enrichment by pressure swing adsorption process: Successive enrichment of deuterium using SZ-5A column

Fusion Engineering and Design 85 (2010) 1992–1998

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Verification of hydrogen isotope separation/enrichment by pressure swing adsorption process: Successive enrichment of deuterium using SZ-5A column K. Kotoh a,∗ , M. Tanaka b , S. Takashima a , T. Tsuge a , Y. Asakura b , T. Uda b , T. Sugiyama c a b c

Department of Applied Quantum Phys. and Nucl. Engineering, Faculty of Engineering, Kyushu University, 744 Moto-oka, Nishi-ku, Fukuoka 819-0395, Japan National Institute for Fusion Science, 322-6 Oroshi, Toki, Gifu 509-5292, Japan Faculty of Engineering, Nagoya University, Furo-cho, Chigusa-ku, Nagoya 464-8601, Japan

a r t i c l e

i n f o

Article history: Available online 19 August 2010 Keywords: Hydrogen isotope separation Pressure swing adsorption Zeolite 5A Deuterium Tritium

a b s t r a c t We have been developing a system of hydrogen isotope separation using a pressure swing adsorption (PSA) method, aiming at applying it in the fusion fuel cycle and/or the convenient deuterium production for fusion or/and fission reactors. Particularly, for the issue that tritium inventory in the DT fusion system must be as low as possible, the PSA method will be advantageous because its process inventory is reasonably less than such as in a cryogenic distillation system. The PSA system is generally composed of several adsorption columns cooperating in sequential procedure and alternative combination among adsorption, desorption and another preparative process. A variety of operational modes are made suitable for producing a material needed to be enriched or isolated. In this work, supposing the production of deuterium from natural hydrogen or the recovery of tritium from such as a spent nuclear heavy-water moderator, we carried out an experimental series of PSA process system operating successive separation and enrichment of tracer D2 from a H2 –D2 mixture, using a single column packed with SZ-5A at 77.4 K. Availability of the PSA hydrogen isotope separation process is endorsed in experimental results. © 2010 Elsevier B.V. All rights reserved.

1. Introduction We have been studied the isothermal and kinetic behaviors of hydrogen isotopes adsorbed onto synthetic zeolites (SZ-) 3A, 4A, 5A and 13X at such as the liquefied nitrogen temperature 77.4 K [1–5]. The knowledge obtained from these studies made us to develop a pressure swing adsorption (PSA) process applicable to hydrogen isotope separation in the fusion fuel cycle or detritiation of hydrogen process gases [6–10]. A similar process for hydrogen isotope separation has been developed and practiced by Heung et al. [11,12]: the thermal cycling absorption process (TCAP) using a palladium-packed column where chemical sorption occurs. Separation behaviors of hydrogen isotopes are different between the chemical sorption and the physical adsorption applied here. Adsorption is conventionally used for isolation, separation and confinement of gaseous materials. Advantage is there in convenience but disadvantage is of batch operation, that is, activation is necessary before adsorption operation. And then, desorption is needed after adsorption when the operation is consecutive. The activation is generally by heating. The heating is effective in acti-

∗ Corresponding author. Tel.: +81 92 802 3507; fax: +81 92 802 3507. E-mail address: [email protected] (K. Kotoh). 0920-3796/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.fusengdes.2010.07.006

vation but inefficient in continuous process operation because a certain period of time is needed for cooling down after activation. The PSA method improves the regeneration process to promote desorption only by evacuation though desorption cannot be perfect. Improvement is to shorten the operational period for generating adsorption columns. This improvement makes a decline in process capacity of one cycle operation but realizes a speed-up of cyclic process operation. Comprehensively, the cyclic process speed-up brings a highly efficient performance of production for adsorptive separation. Hence, recently the PSA process has been popularized to be applied to medium-scale industrial gas-production plants such as an onsite oxygen plant of hospital. Hydrogen isotopes adsorbed onto synthetic zeolites at a cryogenic temperature behave giving their adsorptive priority to heavier isotopes. In an isotopic two-component mixture flowing through a zeolite packed-bed column, this property brings the enrichment of a heavy isotope in the packed-bed while providing the breakthrough volume of the other one isolated from the mixture. After establishing an adsorption process, the PSA process recovers an amount of the mixture enriched in adsorbed phase by evacuation. The evacuation, however, carries out desorption in imperfection for a given operational period, where an isotopic molecular mass-effect occurs in this dynamic mass-transfer process. The kinetic effect promotes the enrichment of heavier one in the residual volume of adsorbed phase.

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sample was supplied to the adsorption column by a diaphragmtype pump. The other bag-type holder (2) was used for sampling the residual amount recovered by heating up after the final evacuation process. The inventory in a gas folder was determined from the ideal gas PVT relation by measuring holder’s weight affected by buoyancy due to hydrogen mixture. The gas holders and sampling lines were beforehand evacuated by the other scroll-type pump. Isotopic fractions in hydrogen samples were measured by a massspectrometric gas-analyzer system. The sampling volumes were considered in the mass balance. The tracer D2 in effluence from the adsorption column was inline-monitored by the gas-analyzer system. 2.2. Operation sequence Successive tracer-D2 enrichment was carried out by the following sequential processes.

Fig. 1. Schematic diagram of cryogenic PSA apparatus.

In this work, we performed an experimental series of cyclic PSA process operation aiming at producing a deuterium-enriched volume from a H2 –D2 mixture with a single column packed with SZ-5A, in order to verify the applicability of PSA method to such as a deuterium production plant or a recovery process of tritium from the spent heavy-water neutron-moderator used in fission reactors. Experimental results demonstrate the successive enrichment of D2 in volumes recovered from the adsorption column in cyclic operation of the PSA system processing a hydrogen mixture containing tracer D2 . And then, a remarkable result is reported here that a highly D2 -enriched volume was recuperated from the column in the final desorption operation by heating up to room temperature in addition to evacuating.

2.2.1. Replacement adsorption Adsorption process starts to prepare its column swamped with pure H2 as “priming water”. After that, the column process a gas stream of hydrogen mixture where the adsorbed phase on SZ-5A in the packed-bed is exchanged from H2 to H2 or D2 in the gas phase: replacement adsorption occurs. During this adsorption process, the column pushes back the amount introduced in advance as “priming water”, and then, produces a volume of H2 isolated from the fed gas mixture. In this experimental series, each adsorption process was stopped when the breakthrough tracer reached the point of its concentration in the original sample mixture, C0 , that is, the breakthrough point is CBP,n /C0 = 1.

2.1. PSA apparatus

2.2.2. Evacuating desorption Desorption is done by evacuation using the oil-free vacuum pump. The exhaust gas is fed back to the main gas holder having a remaining original gas mixture, where the recovered gas is volumetrically reduced in compared with the fed one but is enriched with D2 . The packed column is to be evacuated until attainment of a given vacuum pressure or an operational period conditioned in combination with the other processes. In this experimental series, a point of 70 Pa was chosen as the operational limit of evacuation. This point was not selected under particular consideration, but was a condition apparently approaching equilibrium, achievable within about half an hour. In the PSA process, since desorption is operated in imperfection, some amount adsorbed is leaved in the column. The residual adsorbate is distributed in the packed-bed between its top and bottom ends. This residual quenches the effect of isotope separation in the adsorption process. Therefore, the following operation is needed after evacuating the column.

Fig. 1 shows the schematic diagram of a cryogenic PSA apparatus using this experimental series. The adsorption column used here was made of a 1-in. SS pipe (inner diameter: 21.2 mm), in which a packed-bed was installed of spherical SZ-5A pellets in diameter of 2 mm (MERCK Co. Ltd.). The packed-bed weight and height were 187.4 g and 799 mm, respectively. The packed-bed column was prepared by purging with helium under heating at 573 K for about 3/4 day. After activation, the column was evacuated by a scrolltype vacuum pump having a power of 0.6 m3 /min (ANEST-IWATA Co. Ltd.), and then, was filled with pure hydrogen. After cooling down near room temperature, the column was soaked with liquefied nitrogen in a vacuum pail during cyclic PSA process operation. Pressure was monitored by diaphragm-type gages mounting on a line connecting to the inlet of the test column. Provided from a hydrogen cylinder containing D2 at 1%, a volume of original sample mixture was reserved in the main bag-type holder (1) made of aluminum laminate. From this holder, the gas

2.2.3. Replenishing operation In order to push back the residual tracer distribution toward the inlet of the packed-bed, pure H2 is introduced into the evacuated column from its outlet. When swamped with the replenishment, the column reforms the residual D2 distribution such as an errorfunctional profile. This profile frequently exhibits a range over the concentration of D2 in the feed gas prepared for the subsequent adsorption process, because heavier-component enrichment in the adsorbed phase occurs not only in adsorption but also in desorption process [6–9], that is, in the kinetic process, lighter isotope molecules are removed speedier than  heavier ones. A simple rule of the square-root of a mass ratio Mlight /Mheavy , based on the same kinetic energies of molecules, is assumable for the isotope effect [9], where M means the molecular mass numbers. After finishing the beginning cycle, the PSA system begins the nest cycle operation with the column having the residual distribution in its packed-bed. Therefore, the operational period of

2. Experimental

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K. Kotoh et al. / Fusion Engineering and Design 85 (2010) 1992–1998

Table 1 Conditions and results of PSA process cyclic operation. Sequential processes

Conditions

1st cycle

2nd cycle

3rd cycle

4th cycle

Adsorption process

Flow rate uF,n [LSTP /min] Operation period tBP,n [min] Breakthrough point CBP,n /C0 Waste average concentration C¯ B,n /C0 Feed concentration CF,n /C0 Feed volume VF,n [LSTP ] Net process volume VT,n [LSTP ]

(5.0) 15.00 – – 1.00 – –

4.04 4.88 1.02 0.346 1.05 19.8 7.9a (4.7)

3.99 5.01 1.04 0.349 1.07 20.0 8.4

3.94 5.42 1.04 0.335 1.10 21.4 9.1

3.89 5.33 1.06 0.355 1.13 20.7 9.1

Evacuation process

Attainment pressure PA∗ [Pa] Time required tE,n [min] Recovery concentration CR,n /C0 Recovery volume VR,n [LSTP ] Waste volume VW,n [LSTP ]

70 25.93 1.25 11.9a (15.1) –

70 23.95 1.22 11.6 8.2

70 23.77 1.19 12.3 7.7

70 23.07 1.27 11.6 9.8

70 22.97 1.33 2.44b 12.2 14.7b 8.5

Replenishing process

Flow rate uP,n [LSTP /min] Time required tP,n [min] Priming volume VP,n [LSTP /min]

2.79 3.85 (10.7)

2.79 3.33 (9.29)

2.79 3.97 (11.1)

2.79 3.82 (10.7)

a b

5th cycle

2.79 – –

Corrected by employing an average among the other values of VT,n . ∗ ∗ Comprehensive value taking account of VR,5 and CR,5 .

adsorption process is decreased relatively to that in the beginning cycle. In the 2nd cycle adsorption process, the residual tracer distribution is developing as the forefront of the bulk distribution being generated in the packed-bed. When the residual tracer exhibits over-ranging profile, its forefront profile is progressing with spreading and declining sharpness. Thus, the over-ranging profile frequently conducts the adsorption behavior showing an overshooting breakthrough curve [8,9]. In this experimental series, the operational conditions of evacuation and replenishing processes at the 1st cycle would produce an accomplished column keeping the over-ranging profile in its packed-bed. The residual tracer distribution formed at the 2nd cycle would behave similarly to that in the 1st cycle processes, where the tracer concentration would be increased in comprehension, however. At each cycle in advance, the adsorption process exhausts the almost same volume of waste containing the tracer D2 at less than unity of CBP,n /C0 , and simultaneously subtracts the corresponding volume from the gas sample holder. The subsequent process recovers a volume smaller than the feed volume but the recovery volume is enriched with D2 in comparison to the feed one. 3. Results and discussion The experimental series was carried out in one batch of 5 cycles. An amount of 66.0 L (STP) was prepared in the bag-type main sample holder. Experimental conditions and results are summarized in Table 1. In every adsorption process, except at the 1st cycle, the feed gas was supplied at a flow rate of 4 LSTP /min from the gas holder. The operation period is the spent time until the breakthrough tracer reaches the point around CBP,n /C0 = 1, where the subscript n denotes an ordinal cycle number. At the 1st cycle, the adsorption process was operated as a preparative procedure for making the column in equilibrium at the concentration of D2 , C0 ( = CF,1 ), in the subjective sample gas. Therefore, the adsorption period at the 1st cycle was satisfactorily longer than at the other cycles.

ume recovered at the n cycle, CR,n , is estimated from the following mass balance: ∗ − VF,n )CF,n = VS,n CS,n , VR,n CR,n + (VS,n−1

thus CR,n =

∗ − VF,n )CF,n VS,n CS,n − (VS,n−1

VR,n

,

(2)

where VF,n and VR,n represent respectively the feed volume and the recovery volume. Values of VF,n in Table 1 were given by uF,n · tBP,n that is the product of the feed gas-flow rate and the breakthrough time. The values of VR,n were obtained from the mass balance: ∗ . VR,n = VS,n + VF,n − VS,n−1

(3)

The ratio of CR,n to CF,n indicates an apparent result of enrichment at each cycle, which is defined here as the effective process enrichment factor: EFn =

CR,n . CF,n

(4)

Since PSA process operates desorption imperfectly, the enrichment in adsorption process would not be reflected directly in EFn because another effect takes place in the kinetic process during evacuation. In this adsorption system of hydrogen isotopes onto SZ-5A at 77.4 K, an ideal limit for enrichment factor exists corresponding to the separation factor SFD2 /H2 of D2 diluted in H2 in equilibrium at the atmospheric pressure. The value of SFD2 /H2 was already analyzed to be around 2.0 in a previous paper [1]. Thus, we can consider the ideal enrichment factor for tracer, EFID , with a value of 2.0 in this PSA process. In the adsorption process limited at the point of CBP,n /C0 = 1, while a distribution from CF,n to CBP,n has been developed in the gas phase, a relatively enriched distribution also has been formed in the adsorbed phase in the packed-bed. In this case, an actual enrichment factor is considered assuming an unsteady equilibrium state, as follows:

3.1. Successive enrichment The tracer concentration in a volume fed at an advanced cycle, CF,n , is the same as CS,n−1 in a final volume stored in sample-gas ∗ holder at the previous cycle, VS,n−1 . The final volume is the remainder of a storage volume VS,n−1 just after evacuation process at the ∗ n − 1 cycle: VS,n−1 = VS,n−1 − vn−1 , where vn−1 is an amount of about 0.15 L used for gas analysis. The concentration CF,1 at the 1st cycle is the same as C0 in the original mixture. The concentration in a vol-

(1)

EF∗n

=

EFID

 W0 0

(Cn /CF,n )dW W0

,

(5)

where W is a distance in the packed-bed in the column, and W0 the packed-bed height. Therefore, EF∗n may approach EFID under the operational conditions of adsorption and desorption in this PSA process. The effective factor EFn is difficult to agree with EF∗n because of the quenching effect in evacuation process. However, if the desorption can be perfectly accomplished, EFn may reach

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Table 2 PSA process efficiencies and performance factors. PSA process efficiencies and performance factors

1st cycle

2nd cycle

3rd cycle

4th cycle

5th cycle

Apparent enrichment factor CS,n /CS,0 Effective enrichment factor EFn Multiplied enrichment factor EFn Vol. waste production efficiency n Vol. adsorption process efficiency n Separation process efficiency ∗n Evacuation efficiency ın Effective volume reduction factor RFn Multiplied reduction factor RFn Process depletion factor DFn Averaging depletion factor DFn Effective depletion factor DF∗n Average efficiency depletion factor DF∗n

1.05

1.07

1.10

1.13

1.19

1.25

1.16

1.11

1.16

1.17

1.25

1.45

1.61

1.87

2.18 (4.03b )

–

0.414

0.385

0.458

0.411

–

0.399a (0.237)

0.420

0.425

0.440

–

0.798a (0.475)

0.840

0.850

0.879

(0.812)

(0.624)

(0.661)

(0.624)

(0.656)

–

1.71

1.63

1.84

1.70

–

1.71

2.79

5.14

–

3.04

3.07

3.28

8.74 (7.24b ) 3.19

–

3.04

3.05

3.13

3.15

1.29

1.39

1.40

1.25

1.30

1.33

a b

– –

a

1.21 (0.72) 1.21a

Corrected. ∗ ∗ Comprehensive multiplicative factors taking account of VR,5 and CR,5 .

EF∗n . Additionally, the behavior of SFD2 /H2 depending on adsorption intensity influences the enrichment in adsorbed phase, which exhibits an increase in SFD2 /H2 with decreasing the amount of a mixture adsorbed [1,5]. Table 2 shows experimental values obtained for characteristic efficiencies and factors. The factors EFn except at the 1st cycle are evaluated with an average of 1.15. The EF1 value of 1.25 deviates a little bit from the average. This deviation seems to be derived from the volumetric efficiency in the evacuation process. While an amount of 15.1 L is recuperated at the 1st cycle, an average amount of 11.9 L is recovered at each of the other cycles. ∗ ) at Finally, the tracer concentration in the gas holder (VS,5 the 5th cycle arrived at 1.19 times of its original concentration: CS,5 /CS,0 = 1.19. This comprehensive value is apparent, however. So, the net enrichment accomplished in this experimental series should be evaluated with the following product of EFn n running one to N: EFN =

N 

EFn .

overall factor:



N−1

EFN final =

n=1

EFn ×

C¯ R,N , CF,N

(7)

(6)

n=1

Fig. 2 shows that this PSA system carried out the enriching work of EF5 = 2.18 for 5 cycles. Otherwise, at the final cycle, after the ∗ was recuperated from evacuation process, a volume of 2.48 L as VR,5 the column by heating up to room temperature in addition to evacuation. In this volume, remarkable enhancement was observed of ∗ /C = 7.89. This large value endorses the tracer concentration: CR,5 0 successive enrichment in the residual adsorbed phase in evacuation processes. Taking account of the last recovered volume, the finally realized work of net multiplied enrichment is evaluated with the following

Fig. 2. Enrichment factors EFn and n EFn with respect to ordinal PSA process cycle number.

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where C¯ R,N means the average concentration of tracer in the total volume recovered at the last cycle: C¯ R,N =

∗ C∗ VR,N CR,N + VR,N R,N ∗ VR,N + VR,N

.

(8)

The average concentration C¯ R,5 /C0 was calculated to be 2.44. Listed in Table 2 or shown in Fig. 2, a value of 4.03 is thus given to the final overall multiplied enrichment factor EF5 final . 3.2. Volumetric efficiencies In this PSA system, the net amount of mixture separationprocessed at each cycle is estimated by VT,n = VF,n − VP,n−1 ,

(9)

where VP,n−1 is an amount of priming hydrogen in the replenishing process calculated by uP,n−1 · tP,n−1 : the product of a priming gasflow rate and a time period of operation. Since the replenishing process is to supply a gas volume into the evacuated packed-bed column, a response period of time is necessary for controlling the mass-flow regulator at a given rate. Therefore, overshooting gasflow occurs in the temporary period from just starting to steady state. Accordingly, although VP,n−1 can be calculated, the calculated values were not accepted here because of under-estimation. On the other hand, VP,n−1 should correspond to the amount evacuated at the last step, VR,n−1 , which can be determined from the gravimetric measurement of a hydrogen mixture in sampling holder taking in account the buoyancy. Thus, VR,n−1 instead of VP,n−1 was employed in this work. Efficiency of PSA process can be measured by several types of ratios. The volumetric adsorption process efficiency at a cycle is defined as follows: VT,n . n = VF,n

(10)

Besides, the following definition similar to Eq. (10) means the volumetric waste production efficiency: n =

(VF,n − VR,n ) VW,n = . VF,n VF,n

n = . ID

(12)

Listed in Table 2 the values of ∗n interpret that the hydrogen isotope separation process was effectively utilized at an efficiency above 80% in this PSA process system. Efficiency in evacuation process can be defined by ın =

VR,n , V0∗

for V0∗ . The results shown in Table 2 seem to be a little bit underestimated except at the 1st cycle. These hence suggest probabilities that packed-bed temperature regulation was unsatisfactory, activation was not enough for packed-bed adsorbents, the packed-bed was gravimetrically overestimated, and so on. The successive enrichment brings reduction in a source volume. While EFn indicates the enrichment intensity, the inverse of 1 − n evaluates the reduction intensity. So, the last term is defined as the effective process volume reduction factor: RFn =

(13)

where V0∗ indicates the volumetric adsorption capacity of a hydrogen mixture in the SZ-5A packed-bed column. In this work, the adsorption capacity can be approximated with that of a bulk component, which can be estimated from the isotherm of H2 adsorbed onto SZ-5A at 77.4 K [1]. A value of 18.6 L is ideal but given here

VF,n 1 = . VR,n 1 − n

(14)

Accordingly, the net multiplied volume reduction performance in PSA operation is described by RFN =

(11)

When the sequential processes are ideally cycled under the same operational conditions: VP,n−1 = VR,n and VP,n = VP,n−1 or VR,n = VR,n−1 , the ratios n and n are equal except at the 1st cycle. The efficiency n or n has a limiting value which is determined by the equilibrium separation factor SFD2 /H2 . When an ideal case of stepwise breakthrough curve is assumed in the original adsorption process, a specified value 2.0 for SFD2 /H2 limits n to be 0.5 (where the amount of a gas-phase mixture in the column is discounted because ignorable in mass balance). This limited efficiency is specified here as ID . With this specific value, effective utilization of separation process is measured by ∗n

Fig. 3. Volumetric reduction factors EFn and RFn with respect to ordinal PSA process cycle number.

N 

RFn .

(15)

n=1

As shown in Fig. 3, this PSA system completed the comprehensive volume reduction at RF5 = 8.74 during 5 cycles. Similarly to EF5 final , the eventually accomplished volume reduction factor is written as the following equation taking account of the residual volume recovered finally by thermal operation:



N−1

RFN final =

RFn ×

n=1

VF,N ∗ . VR,N + VR,N

(16)

In this work, a value of 7.24 was obtained as RF6 final . 3.3. Depletion factors By integrating a breakthrough curve in Fig. 4, the following factor measuring a degree of depletion in a waste volume except at the 1st cycle is defined: DFn =

C

V

VF,n

F,n  F,n tBP,n

CB,n dt

0

=

CF,n , C¯ B,n

(17)

where CB,n denotes the breakthrough concentration of the tracer D2 at a cycle. The integral term gives an average concentration, C¯ B,n . For a developing waste production inventory, the following term indicates its averaging depletion degree:

N

DFN =

Nn=2

CF,n VF,n ¯

C V n=2 B,n F,n

,

(18)

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sampling volume used for gas analysis, V¯ samp. , is estimated to be around 1.5 L. The balance of D2 in this system holds in consistence with this volumetric balance. Therefore, the PSA system is usable for such as the production of deuterium from a massive source of natural hydrogen which will be infrastructural as secondary energy resources in the near future. Also, cryogenic energy will be there lavishly. Otherwise, that would be available for an isotope separation process preparing DT fuel mixtures in the fusion fuel cycle. Additionally, the PSA process would be useful in combination with a Combined Electrolysis Catalytic (CECE) process for detritiation of water [13–16] or a cryogenic distillation plant for detritiating the moderator of CANCU reactors [17,18]. 4. Conclusions

Fig. 4. Breakthrough curves of tracer D2 in adsorption process at successive cycles.

Deuterium depletion was carried out comprehensively at DF5 = 3.15 for a waste production of 81.9 L generated during cyclic operations except the 1st cycle. The depletion factor DFn , however, is apparent because the waste production at every cycle is diluted with a volume of priming hydrogen in replenishing process, VP,n−1 . The effective depletion should be treated for the net volume separation-processed, VT,n . Hence, the following factor is defined as an effective depletion factor: DF∗n =

VT,n CF,n VF,n C¯ B,n

= n · DFn .

(19)

Accordingly, the averaging effective factor is written similarly to Eq. (18):

N

DF∗N =

Nn=2

CF,n VT,n

C¯ V n=2 B,n F,n

.

(20)

As shown in Table 2, DFn may develop its value with progress in the cyclic operation because the critical point is regulated to be CBP,n /C0 = 1 in common while CF,n escalates with progressing cyclic operation. This trend appears clearly in the range of DF∗n . The value at the 2nd cycle, however, was corrected because a draft value of 0.72 is inconsistent with DF∗2 being never less than unity. The value is affected by a value of 0.234 for 2 which is too small to be compared with the other values for n . This deviation results in an original value of 15.1 L for VR,2 estimated from the gravimetric difference of inventory in the gas holder between adsorption and evacuation processes, where an experimental error may be reflected. This value is too large in comparison with the other cycle values averaging 11.9 L. Thus, by employing this average value instead of its original one for VR,2 , the 2 value was corrected. And then, the effective factor DF∗2 was revised as the result. Of course, the averaging effective depletion factor DF∗n exhibits a monotone increase with progress in the cyclic PSA operation. The effectiveness of PSA process in application to hydrogen isotope separation was verified by the experimental results demonstrating the successive enrichment of a heaver isotope from a hydrogen gas mixture with an accuracy of about 4% error in overall volumetric valance as follows:

   100{V + 5 VR,n + V ∗ }  S,0  R,5  n=1 Er =  , VS,0  

(21)

where VS,final is the residual gas inventory on the sample holder after finishing the final process operation, which was 46.0 L. The total

In this work, it was verified that the PSA process using SZ-5A at 77.4 K could perform effectively the successive enrichment of tracer D2 in volumes recovered from a hydrogen gas mixture during its cyclic operation. With only about 190 g of zeolite adsorbent, this process established a remarkably high enrichment factor of 7.89 for D2 on the basis of the initial concentration in a sample mixture, in a volume of 2.48 L recuperated in the ending procedure of desorption finally at the 5th cycle. This result would suggest a creative development in application of PSA process to hydrogen isotope separation. Acknowledgements This work is supported by a grant from NIFS (National Institute for Fusion Science, Japan) with budget NIFS08KFSS010. References [1] K. Kotoh, K. Kudo, Multi-component adsorption behavior of hydrogen isotopes on zeolite 5A and [13X] at 77.4 K, Fusion Sci. Technol. 48 (2005) 148–151. [2] K. Kotoh, K. Kimura, K. Kudo, Hydrogen isotope separation using molecular sieve of synthetic zeolite 3A, Fusion Sci. Technol. 54 (2008) 419–422. [3] K. Kotoh, S. Takashima, Y. Nakamura, Molecular-sieving effect of zeolite 3A on adsorption of H2 , HD and D2 , Fusion Eng. Des. 84 (2009) 1108–1112. [4] K. Kotoh, M. Kawahara, K. Kimura, K. Kudo, Thermal transpiration behavior of hydrogen isotopes in cryogenic pump system, Fusion Sci. Technol. 56 (2009) 179–183. [5] K. Kotoh, S. Takashima, T. Sakamoto, T. Tsuge, Multi-component behavior of hydrogen isotopes on synthetic zeolites 4A and 5A at 77.4 K and 87.3 K, in: Proc. 9th Int. Symp. Fusion Nucl. Technol., Dalian, China, October 11–16, 2009. [6] T. Sugiyama, Y. Asakura, T. Uda, K. Kotoh, Measurement of breakthrough curves on pressure swing adsorption for hydrogen isotope separation, Fusion Sci. Technol. 48 (2005) 163–166. [7] K. Kotoh, M. Tanaka, Y. Nakamura, T. Sakamoto, Y. Asakura, T. Uda, et al., Experimental verification of hydrogen isotope separation by pressure swing adsorption, Fusion Sci. Technol. 54 (2008) 411–414. [8] K. Kotoh, M. Tanaka, T. Sakamoto, Y. Nakamura, Y. Asakura, T. Uda, et al., Breakthrough curve analysis of pressure swing adsorption for hydrogen isotope separation, Fusion Sci. Technol. 54 (2008) 415–418. [9] K. Kotoh, M. Tanaka, T. Sakamoto, S. Takashima, Y. Asakura, T. Uda, et al., Overshooting breakthrough curves formed in pressure swing adsorption process for hydrogen isotope separation, Fusion Sci. Technol. 56 (2009) 173–178. [10] K. Kotoh, M. Tanaka, T. Sakamoto, S. Takashima, Y. Asakura, T. Uda, et al., Multicomponent behavior of hydrogen isotopes in zeolite packed-beds used for cryogenic pressure swing adsorption, Fusion Sci. Technol. 56 (2009) 195–200. [11] L.K. Heung, H.T. Sessions, X. Xiao, H.L. Mentzer, Demonstration of the nextgeneration TCAP hydrogen isotope separation process, Fusion Sci. Technol. 56 (2009) 1471–1475. [12] L.K. Heung, H.T. Sessions, A.S. Poore, W.D. Jacobs, C.S. Williams, Next-generation TCAP hydrogen isotope separation process, Fusion Sci. Technol. 54 (2008) 399–402. [13] T.V. Vasyanina, I.A. Alekseev, S.D. Bondarenko, O.A. Fedorchenko, K.A. Konoplev, E.A. Arkhipov, et al., Heavy water purification from tritium by CECE process, Fusion Eng. Des. 83 (2008) 1451–1454. [14] T. Sugiyama, Y. Asakura, T. Uda, T. Shiozaki, Y. Enokida, I. Yamamoto, Present status of hydrogen isotope separation by CECE process at the NIFS, Fusion Eng. Des. 81 (2006) 338–833.

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K. Kotoh et al. / Fusion Engineering and Design 85 (2010) 1992–1998

[15] I.A. Alekseev, S.D. Bondarenko, O.A. Fedorchenko, A.I. Grushko, S.P. Karpov, K.A. Konoplev, et al., The CECE experimental industrial plant for reprocessing of tritiated water wastes, Fusion Sci. Technol. 41 (2003) 1097–1101. [16] J.M. Miller, S.L. Celovsky, A.E. Everatt, W.R.C. Graham, J.R.R. Trembley, Design and operational experience with a pilot-scale CECE detritation process, Fusion Sci. Technol. 41 (2002) 1077–1081.

[17] M. Zamfirache, A. Bornea, I. Stefanescu, N. Bidica, O. Balteanu, C. Bucur, The step of an extraction system coupled to a hydrogen isotopes distillation column, Fusion Sci. Technol. 54 (2008) 423–425. [18] A. Bornea, M. Zamfirache, I. Stefanescu, A. Preda, O. Balteanu, I. Stefan, Investigation related to hydrogen isotopes separation by cryogentic distillation, Fusion Sci. Technol. 54 (2008) 426–429.