1.引言
太(tai)(tai)(tai)陽(yang)(yang)(yang)能(neng)(neng)作為一種可(ke)再生的(de)清潔能(neng)(neng)源(yuan),在(zai)能(neng)(neng)源(yuan)環境領域越來越受(shou)到重視,太(tai)(tai)(tai)陽(yang)(yang)(yang)能(neng)(neng)發電(dian)已經(jing)成為太(tai)(tai)(tai)陽(yang)(yang)(yang)能(neng)(neng)大規模利(li)(li)用(yong)的(de)主要方式。在(zai)未來的(de)可(ke)再生能(neng)(neng)源(yuan)利(li)(li)用(yong)中,太(tai)(tai)(tai)陽(yang)(yang)(yang)能(neng)(neng)熱發電(dian)作為一種太(tai)(tai)(tai)陽(yang)(yang)(yang)能(neng)(neng)利(li)(li)用(yong)技術具有廣闊(kuo)的(de)發展前景(jing)。
太陽(yang)(yang)(yang)能(neng)(neng)(neng)(neng)(neng)(neng)(neng)熱(re)(re)(re)發(fa)(fa)電(dian)的(de)(de)(de)原理(li)是先(xian)將太陽(yang)(yang)(yang)能(neng)(neng)(neng)(neng)(neng)(neng)(neng)轉化為(wei)(wei)熱(re)(re)(re)能(neng)(neng)(neng)(neng)(neng)(neng)(neng),再將熱(re)(re)(re)能(neng)(neng)(neng)(neng)(neng)(neng)(neng)轉化為(wei)(wei)電(dian)能(neng)(neng)(neng)(neng)(neng)(neng)(neng)的(de)(de)(de)發(fa)(fa)電(dian)技(ji)術,但由(you)于太陽(yang)(yang)(yang)能(neng)(neng)(neng)(neng)(neng)(neng)(neng)的(de)(de)(de)密度(du)較(jiao)低,溫(wen)度(du)通常(chang)情(qing)況下低于100℃,需要(yao)(yao)(yao)較(jiao)大(da)的(de)(de)(de)采(cai)光集熱(re)(re)(re)面(mian)通過聚(ju)光改變(bian)光線(xian)傳播方向,使光線(xian)聚(ju)焦以(yi)提(ti)高(gao)能(neng)(neng)(neng)(neng)(neng)(neng)(neng)量密度(du),才能(neng)(neng)(neng)(neng)(neng)(neng)(neng)滿足發(fa)(fa)電(dian)要(yao)(yao)(yao)求。聚(ju)光器作為(wei)(wei)光熱(re)(re)(re)發(fa)(fa)電(dian)系(xi)統(tong)中將太陽(yang)(yang)(yang)能(neng)(neng)(neng)(neng)(neng)(neng)(neng)進(jin)行聚(ju)集以(yi)增加能(neng)(neng)(neng)(neng)(neng)(neng)(neng)量密度(du)的(de)(de)(de)裝置,對聚(ju)光太陽(yang)(yang)(yang)能(neng)(neng)(neng)(neng)(neng)(neng)(neng)熱(re)(re)(re)發(fa)(fa)電(dian)的(de)(de)(de)效(xiao)率(lv)起著(zhu)十分(fen)重要(yao)(yao)(yao)的(de)(de)(de)作用,通過聚(ju)光器將低密度(du)的(de)(de)(de)太陽(yang)(yang)(yang)能(neng)(neng)(neng)(neng)(neng)(neng)(neng)聚(ju)焦后轉換成(cheng)(cheng)(cheng)高(gao)密度(du)的(de)(de)(de)太陽(yang)(yang)(yang)能(neng)(neng)(neng)(neng)(neng)(neng)(neng),再經傳熱(re)(re)(re)介質(zhi)將太陽(yang)(yang)(yang)能(neng)(neng)(neng)(neng)(neng)(neng)(neng)轉化為(wei)(wei)熱(re)(re)(re)能(neng)(neng)(neng)(neng)(neng)(neng)(neng),然后通過熱(re)(re)(re)力(li)循環做功實(shi)現(xian)由(you)熱(re)(re)(re)能(neng)(neng)(neng)(neng)(neng)(neng)(neng)到(dao)(dao)電(dian)能(neng)(neng)(neng)(neng)(neng)(neng)(neng)的(de)(de)(de)轉換。由(you)于太陽(yang)(yang)(yang)輻射不穩定,受晝夜、季(ji)節、地理(li)位置和氣候條件的(de)(de)(de)影(ying)響(xiang)波動(dong)較(jiao)大(da),造(zao)成(cheng)(cheng)(cheng)光熱(re)(re)(re)發(fa)(fa)電(dian)系(xi)統(tong)效(xiao)率(lv)低而成(cheng)(cheng)(cheng)本高(gao)。目(mu)前利(li)用太陽(yang)(yang)(yang)能(neng)(neng)(neng)(neng)(neng)(neng)(neng)進(jin)行聚(ju)光熱(re)(re)(re)發(fa)(fa)電(dian)的(de)(de)(de)形式(shi)(shi)主要(yao)(yao)(yao)有(you)槽(cao)式(shi)(shi)、塔(ta)式(shi)(shi)、碟式(shi)(shi)、菲涅爾式(shi)(shi)等(deng),幾種發(fa)(fa)電(dian)方式(shi)(shi)并(bing)存并(bing)各(ge)自進(jin)行發(fa)(fa)展,但投入商業(ye)化運(yun)營的(de)(de)(de)光熱(re)(re)(re)發(fa)(fa)電(dian)技(ji)術主要(yao)(yao)(yao)是塔(ta)式(shi)(shi)和槽(cao)式(shi)(shi)光熱(re)(re)(re)發(fa)(fa)電(dian)。理(li)論(lun)上塔(ta)式(shi)(shi)效(xiao)率(lv)可以(yi)達到(dao)(dao)23%,但由(you)于單位容量投資大(da),商業(ye)化程度(du)不及槽(cao)式(shi)(shi)太陽(yang)(yang)(yang)能(neng)(neng)(neng)(neng)(neng)(neng)(neng)發(fa)(fa)電(dian)[1],隨著(zhu)科學(xue)技(ji)術的(de)(de)(de)不斷(duan)進(jin)步(bu)和產品的(de)(de)(de)日趨成(cheng)(cheng)(cheng)熟(shu),投資成(cheng)(cheng)(cheng)本也會不斷(duan)降低,會成(cheng)(cheng)(cheng)為(wei)(wei)今后一段時期(qi)光熱(re)(re)(re)發(fa)(fa)電(dian)重點研發(fa)(fa)和利(li)用形式(shi)(shi)。
2.一次聚光塔式光熱發電及其缺點
目前塔式光熱(re)發電系統對于(yu)太(tai)陽(yang)光的(de)(de)聚集和反(fan)(fan)射(she)多采用(yong)一次反(fan)(fan)射(she),即通過鏡場將太(tai)陽(yang)輻(fu)(fu)射(she)聚集到(dao)距離地(di)面(mian)一定高(gao)度的(de)(de)吸熱(re)器(qi)上,吸熱(re)器(qi)直接接受(shou)地(di)面(mian)鏡場反(fan)(fan)射(she)的(de)(de)太(tai)陽(yang)輻(fu)(fu)射(she),吸熱(re)器(qi)中(zhong)(zhong)的(de)(de)傳熱(re)介質(熔融巖)獲(huo)得高(gao)溫熱(re)能,獲(huo)取熱(re)量的(de)(de)傳熱(re)介質通過管道(dao)將輸(shu)送(song)到(dao)熱(re)能地(di)面(mian)儲熱(re)罐(guan),儲熱(re)罐(guan)中(zhong)(zhong)的(de)(de)高(gao)溫傳熱(re)介質再(zai)通過管道(dao)輸(shu)送(song)到(dao)蒸汽發生(sheng)器(qi)產生(sheng)蒸汽推動汽輪機(ji)發電。這(zhe)一系統中(zhong)(zhong),鏡場中(zhong)(zhong)的(de)(de)各定日鏡對于(yu)中(zhong)(zhong)心吸熱(re)塔有(you)著不同的(de)(de)朝向和距離,對每個定日鏡的(de)(de)跟蹤都要進行單獨的(de)(de)二(er)維控制(zhi),且(qie)各定日鏡的(de)(de)控制(zhi)各不相(xiang)同,極大增加了控制(zhi)系統的(de)(de)復雜性(xing)和安裝調(diao)試的(de)(de)難度[1—3]。
采用該(gai)種方式布(bu)(bu)置(zhi)(zhi)(zhi)的(de)吸(xi)(xi)熱(re)(re)器(qi)(qi),由于(yu)距(ju)離地面的(de)高度往往在(zai)100m以上,隨著高度增(zeng)加(jia)風速也(ye)是不斷增(zeng)大(da)(da),在(zai)吸(xi)(xi)熱(re)(re)器(qi)(qi)附近風速肯定大(da)(da)于(yu)地面,吸(xi)(xi)熱(re)(re)器(qi)(qi)外表面對流熱(re)(re)損(sun)較大(da)(da),熱(re)(re)量損(sun)失(shi)較大(da)(da);吸(xi)(xi)熱(re)(re)器(qi)(qi)高空布(bu)(bu)置(zhi)(zhi)(zhi),管(guan)道(dao)較長,熱(re)(re)量從吸(xi)(xi)熱(re)(re)器(qi)(qi)到地面進行管(guan)道(dao)輸送,存在(zai)熱(re)(re)量損(sun)失(shi),熱(re)(re)效率較低(di)(di),同時需(xu)配置(zhi)(zhi)(zhi)高揚程循(xun)環泵(beng)、建(jian)設吸(xi)(xi)熱(re)(re)器(qi)(qi)基礎(chu)及塔(ta)體(ti),設備購置(zhi)(zhi)(zhi)成(cheng)本(ben)、建(jian)設成(cheng)本(ben)增(zeng)加(jia),運行期場用電量也(ye)隨之增(zeng)加(jia);吸(xi)(xi)熱(re)(re)器(qi)(qi)施工安裝和后(hou)期運維難度及安全風險較大(da)(da),運行維護費用加(jia)大(da)(da),電站(zhan)建(jian)成(cheng)后(hou)的(de)運行期間(jian)的(de)經濟性相對降低(di)(di)。這些都成(cheng)為(wei)制約一次(ci)反射塔(ta)式太陽(yang)能熱(re)(re)發電大(da)(da)規模發展(zhan)的(de)因素。
由(you)于吸熱(re)(re)器(qi)是塔式光(guang)熱(re)(re)發電系(xi)統(tong)的(de)(de)(de)核(he)心設備[5—8],在一(yi)(yi)次(ci)(ci)(ci)反(fan)射(she)系(xi)統(tong)中(zhong)吸熱(re)(re)器(qi)位于100m以上的(de)(de)(de)高(gao)(gao)空,建筑成本(ben)、運行維護成本(ben)較(jiao)高(gao)(gao),同(tong)時(shi)運行過程中(zhong)也存在較(jiao)高(gao)(gao)的(de)(de)(de)安(an)全風險,為(wei)了彌補(bu)這(zhe)些不(bu)足,于是便出現了二(er)(er)次(ci)(ci)(ci)反(fan)射(she)系(xi)統(tong)的(de)(de)(de)設計。二(er)(er)次(ci)(ci)(ci)反(fan)射(she)是在一(yi)(yi)次(ci)(ci)(ci)聚(ju)光(guang)系(xi)統(tong)的(de)(de)(de)焦點處安(an)裝(zhuang)所需的(de)(de)(de)光(guang)學元(yuan)件(jian),用(yong)以改變一(yi)(yi)次(ci)(ci)(ci)系(xi)統(tong)匯聚(ju)后光(guang)線的(de)(de)(de)傳(chuan)播方(fang)向(xiang),將(jiang)光(guang)線反(fan)射(she)到地(di)(di)面(mian)吸熱(re)(re)器(qi)。最主要的(de)(de)(de)不(bu)同(tong)在于吸熱(re)(re)器(qi)位于地(di)(di)面(mian),塔架上布置二(er)(er)次(ci)(ci)(ci)反(fan)射(she)裝(zhuang)置,即(ji)通(tong)過在高(gao)(gao)空塔架上布置二(er)(er)次(ci)(ci)(ci)反(fan)射(she)裝(zhuang)置,將(jiang)太(tai)陽光(guang)經(jing)定(ding)日鏡反(fan)射(she)到二(er)(er)次(ci)(ci)(ci)反(fan)射(she)裝(zhuang)置,再經(jing)二(er)(er)次(ci)(ci)(ci)反(fan)射(she)裝(zhuang)置聚(ju)焦位于地(di)(di)面(mian)的(de)(de)(de)吸熱(re)(re)器(qi)上[9—10]。這(zhe)一(yi)(yi)系(xi)統(tong)中(zhong),光(guang)線傳(chuan)播距離較(jiao)一(yi)(yi)次(ci)(ci)(ci)反(fan)射(she)系(xi)統(tong)增加,但輸熱(re)(re)管(guan)道的(de)(de)(de)距離卻縮短,兩個系(xi)統(tong)的(de)(de)(de)能量傳(chuan)遞方(fang)式不(bu)同(tong),能量損失(shi)也有別。
塔(ta)式光熱(re)發電(dian)的(de)光電(dian)轉換效(xiao)(xiao)(xiao)率(lv)(lv)決定于鏡場年均(jun)(jun)光學效(xiao)(xiao)(xiao)率(lv)(lv)、鏡場年均(jun)(jun)運行效(xiao)(xiao)(xiao)率(lv)(lv)、吸熱(re)器(qi)效(xiao)(xiao)(xiao)率(lv)(lv)、儲熱(re)器(qi)系統效(xiao)(xiao)(xiao)率(lv)(lv)、管(guan)道效(xiao)(xiao)(xiao)率(lv)(lv)、蒸(zheng)汽換熱(re)效(xiao)(xiao)(xiao)率(lv)(lv)、汽輪發電(dian)機組效(xiao)(xiao)(xiao)率(lv)(lv)等因(yin)素(su),其(qi)中(zhong)鏡場光學效(xiao)(xiao)(xiao)率(lv)(lv)由鏡面(mian)效(xiao)(xiao)(xiao)率(lv)(lv)、余弦損失、陰影(ying)和(he)阻(zu)擋損失、大氣(qi)衰減、截(jie)斷因(yin)子等因(yin)素(su)有(you)關(guan)。二(er)次(ci)反(fan)射系統相對(dui)于一(yi)次(ci)反(fan)射系統而言,鏡場年均(jun)(jun)光學效(xiao)(xiao)(xiao)率(lv)(lv)相對(dui)略微降低,吸熱(re)器(qi)效(xiao)(xiao)(xiao)率(lv)(lv)及管(guan)道效(xiao)(xiao)(xiao)率(lv)(lv)顯著增加,其(qi)它因(yin)素(su)變化(hua)不(bu)大,在(zai)此忽略。