Exergetic analyses applied in Pilot Plant for Tritium and ... - Wseas.us

Proceedings of the 2nd International Conference on Environmental and Geological Science and EngineeringExergetic analyses applied in Pilot Plant for Tritium andDeuterium SeparationSORIN GHERGHINESCUDepartment : 1 National Institute of R&D for Cryogenics and IsotopesTechnologies (ICIT)Adress : code 240050 - Rm. Valcea, Uzinei 4, CP10, Valcea, ROMANIA,phone:0040 250 736979, fax:0040 250 732746,COUNTRY : Romaniae-mail: sorin@icsi.ro sorin70g@yahoo.comT http://www.icsi.roAbstract : In the nuclear reactors using uranium as fuel and heavy water asmoderator, after a while, due to increased tritium concentration as result of neutronscapture on deuterium nucleus, we have to establish a set of measures to decrease thetritium concentration.The amount of tritium obtained in a CANDU reactor is about 2,4 KCi/MW.The experimental plant realise the separation and extraction of tritium from tritiatedheavy water at 30 Ci/kg (for a higher concentration will be diluted at that level).The tritium request in the USA was 4*10 6 Ci in 1980; in Romania was 2*10 4 Ci in1990, 3*10 4 in 2000 and will continue to increase. On present times the price fortritium is estimated at about 2$/Ci [1] on international market and increasing. This isdue to growing and continues diversification of application fields; nuclear medicine,nuclear fusion, research labs.The experimental Pilot plant for tritium and deuterium separation, part ofNational Research and Development Institute for Cryogenics and Isotopic Technologies- ICSI Rm.Valcea, as principal target have to establish the technology of the waterhydrogencatalyzed isotopic exchange and cryogenic distillation for mixtures ofhydrogen and his isotopes diatomic species.The main target of the experimental pilot plant is to establish the detritiationtechnology of CANDU reactor moderator and to certify the equipments specific forcryogenic domain and tritiated mediums.The most important part of the experimental Pilot plant for tritium anddeuterium separation is module 300(cryogenic distillation of hydrogen/deuterium/tritiummixture). The principal goals on to that module are:a) to insure and maintain the proper temperature for hydrogen condensation inthe head of the distillation column,b) to elaborate the high efficiency contact elements on hydrogen isotopesseparation.Therefore, to accomplish the task presented at the pointa) , the hydrogendistillation column condenser is cooled within a hydrogen cryogenic cycle which isinsuring a level of temperature within 20-30 K, corresponding to the working pressureof the distillation column.Also, it has to be mentioned the special character both for dynamic and staticequipment as for entire measurement and control systems with are parts oftechnological outflow working under liquid nitrogen temperature.The tasks of experimental techniques effectuate within experimental Pilot plantfor tritium and deuterium separations into module 300 are:ISSN: 1790-2769 242 ISBN: 978-960-474-119-9

Proceedings of the 2nd International Conference on Environmental and Geological Science and Engineering‣ establishing the working parameters in different states of nitrogen cryogeniccycle.‣ functioning checkout for dynamic and static equipments (turboexpanders,compressors, etc.) control and measurement equipments specifically forcryogenics liquids operations.‣ overlooking the materials comportment at cryogenic temperatures booth insteady state and in transition states.Key-Words: exergetic analyses, cryogenic cycles, distillation column.1. IntroductionHydrogen is a carefully manipulatingsubstance, in respect with the laborsafety rules, due to its flammablecharacter for large concentrationinterval (4-75%). It also has anexplosion risk for a concentrationbetween 18 and 65%, especially inclosed areas. Special care has to begiven to avoid the presence of solidoxygen into the liquid hydrogen.Hydrogen sources have industrialcharacter and basically consist in thefollowing technological processes:catalytic steam reforming of naturalgas, partial oxidation of combustiblehydrocarbons, electrolysis of water,dissociation of hydrogen molecular ionswithin the pale of 0,4 – 1.10 -4 mol.%Three isotopes of hydrogen are known.The most abundant is protium (a singleproton) followed by deuterium (aproton and a neutron) and the leastabundant tritium (a proton and twoneutrons), the third isotope which isvery rare and radioactive (beta_rayemitter with an energy level at 5.6keVand 12.3 years half-life).Hydrogen isotopes separation is basedon the very small differences betweenthe physical characteristics, as shown intable 2, which will characterize thedevelopment of the separationtechnologies by a large specific volumeand a high sensitivity into theemployment of plant.The specifically behavior of hydrogenis due to different arrangements of theparticle spin which constitute thehydrogen molecule.If the particle spins alignment isparallel we speak about ortohydrogen(o-H 2 ) and if particle spins alignmentis opposite (the nuclei are spinning inopposite directions) we haveparahydrogen (p-H 2 ).Table 2H 2 HDD 2DT T 2T K33,24 35,9 38,2 39,5 40,6KPk12,797 14,6 16, 17,3 18,1kg/cm 2 2V k66,95 _ 60, - 57,1m 3 /mol33 4 5Molecular mass 2(2,016)6g/molBoilingtemperatureat 1atm20,39 22,13 23,57- -At the illustration 1 we can see howthese molecules look like.Figure 1On table 3 we present the principalcharacteristics of the two molecularspecies, orto- and para-hydrogen:Table 3Critical pointBoilingpoint at 1atmOrtho-hydrogenP 12,98 12,759Para-hydrogenT 33,18 32,976ρ 0,01494 0,01559T 20,38 20,2680,0352 0,03511ρ L0,0006606 0,0006636ρ VISSN: 1790-2769 243 ISBN: 978-960-474-119-9

Proceedings of the 2nd International Conference on Environmental and Geological Science and EngineeringTriple pointp->S ->solidP 0,071 0,0695T 13,947 13,803ρS3,04301 0,04291ρL0,03830 0,03821ρV0,0000631 0,0000624atmT -> K2. Operation mode and heat transfercalculationCryogenic cycle of hydrogenTTAt ordinary temperatures, hydrogen is amixture of 75% ortohydrogen and 25%parahydrogen, known as normalhydrogen.The equilibrium percentage of ortoandparahydrogen varies withtemperature as shown in the diagram 2Table 4T(K) 15 20,39 30 50 60 70q(J/s) 527 525 506 364 285 216PPFSRSRTL2.1 Theoretical model for thecalculation of the non-reversible lossesof detention and astrictionTP1TT 2T 22S2TPC303TPTdetentionSFigure 1As the temperature is brought down,the share of parahydrogen increases,reaching 99.8% at equilibrium; this isknown as orto-para conversion, whichtakes place spontaneously in the liquidphase, but very slowly. For example,liquefied normal hydrogen at first hasthe composition of the original gaseoushydrogen. With time, however, thefraction of parahydrogen, (x p-H2 ),increases:LossesLosses1−k⎡ ⎛⎞⎤p k1p1c T⎢ ⎜ ⎛ ⎞ ⎟⎥⎛ ⎞⋅p⎜2p⎟⎢ ⎜ −⎜⎟ ⎟⎥⎝ 2⎢ ⎜ ⎝ ⎠ ⎟⎥⎠⎣ ⎝⎠⎦k −1⎡ ⎛⎞⎤p k⎢ ⎜ ⎛⎟2⎞ ⎥⎢ ⎜1−⎜p⎟ − 1⎟⎥⎛ p ⎞cpT ⎢ ⎜ ⎝ 1 ⎠ ⎟ 2= ⋅⎥ ⋅⎜astrp⎟0⋅ ln 1 +⎢ ⎜ η ⎟⎥⎝ 1 ⎠⎢ ⎜⎟⎥⎢ ⎜⎟⎥⎣ ⎝ P ⎠⎦ir_det=p⋅0⋅ ln 1 − ηdet1ir_astrTTTT212Pk −1k1−kkxp − H 20.25 + 0.00855 ⋅ τ≅1 + 0.00855 ⋅ τWhere τ is the time in hours. Forexample, in 100 h, x p-H2 will be 0.595,and in 1000 h it will be about 0.92.astrictionThe efficiency(η ) of process :SISSN: 1790-2769 244 ISBN: 978-960-474-119-9

Proceedings of the 2nd International Conference on Environmental and Geological Science and Engineeringηηdetastr==h1h1h2sh2−−h2h−−2sh1h1dE2= & m2⋅ [( h2'− h2''− T0⋅ ( s2' '− s2')]with hydrogendE2ηE _ ∆T=dE12.2 Model of calculation the nonreversiblelosses trough trottlingLossesir _ ∆ T=dE1− dE2dE1, dE 2- exergy of the heatexchanged between the two fluidsm&1- flow rate of hot fluid (1)m& - flow rate of cool fluid (2)2Lossesir_trottle= T0⋅ ( s4− s3)2.3 Model of calculation the nonreversiblelosses trough heat transfer1E 2’’dQEE E 1’3.1 Results of exergetic analyses of thecycle:2Losses (%)ir_trottleLosses (%)ir_astrLossesir(%)_ ∆TLosses (%)ir_extηex41 30 15 5 9E − E=E− E1 ` 1`` 2``1= E1`− E1``2= E2``− E2`dEdE2`+ Losses ir_ ∆T3. Experimental data forcryogenic cycleTE321(K)TE322(K)TE325(K)TE326(K)TE330(K)FR306(Nm 3 /h)PR316(bar)PR323(bar)TIME(h)FR306(kmol/h)265 235,7 168,1 164,5 223 29,7 0,32 34 2 1,323977679226 213,6 133,6 128,8 183,3 29,7 0,24 32 3 1,323977679194,9 199,3 115,4 114,7 166,3 31,5 0,4 32 4 1,40421875171,7 189,9 104,6 103,1 154,3 33,3 0,4 36 5 1,484459821154,7 162,5 98,5 93,8 137 37,8 0,24 50 6 1,6850625135,5 140,2 91,4 84,1 120,5 43,2 0,32 61 7 1,925785714119,6 129 87,8 79 113,2 46,8 0,36 66 8 2,086267857114,8 120,8 81,6 71 113,1 48,6 0,48 68 9 2,166508929dE[( h − h − T ⋅ s − )]1m1⋅1' 1' ' 0(1's1''= &ISSN: 1790-2769 245 ISBN: 978-960-474-119-9

Proceedings of the 2nd International Conference on Environmental and Geological Science and Engineering4. ConclusionsIt is seen that the heat evolved duringconversion in liquefied normalhydrogen exceeds the heat ofevaporation (447 J g -1 ). Because ofthis, even in an ideal insulated vessel,normal liquid hydrogen can boil off inthe course of an ortho-para conversion.Therefore, it is usual duringliquefaction to subject the hydrogen toan accelerated conversion in thepresence of solid catalysts eachdisposed in colder areas, starting with65-75K until 20K.[1]SCIENCE, Volume 274, Number5290, Issue of 15 November 1996Bibliography1. Ullmanns Encyklopedie dertechnischen Chemie, Vol.3.EdituraChemie,Weinheim, 1973.2. A.Arkharov, I.Marfenina, Ye.Mikulin: Theory and Designof Cryogenic Systems. EdituraMir, Moscova, 1981.3. R.A.Haefer Kryo-Vakuumtechnik. Grundlagenund Anwendungen. EdituraSpringer, Berlin, 1981.4. M. Peculea : InstalatiiCriogenice , Editura ConphisRm. ValceaISSN: 1790-2769 246 ISBN: 978-960-474-119-9