王春艷,田 磊,俞 敏,劉 毅*

電力行業(yè)水-能耦合關(guān)系研究綜述

王春艷1,田 磊2,俞 敏3,劉 毅1*

(1.清華大學(xué)環(huán)境學(xué)院,北京 100084；2.國(guó)家發(fā)展和改革委員會(huì)能源所,北京 100038；3.國(guó)務(wù)院發(fā)展研究中心資源與環(huán)境政策研究所,北京 100010)

電力行業(yè)消耗了全球約8%的水資源,電力生產(chǎn)與輸配過程中消耗的能源與水資源之間的相關(guān)關(guān)系被定義為電力行業(yè)水-能耦合關(guān)系.本文從電力行業(yè)水耗和節(jié)水潛力研究、電力生產(chǎn)與水資源空間分布匹配研究、電力行業(yè)水-能耦合關(guān)系與其他環(huán)境問題的關(guān)系研究三個(gè)角度對(duì)國(guó)際上相關(guān)文獻(xiàn)的研究?jī)?nèi)容、研究方法和主要結(jié)論進(jìn)行梳理.研究結(jié)果表明:冷卻技術(shù)選擇對(duì)電力行業(yè)的水-能耦合關(guān)系影響較大,電力生產(chǎn)的需水量與各地水資源稟賦在空間上不匹配,電力行業(yè)水-能耦合系統(tǒng)管理體系尚未建立且面臨迫切的實(shí)際需求.

電力生產(chǎn)；水-能耦合關(guān)系；水耗預(yù)測(cè)；環(huán)境問題；綜合管理

初級(jí)能源開采[1]、生物質(zhì)能種植[2-3]、能源加工[4-6]、能源使用[7]等能源部門的生產(chǎn)活動(dòng)需要大量的水資源投入.電力生產(chǎn)的需水量在能源部門中占比最高,約為25%~80%[4].火力發(fā)電的取水量可占全社會(huì)用水量的40%以上[8-10].近年來,能源部門,特別是電力部門水耗研究成為了研究熱點(diǎn).學(xué)者們將電力生產(chǎn)過程中能源與水資源的相關(guān)關(guān)系定義為“電力行業(yè)的水-能耦合關(guān)系(Water-Energy Nexus of the Electricity Sector)”.已有關(guān)于電力行業(yè)水-能耦合關(guān)系的綜述總結(jié)了特定區(qū)域電力行業(yè)的水耗估算方法、不同電力生產(chǎn)方式的水耗差異比較等,但尚未對(duì)電力生產(chǎn)與水資源空間分布不匹配、電力行業(yè)水-能-環(huán)境耦合關(guān)系等方面的研究進(jìn)展進(jìn)行總結(jié)和分析[4,11-14].因此,有必要進(jìn)一步梳理電力行業(yè)水-能耦合關(guān)系研究領(lǐng)域的重點(diǎn)和難點(diǎn),為后續(xù)研究提供基礎(chǔ).

1 電力生產(chǎn)與水資源消耗關(guān)系研究

在研究電力生產(chǎn)過程的水耗時(shí),學(xué)者們往往考慮以下幾個(gè)方面:①發(fā)電方式(如煤電、核電、太陽(yáng)能發(fā)電、風(fēng)電、水電、生物質(zhì)能發(fā)電等);②冷卻方式(如循環(huán)冷卻、直流冷卻、空冷、海水冷卻等);③水源(如地表水、地下水、海水等);④環(huán)境影響(如溫室氣體排放、大氣污染物排放、生態(tài)影響等).

1.1 電力生產(chǎn)水耗現(xiàn)狀分析

對(duì)電力生產(chǎn)水耗分析的相關(guān)文獻(xiàn)從估算方法、數(shù)據(jù)獲取方式、研究對(duì)象、水耗影響因素等幾個(gè)方面分別進(jìn)行歸類總結(jié).

電力行業(yè)水-能耦合關(guān)系研究中常用的方法包括全生命周期評(píng)估方法(LCA)[15-16]、物質(zhì)流分析方法(MFA)[17-19]、投入產(chǎn)出分析方法(I-O)[5,15-16]、基于過程的分析方法(Process-based Analysis)[17-19].其中,基于過程的分析方法通常以鍋爐、冷卻塔、污染物處理設(shè)施等生產(chǎn)環(huán)節(jié)為基本單元,運(yùn)用MFA對(duì)電力生產(chǎn)中的水資源流和能源流進(jìn)行量化和匡算[17-19].此外,部分學(xué)者將上述方法加以混合使用,如IO-LCA方法[15-16].

電力行業(yè)水-能耦合關(guān)系研究的數(shù)據(jù)主要來源于兩方面:LCA模型或者I-O模型中的水耗理論估計(jì)值、大量的電力企業(yè)一手調(diào)研數(shù)據(jù)[20].其中,通過調(diào)研獲取的水耗參數(shù)來源(如企業(yè)上報(bào)、理論估算等)不同,可能會(huì)導(dǎo)致數(shù)據(jù)質(zhì)量可信度較低[21].

從研究對(duì)象來看,學(xué)者主要關(guān)注不同發(fā)電方式、不同冷卻方式的取水量和耗水量差異(表1).電力生產(chǎn)的取水量一般高于耗水量,直流冷的取水量甚至可高于耗水量100倍以上[22].以采用循環(huán)冷卻的煤炭發(fā)電為例,其取水量中約有80%-90%在蒸發(fā)過程中損失,20%-15%的水量轉(zhuǎn)移到了可銷售的固體副產(chǎn)品中,剩余5%在經(jīng)過廢水處理后外排,即耗水量約為取水量的95%[20].此外,已有研究多關(guān)注全生命周期階段和運(yùn)行階段的水耗.例如,中國(guó)風(fēng)力發(fā)電耗水量為0.6L/kWh,其中上游關(guān)聯(lián)產(chǎn)業(yè)的耗水量約占風(fēng)力發(fā)電耗水量的50%[15].需要注意的是,水力發(fā)電的水耗研究仍有一定的爭(zhēng)議.水力發(fā)電,特別是蓄洪式水電站,會(huì)使得水體表面蒸發(fā)量增大[23].但水電站除具有發(fā)電功能外,還有防洪、灌溉等多種功能,在計(jì)算水力發(fā)電水耗時(shí)如何將蒸發(fā)水耗分配到各個(gè)功能上尚缺乏統(tǒng)一認(rèn)識(shí)[24-25].

表1 不同類型發(fā)電方式的取水量和耗水量比較(L/kWh)

此外,學(xué)者們還對(duì)發(fā)電水耗的影響因素進(jìn)行了分析.除了能源品種、冷卻方式外,外界環(huán)境(如溫度、濕度等)也會(huì)影響發(fā)電水耗.例如,火力發(fā)電的夏季耗水量比年平均耗水量高15%以上,而冬季耗水量則低12%以上[20].生物質(zhì)能源作物的耕種方式對(duì)其水耗也有較為重要的影響[3].

1.2 電力生產(chǎn)水耗預(yù)測(cè)

電力是經(jīng)濟(jì)發(fā)展的基礎(chǔ).電力生產(chǎn)與水資源消耗之間關(guān)系密切,越來越多的學(xué)者開始關(guān)注電力生產(chǎn)水耗預(yù)測(cè)問題.已有研究通常以發(fā)電水耗參數(shù)估計(jì)和電力生產(chǎn)結(jié)構(gòu)及產(chǎn)量預(yù)測(cè)為基礎(chǔ),分析未來電力生產(chǎn)的水耗情況,預(yù)測(cè)的時(shí)間跨度(2030年、2050年、2095年等)和空間范圍(全球、美國(guó)、中國(guó)、歐洲等)均較大.表2對(duì)其中代表性文獻(xiàn)的研究方法、時(shí)空尺度以及主要目的和結(jié)論進(jìn)行了總結(jié).目前的研究從微觀企業(yè)的水耗數(shù)據(jù)估算到宏觀區(qū)域?qū)用娴哪茉瓷a(chǎn)、調(diào)配及水耗預(yù)測(cè)都有所涉及,并多以2030、2050年為節(jié)點(diǎn).研究?jī)?nèi)容上,已有研究主要分析電力生產(chǎn)結(jié)構(gòu)、水資源供給方式、冷卻技術(shù)選擇等的變化對(duì)區(qū)域(省級(jí)、流域、或電網(wǎng)等)電力行業(yè)水-能耦合關(guān)系的影響,以及電力生產(chǎn)與其他經(jīng)濟(jì)活動(dòng)之間的權(quán)衡關(guān)系.總結(jié)發(fā)現(xiàn),電力生產(chǎn)水耗預(yù)測(cè)方面的研究尚未建立統(tǒng)一的研究方法和框架.雖然研究方法不盡相同,但研究結(jié)果均表明冷卻技術(shù)選擇對(duì)電力系統(tǒng)的水耗影響較大,水耗和發(fā)電量之間存在一定的權(quán)衡關(guān)系.

表2 電力預(yù)測(cè)及水耗研究進(jìn)展

根據(jù)研究地區(qū)進(jìn)行分類,全球主要國(guó)家的相關(guān)研究結(jié)果如下:

(1)中國(guó)

學(xué)者們分析了電力結(jié)構(gòu)[8,53]、冷卻技術(shù)[8,53]等方面的變化對(duì)中國(guó)2030-2050年的電力生產(chǎn)水耗的影響,結(jié)果發(fā)現(xiàn)電力生產(chǎn)水耗將依然集中在北方和沿海地區(qū),能源效率提高、電力結(jié)構(gòu)調(diào)整和冷卻技術(shù)均有助于節(jié)水,其中冷卻技術(shù)的節(jié)水效果更顯著.Li等[15]還發(fā)現(xiàn)2020年中國(guó)風(fēng)電的推廣應(yīng)用可以帶來23%的碳強(qiáng)度減排,同時(shí)節(jié)約8億m3水資源,相當(dāng)于1120萬(wàn)家庭用水的需求.

(2)美國(guó)

學(xué)者們分別預(yù)測(cè)了美國(guó)2050年[27]和2095年[55]的電力生產(chǎn)的水耗,結(jié)果發(fā)現(xiàn)冷卻技術(shù)變化帶來的部分地區(qū)(如加州)電力系統(tǒng)取水量和耗水量之間的折中關(guān)系尤為突出[55].

(3)英國(guó)

學(xué)者們預(yù)估了2030和2050年英國(guó)電力生產(chǎn)的水耗變化情況[28,31,52],結(jié)果表明到2030年,電力生產(chǎn)水耗將有所降低,但到2050年,若將溫室氣體減排作為約束條件,電力生產(chǎn)水耗會(huì)由于高水耗的低碳技術(shù)的推廣應(yīng)用而增加[31].

(4)歐洲

Behrens等[51]分析了歐洲熱電生產(chǎn)與水資源之間的匹配關(guān)系,發(fā)現(xiàn)到2030年部分流域范圍內(nèi)的熱電企業(yè)會(huì)因?yàn)樗Y源量的減少而降低發(fā)電量.

(5)全球及其他地區(qū)

全球來看,通過提升能源生產(chǎn)技術(shù)的用水效率,特別是可再生能源的用水效率,能源系統(tǒng)水耗到2030年可以降低37%~66%(相對(duì)于2012年)[58].

Parkinson等[59]以成本、水資源可持續(xù)性、和電力部門的CO2為約束,分析了沙特阿拉伯地區(qū)電力生產(chǎn)結(jié)構(gòu)(如燃?xì)獍l(fā)電、太陽(yáng)能發(fā)電、煤電等)、水資源供給結(jié)構(gòu)(地下水、海水淡化、廢水循環(huán)等)、冷卻方式等因素變化對(duì)水-能耦合關(guān)系的影響. Antipova等[56]對(duì)錫爾河流域的水力發(fā)電和農(nóng)業(yè)灌溉用水進(jìn)行優(yōu)化分析,尋求該地區(qū)水電電力供應(yīng)和灌溉水量之間的最佳平衡方式.

1.3 電力生產(chǎn)中節(jié)水潛力分析

學(xué)者們對(duì)電力生產(chǎn)的節(jié)水潛力進(jìn)行了量化分析,包括電力結(jié)構(gòu)的轉(zhuǎn)變帶來的節(jié)水效果[42,60]、電力系統(tǒng)節(jié)能措施帶來的協(xié)同節(jié)水效果[61-63]、電力系統(tǒng)節(jié)能成本等[64].例如Taxes地區(qū)從燃煤發(fā)電到燃?xì)獍l(fā)電的轉(zhuǎn)化帶來的節(jié)水量相當(dāng)于現(xiàn)狀煤電水耗的60%[42];Tucson地區(qū)光伏發(fā)電量增加15%,其電力系統(tǒng)的水耗可以減少17%,同時(shí)還可以減少13%的電力輸送損耗[60].中國(guó)2007~2012能源部門節(jié)能措施的協(xié)同節(jié)水效果主要來自于電力行業(yè),其直接的節(jié)水量約為5.6億m3,上下游相關(guān)產(chǎn)業(yè)的節(jié)水效果為12.5億m3[62].除對(duì)節(jié)水效果絕對(duì)量的考量外,學(xué)者們選取單位節(jié)水量的經(jīng)濟(jì)成本作為指標(biāo),分析電力行業(yè)的節(jié)水潛力[64].

2 電力生產(chǎn)與水資源的空間匹配性研究

學(xué)者們注意到了區(qū)域水資源稟賦與電力生產(chǎn)水耗之間的緊密關(guān)系.研究的空間尺度包括:行政區(qū)域[26,65]、流域?qū)用鎇66]、電網(wǎng)層面[39].例如APEC經(jīng)濟(jì)體中,約55%(437條)的因能源生產(chǎn)帶來的高水資源風(fēng)險(xiǎn)的流域與熱電有關(guān),主要分布于美國(guó)東部、中國(guó)東北部、澳大利亞、俄羅斯西部等地區(qū)[66].學(xué)者對(duì)典型國(guó)家的電力生產(chǎn)與水資源壓力的空間匹配進(jìn)行了更詳細(xì)的分析.例如中國(guó)煤電耗水量占全國(guó)總工業(yè)耗水量的11%,且約75%來自于極度缺水和長(zhǎng)期缺水的地區(qū)[26].美國(guó)東部40%以上的電廠冷卻水耗都取自于缺水地區(qū)[67],到2035年美國(guó)10%~19%的新增熱電企業(yè)有可能會(huì)建在地表/地下水資源缺乏的地區(qū)[65,67].這種水-能矛盾還具有兩個(gè)主要特征:①季節(jié)性差異,一方面是由于季節(jié)性降水差異引起,另一方面是由于冬季結(jié)冰導(dǎo)致可用水量降低,水資源壓力增大[8];②可傳輸性,電力生產(chǎn)和水資源壓力之間的匹配關(guān)系會(huì)隨著電力輸送而產(chǎn)生一定的空間變化,例如中國(guó)水資源較匱乏的東北電網(wǎng)、北方電網(wǎng)、西北電網(wǎng)和中部電網(wǎng)由于電力輸出引起的虛擬水輸出加劇了當(dāng)?shù)氐乃Y源壓力[39,68].總體來看,全球各個(gè)國(guó)家和地區(qū)均存在一定程度的水資源和電力生產(chǎn)空間不匹配的問題,從水-能耦合關(guān)系的角度出發(fā),綜合考慮和評(píng)估未來電力生產(chǎn)布局和水資源稟賦之間的關(guān)系顯得尤為重要.

3 水-能耦合關(guān)系與其他環(huán)境問題

電力行業(yè)是主要的溫室氣體(GHG)排放者,相關(guān)研究主要包括:核算不同能源類型下發(fā)電帶來的GHG排放[15,69-71]、碳捕獲與封存技術(shù)的使用與發(fā)電水耗之間的折中關(guān)系[42]、GHG減排壓力下發(fā)電結(jié)構(gòu)的調(diào)整路徑[59,72]等.除GHG外,電力行業(yè)水-能耦合系統(tǒng)引起的環(huán)境問題還包括冷卻廢水外排時(shí)還會(huì)帶來熱污染問題[1],水力發(fā)電引起的生態(tài)環(huán)境問題[73-74],發(fā)電過程產(chǎn)生的SO2、NO等大氣污染物[19,75].

此外,生物質(zhì)能源的種植占用了大量的土地資源,對(duì)糧食的生產(chǎn)、農(nóng)業(yè)灌溉等均有一定程度的影響[2,76-80].據(jù)估算,全球生物質(zhì)種植消耗了2%~3%的農(nóng)業(yè)用水和用地,相當(dāng)于30%的營(yíng)養(yǎng)不良人口(Malnourished Population)的資源消耗量[2].

除電力生產(chǎn)引起環(huán)境問題外,外界環(huán)境也會(huì)對(duì)水-能耦合關(guān)系有影響.例如干旱不僅會(huì)造成水力發(fā)電的減少,還會(huì)引起地下水使用的增加,從而需要更多的能源(如電力等)提取地下水[81].

現(xiàn)有研究表明,電力行業(yè)水-能耦合系統(tǒng)與環(huán)境問題具有密切的相互作用關(guān)系,但如何量化評(píng)估該作用關(guān)系,進(jìn)一步增加對(duì)耦合系統(tǒng)的認(rèn)識(shí)仍面臨一定的挑戰(zhàn).

4 電力行業(yè)水資源和能源的綜合管理

水、能以及其他環(huán)境要素之間的緊密關(guān)聯(lián)關(guān)系使得單要素的環(huán)境管理措施可能出現(xiàn)偏差.如若維持現(xiàn)有的冷卻技術(shù)不變,中國(guó)東部電網(wǎng)的電力行業(yè)水耗將會(huì)超過“三條紅線”規(guī)定的水耗要求[8].此外,節(jié)能措施的應(yīng)用也可能帶來一定的節(jié)水效果[64].因而多個(gè)要素的綜合管理和核算十分必要[55,82].

學(xué)術(shù)界在水、能綜合管理的方法和框架方面已經(jīng)有初步進(jìn)展.例如以水、能安全為主要目標(biāo)的歐盟COST(European Cooperation in Science and Technology)框架可協(xié)助綜合管理水-能耦合關(guān)系,并制定相應(yīng)的政策制度[83].在模型方面,部分研究試圖將水資源管理和能源管理的相關(guān)模型進(jìn)行結(jié)合,如以電廠水耗數(shù)據(jù)為基礎(chǔ)的ReEDS模型結(jié)合水資源管理模型WEAP,從流域?qū)用嬖u(píng)估發(fā)電對(duì)當(dāng)?shù)厮Y源的影響[84].考慮到水-能耦合關(guān)系具有較高的區(qū)域性特點(diǎn),因此有必要實(shí)施空間差異化管控[85].

5 結(jié)語(yǔ)

對(duì)電力行業(yè)水-能耦合關(guān)系的國(guó)際研究進(jìn)展進(jìn)行了綜述.目前電力行業(yè)水耗分析的研究方法多樣,傳統(tǒng)發(fā)電方式以及可再生能源發(fā)電方式均有關(guān)注.學(xué)者們?cè)诓煌臅r(shí)空尺度下,分別模擬和預(yù)測(cè)了電力生產(chǎn)及其水資源消耗情況,并指出了水資源與發(fā)電量之間的權(quán)衡關(guān)系,量化了電力行業(yè)的節(jié)水潛力.現(xiàn)狀和未來的電力生產(chǎn)和水資源壓力均存在一定的空間不匹配問題,遠(yuǎn)距離輸電更加劇了這種水-能矛盾.此外,電力行業(yè)水-能耦合關(guān)系與溫室氣體排放、大氣污染物排放、生態(tài)系統(tǒng)等有著密切的聯(lián)系.因此,迫切需要綜合評(píng)估水-能耦合關(guān)系與環(huán)境問題,提出空間差異化的水-能耦合系統(tǒng)管控方案.

對(duì)未來關(guān)于電力行業(yè)水-能耦合系統(tǒng)的研究提出以下幾方面建議:①結(jié)合一手?jǐn)?shù)據(jù),研究水-能耦合關(guān)系的區(qū)域特征;②構(gòu)建可推廣的水-能耦合關(guān)系量化分析方法,提供決策支撐;③將水-能耦合關(guān)系研究?jī)?nèi)容延伸到更廣泛的環(huán)境問題上,如水資源匱乏、大氣污染物排放等.

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Review of the studies on the water-energy nexus of the electricity sector.

WANG Chun-yan1, TIAN Lei2, YU Min3, LIU Yi1*

(1.School of Environment, Tsinghua University, Beijing 100084, China；2.Energy Research Institute, National Development and Reform Commission, Beijing 100038, China；3.Institute for Resources and Environmental Policies, Development Research Center of the State council, Beijing 100010, China)., 2018,38(12)：4742~4748

The electricity generation consumes around 8% of global water use. The water use for the electricity generation and transmission is defined as “the water for energy” or “the water-energy nexus of the electricity sector”. This study went through the literatures that are relevant to this topic from the following aspects: the quantification of the water consumption and withdrawal by various electricity generation types; the analysis of the mismatch between electricity generation/transmission and water resources; and other related environmental issues. This study concluded that: the cooling technologies would have significant influence on the water consumption and withdrawal for the electricity generation; there are tremendous spatial disparities of local water resources and electricity generation; comprehensive management of the water and energy is still lacking and urgently needed.

electricity generation；water-energy nexus；water consumption prediction；environmental issues；integrate management

X703.5

A

1000-6923(2018)12-4742-07

王春艷(1991-),女,河南濮陽(yáng)人,博士后,主要研究方向?yàn)樗?能耦合系統(tǒng)分析、環(huán)境系統(tǒng)分析、產(chǎn)業(yè)生態(tài)學(xué).發(fā)表論文3篇.

2018-05-24

國(guó)家自然科學(xué)基金資助項(xiàng)目(71774096);國(guó)家重點(diǎn)研發(fā)計(jì)劃項(xiàng)目(2017YFC0404602)

* 責(zé)任作者, 教授, yi.liu@mail.tsinghua.edu.cn