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

A purification plant for liquid argon (nitrogen)

Hardy Simgen

Max-Planck-Institut für Kernphysik Heidelberg

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

Motivation

Ultra-pure LAr/LN2 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 (222Rn/85Kr/39Ar) and electronegative gases crucial

Developed techniques can be applied in other low-level projects

Gas purification techniques

Distillation: High costs and high energy consumption Big plants

Adsorption: Relatively cheap Successfully applied for 222Rn removal (BOREXINO)

Buy ultrapure gases: If commercial products fulfill requirements If purity can be kept during transport

Adsorption in pores

Column purification

C0

CN

VPVRet H ()

CN

= ½

C0

ads

t

RTm

VH Re

n = Hp

Gas purification by adsorption in a column

Low-level proportional counter

Background for 222Rn: ~1 count/day

Mobile Radon Extraction Unit

222Rn detection limit: ~0.5 Bq/m3 (STP)

Noble gas mass spectrometer

Detection limit: Ar: 10-9 cm3

(STP) Kr: 10-13 cm3

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 222Rn emanation rate

Investigation of initial 222Rn contamination Dependency on commercial gas quality Influence of storage tanks

Determination of column parameters Adsorber mass, geometry, flow-rate, ...

Design of an argon purification plant for GERDA

LAr

Pump

AC

O2removal

ExperimentEl. valve

(Level cont.)

El. valve(Level cont.)

Flow/ massmeterFilter

Filter

Breakthrough curves for krypton in nitrogen @ -186 °C

Selection of adsorber: Kr adsorption from N2 @ -186°C

AdsoberHenry‘s constant

[mol/Pa/kg]

222Rn emanation rate [mBq/kg]

Synthetic carbon CarboAct

0.21 ± 0.02 0.3 ± 0.1

Carbosieve SIII (molecular sieve)

0.34 ± 0.02 0.7 ± 0.2

Kr adsorption ability and 222Rn emanation rate comparable

CarboAct is final choice (grain size, availability and prize)

Initial 222Rn purity of argon

Argon 5.0 (Westfalen AG): 8.4 mBq/m3

Argon 6.0 (Westfalen AG): 0.4 mBq/m3

Argon 5.0 (LINDE): 0.4 mBq/m3

Ar initially less pure than N2 (~0.05 mBq/m3) Systematic effect due to production in air

separation plants?! But large variations further investigations

222Rn emanation of storage tanks for cryogenic liquids

Tank fromQuality of stored gas

Vol. [m3]

222Rn activity in saturation [mBq]

specific 222Rn act. [mBq/m3]

Westfalen AG

technical 3 177 ± 6 59 ± 2

LINDE 7.0 3 2.7 ± 0.3 0.9 ± 0.1

Westfalen AG

6.0 0.67 42 ± 2 63 ± 3

SOL 6.0 16 65 ± 6 4.1 ± 0.4

Wide range for 222Rn emanation of storage tanks observed.(Due to different welding techniques ???)

Total 222Rn budget inside tank: 65 mBqConverted in 222Rn concentration: 6 Bq/m3 (STP)

Decay of inital 222Rn

222Rn adsorption from argon (gas phase, 150 g carbon trap)

Volume

[m3]Initial conc. [mBq/m3]

Final conc. [Bq/m3]

Reduction factor [1/kg]

141 0.197 0.004 <0.5 >2700

80 0.27 0.02 0.7 0.3 2600 150

222Rn removal in gas phase is very efficient

Experimental setup for liquid phase adsorption tests

222Rn adsorption from argon (liquid phase, 60 g carbon trap)

Volume

[m3]Initial conc. [mBq/m3]

Final conc. [Bq/m3]

Reduction factor [1/kg]

48 0.15 0.01 3.3 0.6 740 150

104 0.11 0.01 5.6 0.6 330 40

140 0.21 0.01 5.2 0.5 660 80

200 6.0 0.1 600 23 170 10

222Rn removal in liquid phase less efficient

Not yet fully understood further investigations

Summary

Main focus of project switched from nitrogen to argon Similar thermodynamical properties of N2/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 222Rn than nitrogen, but final

level determined by 222Rn emanation of storage tank 1st GERDA filling without purification?

Only small purification plant for re-filling processes?

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

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