The Study of CECE Process at the Experimental Industrial Plant

FUSION TECHNOLOGY 1998 191 Proceedings of the 20th Symposium on Fusion Technology, Marseille, France, 7-11.09.1998

The study of CECE process at the experimental industrial plant

I.A. Alekseev1, S.D. Bondarenko1, Т.V.Vasyanina1, A.I. Grushko1, S.P. Karpov1, K.A. Konoplev1, V.D. Trenin1, O.A. Fedorchenko1, E.A. Arkhipov2, T.V. Voronina2, V.V. Uborsky2

1Petersburg Nuclear Physics Institute, Gatchina, Leningrad district, Russia 2JSV ”DOL”, Moscow, Russia

The studies of hydrogen isotope separation by CECE method have been carrying out at the experimental industrial plant. The temperature, pressure, gas flow rate, manner of column packing is changed. The hydraulic and separating characteristics of the isotope exchange column were investigated. Tests of plant are shown high efficiency of isotope separation. The CECE process can find an application at the ITER.

1. INTRODUCTION

The Combined Electrolysis Catalytic Exchange (CECE) process, utilising wetproofed catalyst, is ideally suited for extracting tritium from water owing to its high separation factor and near- ambient operating condition. This process is regarded as alternative for detritiation than conventional Water Distillation (DW) and Vapour Phase Catalytic Exchange (VPCE) processes in the ITER Isotope Separation System [1,2]. But only tests of a pilot plant operating at various modes can adduce evidence of practical applicability of this method for tritium recovery. An experimental industrial plant for hydrogen isotope separation using chemical isotopic exchange between water and hydrogen and water electrolysis (CECE process) has been built in Petersburg Nuclear Physics Institute [3,4]. The large-scale studies of hydrogen isotope separation by CECE method have been carrying out at this plant in a wide range of parameters since 1995. The present paper describes the results of testing, design and operation experience of the liquid phase catalytic exchange column of the Plant. 2. BRIF DESCRIPTION OF THE PLANT AND TECHNICUE OF THE EXPERIMENTS

The schematic flow diagram of the plant is presented in Fig. 1. The chemical exchange column 6.9 m overall height with inner diameter 100 mm is filled with alternating layers of wetproofed catalyst and stainless steel spiral-prismatic packing with size 2.2*2.2*0.2 mm The column consists of three separation sections connected through distributor of liquid. The feed points (FP) and sample points (SP) are set between the separation sections, and at the top and at the bottom of the column. The overall separation height of the column is 5.2 m. The wetproofed catalyst used has been developed at the D. Mendeleev University of Chemical Technology of Russia. It consists of platinum deposited on polysorb (0.8 wt. % of Pt) [3]. The size of catalyst spherical granule is 0.5- 1.0 mm. The plant uses an alkaline electrolysis cell with the capacity of 5 m3 /h as the lower reflux device and hydrogen catalytic burners as the upper reflux device. With the help of a special thermosetting system the column can be maintained at any temperature in range of 300-360 K. The operating pressure is 0.13 - 0.4 MPa. In detail the schematic diagram of the plant is presented in the paper [4]. The main results of the studies were obtained at the steady state mode of operation of the plant during processing diluted heavy water. The feed flow contained about 45% deuterium and 10 8 Bq/kg tritium is injected into the column feed point FP3. The heavy water concentrated up to FUSION TECHNOLOGY 1998 192 Proceedings of the 20th Symposium on Fusion Technology, Marseille, France, 7-11.09.1998

99.85- 99.995 is withdrawn from the bottom as a liquid. The top product contained less than 1 % deuterium is withdrawn as liquid, when the catalytic burners are operated, or as elemental hydrogen, when the natural water is fed to the top of the column as reflux. The tritium concentration in the top product is less than 105 Bq/kg. The deuterium and tritium concentration in water and gas from different sample points was analysed. The samples of heavy water were analysed by the IR-spectrophotometer, the samples of gas by gas chromatography. The tritium was measured by liquid scintillation method.

3. RESULTS AND DISCUSSION

The tests of the separation column were carried out at various operation modes. The temperature, pressure, gas flow rate, manner of a column filling is changed. The hydraulic Fig.1 The schematic flow diagram of the plant. and separating characteristics of the isotope exchange column were investigated. To study the hydraulic characteristic the overall pressure drop across the isotope exchange column was measured versus hydrogen load (current load at the electrolytic cell), other conditions being equal. The pressure drop measurements were performed up to the flooding. It was found that the manner of a column filling significantly affected on a limiting hydrogen flow rate. Fig. 2 presents the dependence of the pressure drop across the column versus a linear velocity of gas at the condition of the experiment. The curve A presents the result one of the first run where a considerable hydrogen rate was not achieved owing to flooding. The another manner of the column filling provided with gas flow velocity up to 0.18 m/s without flooding (see curve B). From run to run the pressure drop slightly increased at first and then was stable (see curves B, C, D, E). The analysis of the separating characteristic of the isotope exchange column was carried out on basis of the data of change of deuterium concentration in water and gas across the height of the column. Test conditions as well as results of several runs (deuterium concentration in the feed points and sample points) are shown in Table 1. Example 1 presents the result of the first run. Following the development of the separation technology, the separation efficiency was improved (examples 1 and 2). Fig.2. Pressure drop across the column versus rate of gas. Thanks to sample points between the separation section one can calculate the efficiency of each section. The separation efficiency of the exchange column was determined by two different methods. The first method considers the separation process in the column as counter-current exchange FUSION TECHNOLOGY 1998 193 Proceedings of the 20th Symposium on Fusion Technology, Marseille, France, 7-11.09.1998 process between liquid water and hydrogen – water vapour mixture. The values of height equivalent of a theoretical plate (HETP) were determined at steady state mode at various conditions. The dependence of separation factors of temperature, and deuterium concentration was taken into account. It was found the strong dependence the separation efficiency of a pre-treatment procedure of the column to the run. The developed pre-treatment procedure allows to reduce HETP about three times. The values of HETP were determined usually at the gas flow rate close to the flooding. It is interesting to note that although the packing of the separation section was identical, the efficiency of the lower section was higher than upper section. May be it is explained the continuous activation of catalytic beds in the lower section by hydrogen from electrolytic cell during the plant operation. Fig.3. presents the effect of the temperature on the HETP. The HETP reduce when temperature is increased. It should be noted that the values of HETP determined in our work are nearly the same that were obtained in a 28-mm diameter column [3] and much below than that obtained at the experimental plant [5]. Another way of looking at this process is proposed too. Simulation code “KIO”[6] deals with three streams (liquid water, water vapor and hydrogen gas) and with six components. The temperature and concentration dependency of separation factors is incorporated. The Murphree- type factors are introduced in the code to consider the efficiency of both scrubbing and catalyst layers. The code provides stable and relatively rapid computation of concentration profile if values of both factors are known. But some uncertainties have not allowed meanwhile to solve the problem inversely that is to determine these factors if the concentration profile is experimentally known. A considerable amount of experimental data is required to evaluate the effect of all variables on the Murphree-type factors and in that way to calculate two constants which underline accordingly each of the factors for scrubbing and catalyst layers.

Table 1. Examples of test condition and results

Parameter Example 1 Example 2 Example 3 Pressure, MPa 0.33 0.195 0.145 Temperature, K 340 343 338 Hydrogen load, m3/h (STP) 2.14 2.38 3.71 Feed flow rate, ml/h 0 1400 2220 Reflux flow rate, ml/h 1720 1200 1840 Deuterium concentration in liquid:

XFP3, mol.% - 48.0 47.5

XFP4, mol.% 45.0 0.13 0.015

XSP3, mol.% 88.8 35.7 39.3

XSP2, mol.% 99.4 90.80 93.18

XSP1, mol.% 99.85 99.980 99.957 Deuterium concentration in gas:

YSP4, mol.% 45.0 0.12 0.43

YSP0, mol.% 99.8 99.96 99.92 The interest in the determination of the two constants is that they permit the simulation of the column operated in different conditions than those in which these constants are measured. The investigations are continuing now.

Fig.3. Effect of the temperature on the HETP. FUSION TECHNOLOGY 1998 194 Proceedings of the 20th Symposium on Fusion Technology, Marseille, France, 7-11.09.1998

During the 2700 hours of the plant operation loss of separation efficiency was not observed. Then deterioration in performance was found. Separation efficiency was recovered to its initial one by reactivation of the catalyst. The reactivation procedure consists in the feeding of the column by dry nitrogen with oxygen content about 0.1% and then by dry hydrogen with oxygen content about 0.01% up to 100 hours.

4. CONCLUSION

Tests of plant are shown high efficiency of isotope separation. At temperature 325–340 K and pressure 0.16 MPa the values of the height equivalent of a theoretical plate (HETP) are less than 20 cm. The maximum permissible linear gas flow rate in the column is 0.18 m/sec at these temperatures. The results of investigations allow to consider CECE process as considerable promise for the industrial using in particular for a processing of tritiated water wastes with a high purification from tritium. The CECE process can find an application at the ITER fusion facility.

ACKNOWLEDGMENTS The authors are grateful to professors of the Mendeleev University B.M. Andreev, Y.A. Sakharovsky, M.B. Rozenkevich, and doctor Y. S. Park for their help and support of this work, and to operative personal of the plant for their help at the experiments. REFERENCES

1.Тrenin V.D., Alekseev I.A., Karpov S.P. et al., Fusion Technology , 28, 761-766 (1995). 2.Spagnolo D., Miller A. I.,. Fusion Techn., ., Fusion Technology , 28, 748-754 (1995). 3. Andreev B.M., Sakharovsky Y.A. et al., Fusion Technology, 28, 515-518 (1995). 4. Тrenin V.D., Alekseev I.A., Bondarenko S.D. et. al.,”Experimental industrial plant for the studies and development of reprocessing technology of tritiated water wastes”, presented at the 20th SOFT, Marseilles, Sept. 7-11, 1998. 5. Malhotra S.K., Krishnan M.S., Sadhukhan H.K. «Combined Electrolysis and Catalytic Exchange: Operation of a Single Stage» in Proceedings of National Symposium on Heavy Water Technology. Bhabha Atomic Research Centre, pp. PD6, 1989. 6. Fedorchenko O.A., Alekseev I.A., Trenin V.D., Uborski V.V., Fusion Technology, 28, 1485-1490 (1995).