2.20
104 2.66
103 6.76
106 1.96
104 1.70
103 0.24

1.3
103

1.3
103 3.2
103 3.5
103 3.21
105 7.45
104 4.74
106 8.90
104 8.65
104 1.09
104 1.16
103 2.84
106 8.96
105 1.26
103 0.22

8.5
104

8.50
104 2.8
103 2.8
103 1.54
106 3.59
104 2.82
106 1.77
105 3.53
105 1.09
104 5.56
104 2.65
106 6.88
105 1.01
103 0.12

5.0
104

7.6
103

1.48
103

10.1 MJ primary

4.3
103

8.24
104

9.1 MJ primary

1000 MW ultra-supercritical technology

3.2
103

4.25
104

5.1 MJ primary

956

X. Cui et al. / Energy 45 (2012) 952e959

6.E-03 5.E-03 4.E-03 3.E-03

Landfill Power plant Limestone H2SO4 Crude oil Direct emissions

Wastewater Transport NaOH HCl Coal

a

2.E-03 1.E-03

Normalized value

0.E+00

b

8.E-04 6.E-04 4.E-04 2.E-04 0.E+00

c

8.E-05 6.E-05 4.E-05

landfill disposal of coal ash also played an important role in human toxicity in both the 300 MW and 600 MW scenarios. In the particulate matter formation and terrestrial acidification scores, sulfur dioxide and nitrogen oxides were dominant substances, whereas non-methane volatile organic compounds (NMVOC) and nitrogen dioxide in the air played an important role in photochemical oxidant formation. Sulfur dioxide, NMVOC, and nitrogen oxides were direct emissions from the electricity production stage. In addition, the emission of phosphate-to-water seen from coal ash disposed in landfill stage, nitrogen oxides from the electricity generation process, and coal in soil made dominant contributions to the freshwater eutrophication, marine eutrophication, and fossil depletion (data not shown) categories, respectively. The direct vanadium and nickel emissions from the hard coal ash landfill stage were the dominant pollutants in freshwater ecotoxicity. In marine ecotoxicity, the direct vanadium and nickel emissions from the hard coal ash transport stage were dominant substances for the 300 and 600 MW scenarios, whereas copper, chlorine, and mercury to air, zinc to water were additional dominant substances for the 1000 MW scenario.

2.E-05

3.2. Solid waste disposal

0.E+00

Fig. 3. Normalized total LCIA midpoint results a) 300 MW b) 600 MW c) 1000 MW.

As shown in Fig. 4, the landfill disposal of coal ash made a dominant contribution to the overall environmental impact in the 300 MW scenario. However, the use of coal ash as an aggregate in building material production is currently encouraged in China. Actually, the potential impact on the abovementioned key midpoint categories linearly decreased with the increase in coal ash reuse capacity (Fig. 5). A 50 g/kwh increase in solid waste reuse decreased potential impact on human toxicity, freshwater

100%

a

c

b

80% Others

Others

60%

Methane

Se to water

40%

Carbon dioxide

Others SO2 to air

Hg to air NMVOC to air NOx to air

As to water

20% 0%

e

d

100% 80%

Others

Others

SO2 to air

SO2 to air

NOx to air

NOx to air

g

hh)

60%

f Others Phosphate to water

40% 20% 0%

i

100% others

Others

Nitrate to water NOx to air

Ni to water

80% 60%

Others Cu to air V to water

V to water

Zn to water

40%

Cl to air Ni to water

20%

Hg to air

0% 300 MW

600 MW

1000 MW

300 MW 600 MW 1000 MW

300 MW 600 MW 1000 MW

Fig. 4. Contribution of substances to the mid-point score a) climate change b) human toxicity c) photochemical oxidant formation d) particulate matter formation e) terrestrial acidification f) freshwater eutrophication g) marine eutrophication, h) freshwater ecotoxicity i) marine ecotoxicity.

3.4. Sensitivity analysis To identify the major influence on the LCIA results obtained from present research, the results of the sensitivity analysis of the main contributors are shown in Table 5. In all categories, the efficiency of coal consumption had the highest environmental benefit in the 300 MW scenario, as solid waste and direct waste gas emissions decreased. In contrast, for the 600 MW scenario, the

5.9
103 1.1
102 1.2
102 2.1
105 2.0
106 2.9
106 5.8
105 1.0
104 1.1
105 7.1
105

1.1
104

5.1
107 4.3
105 3.5
104 4.9
107 4.8
108 7.0
108 5.4
107 9.8
108 4.1
105 2.6
104

1.1
106

2.1
108 4.4
105 3.6
104 1.7
107 1.7
108 2.5
108 4.9
107 8.9
107 4.3
105 2.7
104

9.8
107

1.6
105 3.7
105 5.3
105 4.1
108 3.9
109 5.7
109 7.5
107 1.4
106 1.5
108 9.1
108

1.5
106

1.6
106 1.3
105 4.8
109 4.7
1010 6.8
1010 9.7
109 1.7
108 1.6
106 9.7
106

1.9
108

1.4
104 1.8
104 3.2
104 3.0
107 2.9
108 4.2
108 3.7
106 6.7
106 8.4
108 5.2
107

7.4
106

4.0
105 6.7
105 1.1
104 1.1
107 1.0
108 1.5
108 1.8
106 3.3
106 3.6
106

1.3
104 3.0
104 4.4
104 1.6
107 1.6
108 2.3
108 7.1
106

3.9
108

300 MW 300 MW

2.4
107

Road transport Solid waste

600 MW Table 5 Sensitivity of main contributors.

Notably, the road transport aspect of coal collection covered around 100 km in the present study. As coal resource is mainly distributed in China’s northern area [24], large quantities of coal need to be delivered to east or south China, which experiences rapid economic growth. Fig. 4 shows that the road transport of coal to power plants represented an important contribution to the overall environmental impact for the 1000 MW scenario. Sensitivity analysis of road, rail, or sea transport distance is highly needed. For the 300 MW scenario, increases in the distance in road, rail, or sea transport did not lead to significantly higher environmental burden in the abovementioned dominant categories because the landfill disposal of coal ash was the most significant process in the key categories. On the contrary, for the 600 and 1000 MW scenarios, increases in the distance in road, rail, or sea transport led to higher overall environmental burden, specifically in the case of increasing road transport distance, because the transport process played an important role in the key categories shown in Fig. 4. Increasing transport distances will lead to a higher demand for energy (e.g., diesel, heavy fuel oil) use. Results indicate that transport distance and type are other keys to reduce the overall environmental burden.

600 MW

3.3. Transport distance of coal collection

5% 4.3
102 2.1
103

600 MW 1000 MW

eutrophication, freshwater ecotoxicity, and marine ecotoxicity categories to about 39.95 g 1,4-DB eq, 0.05 g P eq, 1.50 mg 1,4-DB eq, and 1.50 g 1,4-DB eq, respectively. Accordingly, changing the end disposal process from landfill to reusing as raw material for building is one key to reduce the overall environmental burden.

1.3
105

Fig. 5. Relationship between key midpoint categories and coal ash reuse capacity.

1.4
105

Hydrochloric acid

Coal ash reuse rate

5% 4.7
102 1.2
102

1000 MW

1.5

1.5
107

1

600 MW

0.5

5% 6.6
105 3.5
105

300 MW

0 0

9.5
107

0

5% 6.4
106 3.4
106

0.002

5% 9.3
106 4.9
106

0.002

5% 3.5
104 2.0
105

0.004 y = 6.88E-03x + 5.89E-05 R² = 1

5% 6.4
104 3.7
105

0.006 0.004

1000 MW

0.008

0.006

300 MW

Freshwater ecotoxicity (kg 1,4-DB eq)

y = 7.27E-03x + 2.72E-05 R² = 1

5% 6.9
104 4.0
105

0

0

5% 1.5
105 1.2
103

y = 2.11E-01x + 2.45E-02 R² = 1

5% 9.3
105 7.8
103

0.0001 0.1

Variation Climate Change kg CO2 eq Human toxicity kg 1,4-DB eq Photochemical oxidant formation kg NMVOC Particulate matter formation kg PM10 eq Terrestrial acidification kg SO2 eq Freshwater eutrophication kg P eq Marine eutrophication kg N eq Freshwater ecotoxicity kg 1,4-DB eq Marine ecotoxicity kg 1,4-DB eq Fossil depletion kg oil eq

0.2

Coal consumption

0.0002 0.3

Freshwater eutrophication (kg P eq)

0.4

5% 2.4
102 4.4
104

0.0003

y = 2.61E-04x + 1.23E-06 R² = 1

Marine ecotoxicity (kg 1,4-DB eq)

Human toxicity (kg 1,4-DB eq)

0.5

957

1.1
1010

X. Cui et al. / Energy 45 (2012) 952e959

958

X. Cui et al. / Energy 45 (2012) 952e959

efficiency of hydrochloric acid consumption produced the least variability in most categories, except for freshwater eutrophication, which also had a relatively high variability because of the changes in phosphate-to-water levels. For the 1000 MW scenario, the efficiency of coal consumption had the lowest environmental benefit in the freshwater eutrophication category because of the lowest changes in phosphate-to-water levels. In addition, the adverse effect generated by the 600 MW scenario was significantly higher than that by the 1000 MW scenario because of the relatively heavy use of coal. 4. Discussion China is known as one of the largest energy consumers and emitters of greenhouse gases in the world because of its rapid industrial development and economic growth [14]. In 2009, the country’s total electricity generation reached 3714.7 TWh, including approximately 77% coal-based thermal power Fig. 1 and Table 1 [1]. Currently, the Chinese government pays much attention to developing clean coal technologies for electricity generation. Many small-sized polluting and inefficient coal-based electricity production sites have been ordered to shut down. For instance, small coal-fired plants with a 76.8 TWh total generating capacity were shut down during the Chinese “Eleventh Five-year Plan” period (2005e2010). As mentioned, approximately 30.57%, 35.43%, 30.5%, and 3.5% of national coal-based electricity generating units had a capacity of 300 MW or less, 300e600 MW, 600e1000 MW, and 1000 MW in 2009, respectively. Fig. 3 shows that the 300 MW scenario has the highest overall environmental burden because of the high value of the net coal consumption and solid waste disposal to landfill. Accordingly, in the “Twelfth Five-year Plan” period, the Chinese government has continued its plan to shut down part of old generating units with a capacity of 300 MW and to increase the number of generating units with a capacity of 600 MW or more [15]. Hence, if the capacity of 300 MW or less is increased to 600 MW, significant environmental benefits will be obtained (Table 6). Table 4 and Fig. 3 also show that the 300 MW scenario has the highest environmental impact in most key categories, except for natural land transformation. The relatively lower impact on natural land transformation is caused by the higher amount of coal ash disposed at landfills. These results indicate that coal ash disposal is a key to decreasing the environmental impact. Notably, coal that is of low quality, high ash content, and low calorific value coal is applied in the small-scale coal-based thermal power plant (Table 1). If high quality, low ash content, and high calorific value coal is applied, higher environmental benefits would be obtained in most categories except for natural land transformation. Also, if all

coal ash would be reused as building materials, significant environmental benefits would be further obtained in the key categories of human toxicity, freshwater eutrophication, freshwater ecotoxicity, and marine ecotoxicity. Consequently, key categories would demonstrate a change. Except for the abovementioned key categories, the potential environmental impact generated from climate change, photochemical oxidant formation, particulate matter formation, terrestrial acidification, marine eutrophication, and fossil depletion categories had an additional important contribution to the overall environmental burden. On the contrary, the potential impact seen from the other categories was small. Similarly, the dominant process would also display a change. For the 1000 MW scenario, direct emissions from the electricity production stage played an important role (accounting for 87% or more) in most key categories except for the freshwater eutrophication, marine ecotoxicity, and fossil depletion categories. The potential impact generated from crude oil and the transport stage played additional important contributions to freshwater eutrophication and marine ecotoxicity, respectively. The coal production stage had a dominant contribution to fossil depletion because of the net use of coal. These results indicate that increasing the efficiency of net coal consumption is another key to decreasing the environmental impact of power generation. Table 3 shows the net coal consumption (0.31 kg/kWh) of a 600 MW coal-based electricity generation unit, which is 10 g/kWh to 15 g/kWh higher than in developed countries (e.g., Italy, Japan and South Korea) [25]. If Japan’s best available technology (net coal consumption at 0.29 kg/kWh) is used in all of the 600 MW coalbased electricity generation units nationwide, the potential impact of electricity generation will be further reduced significantly (Table 6). Specifically, in the climate change and fossil depletion categories, more than 1.76
1011 kg-CO2 eq and 4.54
1010 kg-oil eq environmental benefits would be observed, respectively. Notably, in this study, the direct nitrogen oxides emissions from the electricity production stage were higher than the available technologies in Japan (0.34 g-NOx/kwh), Germany (1.5 g-NOx/ kwh), Canada (1.9 g-NOx/kwh), and the US (3.5 g-NOx/kwh) [26]. Also, only around 14% of coal-fired power plants in China currently have denitrization systems [27]. Thus, if the advanced Japanese technology with 0.34 g-NOx/kWh denitrization efficiency is used in the 600 MW scenario, a potential improvement of approximately 85.5%, 84.4%, 81.6%, and 88.5% will be further observed in the photochemical oxidant formation, particulate matter formation, terrestrial acidification, and marine eutrophication categories, respectively. Approximately 20% of China’s coalfired power plants currently do not have desulphurization systems [27]. If such systems would be employed, significantly greater potential can be further observed in the categories of

Table 6 Environmental benefit of main contributors. Category

Climate change Human toxicity Photochemical oxidant formation Particulate matter formation Terrestrial acidification Freshwater eutrophication Marine eutrophication Freshwater ecotoxicity Marine ecotoxicity Fossil depletion

Unit

Environmental benefit Capacity increase (300 MW / 600 MW)

Net coal consumption decrease (0.31 kg/kWh / 0.29 kg/kWh)

kg CO2 eq kg 1,4-DB eq kg NMVOC

>7.44
1010 >1.67
1011 >2.40
109

>1.76
1011 >1.71
1011 >3.10
109

kg PM10 eq

>7.42
108

>8.96
108

kg kg kg kg kg kg

>2.46 >1.98 >2.94 >5.51 >5.23 >1.95

SO2 eq P eq N eq 1,4-DB eq 1,4-DB eq oil eq









109 108 108 109 109 1010

>2.87 >2.02 >3.80 >5.62 >5.33 >4.54









109 108 108 109 109 1010

X. Cui et al. / Energy 45 (2012) 952e959

photochemical oxidant formation, particulate matter formation, and terrestrial acidification. In addition, integrated gasification combined cycle (IGCC) is world widely considered as a clean coal technology, because of the numerous factors such as higher efficiency improvement potential, better characteristics in terms of carbon dioxide control, less environmental impact and others [28e30]. There were approximately 0.84 kg/kwh, 37.8 mg/kwh, and 42.5 mg/kwh of carbon dioxide, sulfur dioxide, and nitrogen oxides generated from IGCC plant, respectively [31]. The global warming gas emission of IGCC technology was similar to that of 600 MW scenario, but the direct sulfur dioxide and nitrogen oxides emissions of IGCC technology were significantly lower than that emitted from both 600 MW and 1000 MW scenarios. These results indicate that speeding up the development of IGCC technology in China is also a key to decreasing the environmental impact of coal-based power generation, because the direct sulfur dioxide and nitrogen oxides emissions from electricity production play important roles in the overall environmental impact of both 600 MW and 1000 MW scenarios. 5. Conclusions This study identified the electricity production level and the potential for improvement of coal-based electricity production in China. The supercritical technology and ultra-supercritical technologies represent the lower environmental burden, mainly resulting from relatively low net coal use and solid waste. Increasing net coal consumption efficiency, coal ash reusing rate, desulfurization and denitrization system efficiency are key factors in reducing the overall environmental impact of coal-based power generation in China. The life cycle inventories and the potential impact seen in this research will be very helpful to policymakers in China in the aspect of making decisions for the construction of electricity plants in the country. However, numerous factors (e.g., technical assistance and training, government policies, carbon tax, cost, cleaner production, uncertainty propagation, energy efficiency law, sustainable and production law) may affect the technology choice and development for reducing the overall environmental burden. Thus, future research on these factors is highly necessary. Acknowledgments We gratefully acknowledge financial support from the National Natural Science Foundation of China (grant no.41101554), SRF for ROCS, SEM (grant no. 2011-1568), and National High-Tech R&D Program of China (863 program, grant no. 2012AA061705). References [1] National Bureau of Statistics of China. Chinese energy statistical yearbook: 2010. Beijing: China Statistics Press; 2011. [2] Benetto E, Popovici EC, Rousseaux P, Blondin J. Life cycle assessment of fossil CO2 emissions reduction scenarios in coal-biomass based electricity production. Energy Conversion and Management 2004;45(18e19):3053e74. [3] Santoyo-Castelazo E, Gujba H, Azapagic A. Life cycle assessment of electricity generation in Mexico. Energy 2011;36(3):1488e99. [4] Odeh NA, Cockerill TT. Life cycle analysis of UK coal fired power plants. Energy Conversion and Management 2008;49(2):212e20. [5] Xiao B, Suo C, Yan X. Comparing Chinese clean coal power generation technologies with life cycle inventory. Energy Procedia 2011;5:2195e200.

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