Reliability analysis of Solar-Gas Hybrid Receivers for central tower plants

1876-6102 © 2015 The Au ho s. Published by Else ie L d. This is an open access a icle unde he CC BY-NC-ND license (h p://c ea i ecommons.o g/licenses/by-nc-nd/4.0/). Pee e iew by he scien i ic con e ence commi ee o Sola PACES 2014 unde esponsibili y o PSE AG doi: 10.1016/j.egyp o.2015.03.108 In e na ional Con e ence on Concen a ing Sola Powe and Chemical Ene gy Sys ems, Sola PACES 2014 Reliabili y analysis o Sola -Gas Hyb id Recei e s o cen al owe plan s E. Se iena,*, M. F asque a, G. Salioua, M. Sil aa, G. Pinnaa, R. Blázqueza V. Ruiza aCTAER, Sola Depa men , Pa aje Re ama es s/n, 04200, Tabe nas – Alme ia (SPAIN). Abs ac A no el Sola -Gas Hyb id Recei e (SGHR) ha combines he unc ion o a sola ecei e and a gas boile in a single de ice is p esen ed. This concep equi es less equipmen and main enance compa ed o he Sola Gas Hyb id (SGH) concep , in which he boile and he sola ecei e (SR) a e independen de ices. The economic bene i is a ibu ed o he inc eased sha ing o in as uc u es. Addi ionally, i has less he mal s ess, cycles and shocks, which educe he ailu e isk. Howe e , he addi ional bene i in he eliabili y o hese ecei e s has no been analyzed so a . In his wo k, a ma hema ical model o SGHR is p esen ed. I de e mines he s ess in s eady s a e which is used o es ima e he allowable ansien s ess in o de o achie e he equi ed 30 yea s li e design. The esul s show ha he SGHR is exposed o lowe he mal s ess due o much be e empe a u e dis ibu ion. Mo eo e he highe abso be hea lux o SGHR is ansla ed in a highe mechanical s ess wi h could jeopa dizes he du abili y. Howe e he educed numbe o cycles and he lowe he mal s ess o a SGHR allows highe ansien s esses han he con en ional ube ype sola ecei e , which lead o mo e eliable and e icien designs. © 2015 The Au ho s. Published by Else ie L d. Pee e iew by he scien i ic con e ence commi ee o Sola PACES 2014 unde esponsibili y o PSE AG. Keywo ds: hyb id, ecei e , sola , Gas, eliabili y, Mol en Sal s. 1. In oduc ion The la ge amoun o sola ene gy ha eaches he ea h is high enough o p o ide all o he wo ld’s ene gy demands. The use o Cen al Recei e Sys em (CRS) o ans o m his ene gy in o elec ici y is a good ini ia i e o * Co esponding au ho . Tel.: +34 950066052 E-mail add ess: [email p o ec ed]om © 2015 The Au ho s. Published by Else ie L d. This is an open access a icle unde he CC BY-NC-ND license (h p://c ea i ecommons.o g/licenses/by-nc-nd/4.0/). Pee e iew by he scien i ic con e ence commi ee o Sola PACES 2014 unde esponsibili y o PSE AG E. Se ien e al. / Ene gy P ocedia 69 ( 2015 ) 1558 – 1567 1559 educe he ossil uels dependence and a he same ime educe he CO2 emission. Howe e , only a small amoun o he wo ld’s ene gy comes di ec ly om CRS, mainly due o he high ini ial in es men and he echnological isk. On one hand, he o emos cos is associa ed o he la ge helios a ield equi ed o collec he sola ene gy (1). On he o he hand, he echnological isk is mainly associa ed o he eliabili y o he ecei e and o he a iabili y o he sola adia ion h oughou he day, which means he equi emen o a s o age sys em o a oid he in e mi ence and non-dispa chabili y o powe p oduc ion. In his wo k, hyb id ecei e s Sola - biomass gases a e p esen ed as a po en ial solu ion o o e coming he cos , eliabili y and in e mi ency issues. Bo h ene gy sou ces su e om high cos s. Howe e , hei hyb idiza ion is in e es ing due o i s complemen a y na u e. On one hand, sola he mal ene gy has high cos s due o he in e mi en na u e bu he uel i sel has ze o cos s. On he o he hand, he biomass gasses supply is no in e mi en bu he uel cos s a e high. The e o e, he hyb idiza ion o sola and Biogas uels allows o inc ease he dispa chabili y o only sola powe plan s and dec ease he cos s due o he sha ing o in as uc u es. Mo eo e , his concep can be ex ended o cheape ossil uels in o de o achie e a mo e economic ene gy supply. The e o e om now on will be called Sola -Gas hyb idiza ion. Many Sola -Gas hyb idiza ion sys ems ha e been p oposed by se e al au ho s and e iewed in (2). An exhaus i e e iew o he possible in eg a ion sys ems has been done in a p e ious p ojec (3) and i has been selec ed he one wi h he highe po en ial o o e come he cos , he eliabili y and in e mi ence issues. The selec ed in eg a ion sys em is shown in Fig.1. The unc ion o a ube ype sola ecei e (TTR) and a gas boile a e combined in a single de ice, hence o h called Sola -Gas Hyb id Sola Recei e (SGHR).The combus ion o he gas is ca ied ou a he SGHR simul aneously o consecu i ely wi h he sola adia ion. I s hea is used o inc ease he he mal powe o he Hea T ans e Fluid (HTF) and o a oid he sola adia ion dependence. Then, he hea exchange (HE) ans e s he he mal powe o he HTF o he s eam o he Powe Block (PB). Thus he in eg a ion o he gas boile and he sola ecei e in o a single de ice dec ease he amoun o equipmen equi ed o achie e dispa chable ene gy supply wi hou he need o ene gy s o age. Mo eo e , he ope a ion o he combus ion sys em is independen on he adian ene gy a ailabili y, which p e en s SGHR om he mal shocks due o sola adia ion in e mi ence. Fu he mo e, he homogenous empe a u e eached a he ecei e a oids as deg ada ion o he SGHR, inc easing he eliabili y o he plan . Fig. 1.In eg a ion sys em o an HRC. PB SG HR Combus ion o gas  HE Concen a ed sola adia ion 1560 E. Se ien e al. / Ene gy P ocedia 69 ( 2015 ) 1558 – 1567 I is impo an o highligh ha he ubes, which compose he Hea Collec o Elemen (HCE), o a con en ional TTR wo k no only a high he mal and mechanical s ess bu also endu e daily empe a u e incu sion om high ope a ion empe a u e o ambien empe a u e. These se e e condi ions ac i a e deg ada ion mechanisms such as: low cycle a igue, oxida ion a high empe a u es and c eep (4). Al hough he economic bene i s o a simila concep using na u al gas ins ead o biomass gasses we e p o ed in (1), he addi ional bene i o inc eased eliabili y due o educed he mal cycling and he mal s ess has no been analyzed ye and i is wha in his pape is p esen ed. The cons uc i e de ails o he no el SGHR a e desc ibed in de ail and a compa ison o i s eliabili y by means o , s eady s a e he mal s ess, mechanical s ess and allowable ansien s s ess is ca ied ou wi h espec o he well-known TTR, unde simila condi ions. Fo his pu pose, a he mo hyd aulic model o he HCE o bo h de ices is p esen ed. This ma hema ical model ob ains he he mal and mechanical s ess in s eady s a e ope a ion i s ly. Then, hese esul s a e used o es ima e he allowable ansien s ess in o de o achie e he equi ed 30 yea li e design. Nomencla u e Q Powe (W) W Wo k (W) h En halpy (J/Kg) V Veloci y (m/s) g G a i y (m/s2) A A ea (m2) Comb Combus ion ube con Con ec ion ad Radia ion Amb Ambien losses Sky Radia ion o he Sky Sun Sun adia ion m Mass lows (Kg/s) Cp Hea capaci y (KJ/KgºC) I diame e (m) adius (m) in Inne ou Ou e T Tempe a u e (ºC) Poisson a io E Modulus o elas ici y (N/mm2) D The mal expansion coe icien (10í6mm/mm/°C) V S ess (N/mm2) P p essu e (N/mm2) 2. Concep desc ip ion The p esen ed SGHR is composed by a ca i y, a billboa d TTR, mol en sal s as HTF, wo combus ion chambe s (in on o and behind he TTR), a ume exhaus duc , and a mobile enclosu e (as seen in Fig. 2). This disposi ion allows hea o ans e o he ubes, he HCE, om bo h sides, educing he he mal s ess p oduced by ci cum e en ial he mal g adien . On one hand, he on ace o he ubes is hea ed by sola adia ion and combus ion consecu i ely in his way: when he di ec no mal i adiance (DNI) is high enough, he ecei e ’s on ace is hea ed by he sola ield, and when DNI is no enough o main ain he ope a ion, he mobile enclosu e closes E. Se ien e al. / Ene gy P ocedia 69 ( 2015 ) 1558 – 1567 1561 he ca i y and he ubes’ on ace is hea ed by he combus ion chambe . On he o he hand, he back ace o he ubes is hea ed by gas combus ion con inuously. Such combus ion is ca ied ou in adian bu ne s ha allow he spa ial dis ibu ion o he adian lux o a y o he equi ed le el. Finally, he combus ion gases a e add essed o a hea exchange in o de o eco e i s hea . Fig. 2: SGHR componen s ep esen a ion. Al hough any o HTF usually used in TTR could be used in a SGHR, mol en sal s ha e been selec ed in his s udy due o he comple e da a base a ailable in li e a u e. 2.1. Ma hema ical model A ma hema ical model has been de eloped in o de o e alua e he SGHR eliabili y in compa ison wi h he con en ional TTR. Fo his pu pose, he he mal and mechanical s ess in s eady s a e and he allowable ansien s ess o a gi en numbe o cycles ha e been de e mined. Fi s ly, he empe a u e g adien and p essu e dis ibu ion a e ob ained. Secondly, he he mal and mechanical s esses in s eady s a e ope a ion a e de e mined. And inally, he allowable ansien s ess o he p edic ed numbe o cycles is calcula ed using a li e es ima ion me hod. The empe a u e g adien is ob ained by a s eady s a e modeling app oach based on an ene gy balance on he HCE. I includes he combus ion hea and/o concen a ed sola adia ion, he op ical and he he mal losses om he HCE and he he mal gains in he HTF. The he mal model has been sol ed using he Fini e Volume me hod (FVM) o disc e ize he domain and he ene gy conse a ion is applied a each con ol olume (CV). As he empe a u e and p essu e o he HTF a ies only in longi udinal di ec ion, he HTF has been di ided in o NzCVs o equal leng h wi h empe a u e and p essu e con inui y a he bounda ies (see Fig. 3). On he o he hand, he me al empe a u e and hea lux a ies along ci cum e en ial and longi udinal di ec ion. Consequen ly he ube has been di ided in o NzCVs in he axial di ec ion and N݇CVs in he azimu hal di ec ion (see Fig. 3). The ene gy balance equa ion is de e mined by Eq. (1) a each CV: ³³ ¸ ¸ ¹ · ¨ ¨ © § w w   c cs d gz u dA gz hWQ )( 2 ))( 2 ( 22 UU   (1) Fo a CV o he ube, he ene gy balance equa ion is gi en by Eq. 2. The me al p ope ies dependence on he empe a u e was upda ed while i e a i ely sol ing he p oblem. 1562 E. Se ien e al. / Ene gy P ocedia 69 ( 2015 ) 1558 – 1567 0 .,,.,,, ,    ¦ij con HTF ij adSky ij con Amb ij ad sun ij ad comb con comb ij c ij qqqqqqq  (2) Fo a HTF CV‘’' o leng h L, he ene gy balance can be exp essed as gi en in Eq 3.The ans e ed hea ( i con h q, ) o he HTF by he ube CVs has been summed up along he ci cum e ence o each ‘i’ ing using he a ea and empe a u e o he acco ding ‘j’ elemen . The luid empe a u e, he empe a u e dependen p ope ies and he hea ans e coe icien o he nex HTF CV was calcula ed using he ans e ed hea o he p e ious HTF CV. Fully de eloped low and hea ans e a e conside ed. Unlike in he o me analysis o he sola ecei e ubes, aniso opy o u bulen ene gy anspo has been aken in o accoun by employing heo e ical esul s om he Eddy di usi i y in he di e en di ec ions which a e in sa is ac o y ag eemen wi h expe imen al da a (5). >@>@ 11 ,     i HTF i HTF i HTF i HTF i con HTF TTCpmhhmq  (3) Fig. 3.Disc e izi a ion and ene gy balance o he HCE: a) Longi udinal disc e iza ion, b) ene gy balance a HTF CV, c) azimu hal disc e iza ion, d) ene gy balance a he ube CV. The ci cum e en ial hea lux along he ube wall can be conside ed negligible and he e o e he ou e and inne su ace empe a u e o each me al CV can be calcula ed as: h qTT in ou ij con HTF iij in HTF 1 ., I I    (4) ¸ ¸ ¹ · ¨ ¨ © §   in ou ou ij con HTF ij in ij K qTTou I II T ln 2 )( .,  (5) The s ess due o he HCE empe a u e di e ence in axial di ec ion can be elie ed by ca e ully designed s ain elie s uc u es. Howe e , he s ess due o he c oss-wall empe a u e di e ence is di icul o a oid since i is he d i ing o ce o he hea ans e . In consequence he he mal s ess is analyzed as plane- adial s ess p oblem. The mal s ess in he HCE appea s due o he empe a u e di e ence ac oss he ube hickness and he ci cum e en ial ube empe a u e di e ence. In absen o s ess elaxa ion, he empe a u e g adien in he ube wall makes he ou side o expand mo e han he inside which places he ou side unde comp ession and he inside unde E. Se ien e al. / Ene gy P ocedia 69 ( 2015 ) 1558 – 1567 1563 ension. This balanced s ess g adien is biaxial in he z (axial) and ݇ ( angen ) di ec ions. The maximum he mal g adien s ess alues occu a he su aces and a e exp essed as: » » ¼ º « « ¬ ª ¸ ¸ ¹ · ¨ ¨ © §     a g ijijijij ijij T TT TT Einou inou hz h 2)1(2 max,,max,, DVV T (6) The p essu e a ia ion along he segmen “i” is calcula ed as he sum o ic ion losses, e ical heigh di e ence and p essu e change due o accele a ion o he luid as shown in Eq 8.   ax gz P ii P i P i in ic iGzgsenG z P '  ' ' ' ' ' )/1()()2/()( 122 UUDUU I (7) Whe e ic is he Da cy ic ion ac o , and can be es ima ed o a u bulen pipe low wi h he Coleb ook equa ion. Tube ype ecei e s a e composed o se e al ubes a anged in pa allel, wi h he o al head loss ac oss he sys em being cons an . Howe e , due o he he e ogenei y o he sola lux dis ibu ion, each ube ecei es di e en amoun s o hea being he ou le empe a u e and p essu e o each ube di e en o he same inle condi ions. The e o e, he mass low a e a he inle o he ube has been adap ed o each ube wi h an i e a i e algo i hm in o de o achie e cons an head loss. Mechanical s ess induced in he ube is di ec ly p opo ional o he ope a ing p essu e o he HTF and i is calcula ed om: inou ou i ou in i in PP zP II II V   , (8)  )( 22 2 22 ,, ou in i ou i inou in zPP PP II II VV T    (9)  )( 22 2 22 ,, ou in i ou i inou in zP P PP II II VV    (10) Finally, he allowable ansien s ess o a equi ed 30 yea li e design has been de e mined wi h a well- es ablished li e p edic ion model based in UNE-EN 12952-3:2001 no m, which conside s he deg ada ion due o c eep, he mo-mechanical a igue, and oxida ion a high empe a u e. The ansien s ess is ob ained sub ac ing he s eady s a e s ess o he a igue s eng h o he es ima e numbe o cycles.Fa igue, oxida ion and c eep esis ance a high empe a u e a e a ailable om se e al sou ces. In his wo k he du abili y limi s es ablished by he UNE-EN 12952-3:2001 no m ha e been used. The men ioned no m is applicable o high empe a u e p essu e essels up o 800ºC. Mo eo e , in o de o conside he e ec o h ee mechanisms, a damage accumula ion me hod has been used. 1564 E. Se ien e al. / Ene gy P ocedia 69 ( 2015 ) 1558 – 1567 In o de o sol e he ma hema ical model, he p esen ed equa ions ha e been implemen ed wi hin he Visual Basic en i onmen . The inpu s equi ed in he model a e: HTF inle p essu e, empe a u e and mass low a es, inside and ou side diame e ube, ube’s ma e ial, numbe o cycles and hea lux spa ial dis ibu ion. The same HTF inle empe a u e has been conside ed o bo h, he TTR and he SGHR. Howe e he numbe o cycles and hea lux spa ial dis ibu ion a e conside ed di e en due o he speci ic ope a ion condi ion o each compa ed elemen . Rega ding he ope a ion condi ions o bo h ecei e s, i is desc ibed as ollows. In he case o he TTR: du ing a sunny day he Di ec No mal I adiance (DNI) is concen a ed by he sola ield in he HCE on ace while he back ace is no illumina ed. The non-uni o m adia ion dis ibu ion along he ou side HCE is shown in Fig. 4 (a). The longi udinal dis ibu ion has been ob ained wi h WinDelsol so wa e conside ing one aiming poin s a egy and maximum adia ion peak o 1200 kW/m2. A small amoun o he concen a ed sunligh is e lec ed by HCE su ace and he high abso p i i y coa ing abso bs he emaining. A pa o he gained hea is ans e ed o he HTF by o ced con ec ion, ac oss he wall hickness by conduc ion and he o he pa is los by na u al con ec ion and he mal adia ion o he ambien in he on ace while he back ace emains adiaba ic. A TTR mus ope a e cyclically due o i s na u e. I is hea ed o each he ope a ion empe a u e and hen i is allowed o elax up o he he mal equilib ium a leas daily. In addi ion, he TTR is cooled due o clouds and hea ed again se e al imes pe day. 36.000 cycles ha e been conside ed o a design li e o up o 30 yea s. In he case o he SGHR: du ing a sunny day he DNI is concen a ed by he sola ield in he HCE on ace. A he same ime, he hea p oduced in he combus ion chambe eaches he HCE back ace by adia ion. The adia ion ci cum e en ial dis ibu ion is shown in Fig. 4 (b). A small amoun o he concen a ed sunligh is e lec ed by HCE su ace and he emaining is abso bed by he high abso p i i y coa ing. A pa o he gained hea is ans e ed o he HTF by o ced con ec ion, ac oss he wall hickness by conduc ion and he o he pa is los by na u al con ec ion and he mal adia ion o he ambien in he on ace. When he DNI is no high enough o main ain he ope a ion he mobile enclosu e closes he ca i y, and he ubes on ace a e hea ed by he on adian bu ne s. The e o e, he only he mal cycles o he SGHR will be du ing he main enance and echnical shu -downs o he plan . In his case, 60 cycles ha e been conside ed. Fig. 4. Ci cum e en ial hea gain: a) TTR. b) SGHR 3. Resul s The TTR and SGHR eliabili y has been compa ed by means o s eady s a e ope a ion s ess and he allowable ansien s ess o a design li e o 30 yea s. The HCE o he TTR and SGHR a e composed by 10 me e longs panels a anged in se ies. The panels a e composed by aus eni ic s ainless s eel, BS3059 g ade CFS1250 ubes a anged in pa allel wi h 25mm ou side diame e and 2 mm o wall hickness ha is in he usual ange o TTR (6). The mol en sal s empe a u e a he inle o he i s panel has been ixed in 300 ºC and he mass low a e and inle p essu e ha e been adap ed in o de o achie e 565ºC and 5 ba o p essu e a he ou le o he 2nd, 3nd o 5nd panel. Fig. 5 shows he empe a u e e olu ion o HTF CV along he 2, 3 o 5 panels. As can be seen, he empe a u e e olu ion o TTR and SGHR a e supe posed o he 3 cases. Howe e , he mass low a e o he SGHR is almos he E. Se ien e al. / Ene gy P ocedia 69 ( 2015 ) 1558 – 1567 1565 double in all he cases due o he ac ha hea gain is wice han o TTRs. The e o e o a same panel o ubes he SGHR p oduces he double o he mal ene gy. Fig 5. HTF CV empe a u e dis ibu ion along he TTR and SGHR o 2, 3 and 5 panels. Ne e heless, a highe mass low a e o he same ube diame e esul s in highe p essu e d ops. The inle p essu e mus be highe o SGHR han o he TTR as he ou le p essu e has been de ine as a cons an alue o 5 ba s. High inle p essu e can p oduce signi ican ly high mechanical s ess. Fig. 6 shows he dis ibu ion o mechanical s ess p oduced by HTF p essu e in he ou e c own o he ube. As consequence o he high low a e equi ed o abso b he hea lux, SGHR wi hs ands highe mechanical s ess and he e o e i s eliabili y can be jeopa dized. No e ha in o de o each 5 ba in he ou le p essu e, he inle p essu e mus be 26.4 o he 5 panels which co espond o 145 N/m2 unlike in he case o 2 panels TTR ha equi e an inle p essu e o 9.5 ba ., which co esponds o 53 N/m2 in he ube. Fig 6. Tube ou side c own mechanical s ess dis ibu ion along he TTR and SGHR o 2, 3 and 5 panels. On he o he hand, he mal s ess is lowe o SGHR han o TTR. The he mal s ess a ies wi h hea lux dis ibu ion and is maximal a he peak adia ion posi ion.Fig. 7 shown he maximum he mal s ess e olu ion along 1566 E. Se ien e al. / Ene gy P ocedia 69 ( 2015 ) 1558 – 1567 he panels. E en i he hea gain is doubled o SGHR, he he mal s ess is lowe o all he cases. Tha is due o he ac ha he empe a u e dis ibu ion in he SGHR is mo e homogenous han in he TTR. Fig. 7.Maximun he mal s ess dis ibu ion o he mos i adia ed CV along he TTR and SGHR o 2, 3 and 5 panels. Finally, he s eady s a e s ess and he numbe o cycles a e used o de e mine he allowable s ess in ansien s. Fig. 8 shows ha he allowable s ess is much highe in SGHR han in a TTR, so he SGHR is mo e eliable han he TTR and he s a -up and shu down can be done as e . Mo eo e , he 2 and 3 panels TTRs allowable s ess each ze o alue in he adia ion peak lux zone. The e o e his TTR design will no wi hs and he equi ed numbe o cycles o he gi en 30 yea s o ope a ion. Fig 8 Allowable ansien s ess o he mos i adia ed CV along he TTR and SGHR o 2, 3 and 5 panels. 4. Conclusions The cons uc i e de ails o a no el hyb id Sola -Gas ecei e ha e been p esen ed. In o de o e alua e i s eliabili y i has been compa ed wi h espec o he well-known TTR by means o he e alua ion o he s eady s a e ope a ion s ess and he allowable ansien s ess o a design li e o 30 yea s. Fo ha pu pose a ma hema ical