1. A purification plant for liquid argon (nitrogen) Hardy Simgen Max-Planck-Institut für Kernphysik Heidelberg

2. Outline Motivation Gas purification techniques Adsorption Measurement techniques Towards a purification plant Conceptual design Adsorber selection Investigation of initial contaminations Determination of column parameters Summary

3. Motivation Ultra-pure LAr/LN 2 will be used in the GERDA experiment. Cooling medium for Ge crystals Passive shield against external radiation Active shield (LAr scintillation) Removal of radio-impurities ( 222 Rn/ 85 Kr/ 39 Ar) and electronegative gases crucial Developed techniques can be applied in other low-level projects

4. Gas purification techniques Distillation: High costs and high energy consumption Big plants Adsorption: Relatively cheap Successfully applied for 222 Rn removal (BOREXINO) Buy ultrapure gases: If commercial products fulfill requirements If purity can be kept during transport

5. Adsorption in pores

6. Column purification

12. n = H  p Gas purification by adsorption in a column

13. Low-level proportional counter Background for 222 Rn: ~1 count/day

14. Mobile Radon Extraction Unit 222 Rn detection limit: ~0.5  Bq/m 3 (STP)

15. Noble gas mass spectrometer Detection limit:Ar: 10 -9 cm 3 (STP)Kr: 10 -13 cm 3

16. Towards a gas purification plant based on adsorption Conceptual design of a purification plant Selection of appropriate adsorber material Good rejection ability for different contaminants Low 222 Rn emanation rate Investigation of initial 222 Rn contamination Dependency on commercial gas quality Influence of storage tanks Determination of column parameters Adsorber mass, geometry, flow-rate,...

17. Towards a gas purification plant based on adsorption Conceptual design of a purification plant Selection of appropriate adsorber material Good rejection ability for different contaminants Low 222 Rn emanation rate Investigation of initial 222 Rn contamination Dependency on commercial gas quality Influence of storage tanks Determination of column parameters Adsorber mass, geometry, flow-rate,...

18. Design of an argon purification plant for GERDA

19. Towards a gas purification plant based on adsorption Conceptual design of a purification plant Selection of appropriate adsorber material Good rejection ability for different contaminants Low 222 Rn emanation rate Investigation of initial 222 Rn contamination Dependency on commercial gas quality Influence of storage tanks Determination of column parameters Adsorber mass, geometry, flow-rate,...

20. Breakthrough curves for krypton in nitrogen @ -186 °C

21. Selection of adsorber: Kr adsorption from N 2 @ -186°C Adsober Henry‘s constant [mol/Pa/kg] 222 Rn emanation rate [mBq/kg] Synthetic carbon CarboAct 0.21 ± 0.020.3 ± 0.1 Carbosieve SIII (molecular sieve) 0.34 ± 0.020.7 ± 0.2 Kr adsorption ability and 222 Rn emanation rate comparable CarboAct is final choice (grain size, availability and prize)

22. Towards a gas purification plant based on adsorption Conceptual design of a purification plant Selection of appropriate adsorber material Good rejection ability for different contaminants Low 222 Rn emanation rate Investigation of initial 222 Rn contamination Dependency on commercial gas quality Influence of storage tanks Determination of column parameters Adsorber mass, geometry, flow-rate,...

23. Initial 222 Rn purity of argon Argon 5.0 (Westfalen AG):8.4 mBq/m 3 Argon 6.0 (Westfalen AG):0.4 mBq/m 3 Argon 5.0 (LINDE):0.4 mBq/m 3 Ar initially less pure than N 2 (~0.05 mBq/m 3 ) Systematic effect due to production in air separation plants?! But large variations  further investigations

24. 222 Rn emanation of storage tanks for cryogenic liquids Tank from Quality of stored gas Vol. [m 3 ] 222 Rn activity in saturation [mBq] specific 222 Rn act. [mBq/m 3 ] Westfalen AG technical3 177 ± 659 ± 2 LINDE7.03 2.7 ± 0.30.9 ± 0.1 Westfalen AG 6.00.67 42 ± 263 ± 3 SOL6.016 65 ± 64.1 ± 0.4 Wide range for 222 Rn emanation of storage tanks observed. (Due to different welding techniques ???)

25. Total 222 Rn budget inside tank: 65 mBq Converted in 222 Rn concentration: 6  Bq/m 3 (STP)

26. Decay of inital 222 Rn

27. Towards a gas purification plant based on adsorption Conceptual design of a purification plant Selection of appropriate adsorber material Good rejection ability for different contaminants Low 222 Rn emanation rate Investigation of initial 222 Rn contamination Dependency on commercial gas quality Influence of storage tanks Determination of column parameters Adsorber mass, geometry, flow-rate,...

28. 222 Rn adsorption from argon (gas phase, 150 g carbon trap) Volume [m 3 ] Initial conc. [mBq/m 3 ] Final conc. [  Bq/m 3 ] Reduction factor [1/kg] 141 0.197  0.004 <0.5>2700 80 0.27  0.020.7  0.32600  150 222 Rn removal in gas phase is very efficient

29. Experimental setup for liquid phase adsorption tests

30. 222 Rn adsorption from argon (liquid phase, 60 g carbon trap) Volume [m 3 ] Initial conc. [mBq/m 3 ] Final conc. [  Bq/m 3 ] Reduction factor [1/kg] 48 0.15  0.013.3  0.6740  150 104 0.11  0.015.6  0.6330  40 140 0.21  0.015.2  0.5660  80 200 6.0  0.1600  23170  10 222 Rn removal in liquid phase less efficient Not yet fully understood  further investigations

31. Summary Main focus of project switched from nitrogen to argon Similar thermodynamical properties of N 2 /Ar  Developed techniques can still be applied  No delay in project Argon purification plant for GERDA based on adsorption  Decision for CarboAct Liquid phase purification possible  Determination of column parameters ongoing Argon initially contains more 222 Rn than nitrogen, but final level determined by 222 Rn emanation of storage tank 1st GERDA filling without purification? Only small purification plant for re-filling processes?