HYDROGEN – METHANE MIXTURES: DISPERSION AND STRATIFICATION STUDIES A. Marangon, M.N. Carcassi

ICHS 2011 - San Francisco, USA - September 12 -14

HYDROGEN – METHANE MIXTURES: DISPERSION AND STRATIFICATION STUDIES

HYDROGEN – METHANE MIXTURES:DISPERSION AND STRATIFICATION STUDIES

A. Marangon, M.N. Carcassi

Dipartimento di Ingegneria Meccanica, Nucleare e della Produzione Dipartimento di Ingegneria Meccanica, Nucleare e della Produzione (DIMNP),(DIMNP),

University of PisaUniversity of Pisa

Università di Pisa



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).



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).



DESCRIPTION OF THE TEST FACILITY

Volume: ca. 25 m3



DESCRIPTION OF THE TEST FACILITY

Ventilation openings

0,063 m x 0,560 m each.



GAS SUPPLY AND INSTRUMENTATION:



OXYGEN SENSOR – GAS CHROMATOGRAPHY:

Immediate manual immission in the gas chromatograph



OXYGEN SENSOR - VENTILATION OPENINGS POSITION:

n.7 oxygen sensors



MIXTURE CONCENTRATION MEASURED BY THE OXYGEN SENSORS:



TEST MATRIX:

MIXTURE30 H2 – 70 CH4

MIXTURE10 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 - X - - -

X - X - - -

X - X - - -

X - - X - -

- X X - - -

- X - X - -

- X - X - -

- X X - - -

X - X - - -

- X - - X -

- X - - - X

X - - - - X



SOME EXPERIMENTAL DATA:



CVE TOTALLY CLOSED: Release time: 530 s

Release flow rate: 2,016 g/s

TENDENCY TO HOMOGENEIZATION

STRATIFICATION NOT WELL DEFINED IN THE HORIZONTAL

PLANES



CVE TOTALLY CLOSED : Release time: 1580 s


TENDENCY TO HOMOGENEIZATION

STRATIFICATION WELL DEFINED



VENTILATION WITH OPENINGS ON OPPOSITE SIDES:

Release time: 2890 s


FAST DECREASE OF THE CONCENTRATION ONCE THE

RELEASE WAS STOPPED

STRATIFICATION WELL DEFINED



VENTILATION WITH ONE OPENING IN THE UPPER PART:



STRATIFICATION WELL DEFINED IN THE HORIZONTAL

PLANES

ΔT (int-ext)= 5 °C



VENTILATION WITH ONE OPENING IN THE UPPER PART:



ΔT (int-ext)= 15 °CSTRATIFICATION NOT WELL DEFINED IN THE HORIZONTAL PLANES



VENTILATION WITH ONE OPENING IN THE BOTTOM PART:



STRATIFICATION WELL DEFINED IN THE HORIZONTAL

PLANES



METHANE CONCENTRATION (sensors vs. gas chromatograph):



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.



CONCLUSIONS:

For test carried out without natural ventilation a tendency to

homogenization was observed over long residence time (more than 10000

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).



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).



THANK YOU.

Contact Author:

Alessia Marangon (UNIPI-ITALY)

[email protected]

Presented by:

Martino Schiavetti (UNIPI-ITALY)

[email protected]

Documents

HYDROGEN – METHANE MIXTURES: DISPERSION AND STRATIFICATION STUDIES A. Marangon, M.N. Carcassi