1. HYDROGEN – METHANE MIXTURES: DISPERSION AND STRATIFICATION STUDIES
A. Marangon, M.N. Carcassi
Università di Pisa
Dipartimento di Ingegneria Meccanica, Nucleare e della Produzione (DIMNP),
University of Pisa
ICHS San Francisco, USA - September

2. Why the hydrogen – methane mixtures could represent the transition phase towards hydrogen economy?
Experience gained over many year of distribution and use of natural gas (transportation, energy production, domestic application, etc.).
Greater acceptance by the Public Authority and general public with respect to pure hydrogen.
Limited investment in the short term and a significant reduction in emissions, both local and global (greenhouse gases).
ICHS San Francisco, USA - September

3. UNIPI – DIMNP Research activities on HCNG mixtures: 10-90 and 30-70 %vol. hydrogen in methane.
Investigation of the diffusion and stratification properties in confined and semi-confined environments (typical of most of the industrial and commercial environments).
Investigation with the help of the gas-chromatography technique of the tendency or less to separate in different layers for the mixture’s constituents (hydrogen and methane).
CFD simulations of the experimental tests (not presented in the paper).
ICHS San Francisco, USA - September

4. DESCRIPTION OF THE TEST FACILITY
Volume: ca. 25 m3
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5. DESCRIPTION OF THE TEST FACILITY
Ventilation openings
0,063 m x 0,560 m each.
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6. GAS SUPPLY AND INSTRUMENTATION:
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7. OXYGEN SENSOR – GAS CHROMATOGRAPHY:
Immediate manual immission in the gas chromatograph
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8. OXYGEN SENSOR - VENTILATION OPENINGS POSITION:
n.7 oxygen sensors
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9. MIXTURE CONCENTRATION MEASURED BY THE OXYGEN SENSORS:
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10. TEST MATRIX: X - ICHS 2011 - San Francisco, USA - September 12 -14
MIXTURE
30 H2 – 70 CH4
10 H2 – 90 CH4
CVE TOTALLY CLOSED
CVE WITH 2 OPENINGS ON OPPOSITE SIDES
CVE WITH 1 OPENING IN THE BOTTOM PART
CVE WITH 1 OPENING IN THE UPPER PART X -
ICHS San Francisco, USA - September

11. SOME EXPERIMENTAL DATA:
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12. CVE TOTALLY CLOSED: Release time: 530 s Release flow rate: 2,016 g/s
STRATIFICATION NOT WELL DEFINED IN THE HORIZONTAL PLANES
TENDENCY TO HOMOGENEIZATION
ICHS San Francisco, USA - September

13. STRATIFICATION WELL DEFINED TENDENCY TO HOMOGENEIZATION
CVE TOTALLY CLOSED :
Release time: 1580 s
Release flow rate: 1,16 g/s
STRATIFICATION WELL DEFINED
TENDENCY TO HOMOGENEIZATION
ICHS San Francisco, USA - September

14. VENTILATION WITH OPENINGS ON OPPOSITE SIDES:
Release time: 2890 s
Release flow rate: 1,23 g/s
STRATIFICATION WELL DEFINED
FAST DECREASE OF THE CONCENTRATION ONCE THE RELEASE WAS STOPPED
ICHS San Francisco, USA - September

15. STRATIFICATION WELL DEFINED IN THE HORIZONTAL PLANES
VENTILATION WITH ONE OPENING IN THE UPPER PART:
ΔT (int-ext)= 5 °C
STRATIFICATION WELL DEFINED IN THE HORIZONTAL PLANES
Release time: 2560 s
Release flow rate: 1,32 g/s
ICHS San Francisco, USA - September

16. STRATIFICATION NOT WELL DEFINED IN THE HORIZONTAL PLANES
VENTILATION WITH ONE OPENING IN THE UPPER PART:
STRATIFICATION NOT WELL DEFINED IN THE HORIZONTAL PLANES
ΔT (int-ext)= 15 °C
Release time: 2750 s
Release flow rate: 1,31 g/s
ICHS San Francisco, USA - September

17. STRATIFICATION WELL DEFINED IN THE HORIZONTAL PLANES
VENTILATION WITH ONE OPENING IN THE BOTTOM PART:
Release time: 2023 s
Release flow rate: 1,5 g/s
STRATIFICATION WELL DEFINED IN THE HORIZONTAL PLANES
ICHS San Francisco, USA - September

18. METHANE CONCENTRATION (sensors vs. gas chromatograph):
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19. CONCLUSIONS:
In all the experiments a non homogeneous concentration was observed within the CVE, both with and without natural ventilation and independently of natural ventilation openings position.
For test carried out with a higher mixture release flow rate, the gas concentration measured at the centre of the celing of the CVE (Sens. N.1 – 2,82 m above the release point), was higher than the concentration measured by sensor located at the same height but not directly above the release. Instead for smaller release flow rate the concentration was well stratified in the horizontal planes.
ICHS San Francisco, USA - September

20. CONCLUSIONS:
For test carried out without natural ventilation a tendency to homogenization was observed over long residence time (more than seconds).
For test carried out with natural ventilation openings, both well defined stratification in horizontal planes and not well defined (with concentration higher far from the opening location) was observed. This phenomenon depending on the ΔT between the internal volume of the CVE and the external atmosphere (higher the ΔT, worst the stratification).
ICHS San Francisco, USA - September

21. CONCLUSIONS:
Sample analysis with gas chromatograph showed that for the presented experiment configurations and mixture’s residence time within the CVE, the non separation between the mixture constituent gases (hydrogen and methane).
ICHS San Francisco, USA - September

22. Alessia Marangon (UNIPI-ITALY) a.marangon@ing.unipi.it
THANK YOU.
Contact Author:
Alessia Marangon (UNIPI-ITALY)
Presented by:
Martino Schiavetti (UNIPI-ITALY)
ICHS San Francisco, USA - September