Exergy-based resource accounting for China

e c o l o g i c a l m o d e l l i n g 196 (2006) 313–328

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Exergy-based resource accounting for China B. Chen a , G.Q. Chen a,b,∗ , Z.F. Yang b a

National Laboratory for Turbulence and Complex Systems, Department of Mechanics & Engineering Science, Peking University, Beijing 100871, China b Faculty of Environment, Beijing Normal University, Beijing 100875, China

a r t i c l e

i n f o

a b s t r a c t

Article history:

The resource accounting of the Chinese economy in 2000 is presented based on exergy as a

Received 16 January 2005

unified quantifier for natural resources. Major resources entering the economic production

Received in revised form 13 January

include sunlight, wind power, tidal power, wave power, geothermal power, nuclear power,

2006

biomass, straw, hydropower, coal, oil, natural gas, wood, ores, agricultural and aquatic prod-

Accepted 1 February 2006

ucts. The resource conversion embracing the paper, food, iron and steel, nonferrous metal,

Published on line 29 March 2006

chemical and other industries as well as transportation, household and commerce sectors are illustrated. The efficiencies of the thermal conversion procedures including lighting, me-

Keywords:

chanical work, space heating, cooking, water heating and process heating are also estimated.

Exergy

The total exergy input of the Chinese economy was 64.76 EJ, which was 51.0 GJ/cap, whereas

Resource accounting

the total exergy output contained 12.8 EJ or 10.1 GJ/cap, indicating the exergy efficiency was 20%. The present study illustrates the possibilities of increasing exergy efficiencies of different conversion sectors and provides theoretical foundation for policymakers in establishing effective regulatory mechanism of economic production. © 2006 Elsevier B.V. All rights reserved.

1.

Introduction

Resources drive the economic production of the society in the context of ecological system. The quantity and quality scarcities of diverse resources require an efficient and effective biophysical assessment with overall and unified accounting. Resource accounting concerning the evolution of the social– economic–ecological complex systems based on the concept of exergy have thus been emerging as a latest progress in ecological modelling and systems ecology (Jørgensen, 1981, 1992a,b, 1994, 1999a,b, 2000, 2001; Wall, 1977, 1986; Svirezhev, 2000; Jørgensen and Fath, 2004; Jørgensen et al., 2000, 2004; Fath et al., 2004). Exergy for a given system is defined as the maximal amount of work that can be extracted from the system in the process of reaching equilibrium with its local environment, chosen to have a direct bearing on the behavior of the system with

∗

Corresponding author. Tel.: +86 10 62767167; fax: +86 10 62750416. E-mail address: [email protected] (G.Q. Chen). 0304-3800/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.ecolmodel.2006.02.019

respect to the time and length scales, depending on the observer’s objectives and knowledge (Jørgensen, 1992a,b, 1994, 1999a,b, 2000a,b, 2001; Jørgensen et al., 1995, 1998, 1999, 2004a; Chen, 2005, 2006; Szargut, 1971, 1980, 1985, 2004). Moreover, the scarcity of exergy as the fundamental natural resource is illustrated by a study of the cosmic exergy consumption of the earth, and a general scheme for ecological evaluation has been outlined on the basis of embodied exergy (Chen, 2005, 2006). Exergy associated with a system may play distinctive roles as resource, buffering capacity and environmental impact, considering the subjective for observer, system and environment, respectively. For the observer stand facing both the system and the local environment, the exergy can server as the unified measure of the real resource availability. For the system itself, the exergy is regarded as the global buffering capacity (Mejer and Jørgensen, 1979; Jørgensen, 1981; Dincer, 2002; Dincer et al., 2004). Further, the exergy as a built-in measure of quality has been applied as a goal function for structurally dy-

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namic models and indicator for ecosystem health (Xu, 1997; Xu and Tao, 2000; Xu et al., 1999a,b, 2001a,b, 2004; Zhang et al., 2003). Also, the exergy costs to maintain the gene information, i.e., the embodied exergy of gene, are evaluated, thus providing theoretical basis for the exergy calculation of living components of ecological systems (Jørgensen et al., 2004). Finally, the “substitution exergy” may also be used as a measure of the environmental remediation cost to offset the environment impact made by the system on the local environment. Considering the resource level, exergy measures the physical maximum work which can be extracted from the system when it interacts with the environment. Therefore, the definition, calculation and assessment of the resource depend on the determination of the boundary between the system and the environment. Different boundaries lead to different concepts and quantities of resources when the system and the environment are determined at the same time. Exergy per se stands facing both the system, which is the present, and the environment, which is the absent, thereby revealing the differences between the system and the environment and the essence of the resource. When the resource is perceived and explored, the exergy efficiency can be calculated to optimize the procedures of obtaining, allocating and utilizing the resource. Wall (1977, 1986) assumed the reference environment, which is defined by Szargut (1980, 1989) and Szargut and Morris (1985), to be homogeneous, that is, in equilibrium state according to the time and length scale of the researcher. In addition, the environment is large enough that the variation of the parameters of it can be omitted when the system interacts with the environment. According to the second law of thermodynamics, exergy is the real scarce resource consumed in the physical irreversible process. Resources enter into society and become commodity and the traditional commodity accounting is based on the quantities, regardless of the different qualities of the commodities. Except for the exergy accounting introduced by Valero in the field of ThermoEconomics, Extended Exergy Accounting (EEA) also provides a convenient way to unify and measure different types of materials, energy and capital, thereby evaluating the quality of the resources and degradation in the conversion (Sciubba, 1999, 2001a,b; Valero, 2006). Natural resources are traditionally described as energy resources and material resources. Wall (1977, 1986) introduced the concept of exergy, which is a unified measure of matter, energy and information, into resource accounting. Research on exergy conversion in the society has been done in Sweden, Japanese, Norway, Canada, Brazil, Turkey, Italy and the U.S., where appropriate structures of exergy utilization and effective usage of resources are represented and discussed (e.g., Wall, 1977, 1986, 1990, 1993, 1994, 1997a,b, 1998; Rosen, ¨ 1992; Schaeffer et al., 1992; Ozdogan et al., 1995; Ayres et al., ¨ 1998; Ayres, 2002; Ayres and Wall, 2003; Ar´ıf and Gurer, 1998; ˚ and Mielnik, 2000; Ertesvag, ˚ 2001; Wall and Gong, Ertesvag 2001; Dincer et al., 2004; Utlu and Hepbasli, 2003, 2005; Hepbasli and Utlu, 2004). The exergy method applied to society can be grouped into two types. The first method, which follows Reistad’s idea, only considers the flows of energy carriers whereas the latter, which follows Wall’s analysis, accounts for ˚ 2001). all the major energy and material flows (Ertesvag,

The main objectives of this study are to account the resource inflows and outflows of the Chinese economy as the second largest energy consumer in the world and analyze exergy utilization efficiency for the major resource conversion sectors. Since the central-planning economy has been the major part of the Chinese economy from 1949, unified planning and management policies formulated by the government dominate the development of the resource conversion sectors, which is quite different from the other countries. In addition, China has been in shortage of energy and resources for a long period. Therefore, this paper intends to present an overall exergy analysis of the Chinese economy sustained by various resources, which may help the policymakers of the government regulate the relative policies when formulating the state economic developing plans.

2.

Methodology and data used

For the national-scale system, the exergy input contains the imported, gathered, constrained and extracted commodities as exergy carriers while the output contains the consumed or exported products, materials and services (Wall, 1977). The resource base includes sunlight, wind power, tidal power, wave power, geothermal power, biomass, hydropower, forest resources, harvested crops, rangeland resources, iron and nonferrous ores, coal, crude oil and natural gas, whereas the consumption end includes woods, pulp and paper, food, iron and steel products, nonferrous metal products, chemical products, transportation and households. The whole country is chosen as the boundary of the conversion process analysis. The input to the process contains the exploited natural resources and imported commodities flowing into society. For avoidance of repetitive and cross calculations, the entrance boundary points are set at the same level of the conversion chain of the exergy inflow. The output from the process consists of the products, goods and services, which are converted from the raw materials into goods appropriate and compatible for human living and production. The conversion efficiency is defined as the quotient of the input and output at the same level of the process. This paper omits all the heat exergy of the materials. Exergies of mechanics and electricity equal to their energy values. The major part of the input is fossil fuels, mainly consumed in the manufacturing industry and transportation. The exergy content of fossil fuels, as a first approximation, is set equal to the lower heating values (Kotas, 1985; Morris and Szargut, 1989; Schaffer, 1992; Wall, 1977, 1986). Sunlight is used directly by the passive or active solar systems. The calculation of the exergy flow of sunlight into the society is based on the efficiencies of the solar collectors of the passive or active solar systems. Utilization of wind is focused on the wind power, thereafter the exergy inflow of the wind is set equal to the exergy content of the electricity generated by the wind power plant. Notwithstanding part of the wind power used to drive the sailing boat in the transportation sector, the driving power is uncertain and thereby omitted in this paper. Exergy inflows of tide and wave are also calculated in the same way as wind. Exergy inflow of geothermal power is used for both electricity generation and space heating.

e c o l o g i c a l m o d e l l i n g 196 (2006) 313–328

Calculation of the woods exergy produced from the forest has reference to the result of Japan (Wall, 1994). The exergy contents of the dry solid woods from broad-leaved forests and needle-leaved forests are 18.5 MJ/kg and 18.9 MJ/kg, respectively. Assuming the humidity of the wood is 25%, thus the average exergy of the broad-leaved and needle-leaved wood is 13.4 MJ/kg (the area of the broad-leaved timber forest are equal to the area of the needle-leaved timber forest in China according to the results of the National Forest Resource Census). With the average density 0.75 t/m3 , the exergy of the woods is estimated to be 10 GJ/m3 . The exergy contents of the harvested crops and food are derived from the free energy of the nutrients of them, of which protein, fat and carbohydrate are the ˚ and Mielnik, 2000; USDA Nutrient main components (Ertesvag Database, 2003; Wall, 1986, 1990, 1994; Yang et al., 2002). The exergy of the rangeland resources is calculated according to the different types of rangeland and hay yields. The nutrition of the different hay includes rough protein, rough fat, rough fiber, rough ash, nitrogen free extract (NFE), calcium and phosphorous. The rangeland provides large amount of fodder resources for the livestock. As the dietary requirement changes, more food, such as pork, beef, mutton and milk, is needed from livestock husbandry. Increasing yield of livestock, accompanied by the over grazing and desertification, results in serious rangeland resources depletion. As the rangeland resources are digested and converted by the herbivorous livestock and the livestock is regarded as the input interface to the society, the exergy of the rangeland resources are estimated. Exergies of the metals and minerals are calculated on the standard provided by Morris et al. (1986), Szargut (1989), Finnveden et al. (1997)and Ayres (1998). The Chinese iron ore has an average iron content about 55%, which implies 1 kg of iron ore contains 9.8 mol of iron, thus the exergy content of the magnetite iron ore is calculated to be 0.46 MJ/kg (Wall, 1990, 1994). With relatively low grade of the ore output (aluminum 40%, copper 0.57%, lead 2.46%, zinc 4.09% and tin 0.87%), the exergy contents of the aluminum, copper, lead, zinc and tin are also estimated in the same way to be 0.3 MJ/kg, 0.026 MJ/kg, 0.021 MJ/kg, 0.046 MJ/kg and 0.0002 MJ/kg, respectively.

3.

Analysis

3.1.

Chinese economy

Large population (1.27 billion) in China 2000 leads to a low share of the essential natural resources. Also, the resource conversion efficiency of China is relative low compared with the other countries. Thus, shortage of natural resources and extensive way of utilization have impeded the economic development. The elasticity of energy consumption was 0.01 in 2000, indicating the relative low energy growth supports high speed growing economy. Meanwhile, the economic development always has priority than the so-called compatible development of economic, environment and resources and the overwhelming motive to promote GDP makes the resource base overloaded and depleted in China. Fortunately, since the early 1990s, the Chinese economy has achieved a soft-landing after the central government takes some measures to adjust

315

the economic polices and restrain the over expanded infrastructures (Teather and Yee, 1999). Fig. 1 depicts the exergy conversion process in Chinese society 2000, in which all the data available are from the statistical yearbook of the government. The resource exergy flows go from left to right, that is, from the resource base to the consumer, in which the width of the flow is determined by its exergy content. To simplify the conversion figure, only the major exergy flows are presented and all the inflows of the diagram are ranked by the resource classification (Wall, 1986). Forestry, harvested crops, biomass, rangeland and hydroelectric resources are funds. Metals, minerals, coal, oil and natural gas are deposits. The whole exergy flow conversion process is denoted by block diagram (Wall, 1977, 1986). The resources base is listed in the left side of the conversion diagram, whereas the resources demand in society appears in the right side, determining the level of the conversion chain of the resources.

3.2.

Sunlight

There are abundant solar exergy resources in China. It is estimated the solar radiant quantity amounts to 5.9 × 109 J/(m2 year) on the average (Yan, 1995), with the minimum amount in the Sichuan Basin and the maximum in the Qingzang Plateau (both located from 22◦ N to 35◦ N), increasing gradually from east to west and from south to north. Different form the other areas, the solar energy increases with the latitude in the south area from 30◦ N to 40◦ N because of the rainy, cloudy and misty weather. The actual amount of the solar energy at each site varies greatly, depending on the season and the climate, which limits the large scale and centralized utilization as an alternative energy resource of fossil fuel. In addition, solar energy is not widely used because the cost of solar energy utilization is still high compared to the conventional energy, which is readily available and relatively cheap. There are two primary types of utilization of solar energy, including solar collectors (water heater, solar oven and solar building) and solar photovoltaics. Assuming the conversion efficiency of the solar water heater to be 50% with the exergy conversion factor of the heat water being 0.2, the daily exergy output per square meter is estimated to be equivalent to 1693 kJ/m2 (Craig et al., 1996). In China, the efficiency of the solar water heater is about 28% (Li and Dong, 1999). The solar water heater added up to 1.1 × 107 m2 in 2000, which exported exergy 3.83 TJ. There are also 300,000 solar ovens, mainly distributed in Qingzang Plateau, which is convenient for people living in the fuel-scarce area to cook food and heat up water. Assuming the collector is 50% efficient and its area is 1.1 m2 , the gross collector area was 3.3 × 105 m2 (Huo and Zhang, 2001), thus the total exergy output was estimated to be 0.2 TJ. In ancient China, people has designed south-facing house with windows arranged to capture the sunlight and the masonry wall painted in deep color to absorb the solar radiation more efficiently. Nowadays, passive way of utilization of solar energy has changed to active way of utilization of solar energy. There were 8.5 × 106 m2 solar buildings in China, using solar energy for space heating (Huo and Zhang, 2001).

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Fig. 1 – The exergy conversion system in Chinese society in 2000.

e c o l o g i c a l m o d e l l i n g 196 (2006) 313–328

The main energy input to the passive solar building consists of two primary parts: the energy from the south facing windows and the energy from the thermal storage (Trombe) wall. The exergy input directly from the windows can be represented as follows: Exd = Exdin − Exdloss in which




Exdin =
CAd Ir 1 −

(1)

Tout Tin

 (2)

where
is the transmission rate of the glass of the windows, C the clear transmittance area coefficient of the windows, Ad the area of the windows, Ir the irradiance of the south elevation, and Tin and Tout are the average indoor and outdoor temperatures, respectively; And




Exdloss = k 24 −

2ωs 15






(Tin − Tout )Ad hd 1 −

Tout Tin



(3)

where k is the heat transmission coefficient of the windows, Tin and Tout the average indoor and outdoor temperatures, respectively, ωs the hour angle of the sun, 2ωs /15 the hours of the daytime, (24 − 2ωs /15) the hours of the night and hd is the number of days from December to February. The net exergy input from the storage of the thermal storage wall can be written as (Meng et al., 2003; Wang, 1994, 1998; Zhuang, 1997):




Exw = Aw I 1 −

Tout Tin



= Aw r




Tout cos in I 1− cos z h Tin

 (4)

where  is the collector coefficient of the thermal storage wall, Aw the area of the wall, Ir the irradiance of the south elevation, Ih the irradiance of the horizontal plane, in the incident angle of the sunlight and z is the zenith angle of the sunlight. In this paper, the area of the thermal storage wall is assumed to be 40% of the area of the solar house while the area of the windows is assumed to be 50% of the area of the thermal storage wall according to the typical designing mode of the solar house in the northwest and Qingzang Plateau of China; Ih is accumulated to be 970 MJ/m2 on the average from December to February (Huo and Zhang, 2001); Ir is calculated to be 70% of Ih ;  is presumed as 0.2;
is set as 0.75, considering the single glass and C is set as 0.7, considering wood windows; k is presumed as 2.7 W/(m2 ◦ C); Tin and Tout are estimated to be 15◦ and 0◦ in winter, respectively (Zhuang, 1997; Meng et al., 2003). The main exergy input to the solar house system was thereby 36.7 TJ. There were 20 MW photovoltaics generated for transportation signal, communication and lighting in rural and remote areas in 2000 (Gao et al., 2000), of which seven photovoltaic power plant located in Tibet with 420 kWp capacity. Assuming the running time of the photovoltaics is 3000 h on the average, the exergy input of photovoltaics to the society was 0.3 PJ. The upper limit for efficiency of the conversion of solar energy in photovoltaics developed in China was only 14% or so and the cost of the electricity is still high as 2.2 Yuan/kWh. Also of concern is the fact that photoelectric cells made of silicon or other chemicals like gallium arsenide generate environmental pollution.

3.3.

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Wind power

The utilization of wind energy was popular in ancient China where the people hoisted the sail and transport goods by the wind. Merely in the Jiangshu Province, there used to be more than 200,000 wind power water pumping machines in operation (Gu et al., 2001). Since 1980s, a batch of medium- and large-sized wind power generating units introduced from Denmark, Sweden, Germany and the U.S. has come to operation. There were totally 9.3 × 108 kWh (3.35 PJ) generated by the interconnected wind power plant in 2000, with the average price being 0.72 Yuan/kWh. “Wind Development Plan” was proposed by the State Development and Planning Commission (SDPC) to introduce the advance wind power technologies from abroad and improve the domestic technological engineering in manufacturing 300 kW and 600 kW wind generation sets during the ninth 5-year period (1996–2000). In addition, “Brightness Programme” was also set down to develop resources and help the poor, endeavoring to supply 2.3 × 107 people living in windy and rural areas as well as 300 towns, 100 sentries and 100 microwave communication stations with electricity.

3.4.

Tidal power

The tides of the ocean are the result of the gravitational actions from both the moon and the sun. There used to be 50 tidal power plants, remaining 8 still work associated with 1 × 107 kWh (36 TJ) electricity generated. Jiangxia tidal power plant is the third largest tidal power plant in the world with 3.2 MW installed capacity and annually 5.02 × 106 kWh electricity generated, which is only half of the design electricity generation because of the difference between the real state and the design state of the generator. Although the cost of the construction of the tidal power plant is high (11 billion Yuan RMB invested), the tidal exergy can be used in a comprehensive way. Take the Jiangxia tidal power plant for example, it benefits more from the aquatic products generated by the reservoir of the power plant than from the electricity generated by the power plant (Zhang, 1996). There are totally 56 billion kWh developable tidal resources in China. However, the environmental influence of the tidal power plant cannot be neglected. The constructed tidal power plant changes the tidal range, the temperature and quality of the seawater, affects the groundwater, aggravates the coast erosion and destroys the ecological environment of the birds and fish, with the result that suitable sites for tidal power plant is limited.

3.5.

Wave power

Wave power is suitable for the offshore islands and navigation light buoy. There has been nearly 1000 wave power devices for navigation light buoy in operation (each rated power 60–450 W). Since 1990, a wave power plant with 3 kW has been operated in Zhuhai. Twenty-kilowatt shore wave power plant, 5 kW rear elbow floating wave power generation device and 8 kW oscillatory wave power plant were brought into service during the eighth 5-year period (Yu, 1995). One hundredkilowatt oscillation water column wave power plant was es-

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tablished in Shanwei 2000 while another 100 kW oscillatory wave power plant was placed in service in Tianjin 1999.

3.6.

year. Based on CFY (2001), the national forest logs accounted for 6.39 × 107 m3 or 639.2 PJ, with the import was 1.36 × 107 m3 or 136 PJ while the export was 2.7 × 104 m3 or 0.27 PJ. Classified by the consumptive way of the forestry resources, approximately 1.54 × 108 m3 or 1.54 EJ was used as common commercial wood, of which 7.7 × 107 m3 or 0.77 EJ was used in the construction and 1.3 × 107 m3 or 0.13 EJ was consumed by furniture (CFY, 2001). Additionally, part of the forest crops as firewood was discussed in the biomass sector. The major exergy invested in the paper manufacturing industry includes coal, coke, crude oil, gasoline, kerosene, diesel oil, fuel oil, natural gas, electricity, wood, straw, net imported pulp and recirculated paper. The total input was 971 PJ, of which coal was 277 PJ, electricity 82.2 PJ, diesel oil 10 PJ, fuel oil 7.3 PJ, gasoline 5.6 PJ, kerosene 1.7 PJ, natural gas 1.2 PJ, coke 0.5 PJ, PLG 0.2 PJ, crude oil 0.2 PJ, imported pulp 56 PJ, wood 90 PJ, straw 260 PJ and recirculated paper 179 PJ. Meanwhile, the exergy of the paper products, including exported pulp (0.2 PJ), paper and paperboard (4.5 PJ), added up to 520 PJ. Thus, the efficiency of the paper industry was 53%, for the proportion of recirculated paper has been increased despite the waste heat generated in the pulp boiling and paper making process. The forest and wood industry totally used 1.54 EJ from common commercial wood, 0.16 EJ from fossil fuels and electricity in wood logging, transport and processing, and 0.88 EJ from paper industry (excluded 0.09 EJ wood to avoid double accounting). Import gave an additional 0.14 EJ in timber. Altogether, the total exergy input was equal to 2.72 EJ. The production of paper amounted to 0.52 EJ. The other wood products gave an additional 0.61 EJ (CFY, 2001). Thus, the total exergy output of the forest and industry based on forest was 1.13 EJ, which was 42% of the input.

Geothermal power

Geothermal resource are derived by heat release, crustal radioactivity, heat flowing up from mantal convection and the solar-driven sedimentary cycle passing exergy downward as compressive and chemical potentials (Odum, 1994, 1996). In China, the geothermal exergy is used in two ways, including electricity generation and heating. The installed geothermal power plant was 28 MW, the electricity generated being 0.14 billion kWh (504 TJ). Albeit globally insignificant, it is locally important, especially in Lhasa, capital of the Tibet region, known as the world leaf, where 40% of the electricity is provided by Yangbajing geothermal power plant with the installed capacity being 24.18 MW and temperature around the bank 135–140◦ . The geothermal exergy is also used directly for heating. The direct use of geothermal capacity amounted to 17.6 PJ, with its applications being different in different provinces, focusing on greenhouse, space heating, fish culture and bath. The environmental problems involved in geothermal supply resulting in the ground setting and the thermal pollution and the large amount of initial investments limit the generalization of the geothermal resources. Serious scaling and corrosion also add to the maintenance expense of the geothermal power and heating system.

3.7.

Forestry, pulp and paper industry

According to the report of the fifth forest resources census (2000), China possesses 1.59 × 108 ha forests with the percentage coverage 13.92%, increasing 0.3% in contrast to the last

Table 1 – Rangeland hay yield in China Item

Developable areas (ha)

Specific yield (kg/ha)

Temperate meadow steppe Temperate steppe Temperate desert steppe Alpine meadow steppe Alpine steppe Alpine desert steppe Temperate steppe-desert Temperate desert Alpine desert Warm tussock Warm shrubby tussock Tropical tussock Tropical shrubby tussock Arid-tropical shrubby tussock Low-land meadow Mountain meadow Alpine meadow Marsh

1.28E+07 3.64E+07 1.71E+07 6.01E+06 3.54E+07 7.75E+06 9.14E+06 3.06E+07 5.59E+06 5.85E+06 9.77E+06 1.14E+07 1.34E+07 6.39E+05 2.10E+07 1.49E+07 5.88E+07 2.25E+06

1465 889 455 307 284 195 465 329 117 1643 1769 2643 2527 1770 1730 1648 882 2183

Total

3.31E+08

911

Source: Liao and Jia (1996).

Specific exergy (MJ/kg) 16.4 17.6 17.9 17.7 17.7 17.1 16.2 15.4 17.0 17.1 17.3 17.2 16.8 16.4 17.3 17.5 17.7 17.8

Total exergy yield (J)

Fraction (%)

3.08E+17 5.69E+17 1.39E+17 3.27E+16 1.78E+17 2.58E+16 6.89E+16 1.55E+17 1.11E+16 1.64E+17 2.99E+17 5.19E+17 5.71E+17 1.85E+16 6.30E+17 4.30E+17 9.18E+17 8.76E+16

6 11 3 1 4 1 1 3 0 3 6 10 11 0 12 8 18 2

5.13E+18

100

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Table 2 – Intake rangeland resources in China Item

Number (head)

Sheep unit (head)

Intake exergy (J)

Fraction (%)

Cow Buffalo Horse Donkey Mule Camel Goat Sheep

4.89E+10 1.19E+12 8.77E+10 9.23E+10 4.53E+10 3.26E+09 1.57E+12 1.33E+12

2.44E+07 5.37E+08 5.26E+07 2.77E+07 2.27E+07 3.17E+07 1.26E+08 1.33E+08

6.34E+16 1.39E+18 1.36E+17 7.18E+16 5.88E+16 8.23E+16 3.26E+17 3.46E+17

3 56 6 3 2 3 13 14

Total

4.37E+12

9.55E+08

2.48E+18

100

3.8.

Rangeland

The degradation of the rangeland became more serious with the degenerated rangeland areas summing up to 9 × 107 ha and 1% yield decline in 2000 (Wang et al., 2002). The rangeland with its herbaceous and woody forage plants is an important type of territory natural resources. As is shown in Table 1, the rangeland hay is divided into 19 different types with totally 5.13 EJ yielded. The rangeland hay is produced by shift mowing and certain modulation, part of which is stored in the rick yard to settle the unbalance of inter-annual and seasonal forage supply. The simple pattern of rangeland utilization, grazing throughout the year, has been changed with the stocking rate being determined by the annual and seasonal hay production (Zhu et al., 1993). To exploit the feed intake from the rangeland resources by the livestock, the number of the different types of livestock is reduced to the sheep unit. Assuming one sheep unit feed 150 kg hay annually (average 17.3 MJ/kg hay), the intake exergy of the rangeland resources is thereby listed in Table 2.

3.9.

Harvested crops

Harvested crops are mainly converted into food. The conversion chain is limited to the products as outset and the food as end. According to Wall’s paper (1990, 1997a,b), the input includes not only solar radiation, but also fertilizers, fuels and electricity. Fertilizers and some of the fuels and electricity are invested in the growing crops, not the harvested crops. When the growing crops as outset and the harvested crops as end are considered, the exergy input includes fertilizer, fuels and electricity as social input invested in the agriculture, together with the large amount of nutrients resulting in soil fertility loss from the cultivated land which is also part of the resource base. When the harvested crops as outset and the food as end are considered, the exergy input includes the fuels and electricity invested in the food industry, wholesale, retail trade and food services. Regarding the growing crops as conversion outset, the exergy input includes fertilizer, coal, oil, coke, firewood, electricity, etc. The allocation proportions of the total social exergy inflow up to 2.84 EJ that invested in the agricultural production and fishery are shown in Table 3. Also, considering soil fertility erosion from the cultivated land, this paper calculates the major nutrients absorbed by the crops. Based on the agricultural data (Shen, 1998), the N, P and K containing in the harvested crops amounted to 0.36 PJ, 72 PJ and 120 PJ, respectively.

The major harvested crops, livestock and aquatic products are listed in Table 4. The maximum export exergies include rice and corn, which were 46.6 PJ and 46.5 PJ, respectively, the second is dry beans, which was 8.58 PJ whereas the maximum import exergy was soybeans, which was 156 PJ and the second was wheat, which was 12.2 PJ. There are 3.94 EJ from energy carriers and 0.19 EJ from cultivated land. Since the domestic harvest was 8.49 EJ and the import was 0.11 EJ, the total exergy input to the food sector was 11.23 EJ when excluded the 1.50 EJ grain used as fodder. Regarding the harvested crops as conversion outset, through the chain of food manufacturing processing, wholesale, retail trade and food services, the exergy input to the food conversion chain was calculated to be 1.1 EJ, as is shown in Table 5, of which the proportions were 28%, 17% and 55% for food processing, food manufacturing and wholesale, retail trade and food service in each food conversion sector, respectively. The food consumption is calculated by the daily per capita intake exergy. The urban household consumed 2.7 GJ/year/cap, while the rural consumed 4.6 GJ/year/cap. Thus, the food intake of people in China is weighted as 3.9 GJ/year/cap since 36.2% of the total population lived in the urban areas whereas the others in the rural areas. Adding the 0.12 EJ export food, the exergy outflow of the food sector is thereby estimated to be 5.07 EJ. The per capita average cultivated area of the rural residents was 0.13 ha, of which the contract land was 0.126 ha and the family plot was 6 × 10−3 ha associated with per capita average mountain area 0.02 ha and garden area 4 × 10−3 ha. The total sown area added to 1.35 × 108 ha, of which 3 × 107 ha for rice, 2.67 × 107 ha for wheat, 2.31 × 107 ha for corn, 1.27 × 107 ha for soybeans, 1.05 × 107 ha for tubers, 4.86 × 106 ha for peanut, 7.49 × 106 ha for rapeseed, 3.05 × 106 ha for sesame,

Table 3 – Social exergy invested in the agriculture and fishery Item Coal Oil Coke Fertilizer Electricity Total

Raw data 1.65E+07 t 1.50E+07 t 1.44E+07 t 4.15E+07 t 6.73E+10 kWh

Exergy (J)

Fraction (%)

3.89E+17 6.29E+17 4.58E+16 1.53E+18 2.42E+17

14 22 2 54 9

2.84E+18

100

Sources: CAY (2001), RSYC (2001) and SYC (2001).

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Table 4 – Exergy of the major harvested crops, livestock and aquatic products Item

Raw data (t)

Exergy (J)

Rice Wheat Corn Soybean Tubers Peanut Rapeseed Sesame Cotton Hemp Sugarcane Beet Tobacco Cocoon Tea Fruit Pork Beef Mutton Milk Egg Aquatic products Cotton Hemp

1.88E+08 9.96E+07 1.06E+08 2.01E+07 3.69E+07 1.44E+07 1.14E+07 8.11E+05 4.41E+06 5.29E+05 6.83E+07 8.07E+09 2.55E+09 5.48E+08 6.83E+05 6.23E+07 4.03E+07 5.33E+06 2.74E+06 9.19E+06 2.24E+07 4.28E+07 4.42E+06 5.29E+05

2.93E+18 1.52E+18 9.12E+17 7.84E+16 1.22E+17 3.54E+17 4.22E+17 2.35E+16 7.23E+16 8.68E+15 3.42E+17 4.04E+16 2.73E+16 2.47E+15 7.31E+15 1.18E+17 1.01E+18 6.18E+16 4.33E+16 4.50E+16 1.79E+17 2.44E+17 7.02E+16 8.15E+16

Total

8.49E+18

Source: CAY (2001).

4.04 × 106 ha for cotton, 2.62 × 105 ha for hemp, 1.19 × 106 ha for sugarcane, 3.29 × 105 ha for beet, 1.27 × 106 ha for tobacco, 1.09 × 106 ha for tea garden and 8.93 × 106 ha for orchard. The total major exergy of harvested crops summed up to 6.89 EJ. Although the exergy of the harvested crops increased from 4.08 EJ in 1980 to 6.89 EJ in 2000, the fact is the degradation of the cultivated land was exacerbated and covered by the escalated usage of chemical fertilizers, from 1.27 × 107 t in 1980 to 4.15 × 107 t in 2000. There is growing concerns about the food agricultural production ability of China. Soil and water loss is one of the most serious problems by which the agricul-

ture confronts, for large amount of nutrients in nearly 5 billion eroded soil each year carried to the sea from the local areas, weakening the foundation of the agriculture. In addition, over grazing intensity leads to desertification, resulting in decline on the rangeland resources yield and 2460 km2 desertification areas increased each year.

3.10.

Biomass

In rural areas, the biomass resources are mainly composed of firewood, straw and biogas. The exergy consumption of the rural areas depends on the obtainable local resources. The biomass exergy consumption accounts for 56% in daily life and 1.5% in production which alleviate the pressure of the fossil fuel supply (Huo and Zhang, 2001). However, excess demand for biomass exergy will break down the balance of the local ecological environment. For example, the people living in the rural areas prefer to fell too much firewood without any cost than purchase fossil fuel, electricity and promote the exergy utilization efficiency with new technology, which subsequently results in soil and water loss and degradation of the soil fertility in the near future. There were 1.41 × 108 t or 2.05 EJ firewood used for residential consumption and 0.21 × 108 t or 0.3 EJ firewood for agricultural production in 2000. Firewood forest has been constructed gradually since 1981. As the small-size coal kilns are prohibited in China, the peasants cannot get the local coal resources as fuel. Also, the use of LPG is too complicated for the rural areas, regarding the installment of the devices and the safe supply of the LPG. Firewood seems to be an appropriate choice for the peasants with relatively lower income. In view of the ecological environment, the firewood produced by the firewood forest generates little pollution, the CO2 emitted when burned being in balance with the CO2 absorbed by the forest, and is renewable with higher output than the normal forest. For example, the outputs of the firewood forest were 7.5 t/ha, 7.5 t/ha and 3.75 t/ha in southern mountain areas, plain and hilly areas, and northern mountain areas, respectively, whereas the normal forest was only 0.75 t/ha on average (Gu et al., 2001). There was 5.2 × 106 ha firewood forest and roughly 3.2 × 107 t or 0.46 EJ firewood yielded in China 2000, which indicated that

Table 5 – Exergy invested in the food conversion chain Item

Food processing Raw data (t)

Coal Coke Crude oil Gasoline Kerosene Diesel oil Fuel oil PLG Natural gas Electricity

9.15E+06 1.54E+05 4.20E+03 3.00E+05 2.50E+03 2.94E+05 7.46E+04 1.70E+04 1.50E+07 (cum) 1.55E+10 (kWh)

Total Source: CESY (2000–2002).

Exergy (J) 2.16E+17 4.90E+15 1.78E+14 1.41E+16 1.15E+14 1.32E+16 3.13E+15 8.28E+14 6.08E+14 5.58E+16 3.09E+17

Food manufacturing

Wholesale, retail trade and food service

Raw data (t)

Exergy (J)

Raw data (t)

Exergy (J)

5.47E+06 1.40E+05 4.80E+03 1.20E+05 8.00E+02 1.65E+05 9.04E+04 1.46E+04 7.00E+06 (cum) 9.50E+09 (kWh)

1.29E+17 4.45E+15 2.04E+14 5.64E+15 3.67E+13 7.39E+15 3.79E+15 7.11E+14 2.84E+14 3.42E+16

8.15E+06 3.57E+05 1.80E+03 2.10E+06 1.20E+05 2.56E+06 1.16E+05 5.55E+05 3.44E+08 (cum) 3.94E+10 (kWh)

1.92E+17 1.14E+16 7.63E+13 9.84E+16 5.51E+15 1.15E+17 4.86E+15 2.70E+16 1.39E+16 1.42E+17

1.86E+17

6.10E+17

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Table 6 – Exergy of the straw resources Item

Crop (t)

Rice Wheat Corn Soybean Tubers Peanut Rapeseed Sesame Cotton Hemp Sugarcane

1.88E+08 9.96E+07 1.06E+08 2.01E+07 3.69E+07 1.44E+07 1.14E+07 8.11E+05 4.41E+06 5.29E+05 6.83E+07

Total

5.50E+08

Crop/straw 0.97 1.03 1.37 1.71 0.61 1.52 3.00 0.64 3.00 1.70 0.25

Straw (t)

Exergy (J)

Fraction (%)

1.82E+08 1.03E+08 1.45E+08 3.44E+07 2.25E+07 2.19E+07 3.42E+07 5.19E+05 1.32E+07 8.99E+05 1.71E+07

2.56E+18 1.51E+18 2.11E+18 5.20E+17 3.20E+17 3.39E+17 4.83E+17 8.01E+15 2.10E+17 1.39E+16 2.20E+17

31 18 25 6 4 4 6 0 3 0 3

5.75E+08

8.29E+18

100

Source: CAY (2001).

in the rural areas the total firewood served as fuel amounted to 2.35 EJ, with 1.9 EJ or 80% firewood being felled from the normal forests. The residues after being harvested, such as straws, can be directly used as feed stock for paper-making, fertilizer, fodder and fuel (4F). The estimated allocation of the different types of straw is listed in Table 6. The total straws amounted to 8.29 EJ, of which rice, corn and wheat straw were the main components. According to the China Energy Statistical Yearbook, 2.88 × 108 t or 4.16 EJ straw resources were brought into rural residential consumption, with the efficiency of 10% (Niu and Liu, 1983) when burned as direct fuel. About 21% of the straw resources were returned to the farmland and 3% served as materials for paper making (Han et al., 2002). Lack of the forest resources in China, the raw materials used in the pulp paper-making industry is made mainly of straw, wood, waste paper, reed and bagasse, which is quite different from other countries. There was 1.85 × 107 t or 0.26 EJ straw resources invested in paper-making industry in 2000. Along with the development of the energy utilization in rural areas, it is necessary to take advantage of the excess straw resources in reasonable and multiple ways. The simple burning of the straw releases CH4 , which wastes the potential of the biomass exergy of the straw and pollutes the environment. The biogas is obtained from the straw, dung and grass fermented in the tank as secondary energy resource, promoting the conversion efficiency of the biomass energy to 60% (Niu and Liu, 1983). Except for 1.7 × 105 rural household abandoned biogas tanks, there were 6.74 × 106 tanks in practice with 2.25 × 109 m3 or 47 PJ biogas output, 959 urban central supply stations with 1.2 × 108 m3 or 2.5 PJ output and 78,870 town biogas clarifier tanks with 7.23 × 107 m3 or 1.52 PJ output. The biogas can also be used to store the grain, soak the seed and raise the hogs and fish. Also the dregs from the biogas tanks can be regarded as organic fertilizers, sometimes employed to grow mushroom in China.

resource exergy is only 11.6%. For the hydropower generation, the electric resistance and transmission losses of the circuit are 8.52% and the own demand ratio of the hydropower plant is 0.41%. Assuming the water turbine efficiency is 85%, the hydroelectric resource exergy input was estimated to be 0.94 EJ before it was converted into electricity suitable for utilization.

3.12.

In 1991, the first nuclear power plant (NPP) with 300 MW installed capacity was put into operation in Qinshan, Zhejiang Province. The generated electricity in 2000 amounted to 1.67 × 1010 kWh (60.1 PJ). The development and use of nuclear power is to optimize the energy consumption structure, meet the need of the electricity for the economic development of the costal area in China. Uranium resources are explored to be 2,000,000 tons, guaranteeing the normal running load and the further development of the nuclear power plants. Also, Chinese government has established nuclear safety supervision and management organization. In order to lower the environmental influence, the nuclear waste are timely arranged for the necessary treatment as several special disposal sites are constructed (Zheng and Yan, 1997).

3.13.

Hydroelectric resource

The developable hydroelectric resource exergy was 1.92 × 1012 kWh and the total hydropower generation was 2.22 × 1011 kWh. Thus, the utilization efficiency of the hydroelectric

Electricity

Electricity mainly includes hydropower, thermal power and nuclear power. The production, final uses, imports and exports exergy of the electricity (excluded solar power, wind power, wave power and geothermal power) are listed in Table 7. For the thermal power generation, the electric resistance and transmission losses of the circuit are 8.52% and the own demand ratio of the thermal power plant is 8.08%. Thus, the thermal exergy input was estimated to be 2.95 EJ before it was converted into electricity suitable for utilization.

3.14. 3.11.

Nuclear power

Coal, crude oil and natural gas

The coal resources amounted to 1.00 × 1012 t, while the oil 2.46 × 109 t and natural gas 1.51 × 1012 m3 (ensured reserves) in 2000. With regard to the major fossil fuel exergy resources supply and consumption, China relies on the coal, which is gradually depleted and dispersed as ‘dead stocks’ (Wall, 1977)

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Table 7 – Electricity exergy balance sheet Item

Raw data (kWh)

Output Hydropower Thermal power Nuclear power Imports Exports Consumption Final uses Losses in transformation

1.36E+12 2.22E+11 1.12E+12 1.67E+10 1.55E+09 9.88E+09 1.35E+12 1.25E+12 9.37E+10

Table 10 – Natural gas exergy balance sheet Exergy (J)

Item

4.88E+18 8.01E+17 4.02E+18 6.03E+16 5.58E+15 3.56E+16 4.85E+18 4.51E+18 3.37E+17

Output Imports Exports Change in inventory

2.72E+10 0.00E+00 0.00E+00 0.00E+00

1.10E+18 0 0 0

Total consumption

2.45E+10

9.92E+17

Source: SYC (2001).

Table 8 – Coal exergy balance sheet Item Output Imports Exports Change in inventory Total consumption Final consumption Intermediate consumption Power generation Heating Cooking Coal gas generation Losses in coal washing and processing Balance difference

Raw data (t)

Exergy (J)

9.98E + 08 2.18E + 06 5.51E + 07 3.66E + 07 1.25E + 09 4.61E + 08

2.36E + 19 5.14E + 16 1.30E + 18 8.65E + 17 2.94E + 19 1.09E + 19

5.46E + 08 6.69E + 07 1.50E + 08 8.10E + 06 1.44E + 07

1.29E + 19 1.58E + 18 3.54E + 18 1.91E + 17 3.40E + 17

−2.64E + 08

−6.22E + 18

Source: SYC (2001).

accompanied with serious environmental impact. The production, final uses, imports and exports exergy of the coal, oil and natural gas are presented in Tables 8–10, respectively. The distribution of the coal production is unbalanced with 14 ten million ton coal complexes located in the north of the Yangtze River, of which 7 located in the north China, concentrated in Shanxi and Hebei associated with 1.2 × 108 t coal yields (Jin and Jiang, 1997). The intensified exploration

Raw data (cum)

Exergy (J)

Source: SYC (2001).

cannot meet the increasing demand for the coal as necessary resources to support the economic development in the southeast China, which subsequently resulted in the longdistance dispatching and transportation of the coal from north to the east and south. According to the different demands of the power industry and private consumption, the central government will predict the total consumption and schedule the national production. The coal production reached 20.8 EJ (9.99 × 108 t) in 2000. Due to the frequent accidents, 4.6 × 104 small-sized coal mines had been closed with only 2.5 × 104 left by 2000. Moreover, to alleviate the pressure of the civil coal market, the government supported the coal export by providing the refund of the export tax rates and decreasing the freight base and commodity inspection expense, with the result that the coal export amounted to 12.9 EJ (5.5 × 107 t). There are three main oil and gas companies in China, China National Petroleum Corporation (CNPC), China National Petrochemical Corporation (SINOPEC) and China Offshore Oil Corporation (CNOOC). China New Star Petroleum Corporation (CNSPC) was established in 1997 and purchased by SINOPEC in 2000. The demand and processing capacity of crude oil have grown by large margin, while the production increased slowly since 1993. Overreliance on import oil may affect the stable economic development of China when the oversea shopping of oil is impeded. With 0.44 EJ oil exported and 2.98 EJ imported, the oil production amounted to 6.91 EJ and the consumption 9 EJ in 2000, accompanied by the accelerated exploration of oil and gas in Zhunge’er. Shaanxi-Gansu-Ningxia, SonghuajiangLiaohe and Jiuquan. On the contrary, the natural gas utilization in China has been slow owing to the high production cost and incomplete consumer market.

3.15.

Iron and steel industry

Table 9 – Oil exergy balance sheet Item Output Imports Exports Change in inventory Consumption Final consumption Intermediate consumption Power generation Heating Petroleum refineries Losses in oil field for crude oil Balance difference Source: SYC (2001).

Raw data (t)

Exergy (J)

1.63E + 08 7.03E + 07 1.03E + 07 −9.13E + 06 2.12E + 08 6.37E + 06

6.91E + 18 2.98E + 18 4.37E + 17 −3.87E + 17 9.00E + 18 2.70E + 17

8.50E + 05 1.40E + 05 2.03E + 08 1.91E + 06 1.51E + 06

3.60E + 16 5.94E + 15 8.61E + 18 8.09E + 16 6.40E + 16

The iron and steel industry is of great importance in Chinese national economics. Based on CSY (2001), the total iron ore reserves were 45.8 billion tons. The total output value of the iron and steel industry was 473.3 billion Yuan, which was 5.5% of the total industrial output value (8567.4 billion Yuan). The total import product added up to 9.12 × 107 t or 0.62 EJ while the export product 1.17 × 107 t or 0.08 EJ. The total exergy inflow to the iron ore mining was 61 PJ, of which the coke was 15 PJ, the coal was 15.9 PJ and the electricity was 22 PJ. The exergy invested to the iron and steel smelting and pressing amounted to 3.87 EJ, of which the coke was 2.43 EJ, coal was 0.87 EJ and the electricity was 0.39 EJ. Therefore, the major exergy invested in the iron and steel industry was 5.89 EJ, of which the iron ore was 0.1 EJ, the scrape steel 0.34 EJ, the coal 2.63 EJ and the coke 2.33 EJ.

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Table 11 – Exergy invested in the chemical industry

Table 12 – Exergy of the product of the chemical industry

Item

Raw data (t)

Exergy (J)

Item

Coal Coke Crude oil Gasoline Kerosene Diesel oil Fuel oil PLG Natural gas Electricity Pyrite Phosphate

5.05E+07 1.05E+07 6.56E+05 4.51E+05 8.73E+04 1.12E+06 3.32E+06 6.30E+05 9.03E+09 1.11E+11 9.64E+06 1.94E+07

1.19E+18 3.33E+17 2.78E+16 2.11E+16 4.01E+15 5.03E+16 1.39E+17 3.07E+16 3.66E+17 3.99E+17 8.68E+16 7.74E+14

45 13 1 1 0 2 5 1 14 15 3 0

2.65E+18

100

Total

Fraction (%)

Source: CESY (2000–2002).

The air and water emissions and solid wastes are not considered in this conversion chain. The byproducts, including blast furnace gas, coke oven gas, slag, tar and ammonia, though can be used in other economic activities, are not included to calculate the exergy efficiency of the iron and steel industry (Costa et al., 2001). The major product exergy of the iron and steel industry was 1.81 EJ, of which the steel was 0.87 EJ, the pig iron 0.89 EJ and the ferroalloy 0.05 EJ. Thereby, the exergy efficiency of the iron and steel industry was 31%.

3.16.

Nonferrous metal industry

According to the CYNMI (2001), the major import product exergy of the nonferrous metal industry was 81.2 PJ, of which aluminum was the maximum, amounting to 30.1 PJ. The major export product exergy was 15.9 PJ, of which the aluminum and zinc were 6.88 PJ and 3.08 PJ, respectively. In 2000, the major ore exergy invested in the nonferrous industry was 85.5 PJ, of which copper was 35 PJ and tin ore was 28.2 PJ. In the process of mining, dressing, smelting and pressing, about 587 PJ energy, 85.5 PJ ore and 81.2 PJ imported product were invested and 242 PJ output yielded, indicating the exergy efficiency of the nonferrous industry was 32%.

3.17.

Chemical industry

As listed in Table 11, the major exergy invested in the chemical industry was 2.65 EJ, of which the coal was 1.19 EJ, the electricity was 0.4 EJ and the coke was 0.33 EJ. The contribution from other raw materials was neglected. Although a variety of products were produced by the chemical industries, we focus on the major products, that is, fertilizer, cement, etc. The product exergy of the chemical industry was 2.08 EJ. The product exergy of the chemical industry (Table 12) was 2.08 EJ. The exergy efficiency of the chemical industry was thereby 78.5%.

3.18.

Sulfuric acid Sodium hydrate Calcined soda Rubber Cement Fertilizer Pesticide

2.43E+07 8.34E+06 6.68E+06 1.49E+06 5.97E+08 3.19E+07 6.48E+05

Total

Exergy (J)

Fraction (%)

4.05E+16 3.27E+15 1.25E+16 4.85E+16 8.78E+17 1.03E+18 6.48E+16

2 0 1 2 42 50 3

2.08E+18

100

Source: CCIY (2000/2001).

gradually extended in 2000, of which national railways in operation was 6.87 × 104 km (electrified railways reached 1.49 × 104 km), road 1.40 × 106 km (highways 1.63 × 104 km), navigable inland waterways 1.93 × 105 km and civil aviation routes 1.50 × 106 km. The freight traffic amounted to 1.36 × 1010 t, of which railway hold 1.79 × 109 t, highway 1.04 × 1010 t, waterway 1.22 × 109 t and civil aviation 1.97 × 106 t. The average transport distance of freight was 326 km, with railway being 767 km, highway 59 km, waterway 1939 km and civil aviation 2556 km. Rosen (1992) presented an exergy analysis of the transportation sector of Canada. The exergy efficiency for the transportation is obtained by introducing a weighted mean factor, which is the fraction of the total sector energy input that supplies each transportation mode. Dincer et al. (2004) also analyzed the energy and exergy utilization in the transportation sector of Saudi Arabia by considering the exergy flows for the years of 1990–2001. A total of 1.63 EJ was used by this sector, of which 0.55 EJ was from gasoline, 0.40 EJ from diesel, 0.02 EJ from coal, 0.43 EJ from ships fuel, 0.02 EJ from electricity and the remaining 0.21 EJ from air fuel (Table 13). To assess technical performance of transport devices, the exergy efficiency of a vehicle is taken as the quotient of the ˚ (2001) shaft work output over the exergy input. As Ertesvag noted, the conversion ratio of transportation in different countries varies from 0.10 to 0.23 due to different assumptions on efficiencies by the investigators. The exergy consumption of the transportation in this paper is calculated according to Rosen’s method and the rated load of the vehicles seems to be somewhat higher than the other countries. The efficiency of

Table 13 – Transportation energy consumption Mode of transport

Main fuel types

Exergy consumption (EJ)

Fraction (%)

Road

Gasoline Diesel

0.55 0.19

33.9 11.6

Rail

Coal Diesel Electricity

0.02 0.21 0.02

1.2 12.8 1.2

Marine Air

Ships fuel Air fuel

0.43 0.21

26.6 12.7

Transportation

Along with the economic development of China, extensive transportation systems have been built after the economic reform of 1978. The status of the transportation sector has been greatly improved. The length of transportation routes

Raw data (t)

Source: CTY (2001).

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the coal-fueled locomotive is estimated to be 5–9% in China. As ´ Nakicenovi c´ et al. (1996) assumed, 6.0% is more reasonable for the situation in China. As Greene (2004) presented, the propulsion efficiency is the ratio of the output of an engine in useful work to the energy content of the fuel used and the sparkignited, gasoline, internal combustion engine of a modern automobile, in typical urban driving, converts less than 20% of the energy in gasoline into useful work at its crankshaft. Also, typical engine and transmission efficiencies are presented, e.g., the gasoline engine is 10–15% and the diesel engine is 15– 22%. Thus, the efficiency of the gasoline engine is estimated to be 11% and the diesel engine 13.8% in China. The other en´ ´ estimation. The gine efficiencies are based on Nakicenovi c’s exergy efficiency for the whole sector is the weighted average of the exergy efficiencies of all the vehicles, with the exergy consumption fraction of each form of fuels taken as the weighting factor. The detailed discussion about the efficiency ˚ of transportation sector can be referenced to Ertesvag’s work. The transportation energy efficiencies are therefore estimated based on the assumptions given above and the weighted exergy efficiency is calculated as follows:

smoke vent, which in turn lead to insufficient combustion and heavy heat losses. The fossil fuels and electricity, accounting only for 23% of the household exergy resources, are purchased from outside market. The efficiency of the coal stove used for cooking and water heating is averaged to be 15% (Zhou, 1997). The household exergy consumption and conversion is listed in Table 14. The exergy flows in the courtyard ecological systems, which distribute quite widely in the rural areas consist of three parts: producer (grain, vegetable), consumer (people and livestock) and methane bacteria. The different types of grains and vegetables as inflow to the courtyard ecological system feed both the people and the livestock. The livestock provides meat and eggs for the people, with the dung being carried to the biogas tank. Meanwhile, biogas is available from the biogas tank for lighting, cooking and livestock-breed heating. Part of the exergy resources consumed in the rural households is recycled in the courtyard ecological system. It is indicated that the rural household depends on the local ecological resources. On the contrary, the urban household extracts ecological resources from the rural areas and consumes in a unilateral way. Although fewer exergy on simple food is consumed, the urban household consumes the exergy, defined as accumulated exergy by Szargut (2004) embodied in the process to obtain the food, much more than the rural household does. In fact, the point is that the rural household lives in a renewable way, not the renewable resources they live on.

 = (0.34 × 11) + (0.12 × 13.8) + (0.01 × 6) + (0.13 × 25) + (0.01 × 75.8) + (0.27 × 31) + (0.12 × 26.3) = 21%

3.19.

(5)

Households

The population of China in 2000 was 1.27 billion, of which 36.2% (0.46 billion) lived in the cities and towns while 63.8% (0.81 billion) lived in the rural areas. The main part of the rural household exergy consumption depends on the biomass, that is, straw, firewood and biogas. Based on the biomass resources discussed in the preceding sector, the rural consumption per capita was calculated to be 5.14 × 109 J on straw, 2.53 × 109 J on firewood and 5.8 × 107 J on biogas. The straw, 50% of the total household exergy resources, is preferable for rural households in cooking and water heating, for straw is byproduct of the farming without addition cost and can be burned as fertilizer back to the cultured land, whereas the firewood accounts for 26% of the total household exergy resources, which is obtained with little cost. The efficiency for the straw and firewood used for cooking and water heating through the firewood oven are estimated to be 10% (Gu et al., 2001), for the structure of the oven are based on rough soil brick with big combustion chamber, oven door and

3.20.

Commerce

The public services is excluded from the analysis, for the required data is not available. There were 9.77 × 106 employees working in the commerce sector. The commerce sector consumed 227 PJ exergy from coal and coke, 251 PJ from petroleum products, 14 PJ from natural gas and 142 PJ from electricity, for a total of 644 PJ exergy (CESY, 2000–2002). Assuming the efficiency of the commerce sector is 10%, the total exergy output was then 64.4 PJ.

3.21.

Other industry

This sector consists of the industry that is not included in the preceding sectors. This is primarily mechanical industry, where the majority of the energy is used for mechanical work ˚ 2001). In 2000, this sector consumed 3.46 EJ from (Ertesvag,

Table 14 – Household exergy consumption and conversion Purpose

Coal (J)

Gas (J)

Electricity (J)

Straw (J)

Firewood (J)

Total input (J)

Fraction

Efficiency

Output

Cooking and water heating Space heating Lighting Other equipments

5.33E+18

7.13E+17

–

4.16E+18

2.05E+18

1.23E+19

80

0.10

1.23E+18

2.47E+18 – –

– – –

– 1.20E+17 4.82E+17

– – –

– – –

2.47E+18 1.20E+17 4.82E+17

16 1 3

0.06 0.1 0.3

1.48E+17 1.20E+16 1.45E+17

Total

7.81E+18

7.13E+17

6.02E+17

4.16E+18

2.05E+18

1.53E+19

100

0.1

1.53E+18

Source: Zhou (1997).

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Table 15 – Other industry exergy consumption and conversion Purpose

Coal (J)

Oil (J)

Gas (J)

Electricity (J)

Total input (J)

Fraction

Efficiency

Output

Mechanical work Space heating Lighting, equipment Water heating Process heating

– 3.32E+17 – 7.96E+17 2.33E+18

1.73E+17 3.63E+16 – 2.62E+17 2.55E+17

4.70E+15 3.13E+15 – 7.93E+15 3.32E+16

4.00E+17 – 3.64E+16 1.38E+17 7.54E+16

5.78E+17 3.72E+17 3.64E+16 1.20E+18 2.70E+18

12 8 0 25 55

0.50 0.06 0.10 0.15 0.26

2.89E+17 2.23E+16 3.64E+15 1.81E+17 7.01E+17

Total

3.46E+18

7.25E+17

4.90E+16

6.50E+17

4.88E+18

100

0.24

1.20E+18

´ Sources: Nakicenovi c´ et al. (1996) and CESY (2000–2002).

sumed as 6%, corresponding to an indoor temperature of 17 ◦ C in China, which is lower than that of the developed countries, and a representative environmental temperature of 0 ◦ C. Given the exergy efficiency of 6%, the output was 0.15 EJ.

coal, 0.73 EJ from oil, 49 PJ from gas and 0.65 EJ from electricity, for a total of 4.88 EJ exergy. Based on the shares of energy carriers for different energy ´ services provided by Nakicenovi c´ et al. (1996), the exergy consumption and conversion of different purposes in the other industry sector are listed in Table 15. The total exergy output added up to 1.2 EJ, which is 24% of the input.

3.22.

3.23.

Cooking, water heating and process heating

In the households sector, 6.21 EJ from straw and firewood and 6.04 EJ from fossil fuels were used for cooking and water heating. In addition, 1.2 EJ was invested for water heating and 2.7 EJ for process heating form the other industry sector. Thus, the total exergy input for cooking, water heating and process heating was 16.2 EJ. With an assumed average exergy efficiency of 10%, the output was 1.62 EJ.

Space heating

The sectors including Space heating, Cooking, etc., Lighting, etc., Mechanical work, are alternative distributions of the exergy conversions that analyzed in some preceding sectors, presenting a particular perspective to analyze the exergy loss in ˚ and Mielnik, 2000). end-user sectors (Ertesvag In China, the legal space heating area is determined by the standard that the days with average temperature lower than 5 ◦ C exceed more than 90 annually. Outside this legal space heating area, the government will not provide fuel for space heating with no space heating facilities being configured in homes, public services and offices. But in the legal space heating area, the people living in the rural area are excluded from the fixed supply of fuel from the government. They have to use stove as the basic space heating tool, while the people living in the urban area enjoy warm-air heating system. Although the flexible usage of stove can save the coal by intermittent switch, the indoor temperature is unstable with serious air pollution. Adding the consumed space heating exergy in the transitional regions and the legal areas, the total exergy input for space heating sector may be estimated to 2.47 EJ. The representative exergy to heat ratio for all space heating are as-

3.24.

Lighting, electrical equipment, etc.

As listed in Table 16, 602 PJ was used for lighting and the other equipments. Assuming 50% of the electricity is used for lighting and other equipments, 71 PJ was invested from the commerce sector. Also, the electricity from the other industry sector contributed 36 PJ. The total input was then 709 PJ. Given ˚ and that the exergy efficiency of the lighting is 10% (Ertesvag Mielnik, 2000), the exergy output was 70.9 PJ.

3.25.

Mechanical work

The exergy for mechanical work was taken from the sector: other industry, and amounted to be 0.58 EJ. With the assumed ˚ and Mielnik, 2000), average exergy efficiency of 50% (Ertesvag the output of the mechanical work was 0.29 EJ.

Table 16 – Results from the different end-user sector analysis User sector Forest industry Food Iron and steel Nonferrous metal Chemical industry Transportation Lighting, equipment, etc. Mechanical work Space heating Cooking, water heating and process heating Total

Exergy input (EJ) Commodities Energy carriers 2.17 7.29 0.44 0.17

Fraction of input (%)

Exergy output (EJ)

Efficiency

Sum

6.21

0.55 3.94 5.45 0.60 2.65 1.63 0.71 0.58 2.47 9.94

2.72 11.23 5.89 0.68 2.65 1.63 0.71 0.58 2.47 16.2

6 25 13 2 6 4 2 1 6 36

16.28

28.52

44.76

100

1.13 5.07 1.81 0.24 2.08 0.34 0.07 0.29 0.15 1.62 12.8

42 45 31 16 78 21 10 50 6 10 29

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Table 17 – Main exergy conversion in Chinese society 2000 Exergy (EJ)

Total input Lost/used in energy sector Input to end-user sectors Loss in end-user sectors Output from end-user sectors

3.26.

Fraction of total input (%)

64.76 20 44.76 31.96 12.8

100 31 69 49 20

Exergy conversion of the Chinese society

The total exergy input grouped by 10 end-use sectors to the Chinese society is summarized in Table 16, wherein “Lighting, equipment, etc.”, “Mechanical work”, “Space heating”, and “Cooking, water heating and process heating” are alternated by the user sectors, i.e., other industry, households and commerce. The weighted exergy conversion efficiency of all the end-user sectors was 26%. The total exergy flow, with domestic energy sector and the 10 end-user sectors, is shown in Table 17. The total exergy input was 62.9 EJ (53.3 GJ/cap) and the exergy output was 11.66 EJ (9.88 GJ/cap). The GDP of China was 3463.4 billion Yuan RMB (US$ 601.3 billion). Thus, one Yuan RMB (US$ 0.17) corresponded to 3.37 MJ resource exergy output.

4.

Conclusions

In 2000, the total exergy input to the Chinese society was 64.76 EJ (51.0 GJ/cap), exergy output was 12.8 EJ (10.1 GJ/cap), which indicates the exergy conversion efficiency was 20%. The GDP of China was 4870 billion Yuan RMB (US$ 1020 billion). Thus, one Yuan RMB (US$ 0.21) corresponded to 2.63 MJ resource exergy output. There is enough room for the exergy efficiencies of the individual sectors to be promoted significantly. The lighting and electric equipment, transportation, space heating, cooking, water heating and process heating sectors are running with low exergy efficiencies. The irreversibility or loss of exergy of these sectors are approximately 80% or more. Industry generally has a higher efficiency, e.g., the chemical industry.

5.

while, the oil industry even consumed more electricity with more process losses compared to the previous years. The production of the main industries using coal are under supervised by the government according to the administrative plans, with the materials and energy resources purchased and products distributed through fixed modes of sale on state-fixed prices, thereafter to invest large amount of capitals in technical innovations and updating equipments, which is necessary to promote the conversion efficiency, is not preferred. Moreover, to improve the exergy conversion efficiency of the coal used in the household sector, some of which is used for cooking and water heating, and the others for space heating, the structure of the coal stove need to be modified. The full combustion of the coal is realized with secondary air flow from four or more secondary tuyeres and heat panel being configured in the coal stove. The structure of the agriculture is also decided indirectly by the government. The peasants are obligated to remit to the government an agricultural tax assessed in official state-fixed prices attached to the quota produces. The tax is revised by the government to guarantee the supply of the basic foods to the urban areas with subsidized prices, such as grain and vegetables, which make up the primary exergy contents of the agricultural products. As a result, the income of the peasants is extremely low, which in turn leads to the dilemma that the peasants cannot afford the cost of the fossil fuels and electricity from the urban areas when local resources are prohibited to obtain and subsequently the improvement in the efficiency of the utilization of the exergy resources seems impossible in the poor rural areas without the subsidy of the local government. It is not the weak awareness of the advantages of the promotion in the exergy conversion efficiency in the rural areas, but the basic institutional defects and the traditional self-feed and self-dependence living styles affect the allocation and utilization of the resources. The conversion efficiency of the local biomass resources (straw and firewood), which amounted to 10.6 EJ as the main utilization of exergy resources in the rural areas, is also necessary to be improved depending on the plans of the government to generalize and promote the usage of the energy saving heating devices. The courtyard ecological systems should be encouraged to be established associated with the development of the biogas utilization with less pollution and higher conversion efficiency than the simple burning of straw.

Results and discussions

The soil fertility erosion from the cultivated land is estimated to be 0.19 EJ. This kind of soil resource consumption can be neglected in the present national-scale study, which does not ˚ and Mielchange the total exergy efficiency. Also, as Ertesvag nik (2000) noted, the river water released into the sea and took off some chemical exergy due to the salinity difference between the river water and the seawater. Since this kind of chemical exergy has not been exploited and utilized in China, it is excluded from the present analysis. The maximum exergy input to the Chinese society is coal (29.4 EJ). The main indicators of the production process of the coal, including the consumed electricity, recovery ratio and ash of the washed coal, changed little from 1980 to 2000. Mean-

Table 18 – Exergy conversion of different societies Society

Total input (GJ/cap)

Total output (GJ/cap)

Total efficiency

278 310 145 148 44 42 322 51

68 48 24 29 6 10 78 10.1

0.24 0.16 0.17 0.19 0.13 0.23 0.24 0.20

Norway, 1995 Sweden, 1994 Italy, 1990 Japan, 1985 Turkey, 1995 Brazil, 1987 Canada, 1986 China, 2000 ˚ (2001). Source: Ertesvag

e c o l o g i c a l m o d e l l i n g 196 (2006) 313–328

The total inflow of resources per capita is compared with other countries (Table 18). Although it cannot be inferred that the situation of exergy resources utilization in China society is worse than the other societies due to the differences result from the different structures of the societies, this kind of society exergy analysis can be helpful in revealing the degradation of the energy in each sector and providing solid foundation and prompt advices for the government to make the decision ˚ 2001). with the right direction and priority (Ertesvag,

Acknowledgements This work was funded by the State Key Basic Research and Development Plan (973 Plan, Grant No. 2005CB724204), National Natural Science Foundation of China (Grant No. 1037226) and China Postdoctoral Science Foundation (Grant No. 2005038036). We would like to thank Dr. G. Wall for the insightful advices. The valuable comments and suggestions from the two anonymous reviewers and the editor of Ecological Modelling are also useful in improving this paper.

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