COMPARATIVE ANALYSIS OF AN ORGANIC RANKINE CYCLE FOR WASTE COGENERATION PLANTS

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1 Bulltin of th Transilvania Univrsity of Braşov Vol. 10 (59) No Sris I: Enginring Scincs COMPARATIVE ANALYSIS OF AN ORGANIC RANKINE CYCLE FOR WASTE COGENERATION PLANTS L. COSTIUC 1 I. COSTIUC 2 Abstract: For low, modrat and high tmpratur Organic Rankin Cycl (ORC) usd in wast hat rcovry, it is ncssary to slct a fluid with high working tmpratur. In plastic wast powr and hat plants th ORC is usd for cognration. Th analysis of th cycl has bn carrid out considring vaporation tmpratur and condnsation tmpratur of pur cologic HFC working rigrants R134a, R245fa, R227a, R600a, R152a and R123 CFC fluid. Basd on th Hlmholtz thrmodynamic mathmatical modls for working fluids, th ffcts of dsign paramtrs, including that of turbin inlt prssurs, mass flow rats of working fluids and outlt stam fractions of boilr on th systm prformanc ar invstigatd from th viw of both thrmodynamics fficincy and xrgtic fficincy. Ky words: Rankin Cycl, rigrants, wast hat rcovry, cognration, thrmodynamic analysis. 1. Introduction Th us of th nrgy from rcovrabl rsourcs is a modrn mthod on nrgy saving and dcrasing th CO 2 missions. Ths rsourcs cam from th most tchnological procsss. Also, th rquirmnts for nrgy us purposs such as: producing hot-watr, hating and air conditioning ar basd on lctrical nrgy. Th basic Rankin cycl convrts high nrgy strams, cam from coal burning, into lctrical nrgy using watr as working fluid. Th ORC allows nrgy rcovry of wast hat strams that ar low in tmpratur to b convrtd into lctrical powr by convntional vapor cycls using organic fluids, which ar basically working fluids in rigration tchnology. Th us of organic fluids nabls cost-ffctiv lctrical powr rcovry of wast hat. Th managmnt of plastic wasts supposs fdstock rcovry, mchanical rcycling and landfilling which is th last option, mor and mor avoidd. Othr options ar th nrgy rcovry by wast incinration. A promising way is th us of th plastic wast nrgy to obtain lctricity combind with hating and/or cooling with ORC. Th thrmodynamic cycl fficincy of th ORC is influncd by th choic of working fluid. Th Montral protocol forcd industry to us thrmodynamically lss fficint rigrants which ar not containing chlorin, such as ChloroFluoroCarbon compounds (CFC s) and HydroChloroFluoroCarbon compounds (HCFC s). Th non-toxic rigrants 1 Mchanical Enginring Dpt., Transilvania Univrsity of Braşov. 2 Automotiv and Transport Enginring Dpt. Transilvania Univrsity of Braşov.

2 26 Bulltin of th Transilvania Univrsity of Braşov Vol. 10 (59), No Sris I usd in th past as working fluids [1], i.. Dichlorottrafluorothan (CFC114), Trichlorofluoromthan (CFC11) and Dichlorotrifluorothan (HCFC123), wr outlawd sinc ar not chlorin fr. Chlorin basd rigrants and also othr catgoris of rigrants hav highr ozon dpltion potntial (ODP) and ar also disrgardd. This papr considrs cologic rigrants basd on nar to zro ODP and low Global Warming Potntial (GWP), i.. Ttrafluorothan (R134a), Pntafluoropropan (R245fa), Hptafluoropropan (R227a), isobuthan (R600a), Difluorothan R152a and HCFC- R123 in ORC systm fficincy. Th choic of a HCFC non-cologic rigrant was mad for comparison rasons. Th study considrd th basic ORC with diffrnt vaporation and condnsation tmpraturs. 2. Basic Organic Rankin Cycl 2.1. Thrmodynamic Cycl A schmatic dscription of th basic ORC is shown in Figur 1 and consists of four major componnts: pump, vaporator, turbin and condnsr [3-6]. Th saturatd liquid rigrant lavs th condnsr at low-prssur with thrmodynamic stat point 1. Th pump raiss th prssur of th liquid to stat point 2 and fds th vaporator/boilr. In th vaporator th rigrant is hatd in liquid stat to stat point 3, vaporatd to stat point 4 and suprhatad to stat point 5 which is th ntring stat to th turbin. Th xpansion to low-prssur vapor in th turbin at stat point 6 ntrs in th condnsr whr hat is rjctd from th systm during condnsation. In th turbin th mchanical nrgy is rcovrd through xpansion from high-prssur vapor to low-prssur vapor and convrtd into lctrical nrgy through an lctrical gnrator. Th tmpratur ntropy diagram of th baslin Organic Rankin cycl is shown in Figur Thrmodynamic Modl Fig. 1. Rankin schmatics and T-S thrmodynamic cycl Th ORC cycl modling is basd on th consrvation quations for nrgy and mass. To analyz this thrmodynamic systm, th mass and nrgy balanc must b prformd for ach componnt in Tabl 1.

Costiuc, L., t al.: Comparativ Analysis of an Organic Rankin Cycl for Wast Cognration 27 Th xhaust gass from plastic wast incinrators vary btwn 350 and 550 C dpnding on th plastic wast composition.

3 Costiuc, L., t al.: Comparativ Analysis of an Organic Rankin Cycl for Wast Cognration 27 Th xhaust gass from plastic wast incinrators vary btwn 350 and 550 C dpnding on th plastic wast composition. Th prsnc of polyolfins such as polypropiln, polythiln, tc., which hav a high hat of combustion and flam tmpratur dtrmins that th xhaust gas tmpraturs ar vn highr. This was considrd in th study as suprhatd tmpratur of th rigrant btwn 105 and 150 C. Thrmodynamic analysis of th ORC Tabl 1 Componnt Mass flow Enrgy Boilr/Evaporator (2 3) m 3 h 3 h 2 Tubin (3 4) 4 Condnsr (4 1) 4 Pump (1 2) m2 m1 Hot fluid (5 6) Cold fluid (7 8) Thrmodynamic fficincy Exrgtic fficincy 2 m 3 PT h 3 h 4 m 1 c h 4 h 1 P hf p h 2 h 1 m hf mhf c p T 5 T6 m cf mcf c p T8 T7 c cf x PT Pp COP Ex( Pnt ) Ex( ) T Fm is th avrag tmpratur in th vaporator: h3 h2 T Fm s s T amb is th ambint tmpratur. 3 2 P nt P Th thrmodynamic proprtis for prssur, nthalpy and ntropy at saturation stat, subcoold or suprhatd stats ar calculatd using CoolProp [2] softwar routins using prcision Hlmholtz thrmodynamic mathmatical modls for working fluids usd in this papr. Th routins ar usd in EES [8] softwar with ORC modl. Th Tabl 2 prsnts basic proprtis of th slctd rigrants. Chmical data Rfrigrant IUPAC nam Formula Structur R134a R152a R227a R245fa 1,1,1,2- Ttrafluorothan 1,1-Difluorothan 1,1,1,2,3,3,3- Hptafluoropropan 1,1,1,3,3- pntafluoropropan T nt Fm TFm T Rfrigrant proprtis [7], [8] Tabl 2 amb Thrmodynamic and nvironmntal data M T bp T crit P crit OD GWP [g/mol] [ C] [ C] [MPa] P CH 2 FCF C 2 H 4 F C 3 HF C 3 H 3 F

4 28 Bulltin of th Transilvania Univrsity of Braşov Vol. 10 (59), No Sris I Chmical data Rfrigrant IUPAC nam Formula Structur Thrmodynamic and nvironmntal data M T bp T crit P crit OD GWP [g/mol] [ C] [ C] [MPa] P R600a Mthylpropan C 4 H R123 2,2-Dichloro- 1,1,1- trifluorothan C 2 HCl 2 F M - molar mass T bp - normal boiling point T crit, P crit - critical tmpratur and prssur ODP - Ozon Dpltion Potntial (ODP=1 for Trichlorofluoromthan (CCl 3 F)=R11) GWP - Glabal Warming Potntial for 100-yar tim horizon (GWP=1 for CO 2 ) Th ORC systm calculation was mad undr th following conditions: - th maximum boiling tmpratur in th vaporator t,max = +100 C ; - th ambint tmpratur t amb = +25 C; - th condnsing tmpratur t c = t amb +10 C; - th wast hat sourc tmpratur t ws = C; - th turbin fficincy η T = 0.85; - th pump fficincy η P = 0.80; - th xpansion imposd turbin powr of th systm P T 100 kw. Th following variabl paramtr is considrd: th ntring rigrant tmpratur in th turbin t5 = C. 3. Rsults and Discussions Th advantag of this modl is givn by th high valuation accuracy of th stat points, compard with th common mthod, with th lnp-h diagram wr th rading accuracy of th valus is rlativ. Th prformanc valuation of th ORC systm is prsntd in function of inlt turbin tmpratur for ach rigrant for: - th prformanc cofficint or thrmal fficincy, COP - in Figur 2; - th xrgtic fficincy, x, in Figur 3; - turbin work, W T, in Figur 4. Th prformanc cofficint, COP, dpnding on th turbin inlt tmpratur prsnts a maximum of 10% around th valu of 122 C (Figur 2) for R227a rigrant, aftr which it uniformly dcrass. For R152a and R134a th COP uniformly incrass whil inlt turbin tmpratur incrass. Th COP for R123, R245fa and R600a is dcrasing sinc turbin inlt tmpratur is incrasing. Th bhavior for xrgtic fficincy (Figur 3) is with maximum valu of 69.7% for R152a and 67.3% for R134a around th turbin inlt tmpratur valu of 120 C, and 115 C rspctivly. For R123, R245fa, R600a and R227a th xrgtic fficincy is dcrasing sinc turbin inlt tmpratur is incrasing. For tmpratur lowr than 112 C th R245fa has bst xrgtic fficincy thn othr rigrants, and R152a rspctivly for tmpraturs biggr than 112 C.

5 Costiuc, L., t al.: Comparativ Analysis of an Organic Rankin Cycl for Wast Cognration 29 Fig. 2. ORC thrmal fficincy vs. inlt turbin tmpratur for slctd rigrants Fig. 3. ORC xrgtic fficincy vs. inlt turbin tmpratur for slctd rigrants Fig. 4. ORC turbin work vs. inlt turbin tmpratur for slctd rigrants

6 30 Bulltin of th Transilvania Univrsity of Braşov Vol. 10 (59), No Sris I According to Figur 4, th turbin work, which can b convrtd in lctrical work, has incrasing with inlt turbin tmpratur incrasing. Th bst rigrant according th maximum turbin work is R600a. Th studid rigrants can b slctd for lctrical nrgy production in th following ordr as: R600a, R152a, R245fa, R134a and R227a. Th R123 was xcptd bcaus this is an HCFC rigrant. 4. Conclusions 1. This papr has prsntd th Rankin cycl simulation using organic rigrants R600a, R152a, R245fa, R134, R227a and R Th analysis has bn mad for thrmodynamic fficincy, xrgtic fficincy and turbin rsultd work using high accuracy quation of stat using Hlmholtz thrmodynamic mathmatical modl. 3. Th papr has dmonstratd that th nrgy wast rcovry can b usd for lctrical nrgy production. Rfrncs 1. Brasz, L.J., Bilbow, W.M.: Ranking of Working Fluids for Organic Rankin Cycl Applications. In: Intrnational Rfrigration and Air Conditioning Confrnc at Purdu, Bll, I.H., Wronski, J., Quoilin, S., t al.: Pur and Psudo-pur Fluid Thrmophysical Proprty Evaluation and th Opn-Sourc Thrmophysical Proprty Library CoolProp. In: Industrial & Enginring Chmistry Rsarch 53 (2014), p Chang, J.-C., Hung, T.-C., H, Y.-L., t al.: Exprimntal Study on Low-Tmpratur Organic Rankin Cycl Utilizing Scroll Typ Expandr. In: Applid Enrgy 155 (2015), p Costiuc, L.: Solar Powrd Absorbtion Systm. In: Bulltin of th Transilvania Univrsity of Braşov (2013) Vol. 6 (55), Sris I, p Zhang, Y.-Q., Wu, Y.-T., Xia, G.-D., t al.: Dvlopmnt and Exprimntal Study on Organic Rankin Cycl Systm with Singl-Scrw Expandr for Wast Hat Rcovry from Exhaust of Disl Engin. In: Enrgy 77 (2014), p Yang, M.-S., Yh, R.-H.: Thrmodynamic and Economic Prformancs Optimization of an Organic Rankin Cycl Systm Utilizing Exhaust Gas of a Larg Marin Disl Engin. In: Appl Enrgy 149 (2015), p ANSI/ASHRAE Standard , Dsignation and Safty Classification of Rfrigrants. Amrican Socity of Hating, Rfrigrating and Air-Conditioning Enginrs, Inc Tulli Circl NE, Atlanta, F-Chart Softwar: Equation Enginring Solvr v.8.40.

WASTE HEAT RECOVERY USING DIRECT THERMODYNAMIC CYCLE

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