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 2011 - San Francisco, USA - September 12 -14

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 2011 - San Francisco, USA - September 12 -14

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 2011 - San Francisco, USA - September 12 -14

DESCRIPTION OF THE TEST FACILITY Volume: ca. 25 m3 ICHS 2011 - San Francisco, USA - September 12 -14

DESCRIPTION OF THE TEST FACILITY Ventilation openings 0,063 m x 0,560 m each. ICHS 2011 - San Francisco, USA - September 12 -14

GAS SUPPLY AND INSTRUMENTATION: ICHS 2011 - San Francisco, USA - September 12 -14

OXYGEN SENSOR – GAS CHROMATOGRAPHY: Immediate manual immission in the gas chromatograph ICHS 2011 - San Francisco, USA - September 12 -14

OXYGEN SENSOR - VENTILATION OPENINGS POSITION: n.7 oxygen sensors ICHS 2011 - San Francisco, USA - September 12 -14

MIXTURE CONCENTRATION MEASURED BY THE OXYGEN SENSORS: ICHS 2011 - San Francisco, USA - September 12 -14

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 2011 - San Francisco, USA - September 12 -14

SOME EXPERIMENTAL DATA: ICHS 2011 - San Francisco, USA - September 12 -14

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 2011 - San Francisco, USA - September 12 -14

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

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 2011 - San Francisco, USA - September 12 -14

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 2011 - San Francisco, USA - September 12 -14

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 2011 - San Francisco, USA - September 12 -14

METHANE CONCENTRATION (sensors vs. gas chromatograph): ICHS 2011 - San Francisco, USA - September 12 -14

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 2011 - San Francisco, USA - September 12 -14

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

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 2011 - San Francisco, USA - September 12 -14

Alessia Marangon (UNIPI-ITALY) a.marangon@ing.unipi.it THANK YOU. Contact Author: Alessia Marangon (UNIPI-ITALY) a.marangon@ing.unipi.it Presented by: Martino Schiavetti (UNIPI-ITALY) martino.schiavetti@ing.unipi.it ICHS 2011 - San Francisco, USA - September 12 -14