1

Conception and test of a 10 kg

magnesium hydride tank

B. Delhomme, P. de Rango, P. Marty, S. Miraglia

Institut Néel – CRETA – LEGI, Grenoble, FRANCE

2Hydrogen storage

Hydrogen as energy vector :- Fitting of electricity production - Electricity production in off-grid sites- Uninterruptible Power Supply (UPS)

High pressure storage :Pressure = 200 - 350 BarEnergy needed = 25 % H

2 LHV

A safe and efficient mean of storage is still needed

Liquid storage :Temperature = 20 KEnergy needed = 30 % H

2 LHV

Solid storage : magnesium hydride :Moderate pressure : 1 - 15 barTemperature : 300 - 380 °CEnergy needed = 30 % H

2 LHV

Possibility to use wasted heat for the hydrogen desorption

3Magnesium hydride

Material :- MgH

2 ball-milled with TiVCr

- powders are then compacted with Expanded Natural Graphite (ENG)

Properties :- Storage capacity : 6.5 wt. %- Fast reaction kinetics- Improved thermal conductivity- Temperature range : 300 - 400 °C- Pressure range : 0.1 - 1 MPa

Exothermic

Endothermic

75 kJ.mol-1

Temperature (°C)

Pressu

re (MP

a)

Equilibrium pressure

410 kg MgH2 tank

73 MgH2 discs

High temperature heat transfer fluid : MARLOTHERM

Metallic mesh used to improve H2 circulation

5Test bench

Measurement :Temperature : 16 K type thermocouplesHydrogen mass flowPressure

6Tank loading

Loading time = 40 min

Typical loading conditions :- H

2 pressure = 11 bar

- Oil temperature = 240 °C

7Tank unloadingUnloading conditions :

- Oil temperature = 340 °C

- H2 flow = 35 Nl.min-1

Unloading time = 150 min

3 kWe (H2 LHV,

FC=50 %)

8Loading time improvement

Large improvement of the thermal conductivity from the first cycle

Loading time heat exchanges

9Loading time improvement

Deformation of the composites : Improvement of the thermal contact between the composites and the tank wall

10Loading time improvement

Evolution of MgH2 crystallite size :

- before ball-milling : broad peaks with low intensity crystallites with nanometer scale - this partially amorphous state disappears after the first cycle

11Loading time improvement

After ball-milling After 1 cycle

Hydride recrystallization observed by TEM :

100 nm 100 nm

12Evolution of the storage capacity

- Diminution of the storage capacity over the 14 first cycles, then a slight increase is observed.- the hydrogen capacity is linked with the imposed temperature

13Life time stability Small scale tank cycled 600 times :

mMgH2

164 g

Degradation of (un)loading times : no evolution after 390 cycles

Evolution of storage capacity : - diminution during the first cycles- slight increase until 80 cycles- slight decrease from 80 to 600 cycles

0.15 wt.% loss after 600 cycles

14Conclusions

A 10 kg MgH2 tank (600 g H

2) was realised and tested for different

experimental conditions : - High energetic density of 360 Wh.kg-1(composites + tank + measurement devices). - Loading performed in 35 min. - A mean discharging hydrogen flow of 35 Nl.min-1 can be maintained during 2h30.- During the first 10 cycles, an improvement of (un)loading time is observed due to improvement of heat exchanges.- Large microstructure modifications observed from the first hydrogenation cycles. However, reaction kinetic remain fast : (un)loading times limited by heat exchanges and hydrogen circulation.- A small scale tank was cycled up to 600 times. Only a slight diminution of hydrogen capacity is observed after 600 cycles.

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Acknowledgement

NESSHYNovel Efficient Solid Storage for H2

FP6 Integrated Project SES6-518271 (2006-2011)

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Thank you four your attention