0 copyright; 2007 iae. all rights reserved. 2nd ichs 11-13/9/2007 spain study of hydrogen diffusion...

2nd ICHS 11-13/9/2007 Spain 1Copyright; 2007 IAE. All rights reserved.

Study of Hydrogen Diffusion and Deflagration in a Closed System

Yuki Ishimoto1, Erik Merilo2, Mark Groethe2, Seiki Chiba3, Hiroyuki Iwabuchi1, Ko Sakata1

1The Institute of Applied Energy, Japan2SRI International, USA3SRI International, Japan

Yuki Ishimoto1, Erik Merilo2, Mark Groethe2, Seiki Chiba3, Hiroyuki Iwabuchi1, Ko Sakata1

1The Institute of Applied Energy, Japan2SRI International, USA3SRI International, Japan

Poulter Laboratory


OutlineOutline

1. Introduction- Our early studies, motivation and objective

2. Experimental facility- Facility- Measurement

3. Experimental Procedure4. Results5. Summary

Studies were administered through NEDO as part of the “Establishment of Codes & Standards for Hydrogen Economy Society”.


1.Introduction1.Introduction

- A variety of R & D projects including stationary fuel cells, fuel cell vehicles and hydrogen supply infrastructure are being conducted in Japan.

- As a part of this activity, deflagration studies of pre-mixed gas and hydrogen releases in open systems and partially confined systems have been performed.

- However hydrogen concentrations tend to be higher in closed systems under the same release condition.

37m3 300m3 Tunnel 76m long

Facilities for hydrogen deflagration research

Our early study and motivation;


ObjectivesObjectives

- Overpressures caused by the deflagration of hydrogen-air mixtures in closed systems can be larger than that in open systems due to the confinement.

- In closed systems, mechanical ventilation should be used to decrease the hydrogen concentration to levels below the lower flammability limit (LFL).

- In order to reduce the risk associated with hydrogen use in confined spaces it is necessary to study how the ventilation rate and release rate effect the hydrogen concentration in a closed system.

- This work is intended to aid in the estimation of an appropriate

ventilation rate for a confined space in which hydrogen is stored or used.


2. Experimental facility2. Experimental facility

Dimensions - Height: 2.72 m - Width: 3.64 m - Length: 6.10 m - Volume: ~60 m3

The facility: - Constructed out of welded steel, - Designed to be able to withstand an internal detonation.

- The open end was covered with a sheet of 0.0076 mm high density polyethylene (HDPE) for the tests.

- This allowed visible and infrared cameras to capture images of the flame.

- A ventilation intake hole was cut at the bottom of the plastic sheet.

1.22m

0.09m

Experiments were conducted at the SRI International experimental test site


Inside of the facilityInside of the facility

- The release nozzle was installed at the center of the floor.- The hydrogen gas was released toward the ceiling. - Overpressures from the hydrogen deflagration were measured with

four pressure transducers mounted flush on the walls of the facility.

- A constant hydrogen release rate was obtained by using a regulator to control the pressure upstream of a critical flow venturi.

- The hydrogen release rate was measured using a thermal mass flowmeter.


MeasurementsMeasurements

- Gas sampling system: 9 locations

- Fast-response coaxial thermocouples :

to measure the time-of-arrival (TOA) of flame front.

- Electronic spark ignition modules: on the ceiling and next to the release jet.

Sample stations

Sample stations

Sample stations

Thermocouples

Thermocouples

Spark ignition module

Thermocouple

Spark ignition module

Release nozzle

Thermocouple


Gas sampling systemGas sampling system

Sample H2 & air

Hydrogen readout

Pressure readout

Vacuumpump

H2 sensor

Pressure sensor

Valve

Valve

Manifold

Sample H2 & air

Hydrogen readout

Pressure readout

Vacuumpump

H2 sensor

Pressure sensor

Valve

Valve

Manifold

Sampling Setup Measurement Analysis Setup

Evacuated

Sampling

- The bottle was evacuated before the experiment.- The mixture was sampled when valve was 3 was opened- 3 bottles make up one sampling system.

- After the experiment the bottle was attached to the setup to be analyzed.

- The absolute pressure and hydrogen partial pressure were recorded.


VentilationVentilation

- Ventilation rates were measured using a hot wire anemometer.

- A 10-second average flow velocity was measured at seven points before testing to obtain the velocity profile.

- During the experiment an anemometer was placed on the center line of the duct and the velocity was recorded.


3. Experimental Procedure3. Experimental Procedure

1600 sec 2400 sec800 sec

Ventilation

Hydrogen release

Gas sampling: 3 sec

Spark Activated: 5 sec,Interval : 5 sec (on the ceiling) 1 sec (next to the nozzle).

0 sec

- Prior to the test the ventilation rate was measured.

- The hydrogen was released at a constant rate.

- The hydrogen and air mixture near the ceiling was sampled at 3 times and 9 different locations.

- The spark ignition modules installed on the ceiling were activated for 5 seconds just after the third gas sampling. (This procedure of timing the spark ignition modules ensures that there is only a single ignition point.)

- The hydrogen gas release was stopped after the last spark ignition module was turned off.

Time sequence of a test


4. Results4. Results

0

0.1

0.2

0.3

0.4

0.5

0 0.005 0.01 0.015 0.02

Ve

ntila

tion

spe

ed (

m3 /s

)

Hydrogen release rate (m 3/s)

Test 16Test 17

Test 18

Test 19

Test 21

Test 22

Test 23 Test 26

Test 25

Test 24 Test 20

Parameter combination of release experiments


Release rate and VentilationRelease rate and Ventilation

The hydrogen release rate and ventilation rate were nearly constant for each experiment.

Time (seconds) Time (seconds)

Re

lea

se

rate

(N

m3/s

)

Ve

nti

lati

on

ra

te (

Nm

3/s

)


Hydrogen densityHydrogen density

0

0.5

1

1.5

2

2.5

3

3.5

4

0 10 20 30 40 50 60Max

imum

hyd

roge

n c

once

ntra

tion

(%)

Time (min.)

- The hydrogen concentration reached about 1.5% at 4 minutes. - The hydrogen concentration seems to increase very slightly until 30 min. - Based on this result, a release duration of 40 minutes was selected for the rest

of the tests.


Overpressure and impulseOverpressure and impulse

- Hydrogen release rate: 0.02m3/s- Ventilation rate: 0.1m3/s. - Hydrogen concentration before ignition: 15~17%.- The hydrogen-air mixture was ignited by the spark ignition module located on the ceiling. - A pressure pulse was generated when the hydrogen-air mixture ignited on the ceiling. - The highest overpressure and impulse were 0.77 kPa and the 110 Pa-sec, respectively. - The measured overpressures were very low and represented a small risk to people and property.

Time (seconds)

Ov

erp

ress

ure

(k

Pa

)Im

pu

lse (k

Pa

-s)


Flame front velocityFlame front velocity

Time (seconds)

Ra

ng

e (m

)

The flame speed estimated from the TOA data was the highest of all tests and accelerated from 9.3 m/s to 13.7 m/s in this test.


0

5

10

15

20

0 0.05 0.1 0.15 0.2

Max

imu

m h

yrdg

en c

once

ntra

tion

(%)

The ratio of hydrogen release rate to ventilation speed

- The maximum concentration is proportional to the ratio of the hydrogen release rate and the ventilation rate within the range of parameters tested in the present study.

- Therefore a required ventilation rate can be estimated from the assumed hydrogen leak rate within the present experimental conditions.

- Further experiments in closed systems are necessary, varying additional parameters (volume, the direction of the nozzle…). The correlation between the ratio of the hydrogen

release rate to ventilation rate and the maximum hydrogen concentration.

Hydrogen concentrationHydrogen concentration


5. Summary5. Summary- Experiments were performed to study how the ventilation rate

and the release rate effect the hydrogen concentration in a closed system.

- Various combinations of hydrogen release rates and ventilation rates were explored in a test facility (Volume: 60m3).

- The hydrogen release rate ranged from 0.002 m3/s to 0.02 m3/s. The ventilation rate varied from 0.1 m3/s to 0.4 m3/s.

- Overpressures measured in tests were very low and represented a small risk to people and property.

- The maximum concentration inside the facility was proportional to the ratio of the hydrogen release rate and the ventilation rate within the range of parameters tested.

- Therefore a required ventilation rate can be estimated from the assumed hydrogen leak rate within the experimental conditions used in this study.


Acknowledgement Acknowledgement

- Authors would like to thank NEDO for their financial support and fruitful comments.


Thank you for your kind attention !


VentilationVentilation- The flow velocity profile in the ventilation duct was measured by placing an anemometer at different heights and taking the 10-second average at a given location.

Measurements were taken at heights of 1 cm, 5.6 cm, 11.2 cm, 16.8 cm, 22.4 cm, 28.0 cm, and 32.7 cm inside the duct.

- The velocities measured at these locations were then averaged in proportion to the circular area represented by the measurement point in order to obtain the average bulk flow velocity.

- The anemometer was then placed at the centerline of the ventilation tube, and data were recorded for at least 10 minutes prior to the test. This centerline velocity was then averaged.

- The average centerline velocity was then multiplied by the percentage of the bulk average velocity from the profile data.

- This gave an average bulk flow velocity that was multiplied by the duct’s area to obtain an average volumetric flow rate for the ventilation of the facility.

a schematic of the measurement locations


Cross-sectional schematic of the facilityCross-sectional schematic of the facility

Open end: film

6.1m

Spark module

Nozzle

H2

Inlet

Outlet1 2 3

Gas sampling

Pressure transducer

2.72

m