Reading A Introduction
Water footprint ofthermal power in China: Implications from the high amount of industrial wateruse by plant infrastructure of coal-fired generation system
1 Energy and water are generally recognized as two crucial resources to sustain the economy. As being increasingly noticed by the academia as well as the public, a close link exists between energy and water (Hamiche et al., 2016; Zhang and Vesselinov, 2016;Zhou et al., 2016). A large amount of water is required to produce different types of energy, such as thermoelectric power, nuclear power, hydropower, etc. Currently, energy sector ranks the primary place in global fresh water withdrawal, second only to agricultural irrigation (Zhang and Anadon, 2013). In a consumption-oriented world economy with a big population, a rising amount of power demand is expected in the next several decades (Hightower and Pierce,2008). The increasing electricity demand will intensify the pressure on the local fresh water resources, especially in water-stressed nations (Chandel etal., 2011; Rio Carrillo and Frei, 2009). It is predicted that global water consumption associated with power generation is likely to double during the next four decades (van Vliet et al., 2016), thus intensifying the competition for water resources among various industrial sectors. Especially, in context of the global climate change associated with the possibilities of heat waves and droughts (Schar et al., 2004; Wetherald and Manabe, 1999), the availability of freshwater resources for electricity generation is predicted to be further constrained.
2 The scarcity of water resources is particularly urgent in China. With only 7% of the world's freshwater resources, China manages to support one-fifth of the global population (Gu et al., 2016). In context of the unprecedented urbanization and the rising middle class in China, the electricity delivery has more than doubled from 2005 to 2014, increasing from 2494TWh to 5420TWh (NBSC, 2016). However, around two-thirds of China's urban areas are confronted with water scarcity problems. Moreover, the distribution of freshwater resources in China is unbalanced, particularly in the coal and gas-rich regions (Zheng et al., 2016). According to Liu and Yang(2012), the three coal-rich regions in terms of Shanxi, Shaanxi, and Inner Mongolia only occupy around 3% of the national water resources (Zhang andAnadon, 2013). Water has become a vulnerability that severely constrains the expansion of power generation. With this being recognized, a “water for coal”plan is promulgated by the Chinese government as a supplementary provision to the “3 Red Lines” water policies for synergic management of these two resources(Qin et al., 2015). To support policy planning on water conservation in the power sector in China, a preliminary and most crucial step is to figure out the water use of electricity generation, which has gained wide attention within the academic field (Salazar et al., 2011; Zhai et al., 2011; Zhang and Anadon,2013). Coal-fired power plant has long been a research focus, due to its dominant position in power delivery in China. In 2013, electricity generation from coal-fired power plants in China has reached 4221.6TWh (CEPY, 2014), sharing around four fifths of the domestic electricity output. According to International Renewable Energy Agency, coal-fired power plants are responsible for around one-tenth of China's total freshwater withdrawal (IRENA, 2016). Meanwhile, apart from the onsite water use of coal-fired power plant, a considerable amount of water requirement is induced in the upstream supply chain.
3 To depict a holistic picture for water use associated with coal-fired power plants, water footprint assessment is generally applied in existing works, which gives certain consideration to the water requirement in different stages, such as coalmining, coal transportation and power plant operation. Early in 1994, Gleick(1994) took a cradle-to-grave manner to examine the lifetime water requirement by different types of fossil-fueled power generation technologies. Chang et al.(2015) investigated the ETW (extraction-to-wire) water requirement of coal-fired power generation in China; the analysis was confined to consumptive water use. The onsite water use, namely water that is used for cooling and other purposes, accounts for nearly 90% of the total water requirement, while water use associated with coal mining and coal transportation holds accountable for around one-tenth of the total. Using different data and assumptions, other scholars have undertaken similar assessments for water use induced by coal-fired power plants (Feng et al., 2014; Fthenakis and Kim, 2010; Meldrum et al., 2013;Ou et al., 2016).
4 Nevertheless, the water use induced by plant infrastructure of the coal-fired generation system is generally overlooked and not separately discussed. Serving as the foundation for transforming the materials and fuel inputs into electricity, plant infrastructure provides a solid basis for power generation. In 2011 only, the capital investment for thermal power plant infrastructure in China has reached 98 billion CNY (DCEPI, 2011), which occupies nearly one-tenth of total capital investment for domestic secondary industries. Therefore, due to the dominant position of coal-fired power plants in power sector, the water use induced by the plant infrastructure could add up to a large amount. In fact, the large quantity of water use associated with power generation infrastructure has already been demonstrated for renewable power plants (Burkhardt et al., 2011; Klein and Rubin, 2013; Whitaker et al., 2013; Yang and Chen, 2013). Burkhardtet al. (2011) demonstrated that water use associated with manufacturing and construction of a dry-cooled parabolic trough concentrating solar power plant is in magnitude up to around half of the total life cycle quantity. Wu and Chen(2017a) unveiled the high amount of industrial water use induced by plant infrastructure of a pilot solar power tower system, which is comparable to the direct freshwater withdrawal. With regard to coal-fired power plants, Wu et al.(2018a) have previously revealed the striking amount of carbon emissions by the construction stage of coal-fired power generation system. Nevertheless, the water use induced by plant infrastructure has not been explored.
5 It is worth noting that insome of the existing studies, though the plant infrastructure of coal-fired power generation systems is sometimes taken into account, the components aregenerally traced back to some primary materials (such as steel, iron, concrete,etc.) following process-based life cycle assessment (LCA) (Fthenakis and Kim,2010). Since the tracing could be infinite, the process chain is generally truncated after one or two steps to cover only the most important inputs(Bullard et al., 1978). Most of the time, for simplicity, the plant infrastructure is simply converted to a certain amount of primary materials. Actually, the coal-fired power plant consists of several parts, such as boiler system, turbine system, main plant engineering, fuel supply system, electric system and smoke stack. Each part is comprised of several components (for instance, turbine system includes steam turbines, turbo-generators, condensers, pumps, etc.), which require different kinds of material, machinery and service inputs in the upstream supply chain. Vulnerable to the incompleteness of the system boundary, the process-based LCA method is likely to exclude the vast majority of the associated resource use or emissions, which may at the sametime induce quantitative and qualitative errors, as noted by Lave et al.(1995). Also, as pointed out by Ruether et al. (2004) and Bullard et al.(1976), the errors brought about by the ignorance of the virtual inputs may amount to a huge number. Given this, the input-output analysis, which is capable of depicting the intertwined relationship between the various sectors within an economy, is integrated into the process analysis in some studies to unite the advantages of these two methods. For instance, following the classification approach of economic sectors by Ruether et al. (2004), Ou et al.(2016) investigated the water footprint of plant infrastructure of the US pulverized coal-fired plant by combining the input-output model and life cycleanalysis. By establishing a detailed cost inventory coming from National EnergyTechnology of the United States, their work contributes remarkably to existing works by treating each input (material, equipment or service) of plant infrastructure separately and quantifying the related water use by referring to the intensity database generated from input-output analysis. Such analysis for coal-fired power systems in China is however lacking.
6 In this study, the water use induced by plant infrastructure of a most typical coal-fired power generation system in China has been explored in detail. Generally, water use could be roughly categorized into agricultural water use and industrial water use. Freshwater for agricultural production is directly exploited by cultivators for irrigation. As for freshwater for industrial production, it is exploited and then pretreated to meet the water quality standard. From the perspective of industrial production, only freshwater withdrawal for industrial use could be treated as water resources. Therefore, this study will specifically focus on the industrial water use induced. First, an integrated inventory that contains over 70 input items is established for the power plant infrastructure. Second, supported by the industrial water intensity database obtained from systems input-output analysis, the water use induced by each input item is fully addressed. Third, by a comparison with previous estimates and the direct freshwater withdrawal, the high amount of industrial water use induced by plant infrastructure is verified, which offers essential policy implications for management and conservation of water resources in the power sector. In addition, it is worth noting that the term water use in this paper refers to water withdrawal, namely the freshwater resource exploited from a surface or ground water source, whether it eventually gets back to the original catchment or not. (1554 words)
Notes：
1. Authors: X.D. Wu, Xi Ji, Chaohui Li, X.H. Xia, G.Q.Chen (2019). Water footprint of thermal power in China: Implications from thehigh amount of industrial water use by plant infrastructure of coal-firedgeneration system. Energy Policy.
2. Keywords: Water footprint; Industrial water use;Coal-fired power; Plant infrastructure; Systems process
3. Abstract: To reflect an important aspect of the water footprint of thermal power in China, this study as an extension of a previous work (Wu et al., 2018a) uncovers the high amount of industrial wateruse induced by plant infrastructure of a typical coal-fired power generation system. The systems process method is used by combining process analysis and water intensities obtained from systems input-output analysis. Industrial wateruse induced by plant infrastructure is accounted to be several times greater than previous estimates, and approximate to or much larger than that induced by fuel mining, preparation and transport in total. For per unit of electricity output, the water use by plant infrastructure amounts to 8.4% of the direct freshwater withdrawal for the majority of supercritical thermal power plants equipped with wet tower cooling, and even up to 38% of the freshwater withdrawal for some plants with air tower cooling. The annual water use inducedby coal-fired power generation infrastructure in China is estimated to be 0.6%, 7%, and 23% of the annual freshwater withdrawal by China, Japan, and United Kingdom, respectively. The outcome provides a benchmark for policy makers tomeasure and curb the upstream water use by plant infrastructure.
