Fredy Vélez. Centro Tecnológico CARTIF, Valladolid, España.

Transcription

1 Slcting working fluids in an organic Rankin cycl for powr gnration from low tmpratur hat sourcs Frdy Vélz Cntro Tcnológico CARTIF, Valladolid, España. Rcivd: January 21th, d Rcivd in rvisd form: April 29th, Accptd: May 14th, 2014 Abstract This papr prsnts a thrmodynamic study carrid out on th us of low-tmpratur hat sourcs for powr gnration through a subcritical Rankin cycl with organic working fluids. An analysis of th stat of th art of this tchnology shows th slction of th working fluid as an opn rsarch lin, sinc until now thr is no fluid that can mt all nvironmntal and tchnical aspcts to b considrd in ths cycls. Hnc, w hav dvlopd a sris of simulations that allow us to study th bhavior of th Rankin cycl with diffrnt configurations and fluids (wt, dry and isntropic) which has ld us to obsrv th influnc on th ovrall cycl fficincy whn w chang th typ of fluids usd (rfrigrants, hydrocarbons and watr) as wll as th conditions of tmpratur, prssur, flow, tc. With th work ralizd, th viability of this typ of procsss is dmonstratd for th rcovry of hat in industry and/or th us of rnwabl sourcs of low and mdium tmpratur for th production of lctricity. Kywords: nrgy fficincy; organic Rankin cycl; powr gnration; wast hat; rnwabl nrgy. Slccionando fluidos d trabajo n ciclos Rankin para gnración d nrgía a partir d funts d calor d baja tmpratura Rsumn Est trabajo prsnta un studio trmodinámico ralizado sobr l uso d funts d calor d baja tmpratura para la gnración d nrgía a través d un ciclo Rankin subcrítico con fluidos d trabajo orgánicos. Un análisis dl stado dl art d sta tcnología mustra como lína d invstigación abirta, la slcción dl fluido d trabajo, pus hasta ahora, no xist un fluido qu satisfaga todos los aspctos mdioambintals y técnicos a tnr n cunta n stos ciclos. Por llo, s ha dsarrollado una sri d simulacions qu prmitn studiar l comportaminto dl ciclo Rankin con difrnts configuracions y fluidos (húmdo, sco isontrópico), prmitindo con llo obsrvar d qué manra influyn cambios tanto n sos tipos d fluidos utilizados (rfrigrants, hidrocarburos y agua), como d condicions d tmpratura, prsión, flujo, tc., sobr la ficincia total dl ciclo. Con l trabajo ralizado s dmustra la viabilidad d st tipo d procso n la rcupración d calors n la industria y/o aprovchaminto d funts rnovabls d baja y mdia tmpratura para la producción d nrgía léctrica. Palabras clav: ficincia nrgética; ciclo Rankin orgánico; gnración d nrgía; calor rsidual; nrgías rnovabls. 1. Introduction Thr is no doubt that th implmntation of projcts basd on non-convntional tchnologis for nvironmntfrindly nrgy gnration, and with occupational halth and safty critria ar ssntial to nsur social quity and to facilitat conomic activitis rlatd to th public srvic of nrgy off-grid aras, mainly in undrdvlopd countris whr majority of th trritory corrsponds to isolatd aras with high lvls of povrty and without any opportunitis for socio-conomic dvlopmnt, which is causd, among othrs, by th lack of an adquat nrgy supply. Th us of fossil fuls (.g., oil and coal) as an nrgy sourc has many ngativ nvironmntal impacts, such as th rlas of pollutants and rsourc dpltion. A high consumption rat of fossil-fuls will rsult in an incras of nvironmntal pollution during th nxt cntury, du to th mission of CO2 and othr gass that caus global warming through what is known as th grnhous ffct [1]. Ths problms ncourag fforts to dvlop nw tchnologis that transform rnwabl nrgy sourcs such as solar, biomass, gothrmal, as wll as th us of wast and/or low-nthalpy hat now Th author; licns Univrsidad Nacional d Colombia. DYNA 81 (188), pp Dcmbr, 2014 Mdllín. ISSN Printd, ISSN Onlin DOI:

2 dischargd in th industry (which rprsnts a 50% or mor of th hat gnratd thrin) into lctric and/or mchanical nrgy [2]. Howvr, givn that th traditional Rankin cycl dos not prsnt a good prformanc to rcovr or us low tmpratur hat, it is ncssary to analyz othr procsss such as th Organic Rankin Cycl (ORC), which allows to lvrag diffrnt sourcs of low tmpratur to powr output as was proposd by [2-6] and many othr authors. In this sns, th ORC is a promising procss for th convrsion of ths low and mdium tmpratur hat sourcs from rnwabl nrgy and wast hat from industry into lctricity [7-10]. Th ORC procss works lik a convntional stam Rankin cycl, with th diffrnc that th formr uss an organic compound of low boiling point as th working fluid (rfrigrant and hydrocarbon) instad of watr vapor, thrby rducing th vaporation tmpratur. In rcnt yars, commrcial applications of this tchnology, with powr rangs from kw, hav incrasd sharply worldwid. ORMAT, Barbr-Nichols, UTC Powr, Turbodn, tc, ar som of th companis that hav dvlopd plants for using gothrmal nrgy, wast hat in industry, biomass, tc. Howvr, lowr powr moduls ar in a prototyp stag du to lack of appropriat quipmnt (mainly th turbin) and th difficulty in slcting a suitabl working fluid [3]. Th lattr charactristic has grat influnc on th dsign and bhavior of th procss [6], bcaus th fluid must hav optimal thrmodynamic proprtis at low tmpraturs and prssurs and also satisfy many critria such as bing conomical, nontoxic, nonflammabl, nvironmntally frindly, and allow high utilization of th availabl nrgy from th hat sourc, tc; all dpnding on th application, th sourc and th hat lvl to us. If all ths aspcts ar considrd, vry fw fluids can b usd [3,11]. In [11], it is shown that ths working fluid proprtis ar kys in th prformanc cycl. In addition, th low tmpraturs that tak advantag of th ORC caus that th fficincy of th cycl is highly snsitiv to infficincis in hat transfr, which dpnds strongly on th thrmodynamic proprtis of th fluid and th conditions to which it is oprating. A study of 68 potntial working fluids conductd in [12] in 1985, gav th bst rsults only for thr of thm (R11, R113 and R114) which ar nowadays not rcommndd by global nvironmntal consrvation policis [13]. In [2], ORC fficincy was analyzd using azotropic mixturs of 85- fluorinol, 2-mthyl pyridin/watr and substancs such as bnzn, ammonia, R134a, R113, R11 and R12, achiving gratr fficincis for th last two, howvr, thy ar substancs of limitd us. Othr rsarchrs who hav analyzd th charactristics and outcoms of diffrnt fluids for us in ORC systms ar among othrs [4, 6-12] and [14-16], of whos rsarch can conclud that: R245fa and R134a as good candidats in subcritical cycls and CO2 in transcritical cycls for procsss whos hat sourc is low tmpratur. Rcnt publications such as [17] hav studid th bhavior of R134a, R123, R227a, R245fa, R290, and n-pntan from th point of viw of nrgy production capacity and componnt siz. Thy hav shown th xistnc of an optimum prssur that minimizs th hat xchang ara, which obviously dpnds on th sourc and th sourc tmpratur. In [11], a rviw of thrmodynamic proprtis, physical stability, nvironmntal impact, safty, cost and availability of 35 possibl fluids to b usd in a Rankin cycl for th convrsion of low tmpratur hat into lctricity has bn prformd. Th prsnt papr analyzs th bhavior of working fluids, such as watr and som hydrocarbons and rfrigrants in a Rankin cycl in diffrnt configurations and conditions of tmpratur, prssur and flow, thus stablishing th viability of this typ of procss in th rcovry and/or utilization of low-tmpratur nrgy. Nowadays, thr is no a uniqu fluid that fulfills all aspcts to b considrd to us in ORC cycls. This study has slctd R600, R600a, R113, R718, R425fa and Tolun, trying to ncompass and tak into account th optimal physical and thrmodynamic proprtis, conomic, toxicity, flammability, nvironmntal frindly (with null Ozon Dpltion Potntial (ODP) and Global Warming Potntial (GWP)). Of th fluids slctd, R600a and R600 ar hydrocarbons usd as rfrigrants with zro potntial dgradation of th ozon layr and vry low global warming potntial, howvr, thy ar highly flammabl. Tolun is similar in its bhavior, with th drawback of its toxicity. Rfrigrant R113 is not flammabl, nor toxic, but has high global warming potntial and high dstruction potntial of th ozon layr. R245fa is a saf rfrigrant, nonflammabl, nontoxic, has zro ozon dgradation potntial, rlativly high molcular wight, good thrmophysical proprtis, but has a modrat potntial for global warming. Finally, watr (R718), as rfrnc fluid to th bing th working fluid in th convntional Rankin cycl. Additionally, in this study th diffrnc in th typ of fluid has bn considrd and thus, th rsults obtaind nabl to dtrmin whthr th incras in th inlt tmpratur incrass or dcrass turbin cycl prformanc qualitativly but also, allows to know how this incrass or dcrass. 2. Dscription of th cycl Th oprating principl of th ORC is th sam as th convntional Rankin cycl. A pump prssurizs th liquid fluid, which is injctd into an vaporator to produc a vapor that is xpandd in a turbin connctd to a gnrator. Finally, th stam is condnsd and suckd by th pump, starting th cycl again. It may also includ an intrnal hat xchangr (IHX) to furthr xploit th nrgy of th xpandd stam, prhating th fluid xiting th pump and ntring th vaporator, as is shown in Fig. 1. Figur 2 rprsnts th powr cycl on a T-s diagram according to th stat points displayd in th flow diagram of Fig. 1. As an xampl, an idal cycl procss is shown by th sgmnts constructd from stat points 1, 2is, 3 and 4is. Lin sgmnt 1-2is rprsnts an isntropic xpansion with work production. Hat is xtractd from 2is to 3, through a constant subcritical prssur lin to subsquntly rsult to idal comprssion of th subcoold liquid from th prssur at stat point 3 to stat point 4is. Finally, th sgmnt 4is-1 corrsponds to th hat addd to a constant subcritical prssur up to th highst tmpratur point in th cycl in th stat point 1. A cycl, in which both th xpansion and th comprssion ar not idal, is rproducd by sgmnts in points 1, 2, 3 and 4 of th sam Fig

3 Figur 1. Schmatic diagram of organic Rankin cycl with intrnal hat xchangr. Figur 2. Diagram Tmpratur - Entropy of th idal and ral Rankin cycl. Sourc: [18] 3. Slction of th working fluid As mntiond prviously, th slction of th working fluid for us in ORC cycls is a crucial point, bcaus dpnding on th application, th sourc and th hat lvl to us, th fluid must hav optimal thrmodynamic proprtis at lowst tmpraturs and prssurs and also satisfy svral critria such as bing conomical, nontoxic, nonflammabl, nvironmntally frindly, allow a high utilization of th availabl nrgy from th hat sourc, among othrs [3]. This limits th list to only a fw fluids whn considring all rstrictions. Som of ths limitations ar [3]: Environmntal: Som fluids ar rstrictd by Intrnational Agrmnts dpnding on thir Ozon Dpltion Potntial (ODP) dfind and limitd by Montral Protocol or Global Warming Potntial (GWP) by Kyoto Protocol, which, intnd to prvnt th dstruction of th ozon layr and mission of gass that caus th grnhous ffct, rspctivly. Scurity: Th fluid must b non-toxic (bcaus of th problms that can occur in th cas of laks in th atmosphr or in handling), non-corrosiv (it obviously avoids major maintnanc costs and/or installation damag) and non-flammabl. For this, th standard scurity classification 34 of ASHRAE is oftn usd as an indicator of th dangr lvl of fluids. Stability: Th chmical stability of th usd fluid limits th hat sourc tmpratur. Whn fluids ar xposd to crtain tmpraturs, thy could dcompos, producing substancs which could caus a diffrnt cycl opration to that initially dsignd. Morovr, toxic and irritating compounds could induc halth problms in cas laks occur. Prssur: A fluid rquiring high prssur to achiv an fficint procss incrass th cost of quipmnt du to th gratr rsistanc rquird, incrasing also th complxity of th plant. Availability and low cost: A fluid of low availability and/or high cost limits its us in ORC plants for obvious rasons in th financial viability of th projcts. Latnt hat and molcular wight: With highr molcular wight and th latnt hat of th fluid, mor nrgy from th hat sourc in th vaporator will b absorbd and, thus, rducing th siz of th installation and us of th pump du to lowr mass flow rquird. Low frzing point: Th frzing point of th fluid must b lowr than th lowst tmpratur of th cycl. Curv of saturation: Th thrmodynamic proprtis of th fluid imply that th slop of th saturation curv throf is ngativ, vrtical or positiv, which markdly affcting th dsign and fficincy of th ORC. In Fig. 3.a, b and c, a schmatic diagram is shown of Tmpratur - Entropy (T-s) for fluids with a ngativ saturation curv (a), vrtical (b) and positiv (c), calld wt, isntropic and dry, rspctivly. Sinc th objctiv of th ORC focuss on th us of hat of low and mdium tmpratur, th ovrhating of stam as in a convntional Rankin cycl is not appropriat. Furthrmor, as is sn in Fig. 3.a, whn a wt fluid is xpandd without ovrhating (rprsntd by th sgmnt of points 1-2), it falls in th liquid/vapor zon causing damags to th xpandr and cycl infficincis. This happns, among othr rasons, bcaus of th phas shift. Nvrthlss, th contrary occurs with isntropic and dry fluids which, without any typ of ovrhating, suffr xpansion falling into th saturatd vapor zon, Fig. 3.b, and/or suprhatd, Fig. 3.c, rspctivly, and thus, in th lattr cas, it could includ an intrnal hat xchangr to th cycl which allows to us vn mor th nrgy from th xpandd stam, prhating fluid from th pump to ntr th vaporator, thrby incrasing th fficincy of th cycl. In summary, for an organic Rankin cycl, th idal working fluid will b that whos saturatd vapor lin is paralll to th xpansion of th turbin, nsuring maximum fficincy. In this cas, turbin will b always working in th dry stam ara. If both lins convrg, th turbin would oprat in th wt stam rgion. In ordr to avoid this, it should suprhat th working fluid bfor th xpansion. If, howvr, th lins mntiond abov wr divrgnt, th 175

4 output fluid from th turbin would xit ovrhatd. This would incras significantly th siz of th condnsr surfac, an aspct that is rlatd to th oprating prssur. Th major disadvantag of ORC is its rlativly low fficincy (inhrnt to th thrmodynamic constraints) and th rlativly larg sizs of hat xchangrs quipmnt. 4. Modlling of th procss In both cycls, th quations usd for prformanc calculation assum stady stat and constant fficincis of 75% for both th pump and th turbin. In addition, thr ar no hat or prssur losss in th vaporator, hat xchangr or pips, and an ovrall cycl fficincy (ɳ) is considrd as: W W t p (1) Q Whr, W is th powr, t rfrs th turbin, p to th pump and " vaporator. Hnc: W t m t (2) W p m h 1 h 2 h h 3 4 / p (3) m is th mass flow, point i. hi is th nthalpy in th stat Whras as: Q is th hat input in th vaporator dfind Q m h 1 h 4 or (4) m h h Through th thortical basis prsntd in th prcding sctions and using th softwar HYSYS, a sris of simulations has bn dvlopd that allows to study th bhavior of th ORC with diffrnt configurations and fluids (as rfrigrants, hydrocarbons and vn watr), thrby obsrving how th changs influnc th ovrall cycl fficincy for ths typs of fluids usd varying conditions of tmpratur, prssur, flow, tc.,. This simulator is usful for thrmodynamic analysis, spcially in stady-stat conditions, and it has th advantag of including fluid proprtis and optimization tools. Its prdictions hav bn compard with thos of [19] and th rsults ar vry similar. Th flow chart of th simulation is th sam as it was prsntd in Fig. 1, and th mthod to solv all th componnts is fully dscribd in [7,10] and [14]. 5. Rsults and discussions Q 1 4IHX Th rsults obtaind with th simulations for watr, hydrocarbons R600, R600a, Tolun and rfrigrants R113 and R245fa ar shown in this sction Working Fluids: Watr, R600, R600a, Tolun and R113 Figur 3. Diagram T-s for fluids wt (a), isntropic (b) and dry (c). Sourc: [12] Influnc of inlt tmpratur in th turbin on th ovrall cycl fficincy Th influnc of inlt tmpratur to th turbin on th 176

5 Figur 4. Influnc of inlt tmpratur to th turbin on th total fficincy of th cycl at a constant condnsation prssur. ovrall cycl fficincy is prsntd in Fig. 4. Hr, conditions of input and output prssur in th turbin and th fluid flow ar kpt constant for th fiv fluids analyzd and for th diffrnt simulations carrid out with valus of 20 bar, 2 bar and 2.8 kg/s, rspctivly. It is vidnt that th fficincy incrass linarly with th inlt tmpratur to th turbin in th cas of R718 (Watr). Unlik this wt fluid, th dry fluids R600, R600a, R113 and Tolun showd a dcras of fficincy with th incras in inlt tmpratur to th turbin. Thus, thr is a big diffrnc in th fficincis obtaind according to th typ of fluid usd, th highst fficincy obtaind is for th cas of R600a, followd by R600, R718, R113 and Tolun. It is also intrsting to not that as Fig. 4 shows, th us of on fluid or anothr will dpnd on th hat sourc that is intndd to b rcovrd, and th thrmophysical proprtis of th fluid, sinc thr ar fluids which would obtain rlativly high fficincis at rlativly low tmpratur rangs whn compard to othr fluids that ar usful in othr tmpratur rangs Influnc of th working fluid flow on th ovrall fficincy of th cycl Fig. 5 shows th influnc of th working fluid flow on th fficincy of th cycl with th condnsation prssur constant and qual (2 bar) for all th studid fluids, maintaining constant in addition th inlt prssur to th turbin at 20 bar for th fiv fluids analyzd and for all simulations ralizd whras th rat of nrgy supplid to th vaporator is also constant for all simulations carrid out but diffrnt for ach fluid. Valus achivd wr 1500 kw, 1650 kw, 7778 kw, 795 kw and 2270 kw for th R600a, R600, R718, R113 and Tolun, rspctivly. Thrmodynamic proprtis of ach fluid ar diffrnt, thrfor, for th sam stat point, diffrnt valus of nthalpy, ntropy, tc., could b obtaind for two or mor typs of fluids. In addition, th molcular wight and th vaporization latnt hat of a spcific fluid, dtrmins th amount of fluid flow (gratr or smallr) that is rquird to hav to a givn powr, compard to othr fluid. In this sns, to mak th flow valus similar, i.. to kp thm in Figur 5. Influnc of th working fluid flow on th total fficincy of th cycl at a constant condnsation prssur. Figur 6. Influnc of th inlt prssur to th turbin on th total fficincy of th cycl at a constant condnsation prssur. Sourc: compild by author. th sam rang, th input powr to th vaporator was fixd, for th rang of study. In Fig. 5, it is obsrvd that a slight influnc xists of th working fluid on th ovrall fficincy of th cycl for th cas of R600a, R600, R113 and Tolun, whras for th R718, th ffct is clar but opposit to that shown prviously, i., a dcras of th cycl fficincy whn th flow of R718 incrass Influnc of th input prssur to th turbin on th ovrall fficincy of th cycl. Basd on th rsults shown in Fig. 4 and Fig. 6, th influnc of th input prssur to th turbin on th ovrall fficincy of th cycl is analyzd, th fluid flow of 2.8 kg/s was hld constant for th fiv fluids analyzd and for th diffrnt simulations, th rat of nrgy supplid to th vaporator is also constant for th diffrnt simulations but diffrnt for ach fluid and whos valus wr 1500 kw, 1650 kw, 7778 kw, 795 kw and 2270 kw for R600a, R600, R718, R113 and Tolun, rspctivly. Fig. 6 shows that th systm gains in fficincy with th incras of th 177

6 input prssur to th turbin. Rsults ar consistnt for all th fluids utilizd. Highr input prssurs to th turbin rais th nt work that lads to an improvmnt of th fficincy. Although th fficincy of th systm also incrass whn th prssur of th systm riss, this incras of th prssur in th systm is not always fasibl for conomic rasons sinc th capital costs for th wast hat of a boilr and piping systms, as wll as th complxity of th systm and th componnt slction of th matrials must also b takn into account Working fluid: R245fa As it was discussd in th introduction to this papr, th rfrigrant R245fa is a vry promising working fluid for using in low tmpratur ORC bcaus it mts many of th aspcts to b considrd in ths applications. Th R245fa fluid is a saf rfrigrant (nonflammabl, nontoxic), has a potntial ozon dgradation of zro, rlativly high molcular wight, good thrmophysical proprtis (critical tmpratur and prssur, boiling point, tc.), has a positiv saturation curv, which givs highr yilds, allowing th prhating of th fluid xiting th pump using th stam xiting th turbin, tc. Howvr, it has a modrat potntial for global warming as its main disadvantag. For thos rasons, th approach to th thrmodynamic study of this fluid has bn don diffrntly from that illustratd in th prvious sction. In this cas, w hav analyzd th ffct of inlt prssur and tmpratur to th turbin on th othr paramtrs (fficincy, flow, nt work and hat supplid to th vaporator) to an ORC with a fixd output gross powr of 125 kw and an IHX to prhat th liquid fluid from th pump with th output stam from turbin (s Fig. 1). Simulations considrd a P2=2.5 bar and a condnsing tmpratur of th working fluid (T3) of 39.7 C. In addition, th hat rquird for th vaporator ( Q ) dos not tak into account th fficincy for xampl from boilr and hat transfr in th hat xchangr. Figur 7. Mollir diagram of R245fa. Sourc: [20]. Figur 8. Influnc of th inlt prssur P1 to th turbin on th flow of R245fa in a cycl with IHX Influnc of th inlt prssur to th turbin on th fluid flow in th cycl As in this analysis, th work producd by th turbin ( W t ) was constant and qual to 125 kw for all simulations, it can b statd that: kping th condition of turbin discharg constant P2=2.5 bar and considring th fact that th work producd by th turbin is givn by th q. (2), and, supportd by th Mollir diagram of this fluid (Fig. 7), w s that, for any constant inlt tmpratur to th turbin (for xampl, T1=145 C), incrasing th inlt prssur to th turbin (P1), th dlta nthalpy, h, incrass from 30 kj/kg to 42 kj/kg (sgmnt 1-2, rd and blu colors of this Fig. 7, rspctivly) and thrfor, th mass flow ( m ) ncssarily dcrass (for any of th thr tmpraturs studid 90 C, 120 C and 145 C), as dpictd in Fig. 8 and thus to maintain constant valu of th work producd by th turbin. Figur 9. Influnc of th inlt prssur to th turbin P1 on th nt work of th cycl with IHX and R245fa. 178

7 Influnc of th inlt prssur to th turbin on th nt work of th cycl o r d r t o c a r r y o u t Likwis, as is shown in Fig. 9, as inlt prssur incrass in th turbin, it causs a dcras in th nt work producd by th systm ( W nt W t W ), bcaus for th p turbin work to b constant with incrasing prssur, th work consumd by th pump is incrasd for any of th thr tmpraturs studid 90 C, 120 C and 145 C Influnc of th inlt prssur to th turbin on th fficincy and th hat rquird in th cycl. Similarly, and dspit what was discussd abov, th nt work ( W ) always dcrass with incrasing inlt prssur nt to th turbin P1, systm fficincy incrass, as is shown in Fig. 10. This occurs bcaus incrasing such prssur P1, as is sn in Fig. 10, th amount of hat rquird in th vaporator dcrass with a dcrasing mass flow (Fig. 8). This is producd bcaus th mass ndd to b hatd/vaporatd to maintain th work producd by th turbin constant is lss with rspct to its own nt work. Th prvious situation occurs until that by th own charactristics of this fluid, thr is a spcific valu for th prssur (th optimum in fficincy trms), in which an incras of th variabl P1 inducs a ngligibl incras of h (s Fig. 7), and thrfor, a lowr valu of th mass flow, causing th hat from th vaporator to drop a littl but with sufficint valu to countract th dcras in th nt work and thrfor maintaining th fficincy narly constant. In this cas, and according to Figs. 8 to 10, this optimum inlt prssur to th turbin is clos to 20 bar for th tmpratur 145 C, 15 bar for th tmpratur 120 C and 10 bar for 90 C. 4. Conclusions Basd on th discussd in this papr, ORC tchnology sms to hav an normous potntial with rnwabl nrgy sourcs such as biomass, solar and gothrmal nrgy as wll as wast hat from industrial procsss or othr cycl for transforming low tmpratur hat sourcs into lctricity. Howvr, th thrmophysical proprtis, nvironmntal impact, safty and stability as wll as its availability and cost, play a critical rol in th slction of th working fluid in ths cycls. Additionally, according to rsarch carrid out in this work, it can b concludd that using organic working fluids in Rankin cycls, rlativly good fficincis ar obtaind rcovring and/or using hats of low/mdium tmpratur to convrt thm into lctricity. Acknowldgmnts Frdy Vélz would lik to thank th scholarship grantd by th Programa Ibroamricano d Cincia y Tcnología para l Dsarrollo, CYTED, CARTIF Tchnological Cntr and th Univrsity of Valladolid in Figur 10. Influnc of th inlt prssur to th turbin P1 on th fficincy and th hat rquird by th vaporator in a cycl with IHX and R245fa. his doctoral thsis, on which this papr is basd. In addition, th author xprsss his spcial gratitud to th Dpartmnt of Rnwabl Enrgy Srvic of th Spanish Company Nicolás Corra, SA, for all th tchnical support providd in th prparation of this rsarch. Rfrncs [1] Ralp, A. and Diazgranados, J. A. Elctricity gnration and wind potntial assssmnt in rgions of Colombia. Dyna, 79(171), pp , [2] Hung, T. C., Shai, T. Y. and Wang, S. K. A rviw of organic Rankin cycls (ORC`s) for th rcovry of low-grad wast hat. Enrgy, vol. 22(7), pp , [3] Vélz, F., Sgovia, J., Martín, M. C., Antolín, G., Chjn, F. and Quijano A. A Tchnical, conomical and markt rviw of organic rankin cycls for th convrsion of low-grad hat for powr gnration. Rnwabl & Sustainabl Enrgy Rviws, 16(6) pp , [4] Salh, B., Koglbaur, G., Wndland, M. and Fischr, J. Working fluids for low tmpratur organic Rankin cycls. Enrgy, vol. 32(7), pp , [5] Quoilin, S., Dclay, S., Tchang, B. F. and Lmort, V. Thrmoconomic optimization of wast hat rcovry organic Rankin cycls. Applid Thrmal Enginring, 31(14), pp , [6] Tchang, B.F., Papadakis, G., Lambrinos, G. and Frangoudakis, A., Fluid slction for a low-tmpratur solar organic Rankin cycl. Applid Thrmal Enginring, 29(1), pp , [7] Vélz, F., Chjn, F., Antolín, G. and Quijano, A. Thortical analysis of a transcritical powr cycl for powr gnration from wast nrgy at low tmpratur hat sourc. Enrgy Convrsion and Managmnt, vol. 60, pp , [8] Mago, P. J., Chamra, L. M., Srinivasan, K. and Somayaji, C. An xamination of rgnrativ organic Rankin cycls using dry fluids. Applid Thrmal Enginring, 28(8), pp , [9] Schustr, A., Karllas, S., Kakaras, E. and Splithoff, H., Enrgtic and conomic invstigation of organic Rankin cycl applications. Applid Thrmal Enginring, 29(8-9), pp ,

8 [10] Vélz, F., Sgovia, J., Chjn, F., Antolín, G., Quijano, A. and Martín, M.C. Low tmpratur hat sourc for powr gnration: xhaustiv analysis of a carbon dioxid transcritical powr cycl. Enrgy, 36(9), pp , [11] Chn, H., Goswami, Y. and Stfanakos, E. A rviw of thrmodynamic cycls and working fluids for th convrsion of low-grad hat. Rnwabl and Sustainabl Enrgy Rviws, 14(9), pp , [12] Badr, O., Probrt, S. D. and O'callaghan, P.W., Slcting a working fluid for a Rankin-cycl ngin. Applid Enrgy, 21(1), pp. 1-42, [13] U.S. Environmntal Protction Agncy. Class I Ozon Dplting Substancs. [Onlin]. [dat of rfrnc March 11th of 2013] Availabl at: [14] Vlz, F., Sgovia, J., Martín, M. C., Antolín, G., Chjn, F. and Quijano, A. Comparativ study of working fluids for a Rankin cycl oprating at low tmpratur. Ful Procssing Tchnology, vol. 103, pp , [15] Yamamoto, T., Furuhata, T., Arai, N. and Mori, K. Dsign and tsting of th organic Rankin cycl. Enrgy, 26(3), pp , [16] Drschr, U. and Brüggmann, D. Fluid slction for th organic Rankin cycl (ORC) in biomass powr and hat plants. Applid Thrmal Enginring, 27(1), pp , [17] Lakw, A., Bolland, O. Working fluids for low tmpratur hat sourc. Applid Thrmal Enginring, 30(10), pp , [18] Monsalv, E., Ccchi, P., Vidal, A., Zuñiga, A. Inform I: Ciclo d Rankin., Dpartamnto d Ingniría Mcánica, Facultad d Cincias Físicas y Matmáticas, Univrsidad d Chil, Santiago d Chil, Chil, [19] Lmmon, E. W., Hubr, M. L. and Mclindn, M. O. Rfrnc fluid thrmodynamic and transport proprtis (REFPROP). NIST Standard Rfrnc Databas 23, Vrsion 8.0; [20] Organic-rankin-cycl.blogspot. [n lína] [dat of rfrnc January 15 th of 2014]. Availabl at: Ára Curricular d Ingniría Química Ingniría d Ptrólos Ofrta d Posgrados Mastría n Ingniría - Ingniría Química Mastría n Ingniría - Ingniría d Ptrólos Doctorado n Ingniría - Sistmas Enrgéticos Mayor información: Abl d Jsús Naranjo Agudlo Dirctor d Ára curricular qcaypt_md@unal.du.co (57-4) F. Vélz, PhD. in Enrgtic and Fluid-Mchanical Enginring by Univrsity of Valladolid (2011). MSci in Enginring -Emphasis in Chmical Enginring- (2007) and Chmical Enginring (2004), both by Colombian National Univrsity, whr h was also an Associat Profssor at th Enrgy and Procss School. H startd to work as rsarchr in th fild of rnwabl nrgis in Sinc 2007 h is activly working in th Enrgy Dpartmnt of CARTIF in RTD projcts about nrgy fficincy and intgration of rnwabl nrgy (solar, gothrmal, biomass) for th production of hating and cooling and/or lctricity gnration in buildings (to achiv zro mission buildings and nar-zro nrgy balanc) and industrial procsss. H has xprinc in national and intrnational (Europan and Latin Amrican) projcts, and has publishd many paprs in pr rviw and tchnical journals and contributions in confrncs about ths thms. ORCID