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Journal of Cleaner Production xxx (2014) 1e8

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Journal of Cleaner Production

journal homepage: www.elsevier .com/locate/ jc lepro

CO2-EWR: a cleaner solution for coal chemical industry in China

Qi Li*, Ya-Ni Wei, Guizhen Liu, Hui ShiState Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan 430071,China

a r t i c l e i n f o

Article history:Received 1 May 2014Received in revised form30 August 2014Accepted 19 September 2014Available online xxx

Keywords:CO2-EWRCoal chemical industryCCSEnergy securitySaline aquiferCO2 utilization

* Corresponding author. Tel.: þ86 2787198126.E-mail address: qli@whrsm.ac.cn (Q. Li).

http://dx.doi.org/10.1016/j.jclepro.2014.09.0730959-6526/© 2014 Elsevier Ltd. All rights reserved.

Please cite this article in press as: Li, Q., et a(2014), http://dx.doi.org/10.1016/j.jclepro.20

a b s t r a c t

Anthropogenic greenhouse gas emissions become the primary factor for the global warming, whereascarbon dioxide (CO2), as one of the primary greenhouse gases, takes an inescapable responsibility forclimate change. Currently, various energy conservation and carbon emission reduction technologies,including the carbon capture and storage (CCS) technology, as well as other clean, low-carbon energyexploitation technologies exhibit a rapid development trend to alleviate the growing crisis of climatechange. Other than traditional CO2 geological storage, a novel geoengineering approach of CO2 geologicalutilization and storage, named CO2 geological storage combining with deep saline water/brine recovery(CO2-EWR), is put forward to solve the dilemma between the increasing carbon emissions from coalchemical industry and national energy and water security in China. Compared with the traditional CCStechnology, CO2-EWR has two advantages: (1) it can control the relief of reservoir pressure and waterproduction by a reasonable design of pumping wells to achieve the security and stability of the large-scale geological storage of CO2; (2) it can collect and process deep saline water after a treatment forlife drinking, industrial and/or agricultural utilizations to alleviate the water shortage situation as well asecological environmental problems, and in addition, the deep brine resources may create considerableprofit margins by cascade extraction, which could be used to fill the gap of cost primarily criticized fromcapture and sequestration processes of current CCS technologies. China mainland can be partitioned intothree potential CO2-EWR zones primarily according to different types of aquifer system, whereasconsidering research and development maturity and cost prediction of the potential technology adopted,it can be found that coal power and coal chemical enterprises in China's western region have an earlyopportunity. Three sub-modules of CO2-EWR technology including CO2 storage in deep saline aquifer,saline water extraction and desalination as well as brine resources utilization are analyzed from a pro-spective of energy conservation, carbon emission reduction and environmental friendship. Throughdetailed analyses, it can be concluded that CO2-EWR technology can be absolutely considered as a cleantechnology for environmental improvement and green development, and finally development directionand future prospective of the CO2-EWR technology are pointed out.

© 2014 Elsevier Ltd. All rights reserved.

1. Introduction

Global warming has been a hot topic for academia around theworld for decades. Anthropogenic greenhouse gas emissionsbecome the primary factor for the global warming, whereas CO2, asone of the primary greenhouse gases, takes an inescapable re-sponsibility for climate change (Metz et al., 2005). Currently,various energy conservation and carbon emission reduction tech-nologies, as well as other clean, low-carbon energy exploitationtechnologies exhibit a rapid development trend to alleviate the

l., CO2-EWR: a cleaner solutio14.09.073

growing crisis of climate change (Camara et al., 2013; Huisinghet al., 2013; Zhang et al., 2014). Carbon capture and storage (CCS)technology, as an effective essential approach to reduce CO2 level inthe atmosphere at a large scale, has been paid high attention bygovernments around the world. Particularly in China, because ofwith fewmature carbon emission reduction technologies (Liu et al.,2005), there is a huge development space for CCS (Chen et al., 2013;Climate Group, 2010; Vishal et al., 2013). Whereas with furtherdevelopment of CCS technology, various problems appeared needto be solved urgently, two aspects including huge cost (energypenalty) and uncertain environmental risks are the primary issues(Chaudhry et al., 2013; Teng and Zhang, 2010; Wang et al., 2013).CCS cost is primarily affected by capture technology, transportationoption, distance matching of sources and sinks, and sequestrable

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Q. Li et al. / Journal of Cleaner Production xxx (2014) 1e82

reservoirs, so there is a very big difference in the total cost ofdifferent CCS technologies, whereas overall, the cost is much high,which makes a number of energy companies prohibitive or nega-tive (Court et al., 2011; Xie et al., 2013). Furthermore, during thesequestration process, a large scale CO2 injection will lead toreservoir pressure increase and saline water replacement (IEAGHG,2011). The increasing pressure may make the overlying cap rockbreakage or fault reactivation and CO2 leakage occurs consequently(Lei et al., 2013; Liu and Li, 2013). However, saline water

Fig. 1. Partition of sedimentary basins wi

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replacement may have an effect on groundwater system, includingits migration to shallow formations, so as to cause contamination ofshallow groundwater (Birkholzer et al., 2009; IEAGHG, 2011).

In view of the above problems faced by a traditional CCS tech-nology, some scholars doubt about how CCS can be treated as acleaner technology (Camara et al., 2013). Whereas an alternativegeoengineering approach of a CCUS (carbon capture, utilization andstorage) technology, named CO2 geological storage combining withdeep saline water recovery (CO2-EWR) technology (Li and Wei,

th major aquifers in China mainland.

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Fig. 2. Full chain modules of CO2-EWR.

Q. Li et al. / Journal of Cleaner Production xxx (2014) 1e8 3

2013; Li et al., 2013aec), is put forward to make up for deficienciesof a traditional CCS technology. It is a process of injecting CO2 intodeep saline aquifers for CO2 sequestration with enhanced salinewater/brine recovery. Compared with traditional CO2 geologicalstorage, CO2-EWR has two advantages: (1) it can control the reliefof reservoir pressure and water production by a reasonable engi-neering design of pumping wells to achieve the security and sta-bility of the large-scale geological storage of CO2 (Court et al., 2011);(2) it can collect and process deep saline water after a treatment forlife drinking, industrial and/or agricultural utilizations to alleviatethe water shortage situation as well as ecological environmentalimpacts (Kobos et al., 2011). In addition, the collected water withhigh salinity or brine resources may create considerable profitmargins by mineralization utilization, such as employingMgCl2$H2O to mineralize CO2, so as to recover hydrochloric acidand magnesium carbonate (Barbero et al., 2013; Xie et al., 2013), orcascade extracting liquid mineral resources including potassium,bromine, lithium, and so on, which could be used to fill the gap ofcost primarily generated from capture and sequestration processesof current CCS situations. Therefore, the CO2-EWR technology canbe considered as a clean technology for CO2 reduction in large-scaleand environmental improvement by alleviating the crisis of waterresources shortage.

The CO2-EWR technology is primarily assembled by two coremodules, i.e. CCS and salt/brine extraction. According to differenttypes of aquifer systems, China mainland can be partitioned intothree potential CO2-EWR zones (Fig. 1) (Li et al., 2013c). In China'swestern region (Zone I), the type of aquifer system is primarilyalluvial and lacustrine sand, fine sand and cohesive soil, enrich-ment of coal, oil, natural gas and other fossil fuels make various coalchemical industries and oil and gas industries come into being.Whereas high concentrations of CO2 emissions as well as a hugedemand of industrial water become a serious obstacle for thedevelopment of these enterprises. Therefore, CO2-EWR has a greatpotential to be implemented by these coal chemical industries andother oil and gas industries in Xinjiang, Inner Mongolia and otherregions with a rapid development but a lack of water resources. InChina's eastern region (Zone II), the aquifer type is primarily looserocks with sandy gravel and medium-coarse sand, excessiveextraction of groundwater has caused severe land subsidence innorth China, Suzhou, Wuxi, Changzhou and other regions, and thepumping depth of groundwater has increased year by year,whereas the deep saline water extraction and desalination hasconsiderable prospect to alleviate these man-made geologicalhazards. In addition, with the high carbon intensity in the easternregion, deep saline aquifer storage can be the primary choice of CO2emission reduction (Li et al., 2013c). In China's southern region(Zone III), the aquifer type is primarily carbonate rock mixed withclastic rock, ore-controlling mechanism of cracks enrichment andpores occurrence enriched brine resources, such as the ones inSichuan Basin and Jianghan Basin. Taking use of CO2 for recovery ofbrackish water or brine resources and developing comprehensiveutilization of them, not only can solve the acute shortage of stra-tegic mineral resources for national economic development, butalso generate considerable economic and social benefits (Li et al.,2012).

2. Modules of CO2-EWR technology

Currently, there is no operating CO2-EWR project except forGorgon project (the world's first demonstration project adopting aCO2-EWR technology) (Flett et al., 2008) in the worldwide, and afew CCUS projects definitely plan to adopt a CO2-EWR technologyor some projects are under consideration. Research regardingCO2-EWR is now in the stage of theoretical study throughout the

Please cite this article in press as: Li, Q., et al., CO2-EWR: a cleaner solutio(2014), http://dx.doi.org/10.1016/j.jclepro.2014.09.073

world. Considering development and cost of the CO2-EWR tech-nology in current situation, a large scale application and devel-opment in China may not be realistic in a short term. Whereas inChina's western region, the inverse correlation of rich in coal re-sources and poor in water resources makes coal power and coalchemical industries face severe water shortage challenges. Inaddition, the growing carbon emission reduction pressure un-doubtedly gets the situation worse, the CO2-EWR technology maybring the gospel to these enterprises, so in China west the tech-nology has an early development opportunity. Therefore, analysisand evaluation primarily focus on coal chemical industry inChina's western region. Full chain modules can be depicted inFig. 2 (Li et al., 2013c). Three modules of the CO2-EWR technologyincluding CO2 storage in deep saline aquifer, saline water extrac-tion and desalination as well as brine resources utilization areanalyzed from a prospective of energy conservation, carbonemission reduction and environmental improvement (Bagatinet al., 2014).

2.1. CO2 storage in deep saline aquifer

China's energy mix is dominated by coal resources. According toIEA's forecast, by 2050, under the baseline scenario, China's CO2emissions will account for 27% of the world's total emissions, mostof which will come from the coal (Climate Group, 2010; OECD/IEA,2013). However, China's coal resources take the distribution patternof rich in the north and west and poor in the south and east. Sixprovinces, Shanxi, Shaanxi, Inner Mongolia, Ningxia, Xinjiang andHeilongjiang, with relatively abundant coal resources, account forapproximately 79% of its reserves of the country (Song et al., 2012).This distribution pattern makes coal power and coal chemical in-dustries facing severe pressure for carbon emission reduction innorthwest region with a relative shortage of water resources and amore fragile ecological environment. The CO2-EWR technologymay achieve direct carbon reduction primarily by storage of CO2into deep saline aquifers. Table 1 shows the data from the Austra-lian Greenhouse Office. It can be observed that CO2 emission maydecrease 1% compared with the ones in 2002 after the operation of

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Table 1Impact of Gorgon project for the entire Australia's CO2 emissions.

Annual CO2

emissions (Mt)Emissions incrementalrelative to the baseline 1990 (%)

Australia's CO2

emissions in 1990536.9 e

Australia's CO2

emissions in 2002541.8 0.9

CO2 injection amountof Gorgon project

4 0.8

Source: Australian Greenhouse Office, 2005.

Q. Li et al. / Journal of Cleaner Production xxx (2014) 1e84

Gorgon project. Therefore, the implementation of Gorgon projecthas a certain control on CO2 emissions throughout Australia.

There are a large number of sedimentary basins distributed inthe mainland and continental shelf, with the features of wide dis-tribution area, large sediment thickness and considerable volumeof saline reservoir for CO2 storage. The CO2 storage capacity forChina's 25 major sedimentary basins is evaluated using universalpyramid method (CSLF, 2008), and the total value reachesapproximately 1191.95�108 t, which is equivalent to 14.31 times ofthe whole CO2 emissions in 2010 for China (Li et al., 2013aec). Inaddition, the storage capacity in China's western region is up to661.53 � 108 t, accounting for 55.49% of total storage capacity,which may be a considerable storage potential (Li et al., 2013b).

Compared with the traditional CCS and CO2-EOR (CO2 EnhancedOil Recovery) technologies (Yang et al., 2014), the CO2-EWR tech-nology owns relatively high security. It is primarily because thereservoirs generally do not go through the pre-development, andthe overlying cap rock has not been damaged or destroyed. Inaddition, setting pumping wells may effectively alleviate thepressure accumulation caused by CO2 injection and consequentlyreduce the leakage risk (Buscheck et al., 2012; Li et al., 2014).However, potential safety problems may still exist, which primarilyfocus on CO2 local leakage through pumping wells. If under theguarantee of perfect monitoring and early warning system as wellas emergency measures (He et al., 2011; Li et al., 2011, 2013a), therisk should be generally low.

There are many uncertainty factors and deficiencies existed inCO2 geological storage in the international and China, such astheoretical research, engineering experience or setting regulations.

Fig. 3. Depiction of the C

Please cite this article in press as: Li, Q., et al., CO2-EWR: a cleaner soluti(2014), http://dx.doi.org/10.1016/j.jclepro.2014.09.073

The Climate Group (2010) concluded the primary difficulties of theCCS technology facing in China as follows: (1) lack of clearsequestration site selection criteria and site investigation tech-niques. Currently, China has not yet introduced explicit, quantifi-able site selection criteria, and in addition, access to siteinformation technology, although applied in the oil and gas in-dustry, still needs to be verified in the process of CO2 sequestration;(2) lack of methods for evaluation of site mechanical stability.Eurasian plate including China is squeezed by around plates, whichconsequently leads to more frequent tectonic activities and highfault densities, the long term mechanical stability assessment inChina seems to be more important than that one in Europe andNorth America. Therefore, mechanical stability assessment refer-ring to long term geochemical processes (Tian et al., 2014) andbackground tectonic activity effects needs to be enhanced (Fu et al.,2010); (3) need for further development of emergency and reme-dial measures for CO2 leakage. Different CO2 leakage pathwayscorrespond to different remedial measures (Liu et al., 2014), whichhave been applied in oil and gas production industry, and there area number of practical experience in demonstration projects inChina. Whereas further development of restoration measures forCO2 leakage needs to be enhanced, particularly the exploitation ofsealing restoration technology against defect formation.

2.2. Extraction and desalination of saline water

2.2.1. Extraction of saline waterChina's water resources exhibit the distribution pattern of rich

in the south and poor in the north. The inverse correlation with thedistribution pattern of coal resources makes coal power and coalchemical industries face severe water stress, and consequentlytriggered a series of sharp, complex social, economic and envi-ronmental issues. Taking Zhundong coal base located in Junggarbasin in Xinjiang as an example, the estimated coal reserves reachto 390 billion tonnes, accounting for 17.81% of Xinjiang's totalpredicted reserves (Song et al., 2012). Whereas the coal industrydevelopment is inseparable from the guarantee of water resources,particularly for the coal chemical industry, which belongs to aresource-intensive industry and the water consumption is veryhuge. Unfortunately, the Zhundong region belongs to a desert zonewith an extreme lack of water resources, and in Xinjiang, most ofthe total 31 rivers are independent and short. Currently, surface

O2-EWR technology.

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Table 2CO2 storage capacity associated with deep saline water/brine recovery potential ofthe major sedimentary basins in China.

Sedimentary basins CO2 storagecapacity (�108 t)

Water recoverypotential (�108 t)

Zone I Junggar Basin 44.36 2.02Tarim Basin 446.88 13.20Turpan-Hami Basin 15.42 0.51Erdos Basin 43.31 1.71Qaidam Basin 104.83 2.38Jiuquan-Minle Basin 5.59 0.17Qinshui-Linfen Basin 1.13 0.04

Zone II Hailar Basin 6.70 0.39Songliao Basin 20.75 1.67Erlian Basin 11.47 0.71Bohai Bay Basin 65.52 2.20Northern Yellow Sea Basin 4.41 0.18Southern Yellow Sea Basin 49.25 1.99East China Sea Basin 126.00 5.08Taixi Basin 15.12 0.61Taixinan Basin 21.42 0.86Pearl River Mouth Basin 71.00 2.49Beibuwan Basin 11.25 0.53Subei Basin 16.91 0.59

Zone III Nanxiang Basin 5.36 0.17Sichuan Basin 90.72 2.89Jianghan Basin 9.53 0.34Dongtinghu Basin 5.04 0.16

Fig. 5. Comparison of the levelized costs of reverse osmosis (RO) desalination for sa-line water for which the pressure is supplied by CO2 injection, vs. the costs for aconventional system where the pressure is supplied by external high-pressure pumps.Water production scale 2 MGD (million gallons per day) equivalent to 2.27 � 104 m3.The reason why the blue (diamond) curve behaves more gently, mainly because of theRO pressure from internal reservoir, so little impact on the levelized costs. RO usingreservoir pressure significantly lowers processing costs. AC-FT: per acre-foot (326,000gallons) water. (After Wolery et al., 2009). (For interpretation of the references to colorin this figure legend, the reader is referred to the web version of this article.)

Q. Li et al. / Journal of Cleaner Production xxx (2014) 1e8 5

water utilization in the Zhundong region has exceeded the warninglevel, and in addition, the largest groundwater funnel area hasformed due to severe over-exploitation (Li and Wei, 2013). Theconstant dewatering and drainage make aquifer system bordermove outward, water sources dry up, and consequently lead toparched vegetation, soil fertility reduction and crop losses, and soon. If the groundwater pumping continues, the irreparableecological and environmental problems must be caused in the re-gion with an original fragile ecological environment.

The CO2-EWR technology (Fig. 3) stores CO2 stably in deep salineaquifers, as well as pumps the saline water, which can be used forlife drinking and industry or agriculture after a desalination treat-ment. The CO2-EWR technology effectively alleviates the watershortage situation, and consequently reduces a series of ecologicaland environmental problems. The recovery potential of saline wa-ter in seven primary basins in Zone I (Table 2), including Junggarbasin, Tarim basin, Turpan-Hami basin, Erdos basin, Qaidam basin,Jiuquan-Minle basin and Qinshui-Linfen basin in northwest region,is evaluated to be approximately 20.02 � 108 t (Li et al., 2013b),

Fig. 4. Salinity distribution associated with main water desalination technologies. TDS:total dissolved solids.

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which may support 10 coal chemical industries on the scale to beoperated normally for approximately 10 years.

During the process of saline water extraction, if the pumpingtime is too short, the salinewater amount is limited, and the energyconsumption and costs may be a great waste. Whereas if the time istoo long, CO2 leakage may easily occur through pumping wells, andshallow water and atmosphere is consequently contaminated withCO2. Therefore, some key issues arise regarding how to minimizereservoir pressure and to utilize deep saline water on an utmostscale. Various factors including arrangements of pumping wells(such as pumping well number, pumping rate and distance), for-mation parameters, filter pipe length and location and so on mayhave different impact on reservoir pressure and migration anddissolution mechanism of CO2 (Li et al., 2013c). Due to thecomplexity of the underground environments, numerical modelsand simulations play an important role in the evaluation of CO2

migration and saline water recovery for CO2-EWR. Therefore,simulation should be adopted to optimize various factors forseeking a best solution with a lower leakage risk, a more waterrecovery and a less energy consumption (Chabora and Benson,2009).

2.2.2. Desalination of saline waterCrystallizer, electrodialysis reversal, distillation, reverse osmosis

(RO) and ion exchange are the primary technologies for desalina-tion (Li andWei, 2013). Of which, reverse osmosis is applied widelyfor its less energy consumption, simple equipment, high efficiency,small footprint and easy operation. Energy & EnvironmentalResearch Center (EERC) makes statistics on different desalinationtechnologies corresponding to various water salinity range, asillustrated in Fig. 4. It can be seen that when the salinity is between0 and 50 g/L, reverse osmosis is the most appropriate technology,fortunately, the deep groundwater salinity is almost within thisrange, so reverse osmosis is no doubt a best choice for deep salinewater desalination. Additionally, the driving force in reverseosmosis process is pressure, and there is no phase change. Windenergy as well as solar power can be used as driving forces,therefore, in this regard, reverse osmosis can be considered as aclean technology.

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According to Wolery's studies (Aines et al., 2011; Bourcier et al.,2011), the strong reservoir pressure derived from CO2 injection canbe used as a driving force in the reverse osmosis process, which canreduce the energy consumption in a large scale and consequentlylower the cost (Fig. 5). By a draft calculation, when the scale ofreverse osmosis is 22,700 m3/d, under the guarantee of a sufficientpressure in the reservoir, the cost for deep salinewater desalinationwith reservoir pressure is approximately 32e40 US cents/m3,whereas with the external pressure, the desalination cost is up to60 to 80 US cents/m3 (Wolery et al., 2009). Therefore, in the processof desalination, taking use of reservoir pressure as a driving powercan be an economical and reliable energy conservation technology.

2.3. Extraction and utilization of brine resources

The produced deep saline water can be classified into two types:water with low salinity and water with high salinity. For water withlow salinity (referring to saline water), reservoir pressure can beutilized for desalination tomeet life drinking as well as industrial oragricultural demands. Whereas for water with high salinity(referring to brine), the rich MgCl2 contained can be employed to

Fig. 6. Cascade extraction of variou

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mineralize CO2 and to recover high-value hydrochloric acid andmagnesium carbonate, in addition, potassium, bromine, lithium,and other important mineral resources contained in brine also canbe extracted by cascade extraction. These resources may producesignificant economic and social benefits to fill the gap of cost pri-marily from capture and sequestration processes of current CCSsituations.

In China's southwest and southern regions, the aquifer type ofsedimentary basins is primarily carbonate rock mixed with clasticrock, ore-controlling mechanism of cracks enrichment and poresoccurrence enriched brine resources. Additionally, deep under-ground brine resources also take on its distribution in the southwestrim of Tarim basin, southern Qinghai, eastern Tibet, and so on. Richsaturated brine and mineral resources in salinization area of QaganTesla were found by the Institute of Tibetan Plateau Research, Chi-nese Academy of Sciences with funding support of Sino-Germanwestern Qaidam basin km Scientific Drilling Project, the chemicalcomposition of the brine and mineral deposit type and quality areremained to be determined. According to researchers' estimation,potassium, boron, lithium, magnesium and other ingredients maybe contained and the reserves are considerable.

s valuable elements in brine.

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Q. Li et al. / Journal of Cleaner Production xxx (2014) 1e8 7

Some ideas are put forward in China that employingMgCl2$6H2O rich in seawater or salt lakes to mineralize CO2 and torecover hydrochloric acid and magnesium carbonate as well asother valuable products (Xie et al., 2013). Experimental resultsshow that every 10 tonnes of MgCl2$6H2O may mineralize 1.5tonnes of CO2, and simultaneously produce 1.8 tonnes of hydrogenchloride (about five tonnes of hydrochloric acid with concentra-tions of 36%), as well as 2.9 tonnes of magnesium carbonate, theprofit margin is much considerable. With this new idea, MgCl2 indeep brine also can be utilized for mineralization to obtain valuableproducts and so as to create social and economic benefits. Salt LakeResearch Group in the Institute of Comprehensive Utilization ofMineral Resources, Chinese Academy of Geological Science firstlyperformed experimental research on availability of potassium-richbrine contained in Jiangling depression (http://www.cgs.gov.cn/xwtzgg/gzdongtai/20509.htm), after approximately 3 years of lab-oratory studies, the methodology with phased extractioncombining various processes is determined to effectively extractvaluable elements (Fig. 6). The results show that the extractionstage complement one another to make the element maximizerecovery: potassium recovery of 73.02%, sodium recovery of 95.34%,boron recovery of 81.37%, lithium recovery of 78%, iodine, brominerecovery of approximately 80%, and the products mostly meet na-tional quality standards. This study provides a feasible program forthe industrial development and utilization of brine resources.

Currently, a serious potassium shortage exists in China. Theconsumption of potash products is more than 11 million tonnes, ofwhich more than 70% depends on the import, so potassium is oneof few bulk minerals with more than 50% of external dependence.Additionally, many resources containing potassium cannot beexploited and utilized due to complex occurrence conditions and alow technological level. The bromine price reached 18,025 RMB(Chinese Yuan) per tonne at the end of June, 2012. Therefore,exploiting and utilizing the brine to mineralize CO2 or extractvaluable mineral resources may make up for the shortage of somestrategic mineral resources to a certain extent, and in addition italso creates considerable economic benefits to make up for thecurrent cost gap from capture and sequestration processes of CCS.

3. Conclusions

Based on traditional CO2 geological storage, a novel CCUS optionnamed the CO2-EWR technology is put forward in this paper, whichis an industrial process of injecting CO2 into deep saline aquifers forlong term and stable sequestration with enhanced saline water/brine recovery. Compared with the traditional CCS technology, CO2-EWR has two advantages: (1) it can control the relief of reservoirpressure and water production by a reasonable design of pumpingwells to achieve the security and stability of the large-scalegeological storage of CO2; (2) it can collect and process deep sa-line water after a treatment for life drinking, industrial and/oragricultural utilizations to alleviate the water shortage situation aswell as ecological environmental problems, and in addition, thecollected brine resources may create considerable profit margins bymineralization or cascade extraction, which could be used to fill thegap of cost primarily from capture and sequestration processes ofcurrent CCS situations. Therefore, the CO2-EWR technology can beconsidered as a clean technology for a large-scale reduction of CO2

and environmental improvement by alleviating the shortage crisisof water resources.

According to the different types of aquifer systems, Chinamainland can be partitioned into three potential CO2-EWR zones,i.e. carbon emission reduction and water supply of coal power andcoal chemical industries in China's western region, land subsidenceremediation in China's eastern region and brine exploitation in

Please cite this article in press as: Li, Q., et al., CO2-EWR: a cleaner solutio(2014), http://dx.doi.org/10.1016/j.jclepro.2014.09.073

China's southern region. However, considering the developmentand cost of CO2-EWR technology in current situation, large scaleimplementation and development in China may not be realistic in ashort term. Whereas in the western region, the inverse correlationof rich in coal resources and poor in water resources makes coalpower and coal chemical industries face dual high pressure withsevere water shortage stress and carbon emission reduction. TheCO2-EWR technology may bring the gospel to these enterprises, soin China's western region, this technology has an early develop-ment opportunity. Three modules of the CO2-EWR technologyincluding CO2 storage in deep saline aquifer, saline water extractionand desalination as well as brine resources utilization are analyzedfrom a prospective of energy conservation, carbon emissionreduction and environmental improvement in this paper. Throughaforementioned analyses, it can be concluded that the CO2-EWRtechnology can be absolutely considered as a clean technology forenvironmental improvement and green development.

Research regarding CO2-EWR is now in the stage of a theoreticalstudy throughout the world, and it has not been demonstrated inan actual project except for the constructing Gorgon project,Australia. More intensive studies should be performed in the future,such as optimization between production and energy consumption,chemicalemechanical interaction problems, leakage risks, and soon, and they could provide a reliable guide to future CO2-EWRprojects.

Acknowledgments

This research is partially supported by National Natural ScienceFoundation of China (NSFC) (Grant No. 41274111), China CleanDevelopment Mechanism (CDM) Fund (Grant No. 2012087), NZACIIA, the Hundred Talents Program of the Chinese Academy of Sci-ences, and Early Research Program on Major Issues of China NEA's13th Five-Year Energy Plan (Grant No. 2014-21). We alsoacknowledge financial support from the China Australia GeologicalStorage of CO2 (CAGS) Project funded by the Australian Governmentunder the auspices of the Australia China Joint Coordination Groupon Clean Coal Technology. We would like to thank all the reviewersfor their insightful comments on the manuscript, as these com-ments led us to a great improvement of the article.

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