Performance Analysis of Ammonia-Water Power Generation Cycle Utilizing LNG Cold Energy

Transcription

1 Journl of Autotion nd Control Engineering Vol. 3, No. 1, Februry 2015 Perfornce Anlysis of Aoni-Wter Poer Genertion Cycle Utilizing LNG Cold Energy Kyoung Hoon Ki, Je Hyeong Oh, nd Hyung Jong Ko Deprtent of Mechnicl Engineering nd Grdute School, Kuoh Ntionl Institute of Technology, Dehk-ro 61, Gui, Gyeongbuk , Kore Eil: {khki, jho, bsed on het-exchnger netork syntheses to study nd optiize the perfornce of n oni-ter Rnkine cycle. They shoed tht the design of het exchnger netorks cn hve significnt ipct on the perfornce of poer cycles. Zfirescu nd Dincer [5] nlyzed trilterl oni ter Rnkine cycle tht uses no boiler, but rther the sturted liquid is flshed by n expnder. Roy et l. [6] studied oni-ter Rnkine cycle ith finite size therodynics nd their therodynic clcultions ere crried out in the context of resonble teperture differences in the het exchngers. Wger et l. [7] nlyzed the oni-ter Rnkine cycle using scroll expnder. Ki et l. [8]-[9] studied the Rnkine cycle using oni-ter ixture s orking fluid for use of lo-teperture ste het, nd copred the regenertive Rnkine cycle ith the siple Rnkine cycle. Ki et l. [10] crried out the coprtive nlysis of oni ter bsed Rnkine (AWR) nd regenertive Rnkine (AWRR) poer genertion cycles by investigting the effects of oni ss concentrtion in the orking fluid on the therodynic perfornce of the systes. They closely exined the teperture distributions of fluid stres in the het exchnging devices t different levels of oni concentrtion. It is recognized tht liquefied nturl gs (LNG) is one of the clenest fossil fuels nd is considered to be the ost perspective energy source in forthcoing decdes. The nturl gs shre in the globl energy rket shos stble groing tendency. LNG hs high energy density round 600 ties higher thn tht in gseous for. Trnsporttion of nturl gs in its liquid for is lso ttrctive for short tie orking boreholes, s is lso the cse ith unconventionl gs. The LNG shre in overll nturl gs turnover shos stble groing tendency nd is expected to exceed 25% soon. Due to this observed increse there is strong interest in iproving the econoicl blnce of the hole LNG process chin [11]-[12]. Nturl gs is idely used in ny res becuse of its better environentl chrcteristics. For the convenience of trnsport, nturl gs is liquefied into the LNG by cryogenic refrigertion fter reoving the cid nd ter. During the liquefction process, LNG hs very lo teperture nd contins uch cold energy fter this process. With the incresing dend for clener fuels, Abstrct The poer genertion systes using oni ter ixture s orking fluid re proven to be one of the fesible ethods for utilizing lo-grde het sources. Since the liquefied nturl gs (LNG) hs gret cold energy, the perfornce of the poer genertion syste cn be iproved if the cold energy of LNG is used s its het sink. In this pper coprtive therodynic perfornce nlysis is crried out for the cobined poer cycle consisted of n oni-ter Rnkine cycle ith nd ithout regenertion nd LNG poer genertion cycle. Bsed on the therodynic odels of the cobined cycle, the effects of the key preters such s oni concentrtion nd turbine inlet pressure on the syste perfornce re extensively investigted. The results sho tht the therodynic perfornce of the cobined poer genertion cycle is strongly dependent on the oni concentrtion nd turbine inlet pressure. Index Ters oni-ter Rnkine cycle, liquefied nturl gs (LNG), cold energy, regenertion I. INTRODUCTION Since the evportion tkes plce s vrible teperture process, non-zeotropic ixture used s orking fluid in poer cycles hs soe therodynic dvntges copred ith pure orking fluid. The poer genertion systes bsed on oni-ter ixture re proven to be one of the fesible ethods for the conversion of lo-grde het sources in the for of sensible energy into useful ork. Other thn tht oni is reltively inexpensive, the use of oni in the binry ixture ith ter possesses severl erits. Aoni nd ter hve the siilr oleculr eights nd thus, trditionl design of ste turbines cn be used in the oni-ter poer cycles fter soe inor odifictions. In ddition, the boiling point of oni is substntilly loer thn tht of ter, hich kes it prcticlly useful to utilize the lo-teperture ste het in the poer genertion systes. Conventionl ste cycles cn be converted into the oni-ter poer cycles ithout severe chnges [1]-[3]. Ibrhi [1] studied n oni-ter Rnkine cycle nd found tht the design of het exchnger netorks cn hve significnt ipct on the perfornce of poer cycles. Ibrhi nd Klein [4] developed ethodology Mnuscript received Deceber 12, 2013; revised Februry 10, doi: /joce

2 Journl of Autotion nd Control Engineering Vol. 3, No. 1, Februry 2015 turbine inlet pressure on the syste perfornce re extensively investigted. LNG is plying significnt role s energy resource. Thus, ny reserchers eployed LNG s het sink of poer syste to recover the LNG s cold energy. Choi nd Chng [13] therodyniclly studied poer genertion cycle utilizing the LNG cold energy. LNG s used s het sink, nd the poer cycle consisted of the open nd closed Rnkine cycles, nd the closed Bryton cycle. Miyzki et l. [14] copred the conventionl refuse incinertion poer cycle ith cobined poer cycle using LNG cold energy. Shi nd Che [15] proposed cobined syste consisted of the Rnkine cycle ith oni-ter ixture s orking fluid nd the LNG poer genertion cycle. Wng et l. [3] proposed n oni-ter poer syste ith LNG s its het sink. Ki et l. [16] studied n oni-ter regenertive Rnkine cycle ith LNG s its het sink. Ro et l. [17] proposed cobined cycle, in hich loteperture solr energy nd cold energy of LNG cn be effectively utilized together. This pper perfors the coprtive therodynic nlyses for cobined poer cycle consisted of n oni-ter Rnkine cycle ith nd ithout nd LNG cycle. It is considered tht LNG is used to produce the soe poer output s ell s to condense the oni-ter ixture s het sink. The effects key syste preters such s oni concentrtion nd II. SYSTEM ANALYSIS A cobined poer genertion cycle consisted of n oni-ter Rnkine cycle ith nd ithout regenertion nd LNG cycle is considered. The syste uses lo-teperture het source in the for of sensible energy nd uses LNG t cryogenic teperture of -162oC, s shon in Fig. 1. In the oni-ter Rnkine cycle, the ixture is copressed through puping process in pup 1 fro stte 1 to ste 2, preheted by the het of the turbine 1 outlet ixture in regenertor to stte 3, nd heted ith the source ir in het exchnger I to stte 4. Then, it is expnded in turbine 1 fro stte 4 to stte 5, cooled don hile heting the ixture exiting the pup to stte 6, nd cooled don gin by the het exchnge process ith the LNG cycle in het exchnger II bck to stte 1. In the LNG cycle, enhile, LNG of stte 7 supplied fro the reservoir is evported nd pressurized in pup 2 fro stte 7 to ste 8. Lter, LNG enters het exchnger II nd releses the cold energy in order to condense the oni-ter ixture, nd heted by the het of the ixture to stte 9. After tht LNG enters turbine 2 nd produces soe ork, finlly reches stte 10. Figure 1. Schetic digr of the syste (ith regenertion). rte of orking fluid. In the syste, hen the inlet pressures of turbine 1 nd 2 is PH, PH2, respectively nd ss frction of oni in the oni-ter ixture is xb, therodynic stte of the fluid in ech syste eleent is deterined fro the eqution of stte, nd the ss nd energy blnce equtions. In this pper, therodynic properties of liquid nd vpor phse of the oni-ter ixture re evluted by using the excess Gibbs free energy GE s [18]; In this pper, the high-teperture het source of the cobined cycle is ssued to be stndrd ir ith n inlet teperture of Ts. In ddition, the het loss except t the het exchngers nd the pressure vrition except t the turbines nd pups re ignored. Isentropic efficiencies of pup nd turbine re ssued to be constnt nd hve vlues of ηp1, ηp2, ηt1, ηt2, respectively. The teperture difference beteen hot nd cold fluids in the het exchngers re intined to be greter thn prescribed pinch point teperture difference ΔTpp, hile the iniu teperture difference in the regenertor is equl to ΔTpp. The oni-ter ixture is heted in het exchnger I to teperture loer thn the source inlet teperture by ΔTH. In the cse of producing poer using the loteperture het sources in the for of sensible het, it is desirble to produce the xiu poer fro the supplied het source. Therefore, e ssue tht the syste is driven under the condition of xiu flo G E / RT x(1 x) F1 F2 (2 x 1) F3 (2 x 1) 2 (1) Here, R is the universl gs constnt, T is the bsolute teperture, nd x is the ole frction of oni in the ixture, nd F1, F2, nd F3 re the functions of teperture nd pressure. The equilibriu sttes of liquid nd vpor phse re clculted using the pproch of Ki et l. [10], given by G l G g l g N T, P, N N T, P, N 62 (2)

3 l g l G G N N T, P, N T, P, N Here, μ is the cheicl potentil, N, N, nd N re nubers of oles of oni, ter, nd the ixture, respectively. Superscripts l nd g denote the liquid nd gs phse, respectively. The Gibbs free energy of G for liquid or gs phse is ritten s G g E G RT x N G RT ln(1 x NG (3) N ln ) (4) Finlly, for the nlysis of LNG cold energy cycle, LNG is ssued to be pure ethne, nd its therodynic properties re evluted by using the Ptel-Tej eqution of stte [19]-[20]: RT ( T ) P (5) v b v( v b) c( v b) unit ss of source fluid is shon in Fig. 2. Het ddition is equl to the product of the ss flo rte of orking fluid nd the enthlpy difference beteen inlet nd outlet of het exchnger 1. In the siple cse the het ddition increses ith incresing oni concentrtion nd decreses ith the turbine inlet pressure, hich is inly due to incresing of ss flo rte of the ixture in the het exchnger I. In the regenertion cse, hoever, s oni concentrtion increses, the het ddition increses first, nd then its incresing rte is reduced or decreses, nd increses gin, hich is inly due to the behvior of het trnsfer of regenertion. 2 2 ( T ) T R T c ( ) (6) P c RT b c b P c (7) RT c c c P c (8) III. RESULTS AND DISCUSSIONS In this pper the cobined syste ithout regenertion (siple cse) nd ith regenertion (regenertion cse) re coprtively investigted. The oni concentrtion, x b, nd turbine inlet pressure of oni-ter cycle, P H, re used s the key syste preters nd the syste perfornce is investigted for vrying vlues of these preters. Other bsic dt of the syste vribles re s follos: T s = 200, ΔT H = 20, T c = 5, ΔT pp = 10, P H2 = 30br, P L2 = 4br, η p1 = η p2 = 0.70, η t1 = η t2 = 0.80, q t = 0.90, respectively. Figure 3. Effect of oni concentrtion on het trnsfer of regenertion per unit ss of source for vrious turbine inlet pressures. Fig. 3 shos the effect of oni concentrtion nd turbine inlet pressure on the het trnsfer of regenertion per unit ss of source fluid. The regenertion hs pek vlue ith respect to oni concentrtion for ech turbine inlet pressure. Hoever, it decreses ith the increse of turbine inlet pressure. Figure 4. Effect of oni concentrtion on net ork per unit ss of source for vrious turbine inlet pressures. Figure 2. Effect of oni concentrtion on het ddition per unit ss of source for vrious turbine inlet pressures. The effect of oni concentrtion nd turbine inlet pressure on the ount of het ddition to the syste per The effect of oni concentrtion nd turbine inlet pressure on the net ork production per unit ss of source fluid is shon in Fig. 4. The net ork production is equl to the difference beteen the het dded to the syste nd het dischrged fro the syste. In the 63

4 siple cse the net ork increses ith incresing oni concentrtion nd is lrger for loer turbine inlet pressures. In the regenertion cse, there exists locl xiu vlue ith respect to oni concentrtion. Figure 5. Effect of oni concentrtion on therl efficiency for vrious turbine inlet pressures. Fig. 5 shos the effect of oni concentrtion nd turbine inlet pressure on the therl efficiency of the syste. Here, the therl efficiency of the cobined cycle is defined s the rtio of net ork production to the het ddition to the syste. As oni concentrtion increses in the siple cse, it decreses first nd reches iniu vlue nd the increses gin. As oni concentrtion increses in the regenertion cse, it decreses first nd then increses to locl xiu vlue nd then decreses gin. For fixed oni concentrtions, both the siple nd regenertion cse ith higher turbine inlet pressure yield higher therl efficiency. Figure 6. Effect of oni concentrtion on the totl therl conductnce for vrious turbine inlet pressures. The effect of oni concentrtion nd turbine inlet pressure on the totl therl conductnce, UA tot, is shon in Fig. 6. The totl conductnce of the cobined syste is the su of the therl conductnce of het exchngers in the syste. The totl therl conductnce increses ith incresing oni concentrtion nd decreses ith incresing turbine inlet pressure. For the vlues of turbine inlet pressure nd for rnge of oni concentrtion considered the totl therl conductnce of regenertion cycle is higher thn tht of siple cycle. IV. CONCLUSIONS In this pper the coprtive perfornce nlysis is crried out for the cobined cycle of oni-ter poer genertion cycle ith nd ithout regenertion nd LNG cycle. The in results cn be surized s follos: The het trnsfer of regenertion hs pek vlues ith respect to oni concentrtion. The net ork of the cobined cycle increses ith oni concentrtion in siple cse, but there exists pek vlue in regenertion cse. There exists iniu therl efficiency ith oni concentrtion in siple cse but xiu one in regenertion cse. The totl therl conductnce increses ith oni concentrtion nd decreses ith turbine inlet pressure. ACKNOWLEDGMENT This pper s supported by Reserch Fund, Kuoh Ntionl Institute of Technology. REFERENCES [1] O. M. Ibrhi, Design considertions for oni-ter rnkine cycle, Energy, vol. 21, pp , [2] K. H. Ki, H. J. Ko, nd K. Ki, Assessent of pinch point chrcteristics in het exchngers nd condensers of oni ter bsed poer cycles, Applied Energy, vol. 113, pp , [3] J. Wng, Z. Yn, M. Wng, nd Y. Di, Therodynic nlysis nd optiiztion of n oni-ter poer syste ith LNG (liquefied nturl gs) s its het sink, Energy, vol. 50, pp , [4] O. M. Ibrhi nd S. A. Klein, Therodynic perfornce ssessent of n oni ter rnkine cycle for poer nd het production, Energy Conversion nd Mngeent, vol. 51, pp , [5] C. Zfirescu nd I. Dincer, Therodynic nlysis of novel oni-ter trilterl Rnkine cycle, Therochi. Act, vol. 477, pp. 7-15, [6] P. Roy, M. Désilets, N. Glnis, H. Nesreddine, nd E. Cyer, Therodynic nlysis of poer cycle using loteperture source nd binry NH 3 H 2O ixture s orking fluid, Int. J. Ther. Sci., vol. 49, pp , [7] W. R. Wger, C. Zfirescu, nd I. Dincer, Absorption poer cycle, Energy, vol. 21, pp , [8] K. H. Ki, S. W. Ki, nd H. J. Ko, Study on the Rnkine cycle using oni-ter ixture s orking fluid for use of loteperture ste het, Trns. of the Koren Hydrogen nd Ne Energy Society, vol. 21, pp , [9] K. H. Ki, C. H. Hn, nd K. Ki, Coprtive exergy nlysis of oni-ter bsed rnkine cycles ith nd ithout regenertion, Int. J. Exergy, vol. 12, pp , [10] K. H. Ki, C. H. Hn, nd K. Ki, Effects of oni concentrtion on the therodynic perfornces of oni ter bsed poer cycles, Therochiic Act, vol. 530, pp. 7-16, [11] Interntionl Energy Agency, Golden rules for golden ge of gs, World energy outlook specil report on unconventionl gs, Noveber [12] E. A. Roszk nd M. Choroski, Exergy nlysis of cobined siultneous liquid nturl gs vporiztion nd dsorbed nturl gs cooling, Fuel, vol. 111, pp ,

5 [13] K. I. Choi nd H. M. Chng, Therodynic nlysis of poer genertion cycle utilizing LNG cold energy, Superconductivity nd Cryogenics, vol. 1, pp , [14] T. Myzki, Y. T. Kng, A. Akis, nd T. Kshigi, A cobined poer cycle using refuse incinertion nd LNG cold energy, Energy, vol. 25, pp , [15] X. Shi nd D. Che, A cobined poer cycle utilizing loteperture ste het nd LNG cold energy, Energy Conversion nd Mngeent, vol. 50, pp , [16] K. H. Ki, J. H. Oh, nd S. W. Ki, Anlysis of regenertive poer cycle utilizing lo-grde het source nd LNG cold energy, Int. J. Mining, Metllurgy Mech. Eng., vol. 1, pp , [17] W. J. Ro, L. J. Zho, C. Liu, nd M. G. Zhng, A cobined cycle utilizing LNG nd lo-teperture solr energy, App. Ther. Eng., vol. 60, pp , [18] F. Xu nd D. Y. Gosi, Therodynic properties of oni-ter ixtures for poer cycle, Energy, vol. 24, pp , [19] K. H. Ki nd C. H. Hn, Anlysis of trnscriticl orgnic rnkine cycles for lo-grde het conversion, Advnced Science Letters, vol. 8, pp , [20] T. Yng, G. J. Chen, nd T. M. Guo, Extension of the ongsndler ixing rule to the three-preter ptel-tej eqution of stte: Appliction up to the ner-criticl region, Cheicl Engineering Journl, vol. 67, pp , Kyoung Hoon Ki received the Ph.D. degree in echnicl engineering fro Kore Advnced Institute of Science nd Technology (KAIST) in He is currently Professor in the Deprtent of Mechnicl Engineering t Kuoh Ntionl Institute of Technology, Kore. His reserch interests re in the res of nlysis nd design of energy systes. Je Hyeong Oh received his BA degree in echnicl engineering fro Kuoh Ntionl Institute of Technology (KIT), Gui, Kore in He is currently Mster Cndidte t the KIT. His current reserch interests re in the res of odeling nd design of energy systes. Hyung Jong Ko received his MS nd Ph.D. degrees in echnicl engineering fro Kore Advnced Institute of Science nd Technology, Seoul, Kore in 1983 nd 1988, respectively. He currently orks s Professor in the Deprtent of Mechnicl Engineering, Kuoh Ntionl Institute of Technology, Kore. His current reserch interest is in the re of fluids nd therl syste odeling. 65