Laboratory Plant for Studies Regarding the Behaviour of the Sintered Materials in Oxygen Isotopic Distillation

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1 6th IASME/WSEAS Interntionl Conference on HEAT TRANSFER, THERMAL ENGINEERING nd ENVIRONMENT (HTE'08) Lortory Plnt for Studies Regrding the Behviour of the Sintered Mterils in Oxygen Isotopic Distilltion FLOAREA POP, CORNELIA CROITORU, IOAN STEFANESCU, CONSTANTIN CIORTEA, SEBASTIAN BRAD, GHEORGHE TITESCU, VASILE STANCIU, MIHAI CULCER, MARIANA ILIESCU Ntionl R&D Institute for Cryogenics nd Isotopes Technologies ICIT Rmnicu Vlce, Uzinei no.4 Street, mil code , PO 4, POB 10, Rm. Vlce, Romni, Astrct: - The pper presents cryogenic lortory distilltion plnt, uilt in our institute for oxygen isotopes seprtion studies. Oxygen isotopes seprtion y distilltion is more difficult thn other cryogenic gs, hydrogen or helium for exmple, ecuse its seprtion fctor is very smll. For this reson it is necessry to find mterils with high specific surfce. Sintered mterils offer higher contct surfce thn unsintered mterils. Becuse the high rectivity of oxygen, on this plnt it will test just pcking from sintered stinless steel. Key-Words: - Keywords: Isotope, Oxygen, Cryogenics, Distilltion, Sintered mteril 1. Introduction Nturl oxygen is mixture of three stle isotopes with weight 16, 17 nd 18, with the composition presented in Tle 1 [1]. Isotope Percentge (mol %) Atomic weight 16 O 99,759 15, O 0,037 16, O 0,204 17,9991 Tle 1 Oxygen isotopes The oxygen isotopes seprtion y distilltion is possile ecuse the difference etween vpour pressures of moleculr species tht hold these isotopes. The seprtion fctor, defined s rte of vpour pressures of isotopes moleculr species, is one of the quntities tht chrcterize the seprtion process. A low vlue of this rte indictes difficult seprtion. Oxygen-18 seprtion y distilltion is more difficult thn other cryogenic gs, deuterium for exmple, ecuse its seprtion fctor is very smll, tle 2 [2]. 16 O 2 16 O 18 O H 2 - HD H 2 D 2 T (K) α Tle 2 Seprtion fctor vlues For this reson it is necessry to find mterils with high specific surfce. Sintered mterils offer higher contct surfce thn unsintered mterils. Oxygen is very rective gs, nd its rectivity increses with pressure, temperture, nd concentrtion incresing. Most mterils, oth metls nd nonmetls, re flmmle in highpressure oxygen. Therefore the distilltion plnt must e designed to reduce or eliminte ignition hzrds. Stinless steels re the most ignition- nd urn-resistnt metllic mterils nd re used extensively in high-pressure oxygen systems. 2. Structured pcking from sintered mteril In isotopic seprtion plnts from Romni, experimentl or industril plnts, the distilltion columns were equipped with structured pcking. This pcking hs good efficiency nd introduces low pressure drop comprtive thn rndom pcking. Structured pcking ws mnufctured from phosphorous ronze for wter distilltion nd stinless steel for hydrogen distilltion (cryogenic distilltion). In lst time, on interntionl pln, it ws pulished tht sintered mteril ws employed to mnufcture liquid-vpour contct elements for produce ethylic lcohol of 94%, in n experimentl column with pltes [3]. Becuse t the moment the principl utiliztion of sintered stinless steel is like ISSN: ISBN:

2 6th IASME/WSEAS Interntionl Conference on HEAT TRANSFER, THERMAL ENGINEERING nd ENVIRONMENT (HTE'08) construction mteril for filters with high performnces, we succeed to uy five-lyer sintered metl wire cloth, from. The five-lyer sintered metl wire cloth is presented in figures 1 nd 2 (microscope imges) [4]. surfce tension is more less thn liquid wter; t norml oiling point (P=1tm) they rtio is γ H O γ = 6.6 [5]. 2 O 2 Fig. 3 Device for wettility test Fig. 1 Sintered stinless steel lyer 1 Fig. 2 Sintered stinless steel lyer 5 Mterils used to structured pcking mnufcturing must hve good wettility. Wettility is the degree to which surfce is wetted y liquid. The wettility tests of five-lyer sintered metl wire cloth were performed to id the device from figure 3, with distillted wter. Tests results showed very, very good wettility. A constnt flow rte of wter ws introduced t the top, with syringe needle. Liquid distriution ws uniformly on the whole re of mteril smple. Wter rtes in the 11 mesurement points, 11 test tues, were pproximte equls. In tht condition we hve the certinty tht in the cse of liquid oxygen it will hve lso good wettility, ecuse liquid oxygen 3. The experimentl plnt schem The experimentl plnt uilt for studies regrding sintered mterils ehviour in oxygen isotopic distilltion is schemtic presented in figure 4. This plnt permits distilltion column opertion t constnt pressure. To ensure, t pressure P, the required vpour flow rte in column, it introduced in oiler the Q oiler het quntity. Becuse it is impossile to provide the totl therml insultion given to the open spce, in the system penetrtes the Q ins het quntity. The refrigerting cpcity Q of cryogenic engine, tht ensure the therml gent in condenser, is constnt. The difference etween refrigerting cpcity of cryogenic engine nd cold quntity necessry for column, (Q oiler + Q ins ), is compensted y the het introduced in the condenser y mens of new electric het source, in ccordnce with the therml lnce eqution: Q cond = Q - (Q oiler + Q ins ) (1) Oxygen is cryogenic gs tht oils, in norml conditions, t K, tle 3 [1]. Chrcteristic quntity Temperture (K) Pressure (r) Boiling point Criticl point O 2 N 2 O 2 N 2 90,18 77, , , , , ,9996 Tle 3 Two fixed points of oxygen nd nitrogen ISSN: ISBN:

3 6th IASME/WSEAS Interntionl Conference on HEAT TRANSFER, THERMAL ENGINEERING nd ENVIRONMENT (HTE'08) 1 - nitrogen liquefctor 2 - condenser 3 - distilltion column 4 - structured pcking 5 - oiler 6 - vcuum jcket 7 - therml insultion 8, 9 - DC source of electric heter 10 - oxygen store (gs) 11 - nitrogen store (gs) 12 vcuum pump Figure 4. Schemtic digrm of the oxygen cryogenic distilltion plnt A condenser, cooled with liquid nitrogen, provides the reflux for column. The column is operted t totl reflux. In these conditions the liquid/vpour rte is known. 4. The experimentl plnt The experimentl plnt for oxygen isotopes seprtion is composed of cryostt, cryogenertor nd control ord. The cryostt is presented in figure 5. Its sic components, distilltion column, condenser nd oiler, re introduced in cold ox with 465 mm dimeter nd height of 1750 mm. The cold ox is composed fixed cylinder nd two movle cylinders. They form the vcuum jcket of the cryogenic re. Fig. 5 Experimentl cryostt fixed cylinder movle cylinder ISSN: ISBN:

4 6th IASME/WSEAS Interntionl Conference on HEAT TRANSFER, THERMAL ENGINEERING nd ENVIRONMENT (HTE'08) Distilltion column, presented in figure 6 (), hs 50 mm inner dimeter nd is equipped with structured pcking on height of 1000 mm. c Fig. 6 Cryostt detil column condenser The structured pcking presented in figure 7 is mnufctured from sintered stinless steel. It hs height of 50 mm. It is hyrid pcking, from fivelyer sintered stinless steel wire cloth nd stinless steel mesh. 1 Fig. 8 Cryogenertor - condenserhed electricl motor c - crter Fig. 9 Cryostt detil oiler column 2 Figur 7. Structured pcking 1 sintered stinless steel 2 unsintered stinless steel The plnt hs verticl multituulr condenser, figure 6 (), tht hs 76 copper tues of φ10x2x160 mm. Condenser jcket, of stinless steel, communictes with liquid store, equipped with electric heter. This heted liquid store permits to mintin constnt temperture in column. The vpours from condenser re liquefied y mens of cryogenertor with reversed Stirling cycle, t 80K level. The cryogenertor, shown in figure 8, used 99.9% helium s working gs. The electric oiler of plnt, lso of stinless steel, presented in figure 9, hs height of 230 mm nd inner dimeter of 55.5 mm t top nd 80 mm t ottom. The control ord of plnt is, presented in figure 10. c Fig. 10 Control ord - ord - supply source c - milivoltmeters ISSN: ISBN:

5 6th IASME/WSEAS Interntionl Conference on HEAT TRANSFER, THERMAL ENGINEERING nd ENVIRONMENT (HTE'08) 5. Preliminry tests The preliminry tests for structured pcking from sintered mteril foresees pressure drop in pcking determintion nd mesurement pcking efficiency. Mesurements will e effected t totl reflux, for more vpour speeds. Studies regrding the utiliztion of sintered mterils in isotopic distilltion re finncing from N Studies regrding the utiliztion of sintered mterils in isotopic distilltion re finncing from Ntionl Authority for Scientific Reserch, Buchrest, Romni, Project PN References: [1] * * *, Encyclopedie des gz, Elsevier L'ir Liquide, Frnce, 1976 [2] Rozen A. M. - Teori rzdeleni izotopov v kolonh, Ed. Atomizdt, Moscow, 1960 [3] Fhmi A. Au Al-Ru, Jmil Akili nd Rvindr Dtt Distilltion of Binry Mixtures with Cpillry Porous Pltes, Sep. Sci. Technology, 33(1998), 1529 [4] Pop F., Croitoru C. Reserch Rport INC- DTCI ICSI, no. 9486/ [5] Arkhrov A. - Theory nd Design of Cryogenic Systems, Mir Pulishers, Moscow, 1981 ISSN: ISBN: