Scenario-based Analysis on Water Resources Implication of Coal Power in Western China

Currently, 58% of coal-fired power generation capacity is located in eastern China, where the demand for electricity is strong. Serious air pollution in China, in eastern regions in particular, has compelled the Chinese government to impose a ban on the new construction of pulverized coal power plants in eastern regions. Meanwhile, rapid economic growth is thirsty for electric power supply. As a response, China planned to build large-scale coal power bases in six western provinces, including Inner Mongolia, Shanxi, Shaanxi, Xinjiang, Ningxia and Gansu. In this paper, the water resource implication of the coal power base planning is addressed. We find that, in a business-as-usual (BAU) scenario, water consumption for coal power generation in these six provinces will increase from 1130 million m 3 in 2012 to 2085 million m 3 in 2020, experiencing nearly a double growth. Such a surge will exert great pressure on water supply and lead to serious water crisis in these already water-starved regions. A strong implication is that the Chinese Government must add water resource constraint as a critical point in its overall sustainable development plan, in addition to energy supply and environment protection. An integrated energy-water resource plan with regionalized environmental carrying capacity as constraints should be developed to settle this puzzle. Several measures are proposed to cope with it, including downsizing coal power in western regions, raising the technical threshold of new coal power plants and implementing retrofitting to the inefficient cooling system, and reengineering the generation process to waterless or recycled means.


Introduction
The extensive development mode in China has led to rapid economic growth in a short time, but has been followed by a lot of environmental problems, especially air pollution, in recent years.Taking the increasingly serious air pollution into consideration, the Chinese government announced the ban on new energy-and-pollution intensive projects in eastern regions, among which coal-fired power plants are strictly banned [1].
In order to meet the growing energy demand, five comprehensive energy bases located in Shanxi, Ordos, Xinjiang region, and eastern and southwestern Inner Mongolia will be built, according to the 12th FYP [4].The 12th Energy Development plan also intended to develop 14 large coal mine bases and 16 coal power bases, and the total size of thermal power capacity is expected to reach more than 600 GW in these bases [5,6].
However, the water resource constraint in the coal power bases and the implication of the coal power bases on regional water resource is not fully considered in the planning.This paper is an attempt to address these two interweaved issues.The structure of the paper is as follows.Section 1 presents the background and purpose of the study.Section 2 will briefly review the water-energy nexus and provide background information on water resource and consumption in China's coal power base provinces.Section 3 will propose the model for analyzing water usage of thermal power generation.Section 4 will analyze the demand and impact of the coal power planning on water resource in China's coal power base provinces.Section 5 will provide analysis on water saving measures and an alternative scenario and Section 6 concludes the paper.

Energy-Water Nexus
Globally, 80% of electricity generation comes from thermo-electric power stations (such as fossil fuels and nuclear), all of which require cooling for efficient and safe operation [7].Most of the cooling system is provided by water abstractions from, and thermal discharges to, the natural environment, including rivers, tidal estuaries and coasts.The production of energy requires large quantities of water in processes such as thermal plant cooling systems or raw materials extraction.Analysis on whether water resources in a given region can support energy production will be a critical issue in the near future.The energy-water nexus has been a topic of increasing importance in recent years.In 2003 and 2006, numerous power plants in Europe had to be throttled in summer due to water shortages and high water temperatures caused by a hot and dry summer [8].The agriculture sector currently has the highest water demand at the global scale, followed by the industry-energy sector that is responsible for 20% of the total water withdrawals [9].In the U.S., the energy sector is expected to be the fastest growing water consuming sector, being responsible for 85% of the increase in domestic water consumption during 2005-2030 [10].In some MENA (Middle Eastern and Northern Africa) countries, the interdependencies are already being manifested.For instance, in Saudi Arabia almost all of the natural gas currently produced is consumed domestically, primarily in the petrochemical industry and in seawater desalination [11].Joint consideration of both water and energy domains can identify new options for increasing overall resource use efficiencies [12].Gleick calculated the water consumption of different forms of energy [13].Morgan Bazilian et al. (2011) considered the energy, water and food nexus, primarily from a developing country perspective [14].Hagen Koch et al. described how to integrate the calculation of water demand of power plants into water resource management model [15].Alexander et al. [16] studied the relationship between water and energy in an interactive lifecycle framework.Benjamin et al. [17] highlighted the most likely locations of severe water shortages in 22 counties because of thermoelectric capacity additions, and identified an assortment of technologies and policies that could respond to these electricity-water tradeoffs.Edward et al. [18] presented a model that quantifies current water use of the UK electricity sector, disaggregated by generation type, cooling method and cooling source.Also, it tested six decarbonisation pathways for the UK by combining projections of cooling methods and cooling sources for future thermoelectric generation.Aurelie et al. [19] proposed a model to assess optimal "water-energy" mix considering opportunities for water reuse and non-conventional water use in the water-scarce Middle East region.Kuishuang et al. [20] applied an integrated hybrid LCA approach to eight different electricity generation technologies in China to calculate their total life-cycle CO2 emissions and water consumption throughout national supply chains.
China is a drought-hit country.Though total freshwater resources reach 2.8 trillion m 3 , accounting for 6% of global water resources, ranking fourth in the world after Brazil, Russia and Canada, per capita water resource is just 2200 m 3 , a quarter of the world average, or 1/5 of the United States level [21].Energy and water have become major factors limiting sustainable development in China.Energy efficiency and optimization of water management are critical for the healthy growth of the Chinese economy [22].In addition to energy shortages, China is also confronted with numerous water resource challenges, including shortage, pollution and aquatic environment deterioration.
It is noteworthy that the development of China's coal power base is uncoordinated with the distribution of water resources.The coal-rich regions often face water scarcity, while regions with plentiful water resources mostly face coal shortage [23].According to the 12th Energy Development Plan [5], coal and energy supply in China is relying on the west coal-rich regions, but these areas are mostly located in the dry arid and semi-arid regions.That is to say, water resource conditions will inevitably become an important factor in the development of coal power bases.Because of limited freshwater resources, decision-making has to take the most valuable use of this limited resource into consideration.In water-stressed areas of the coal power bases, power plants will increasingly compete with other water users.Large-scale coal power bases in arid region of northwest will lead to severe water crisis, and the conflicts between coal resources and water are most significant in the following six provinces (autonomous regions), including Inner Mongolia, Shanxi, Shaanxi, Xinjiang, Ningxia and Gansu.To the best scope of our knowledge, only a book [24] explicitly addressed this issue, but it only raised a question and did not provide a solution to it.It is rightly the study scope of this paper.

Water Resources in China's Western Coal Power Base Provinces
According to the China Statistical Yearbook 2013, the data of water resources and water use of the main coal power bases is reported in Figure 1.In terms of total water resources, Xinjiang is the richest while Ningxia is the poorest region in these provinces.In particular, the water use in Ningxia is much more than its total water resources, indicating that water is scarce.Though the water resource in Xinjiang Uygur Autonomous Region seems rich, the water resources in Hami (coal power base) is merely 1.696 billion m 3 , accounting for only 2.13% of its total water resource endowment [24].As is shown in Figure 1, the water resource in Inner Mongolia Autonomous Region is second to that of Xinjiang, but its coal power bases' water resources are not as rich.With the exception of Hulunbeir coal power base, other bases all have water shortage issues at varying degrees.For example, water resource in Jungar coal power base account for just 0.67% of Inner Mongolia water endowment [25].For Xilingol League coal power base, the figure is 5.8%, for Ordos coal power base, 5.4% [26], and for Holingol coal power base, 0.09% [27].The coal power bases located in the other four provinces all have water shortage issues.Especially, the condition of water shortage in Ningxia is the most serious, whose water resource ranked the last in this country.

Water Use in the Coal Power Base Provinces of Western China
The consumption of water resources can be divided into the following categories: agricultural water use, household water use, ecological water use and industrial water use.The electricity sector is one of the largest water consumers in China after agriculture [28].Thus, the electricity sector can be a contributor to water scarcity which has already occurred in many parts of the country, in particular in Northern China [29].The water use of the main coal power base provinces in 2012 is shown in Figure 2 [30].
From Figure 2, we can easily see that agricultural water use absolutely takes up the most part of whole water use, and industrial use is only second to agricultural use.Though total water use in Shanxi and Shaanxi is not as much as that in Xinjiang, their industrial water use has accounted for much larger share.Because of water shortage and agricultural water demand, Ningxia does not seem to have enough water to support industry development, including coal power bases.Considering total water resources and water use, the potential of developing coal power bases in Shanxi, Gansu and Ningxia does not look optimistic.

Originality and Novelty of the Study
The energy-water nexus has been a topic of increasing importance in recent years.Indeed, water is needed for the energy sector (fuel production and electricity generation), and energy is used to clean, desalinate and transport water.This relationship is referred to as the water-energy nexus, a concept originally formulated by Gleick in the 1990s with his seminar study [13].Current studies and research mainly focus on water issues and energy consumption related to water management, and coupled water and energy challenges have been described for the energy production sector, i.e., for the United States [31], Australia [32], Spain [33], the UK [18], Middle East [19], and China [22].However, though few studies have indicated that China could face water shortages resulting from the addition of thermoelectric power plants, no precise estimate or policy study have been conducted.The goal of the present study is to reveal the potential water issues in China's coal power bases, and to provide a solution for it.

Methods and Data
According to the US Geological Survey's (USGS) water use survey data, Each kilowatt-hour (kWh) of thermoelectric generation requires the withdrawal of approximately 25 gallons of water (weighted-average for all thermoelectric power generation), which is primarily used for cooling purposes.Power plants also use water for operation of flue gas desulfurization (FGD) devices, ash handling, wastewater treatment, and wash water [34].
When discussing water and thermoelectric generation, it is necessary to distinguish between water withdrawal and water consumption.Water withdrawal represents the total water taken from a source but then returned to it, while water consumption represents the amount of water withdrawal that is not returned to the source.Water withdrawal is defined as the removal of water from any source or reservoir for human use.The water withdrawal constitutes the conveyance losses, consumptive use and return flow.Water consumption is defined as the amount of water extracted from a source that is no longer available for use, because it has evaporated, transpired, been incorporated into products and crops, consumed by man or livestock, ejected into the sea, or otherwise removed from freshwater resources [33].The industry chain of large coal bases includes coal mining industry, thermal power industry and coal chemical industry.The focus of this paper is on the water consumption of thermal power industry and thus the terminology of "water consumption" is used in our analysis.

The Water Link of Thermal Power Plant
The composition of water consumption in thermal power plants are as follows: (a) water recharge of the cooling system; (b) ash and slag removal system; (c) boiler water feed system; (d) auxiliary cooling system; (e) desulfurization system; (f) water use of coal yard; and (g) domestic water use [35].
Thermal plants use fossil fuels to generate electricity or heat, and their water needs can vary drastically depending on the type of plant, type of refrigeration system, type of fuel and region [36].The amount of water withdrawal and consumption depends on the type of technology used at a given plant.According to Meldrum et al. [37], water used for cooling purposes dominated the life cycle water use of electricity generation.
Large quantities of cooling water are required for thermoelectric power plants to support the generation of electricity.There are basically three types of cooling system designs: wet recirculating (open-loop and closed-loop) and dry recirculating (air-cooled).Open-loop (once-through) systems do not consume large quantities of water but require large quantities of water withdrawal in the cooling process.Closed-loop systems require smaller withdrawal of water, but most of the water withdrawal is lost in evaporation [13].Air-cooled systems, also referred to as dry recirculating cooling systems, use either direct or indirect air-cooled steam condensers.In a direct air-cooled steam condenser, the turbine exhaust steam flows through air condenser tubes that are cooled directly by conductive heat transfer using a high flow rate of ambient air that is blown by fans across the outside surface of the tubes.Therefore, cooling water is not used in the direct air-cooled system.In an indirect air-cooled steam condenser system, a conventional water-cooled surface condenser is used to condense the steam, but an air-cooled closed heat exchanger is used to conductively transfer the heat from water to ambient air [38].

Water Consumption Rate in Coal Power Plants
China Electricity Council (CEC) is responsible for energy efficiency benchmarking in the power industry and releases detailed energy efficiency and water efficiency statistics [39].By collating and analyzing the data, we calculated the water consumption and coal consumption indexes for power generation in the 600 MW units.Table 1 reports the water consumption rates while Table 2 reports the heat rates of the coal power units with different cooling system (Interested readers may refer to the Appendix for detailed information).As shown in Table 2, on the average, air-cooled unit performs worst in energy efficiency, with about 25 grams coal equivalent gce/kWh more than water-cooled units; while open-loop water cooling system is with lowest heat rate.Combining the information reported in Tables 1 and 2, we can easily see that the open-loop system is the most efficient, because of the lowest heat rate and the lowest comprehensive water consumption rate.However, the pre-condition for open-loop water-cooled system is the existence of large body of fresh water like rivers or lakes adjacent to the power plant.Also, the direct pollution of freshwater also indicates the infeasibility of open-loop water-cooled system.

Method
According to the data on installed capacity and comprehensive water consumption rates of thermal power plants by [39], we can calculate the water consumption of thermal power plants in these coal power bases located in western provinces.The water consumption of power plants is calculated by: open-loop cooling system i = 3 air-cooled cooling system The methodology for water consumption estimate and scenario study is presented in Figure 3.In its simplest form, water consumption is calculated by multiplying the electricity generated from a certain technology and the consumption factor for that technology, which is subject to various assumptions in our study.Because of the scope of our study, we limit our study in the above-mentioned six western coal power base provinces.

Current Water Consumption Status
Annual Development Report on China's power industry 2013 by CEC has counted the whole-diameter capacity in every province by the end of 2012 [2].According to this report, by the end of 2012, the installed coal power capacity is 50,110 MW in Shanxi, 60,190 MW in Inner Mongolia, 22,270 MW in Shaanxi, 22,570 MW in Xinjiang; 16,400 MW in Ningxia and 15,510 MW in Gansu.
According to the 2012 basic information and scoring statistics on nationwide 600 MW thermal power units announced by CEC in 2013, we can estimate the distribution of cooling systems in these coal power provinces.There are approximately 75% of units adopting air-cooled system and other 25% of units adopting closed-loop cooling system, as shown in Table 3. Open-loop system, constrained by resource endowment in these western regions, is rarely deployed.According to Equation (1), we can estimate the water consumption by thermal power plants in these provinces, and the results are shown in Table 4. Then according to the statistical data on industrial water consumption, we can estimate the proportion of thermal power generation in the overall industrial water use in these provinces.The results are shown in Figure 4.
It is found that in both Ningxia and Shanxi provinces, coal power accounts for as high as 20% of industrial water consumption.For Inner Mongolia, coal power consumes 15% of the industrial water use.For Xinjiang and Shaanxi provinces, the percent is 10%.Only in Gansu province the percentage is less than 10%.Because of the scarcity of water resource in these provinces, we assume that further increase in industrial water supply is impossible or is much likely to bring conflicts between industrial water use and other purposes (ecological use or household use, for example) [18].Therefore, we assume that further big increase in coal power/industrial water use percent is definitely unacceptable in the perspective of sustainable development in these provinces.

BAU Water Consumption Scenario in 2020
According to the "Power Development Strategic Research Report 2013" by CEC, the capacity of China's coal power plants in 2020 is expected to reach 1100 GW, and coal power bases will account for 55% of total newly-constructed plants.The BAU power demand and power planning is shown in Table 5. Assume constant water consumption rates, we can estimate the business-as-usual (BAU) scenario of water consumption by coal power plants in these coal power base provinces in 2020 (Table 6).According to the BAU scenario, it is estimated that water consumption for coal power generation will double during 2012-2020, provided that the comprehensive water consumption rates and the composition of cooling system are unchanged (Figure 5).It is worthwhile pointing out that all these coal power bases are puzzled by water shortage, and a double growth in water demand will certainly break the balance of water ecology system in these regions.Furthermore, current water consumption by the power generation is substantial in volume and critical to its operation, but pressures of population growth, hydrological variability and climate change will complicate the issue.Water consumption in these provinces is always constrained by available supply and consumption in other industries is relative stable in the past.Hence, we hypothesize that water consumption in other industrial sectors will hold constant during 2012-2020, and then we can update the percentage of coal power/industrial water use for these provinces in 2020 (Figure 6).According to the estimate, with the exception of Gansu province, in the other five provinces, the percentages of coal power/industrial water use will be largely enlarged.In Shanxi and Ningxia provinces, coal power is expected to consume 30% of industrial water use in the BAU scenario; while in Xinjiang, Inner Mongolia and Shaanxi, coal power is expected to consume around 20% of industrial water use.In other words, the BAU scenario envisions higher possibility of water resource conflicts in these provinces.

Water Conservation Measures and Alternative Scenario
Our projected result in these provinces has clearly indicated that serious water crisis will be likely to erupt in the BAU scenario.A strong implication is that the Chinese Government must take water resource constraint into consideration as a critical point in its overall sustainable development plan, in addition to energy supply and environment protection.The point is that an integrated energy-water resource plan with regionalized environmental carrying capacity as constraints is a desideratum to settle this puzzle.Hence, in this section, firstly possible measures to cut down (or avoid) water consumption will be discussed.Then, an alternative scenario will be proposed to guide the sustainable energy development in these coal power base provinces.

Downsizing Coal Power Capacity
The most effective measure to cope with water resource crisis caused by power generation is cutting down the scale of coal power capacity in western provinces.In other words, an alternative power plan is needed.The following strategies can be employed in developing the power sector plan:  Reducing electric power demand by active energy efficiency efforts.Energy efficiency has been regarded as the fifth energy source besides coal, oil, gas and hydropower.Worldwide experience has also clearly demonstrated the efficacy of energy efficiency in optimizing energy system.We estimate that with active energy efficiency efforts, the demand growth for electric power can be slowed down by 2%-3% and results in energy conservation at 200-300 TWh annually.The energy efficiency potential into 2020 by various active efforts is shown in  Optimizing generation mix by deploying clean and sustainable energy sources.On one hand, in China the hydropower development is yet to reach its economically developable resource limit.
On the other hand, China is endowed with abundant renewable energy sources like wind power and solar power, and active support of renewable energy development can make a big difference. Optimizing the regional distribution of coal power.With the development of zero emission technology, coal power can generate electricity at emission levels (SO2, NOx and dust) closer to or even lower than gas power [40].Hence, the government can lift the ban on the new construction of coal power plants in east regions and plan to build some coal power plants with cutting-edge pollutant control technologies in the load centers.The benefits are twofold.First, China's potential water resource crisis in western can be partly relieved.Second, the demand on long-distance electric power transmission-another important concern of decision-makers-can also be reduced.

Saving Water by Improving the Cooling System
The cooling system consumes most of water in the power generation process.Therefore, another priority of water conservation is to improve the cooling system in coal power plants.In the existing coal power fleet, these plants with advanced closed-loop water cooling system perform as effectively as those with air-cooled system in terms of the comprehensive water consumption rate while enjoying super energy efficiency advantage.Here, an important measure is to raise the technical threshold of new coal power plants and require that all the newly-constructed coal power plants perform better in their water consumption than the existing records.For existing plants, technical retrofitting can be implemented in those plants with below than average water efficiency performance.

Saving Water in Other Links
The demand on water quality in the other links of power plants is not as strict as in the cooling system.For example, treated wastewater, instead of fresh water, can be used in the desulfurization system and the coal yard.Use of nontraditional water sources, such as secondary-treated municipal wastewater, provides an option to reduce freshwater usage in thermal power production [41].In the subsequent subsection, concrete water conservation measures are proposed from many links in the generation process.
 Ash and slag removal system: Dry-type ash and slag removal system, which consumes no water at all, is a mature option.On the other hand, with this process, the produced ash and slag can be reclaimed as building material [41]. Cooling system of auxiliary systems: The cooling water for the auxiliary systems can be processed in a centralized way.Similarly, a small-scale wet recirculating or dry recirculating cooling system can be employed for the cooling of the pooled water. Desulfurization system: Dry desulfurization process consumes much less water than wet process.
For the wet desulfurization process, the cyclic utilization of processing water is a feasible option.Other option is to use the reclaimed water in the cooling system for the auxiliary systems in desulfurization process. Water use of coal yard: The water quality demand in the coal yard is much lower.Retreated industrial wastewater or domestic wastewater can be collected for this purpose.Besides, the wastewater produced in coal yard can also be reutilized to further cut down water consumption.

An Alternative Water Consumption Scenario
In the alternative water consumption scenario, with energy efficiency efforts, electricity demand is projected to drop from 7705.5 TWh to 7560 TWh.In addition, with more clean and sustainable energy sources, the demand for thermal power is reduced by almost 100 GW, as shown in Table 8.Due to technological advances and structural optimization, the comprehensive water consumption rate could be cut down by a large extent in the alternative scenario.Our estimate is that the water consumption rate could be cut down by 30% from the existing level.In addition, we project that more air-cooled units would be built.The details of the alternative scenario are reported in Table 9.In the alternative scenario, planned coal-fired generation capacity in these provinces would be 13 GW lower than in the BAU scenario.Also, the comprehensive water consumption rate of the closed-loop cooling system would be lowered to 1.27 m 3 /MWh.The water consumption by coal power in these provinces will be 1212 million m 3 , with only a slight increase relative to 2012 level.In this way, the envisioned water crisis caused by the electric power industry in these water-deprived provinces could possibly be avoided.However, we should not be too optimistic about it.Great risk exists in the implementation of water conservation measures and their actual effects.

Concluding Remarks
Coal power is an inevitable choice for meeting the increasing electric power demand in China.Considering the ever worsening atmospheric pollution, the Chinese Government has to adhere to the path of developing large-scale coal power bases in western provinces.However, the analysis presented in this paper clearly indicates that there will be furious water-energy conflicts in the development of coal bases, and water resource constraints will seriously restrict their development.An integrated planning of energy and water resources which takes regionalized environmental carrying capacity as the constraint is a final resort to this sustainable development puzzle.Several concrete water conservation measures are proposed to address the water crisis in China's coal power bases.
Certainly, our study is suffering from some limitations.For example, the perspective employed in the study is water resource constraint.Other important factors, such as the deployment cost of new cooling system and the retrofitting cost of existing cooling system, the economic appraisal of water conservation in links other than cooling system, are not addressed in the study.Water issue is only projected to worsen in the future, as a consequence of climate change.Therefore, further and more in-depth analysis on the issues presented here is needed to provide guidance for Chinese government and other stakeholders.

Figure 1 .
Figure 1.The water resources and water use in China's coal-power base provinces.

Figure 2 .
Figure 2. Water use of main coal power base provinces in 2012.

Figure 3 .
Figure 3. Methodology framework of our study.

Figure 4 .
Figure 4. Coal power vs. industrial water use in the coal power base provinces, 2012.

Figure 5 .
Figure 5. 2020 BAU vs. 2012 water consumption by coal power in coal power base provinces.

Figure 6 .
Figure 6.Percentage of coal power/industrial water use in the BUA scenario.

Table 1 .
Water consumption rates in China's 600 MW coal power units, 2012.

Table 3 .
Statistics on different cooling systems in China's coal power base provinces.

Table 4 .
Water consumption by thermal power plants in coal power base provinces, 2012.

Table 5 .
BAU (business-as-usual) power demand and power planning.

Table 6 .
BAU Water consumption by thermal power plants in coal power base provinces, 2020.

Table 7 .
The energy efficiency potential of active efforts into 2020.

Table 8 .
Alternative power demand and power planning.

Table 9 .
Alternative water consumption in coal power base provinces.