The Effect Of Type-III Antifreeze Proteins (AFPs) On CO2 Hydrate Slurry Formation

Transcription

1 Purdue Unversty Purdue e-pubs Internatnal Refrgeratn and Ar Cndtnng Cnference Schl f Mechancal Engneerng 2014 The Effect Of Type-III Antfreeze Prtens (AFPs) On CO2 Hydrate Slurry Frmatn Hngxa Zhu Delft Unversty f Technlgy, Netherlands, The, h.zhu-1@tudelft.nl Carls A. Infante Ferrera Delft Unversty f Technlgy, Netherlands, The, C.A.InfanteFerrera@tudelft.nl Fllw ths and addtnal wrks at: Zhu, Hngxa and Infante Ferrera, Carls A., "The Effect Of Type-III Antfreeze Prtens (AFPs) On CO2 Hydrate Slurry Frmatn" (2014). Internatnal Refrgeratn and Ar Cndtnng Cnference. Paper Ths dcument has been made avalable thrugh Purdue e-pubs, a servce f the Purdue Unversty Lbrares. Please cntact epubs@purdue.edu fr addtnal nfrmatn. Cmplete prceedngs may be acqured n prnt and n CD-ROM drectly frm the Ray W. Herrck Labratres at Herrck/Events/rderlt.html

2 2405 Page 1 The effect f Type-III Antfreeze Prtens (AFPs) n CO 2 hydrate slurry frmatn Hngxa ZHOU *, Carls INFANTE FERREIRA Delft Unversty f Technlgy, Department Prcess & Energy Delft, NL 2628 CB 39, The Netherlands h.zhu-1@tudelft.nl * Crrespndng Authr ABSTRACT CO 2 hydrate slurry s a favurable drect clant f fresh prducts due t ts large latent heat and phase change temperature arund 5 C. Cntnuus prductn f ths slurry s, hwever, dffcult t realse due t the hgh rate f hydrate frmatn. The use f addtves s prpsed wth the purpse f decreasng the frmatn rate s that the cntrllablty f the prcess s mprved. Type-III Antfreeze Prtens (AFPs) are nn-psnus addtves whch have prven t be nhbtrs f hydrate frmatn. These addtves have als shwn t prtect the b-cells f fresh prducts frm damagng by freezng. The effect f these addtves n the CO 2 hydrate frmatn rate s expermentally nvestgated. The experments have been perfrmed n a cl heat exchanger wth 6 mm nternal dameter under peratng cndtns crrespndng t hydrate frmatn cndtns. The cncentratn f Type-III AFPs has been vared: n addtves, 5 ppm and 10 ppm. The mxture f addtves and CO 2 -water slutn s cled dwn untl the hydrate frmatn cndtns are attaned. The grwth rate f hydrates n the wall f the heat exchanger has been derved frm the varatn f the verall heat transfer ceffcent wth tme. Results shw that the addtn f AFPs changes the supersaturatn degree f CO 2 water slutn needed t ntate the hydrate frmatn prcess. A lw cncentratn f the prpsed addtves s suffcent t slw dwn the frmatn rate f CO 2 hydrate mprvng sgnfcantly the cntrllablty f the hydrate prductn prcess. 1. INTRODUCTION The depletn f the zne layer and the emssn f greenhuse gases are tw majr envrnmental ssues whch pse great cncerns t manknd and specfcally t the refrgeratn ndustry. Bth envrnmental cncerns and legal safety requrements frce the search fr new ways t phase ut the ptent greenhuse gases. One f the pssble cntrbutns t the reductn f these emssns s by reducng the quantty f prmary refrgerants by utlzng secndary fluds. Prmary refrgerants such as CFCs and HCFCs have been r are beng phased ut n cmplance wth the Mntreal Prtcl. Als HFCs are beng lmted due t ther sgnfcant cntrbutn t glbal warmng. Phase change materals (PCMs) can be used as secndary fluds whch underg a phase change frm sld t lqud r lqud t gas r vce versa. Clathrate hydrate slurry cnsstng f water and fne sld clathrate partcles s a prmsng canddate PCM fr rapd chllng f fresh prducts. CO 2 hydrate slurry s a favurable secndary flud whch can be appled n drect cntact t fresh prducts: t has a large latent heat (507 kj/kg) and pstve phase change temperature (4-8 C). Ths allws fr the applcatn f prmary refrgeratn cycles whch perate at sgnfcantly hgher evapratng temperatures than cycles appled n cnventnal rapd chllng plants. The refrgeratn cycle effcency s crrespndly sgnfcantly hgher than usual.

3 2405 Page 2 There are three types f AFPs whch have been slated frm the bdy fluds f many speces f plar fsh. AFPs are classfed n the bass f ther cmpstn and tertary structures (Snnchsen et al., 1995). AFPs are envrnmental frendly addtves that are able t prevent hydrate grwth (Zeng et al., 2003) by bndng t the surface f hydrate nucle (Kelland, 2006) actng as knetc nhbtrs f crystal grwth. Ths study nvestgates the nfluence f AFPs n the frmatn rate f CO 2 hydrate. The results are relevant when cntnuus prductn f CO 2 hydrate slurry s t be develped. 2.1 Expermental apparatus Fgure 1 shws a schematc dagram f the expermental setup. The system cntans tw thermstatc baths wth tw cl heat exchangers, a gear pump, tw vessels (nt shwn), tw glass wndws and a range f sensrs. The sensrs are placed befre and after the cld bath where the hydrates wll frm. The flw s crculated wth the gear pump (0.37 kw) wth adjustable speed and vsualzed frm the tw sght glasses. The water s ultra denzed water. 2. EXPERIMENT Fgure 1: Set-up fr CO 2 hydrate frmatn. 2.1 Expermental methd After the system has been brught t vacuum the CO 2 water slutn wth r wthut the addtn f AFPs s added. The system s cled by the thermstatc bath flled wth water frm 10 C wth steps f 0.5 K untl there are crystals appearng n the sght glasses. The effectve clng capacty f each bath s 0.3 kw. The secnd thermstatc bath (warm bath) s kept abut 1 K hgher than the frst ne (cld bath). Temperature f the fluds s measured at the nlet and utlet f the cld cl heat exchanger by PT temperature sensrs. Tw pressure sensrs are lcated befre and after the cl heat exchanger n the cld thermstatc bath t measure the pressure drp. The densty s measured wth a Crls Fgure 2: Hydrate frmatn n the wall f the cl. tubes mass flw meter. Temperatures, pressures, flw rate and densty are stred every 5 secnds by a data lgger. It s assumed that the hydrate crystals wll frstly frm n the wall f the tube lcated n the cld bath, whch wll ncrease the thermal resstance f the system, as depcted n Fgure 2. The expermental verall heat transfer ceffcent f the system s calculated based n the measured temperatures, pressures and flw rates

4 2405 Page 3 U e x p... P m m Q l s s s A Tln (1) Where T ln s defned as T ln ( T T ) ( T T ) n le t b a th u tle t b a th T ln T n le t u tle t T T b a th b a th (2) The energy lss n Eq. 1 equals t 3 W. The verall heat transfer ceffcent frm the mdel wthut hydrates frmatn s calculated by Equatn (3) d d ln 1 1 d d 1 (3) U h 2 k d h w Equatn (4) s used t calculate the verall heat transfer ceffcent after hydrate crystals are frmed d d d ln d ln 1 1 d d d 1 h (4) U h 2k 2k d h h w h h Prevus studes have shwn that the uter heat transfer ceffcent frm the thermstatc bath s best predcted wth the crrelatn f Churchll and Chu (1975) Nu * Ra 1 / (1 ( ) ) Pr 9 /1 6 4 / 9 (5) Smlarly nner heat transfer ceffcent s best predcted wth the equatn f Edwards et al. (1979) Nu s d R e P r L d R e P r L c c 2 / 3 (6) 3. RESULTS 3.1 Phase equlbrum f CO 2 +H 2 O hydrate Damnd and Aknfev (2003) nvestgated the CO 2 slublty n water. Yang et al. (2000) measured the phase equlbrum fr CO 2 +H 2 O n hydrate frmatn cndtns (shwn n Fgure 3). Hydrates can nly be frmed n the left sde f pnt Q2. The supersaturatn degree at hydrate frmatn s defned as

5 Temperarure, C Pressure, bar 2405 Page 4 T T T The degree f supersaturatn s qute an mprtant factr t determne the ntalzatn f hydrate frmatn. The supersaturatn f CO 2 slutn at hydrate frmatn wth and wthut the addtn f Type-III AFPs n dfferent cncentratns wll be expermentally nvestgated. eq e x p 3.2 Experments Set-up calbratn Befre the system s appled fr the expermental research, t s necessary t calbrate the system t make sure that t s accurate enugh fr the current wrk. Q2 The calbratn experments were dne wth CO 2 water slutn nsde Fgure 3: Phase equlbrum f CO 2 -H 2 O the tube. Fgure 4 and Fgure 5 shw the temperature and pressure hydrate. Frm Yang et al. (2000). change wth tme. In the whle prcess, the cndtn f the slutn s ut f the hydrate frmatn regn whch can be derved frm Fgure 3. The wall temperature has been derved frm the nternal heat flux, wth Equatns (5) and (6) Temperature change durng hydrates frmatn pressure change durng hydrates frmatn nlet pressure utlet pressure nlet temperature utlet temperature bath temperature nsde wall temperature equlbrum temperature Fgure 4: Temperature change wthut hydrate frmatn. Fgure 5: Pressure change wthut hydrate frmatn. The verall heat transfer ceffcent s predcted wth Equatn 3, n whch the external and nternal heat transfer ceffcents are btaned wth Equatns (5) and (6). Fgure 6 shws a cmparsn between the predcted and expermental values whch are btaned frm Equatn (1). The devatn s attrbuted t the predctn f the natural cnvectn heat transfer ceffcent utsde the cl. The expermental data have been used t determne the average values f the ceffcents f Equatn (7). b N u a R a (7) Fgure 7 shws the cmparsn f the verall heat transfer ceffcent derved when Equatn (5) s substtuted by Equatn (7) wth ceffcents a = 0.58 and b = 0.2.

6 Temperarure, C Pressure, bar verall heat transfer ceffcent, W m -2 K -1 verall heat transfer ceffcent, W m -2 K Page expermental predcted expermental predcted Fgure 6: Cmparsn f verall heat transfer ceffcent expermental and predcted wth Equatn (5) Fgure 7: Cmparsn f verall heat transfer ceffcent expermental and predcted wth Equatns (6) and (7) Hydrate frmatn wthut the addtn f AFPs CO 2 hydrate frmatn experments were dne frstly wthut the addtn f AFPs. Fgure 8 and Fgure 9 present the temperature and pressure change durng the clng dwn f CO 2 water slutn. Fgure 8 shws that the temperature f slutn s cled dwn gradually frm the begnnng. When the nsde temperature reached abut 7.0 C and pressure was abut 30 bar, temperature started ncreasng whle the pressure n the nlet jumped frm 30 bar t 40 bar suddenly Temperature change durng hydrates frmatn nlet temperature utlet temperature bath temperature nsde wall temperature equlbrum temperature pressure change durng hydrates frmatn nlet pressure utlet pressure Fgure 8: Temperature change durng hydrate frmatn wthut the addtn f AFPs Fgure 9: Pressure change durng hydrate frmatn wthut the addtn f AFPs. Wth Equatn (7), the verall heat transfer ceffcent s predcted wth a=0.58 and b=0.2. Hydrate dameter s then derved frm Equatn (1), Equatn (4) and Equatn (6). Fgure 10 shws durng hydrate frmatn cndtns the expermental and predcted verall heat transfer ceffcent whch shw a reasnable match when there are n hydrates frmed. Cmbnng wth Fgure 11, t seems that there s n hydrate frmatn untl secnds when a large amunt f hydrates were frmed and the ppes were blcked qute sn.

7 Temperarure, C Pressure, bar verall heat transfer ceffcent, W m -2 K -1 nternal dameter durng hydrate frmatn, m 2405 Page expermental predcted 10 x 10-3 hydrate dameter Fgure 10: Cmparsn f verall heat transfer ceffcent expermental and predcted wth Equatns (6) and (7) Fgure 11: Hydrate dameter change wth Equatns (1), (4), (6) and (7) Hydrate frmatn wth the addtn f 5 ppm AFPs Fgure 12 and Fgure 13 shw the temperature and pressure change durng CO 2 water slutn clng dwn wth the addtn f 5 ppm AFPs n weght percent. The temperature was lwered gradually untl a blckage tk place Temperature change durng hydrates frmatn nlet temperature utlet temperature bath temperature nsde wall temperature equlbrum temperature pressure change durng hydrates frmatn nlet pressure utlet pressure Fgure 12: Temperature change when CO 2 hydrate frmed wth 5 ppm AFPs Fgure 13: Pressure change when CO 2 hydrate frmed wth 5 ppm AFPs. When the ceffcents f Equatn (7) are a = 0.58 and b = 0.2, the cmparsn f the veral heat transfer ceffcent s shwn n Fgure 14. The devatn s attrbuted t the calculatn f the nternal heat transfer ceffcent. When Equatn (6) s mdfed t Nu s d R e P r L d R e P r L c c 2 / 3 (8)

8 nternal dameter durng hydrate frmatn, m verall heat transfer ceffcent, W m -2 K -1 verall heat transfer ceffcent, W m -2 K Page 7 there s a gd match f the predcted and expermental values f the verall heat transfer ceffcent, whch can be seen frm Fgure 15. The secnd part f Equatn (8) s qute small cmpared wth the frst part, therefre, n ths case, by usng Equatn (8) the nsde heat transfer ceffcent s reduced by abut 30% due t the addtn f AFPs expermental predcted expermental predcted Fgure 14: Cmparsn f verall heat transfer ceffcent wth 5 ppm AFPs expermental and predcted wth Equatns (6) and (7) Fgure 15: Cmparsn f verall heat transfer ceffcent wth 5 ppm AFPs expermental and predcted wth Equatns (7) and (8). Then the hydrate dameter s calculated as a functn f tme by usng f Equatn (1) and Equatn (4). It can be seen frm Fgures 15 and 16 that hydrates started frmng frm abut secnds, whle there were n crystals vsble n the sght glasses mentned abve. Therefre, t s assumed that the hydrate crystals are pssbly frmed n the wall f the tube n the cld bath frstly. There was a sharp temperature decrease at secnds, that pssbly caused the crystal frmatn. Frm then n, hydrates frmed untl abut secnds when the ppe was blcked. Ths can be seen frm Fgure 16 that shws that the hydrate dameter reduced t almst zer hydrate dameter Fgure 12 shws that at the mment hydrates started frmng the dfference between the nsde wall temperature and the equlbrum temperature s qute small (0.3 K). It means that the addtn f 5 ppm desn t change t much the superclng degree f the CO 2 slutn Fgure 16: Hydrate dameter change wth the addtn f 5 ppm AFPs. The hydrate grwth rate can be derved frm Fgure 16 by usng Equatn (9). The average grwth rate s kg/h frm secnds t secnds. The hydrates frmed rapdly n the begnnng and then kept stable untl the ppe was blcked. G h 2 2 ( d d ) L h h c 4 t (9) The average hydrate grwth rate s abut 0.5 µm/s durng the tme frm secnds t secnds whle the superclng was ntally abut 0.3 K.

9 Temperarure, C Pressure, bar 2405 Page 8 v d d h (10) t Whle the hydrate grwth rate derved frm Uchda et al. (2002) by Equatn (10) when the superclng degree equals t 0.3 K s mm/s. vu c h d a T (11) Hydrate frmatn wth the addtn f 10 ppm AFPs Fgure 17 and Fgure 18 shw the temperature and pressure change durng hydrate frmatn wth the addtn f 10 ppm AFPs. The slutn s cled dwn frm abut 10 C n steps untl there s a sharp ncrease accmpaned by a sudden rse f pressure. Smlarly t the prevus case, when the ceffcents f Equatn (7) have been mdfed as a = 0.58 and b = 0.2, and the nternal heat transfer ceffcent s calculated by Equatn (8), the values f the expermental and predcted verall heat transfer ceffcent shw a gd match, whch can be seen frm Fgure 19. The hydrate dameter s calculated as a functn f tme by usng Equatns (1), (4), (7) and (8) Temperature change durng hydrates frmatn nlet temperature utlet temperature bath temperature nsde wall temperature equlbrum temperature pressure change durng hydrates frmatn nlet pressure utlet pressure Fgure 17: Temperature change when CO 2 hydrate frmed wth 10 ppm AFPs Fgure 18: Pressure change when CO 2 hydrate frmed wth 10 ppm AFPs. Fgure 19 and Fgure 20 shw that frm abut secnds (14.4 hurs) n, a devatn between the expermental and predcted verall heat transfer ceffcent starts t appear. But the hydrate dameter decreased suddenly at abut secnds, and kept cnstant untl t went dwn agan frm secnds. t s pssbly because the sharp decrease at secnds seen frm Fgure 17 whch nduced the frst decrease. Therefre, hydrate s assumed t start frmng frm secnds, wth nsde all temperature and pressure 5 bar hle the e ulbrum temperature at 5 bar s abut hen the superclng degree th the addtn f 10 ppm AFPs s 2.1 K as the frst crystals are frmed. The average hydrate grwth rate frm Fgure 20 derved frm Equatn (9) s kg/h frm secnds t secnds. The hydrate thckness grwth rate derved by usng Equatn (10) s abut 0.033µm/s when the hydrate started frmng at ntal superclng degree f 2.1 K, whle the grwth rate btaned frm Equatn (11) s 3.63 mm/s at superclng degree f 2.1 K.

10 verall heat transfer ceffcent, W m -2 K -1 nternal dameter durng hydrate frmatn, m 2405 Page hydrate dameter expermental predcted Fgure 19: Cmparsn f verall heat transfer ceffcent wth 10 ppm AFPs expermental and predcted wth Equatns(7) and (8) Fgure 20: Hydrate dameter change wth the addtn f 10 ppm AFPs. 3.3 Dscussn Table 1 summarzes the nfluence f AFPs n CO 2 hydrate frmatn cmpared wth the results frm Uchda et al. (2002). It ndcates that the superclng degree f CO 2 hydrate frmatn s nfluenced sgnfcantly when the cncentratn f AFPs s 10 ppm, whle wth 5 ppm AFPs there was almst n effect n the superclng degree. The hydrate frmatn rate can be derved when there s an addtn f AFPs n the slutn, and t s sgngcantly lwered dwn wth the addtn f AFPs. Cncentratn f AFPs / ppm Table 1: Influence f AFPs n hydrate frmatn vares wth cncentratn h wth /h wthut Superclng / K Grwth rate / (kg/h) Frmatn rate (Eq. 9/Eq. 10) / (mm/s) e-3/ e-3/3.63 The experments have ndcated that the addtn f AFPs t the CO 2 -water slutn als reduces sgnfcantly the heat transfer ceffcent whch can be seen frm Table CONCLUSIONS The addtn f Type-III AFPs changes the CO 2 hydrate frmatn behavur. Wth the addtn f 10 ppm AFPs n weght percent, the superclng degree s ncreased a lt cmpared wth that wthut the addtn f AFPs. The addtn f 5 ppm AFPs has a much smaller effect. Wth the addtn f 5 ppm and 10 ppm AFPs, the hydrate prductn rate can be determned. Whle n the case wthut the addtn f AFPs the grwth rate s t large s that ts rate cannt be determned frm the present experments. NOMENCLATURE A Area m 2 ν Flm grwth rate m s -1

11 2405 Page 10 d Dameter m π P h Heat transfer ceffcent W m -2 K -1 ρ Densty kg m -3 Enthalpy J kg -1 Subscrpt k Thermal cnductvty W m -1 K -1 bath Bath L Length m c Cl ṁ Mass flwrate eq Equlbrum Nu Nusselt number exp Expermental P Pressure Pa h Hydrate Pr Prantl number Inner Q Energy flw J s -1 nlet Inlet Ra Raylegh number ln Lgarthmc Re Reynlds number lss Lss T Temperature K mean Mean t Tme s Outer U Overall heat transfer W m -2 K -1 utlet Outlet ceffcent Greek s Slurry Δ Dfference w Wall REFERENCES Churchll, S.W., Chu, H.H.S., 1975, Crrelatng equatns fr lamnar and turbulent free cnvectn frm a hrzntal cylnder. Int. J. Heat Mass Transfer. vl. 18, p Damnd, L.W., Aknfev, N.N., 2003, Slublty f CO 2 n water frm -1.5 t C and frm 0.1 t MPa: evaluatn f lterature data and thermdynamc mdellng, Flud Phase Equlbra, vl. 208, p Edwards, D.K., Denny, V.E., Mlls, A.F., 1979, Transfer Prcesses, 2nd ed., Hemsphere, Washngtn, D.C.. Kelland, M.A., 2006, Hstry f the develpment f lw dsage hydrate nhbtrs, Energy Fuels 20, p Snnchsen, F.D., Sykes, B.D., Daves, P.L., 1995, Cmparatve mdellng f the 3-dmensnal structure f type-ii antfreeze prten, Prten Sc. vl. 4, n. 3 : p Uchda, T., Ikeda, I.Y., Ebnuma, T., Naga, J., Narta, H., 2002, CO 2 hydrate flm frmatn at the bundary between CO 2 and water: effects f temperature, pressure and addtves n the frmatn rate, Jurnal f Crystal Grwth, p Yang, S.O., Yang, I.M., Km, Y.S., Lee,C.S., 2000, Measurement and predctn f phase equlbra fr water+co 2 n hydrate frmatn cndtns, Flud Phase Equlbra, vl.175, p Zeng, H., Wlsn, L.D., Walker, V.K., Rpmeester, J.A., 2003, The nhbtn f tetrahy- drfuran clathratehydrate frmatn wth antfreeze prten, Can. J. Phys, vl.81, p