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Hydrogen Safety System SummaryHydrogen Safety System Summary

MICE Collaboration Meeting, Osaka, August 1-3, 2004

Elwyn Baynham, Tom Bradshaw , Yury Ivanyushenkov

Applied Science Division,Engineering and Instrumentation Department

RAL

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• Status of hydrogen absorber and system safety

• Hydrogen system:

- changes in the system according to the Safety Review Panel

recommendations;

- ongoing work on safety issues;

• Hydrogen absorber/system operation:

- instrumentation and control.

• Hydrogen R&D

Scope

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Safety = Safe Design + Safe Operation Safety = Safe Design + Safe Operation

Design:• Internal safety review - passed( many useful comments, response is ready)• Preliminary HAZOP - done• Instrumentation - to be implemented

Operation:• Operation analysis - started• Safety system analysis - started• R&D stage - to be done• Operation manual - to be written

Final safety review – to be passed

Status of hydrogen absorber and system safety

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Changes in MICE hydrogen system

AFC Safety Review Panel recommendations are implemented:

• Buffer vessel is removed from venting path.

• Vent manifold is added. The manifold is filled with nitrogen.

• Venting lines are separated.

Other changes:

• Buffer vessel is added in between absorber vessel and hydride bed: - together with liquid hydrogen vessel and hydrogen condensation pot forms a quasi-closed system; - improves time response of safety devices in case of catastrophic failure.

• Ventilation system is removed. Most of the equipment is now sits under hydrogen extraction hood.

5Pressuregauge

Non-return valve

P P VP Vacuum pumpBursting diskPressure relief valve

ValvePressureregulator

Pre-coolingOut In

Metal Hydride storage unit

(20m3 capacity)

Purge valve

0.5 bar

0.9 bar

H2 Detector

P

P

VP1

VP2

Purge valve

Chiller/Heater

Unit

1 bar

PP

0.5 bar

0.9 bar Helium supply

Hydrogen supply

High level vent

Buffer vessel

Vent outsideflame arrester

Extract hoodH2Detector

PP

Nitrogen supply

PP

PP

1 m3

Hydrogen zone 2

Vent manifold Vent manifold

P1

PV1

PV7

PV8

PV2

PV3

PV4

HV1

Fill valve

Tbed

HV2

HV3

P3

P

P2

PV6

High level vent

Non return valve

0.1 bar

MICE hydrogen system

Liquid level gauge

Internal Window

LH2 absorber

Safety windows

Vacuum

Vacuum vessel

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Safety issues: Ongoing work

• Pressure rise rate calculations

• Valves

• Hydrogen sensors

• Control

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Operation issues: Ongoing work

• Operation from cryocoolers

• Instrumentation and control

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Instrumentation to be implemented into absorber design:

• Hydrogen level sensor/s: - their functions (what do we need them for)? - continuous/ discrete? - how many and where?

• Temperature sensors: - their functions ? - how many and where?

Hydrogen absorber instrumentation

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24-M4

4-M6

24-M8

Point level sensors

Continuous level sensor

Hydrogen level sensors

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The capacitance-based liquid level sensor, used in conjunction withthe Model 185 and 186, is manufactured of stainless steel tubing.Upon request, special assembly techniques can be applied forsensors required for liquid oxygen or hydrogen measurement _including minimization of oils during construction and no use ofepoxies. Sensors can be supplied in single-section overall lengthsof up to 30 feet. Multi-section lengths in excess of 50 feet areavailable upon request.Three standard sensor mounting configurations are available. Thetypical configuration includes a hermetically sealed BNC connectorwith an adjustable 3/8" male NPT nylon feed-through. For higherpressure or vacuum applications, a welded stainless steel 3/8"male NPT fitting or conflat flange fitting is available. Twelve feetof connecting coaxial cable and in-line oscillator/transmitter areincluded with the sensor. With additional cable the sensor canbe remotely mounted over 500 feet from the instrument withouteffecting performance.Sensor options include:1. Rugged service construction 1/2" or 3/4" OD2. Miniature sensors of 3/16" and 1/4" OD3. Radius bends up to 90°4. Capacitance or RTD point sensing elementsCustom sensors are available from AMI to meet your individual

Cryogenic liquid level sensors from AMI

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Continuous level sensor

Connector required(Swagelok VCR Metal gasket

face seal fittings ?)

Level sensor implementation

Can a sensor be manufactured to this shape ?

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Table 1 The specification of the MH tank for RAL 

Hydrogen Storage Capacity 20 Nm3

Tank number/system 1

Tank Description:

Heat Transfer Medium Water

MH Weight 155kg

Tank Structure Shell & Tube type

Dimensions φ216.3×L1600 （ mm ） ( not include attachments )

Tank Total Weight 220 Kg

Operating Condition:

Charging Gas Component Hydrogen of 99.99% purity

Charging Gas Pressure 1.2 barA

Hydrogen Charging Rate 70NL/min

(up to 90% of Storage Capacity)

Discharging Gas Pressure 1.2 barA

Hydrogen Discharging Rate 70NL/min

(up to 90% of Storage Capacity)

Utility Requirements:

Cooling Medium Water

Below -10 ℃ （ At 20L/min ）

Heating Medium Above 20 ℃ （ At 20L/min ）

Design Code （ AD Merkblaetter )

Certification （ Declaration of Conformity to Pressure Equipment Directive 97/23/EC

Certified by a Notified Body ）

REFERENCE 

What is known about metal hydride tank

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(1600)

φ216.3

140

(1810)

2-Rc3/4Relief valve

Filter

Valve

Fig.1 Schematics and dimensions of the MH tank

What is known about metal hydride tank (2)

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0 50 100 150 20010-2

10-1

100

17℃

10℃

0.12MPa

-10℃

30℃

Hydr

ogen

Press

ure

(MP

a)

Hydrogen Content (cc/g)

Fig.2 P-C-T curves of metal hydride for RAL

What is known about metal hydride tank (3)

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Annotation by JSW:

Attached please find the temporary specification of a 20Nm3 metal hydride(MH) tank, its sketch and the pressure-composition-temperature diagram ofthe candidate MH alloy.It would be better to explain the temperatures and pressures on charging anddischarging hydrogen, referring to the PCT diagram.

As you can see in the diagram (Fig. 2), it is possible for the alloy toabsorb hydrogen gas almost to its maximum capacity at 0 degC if the pressureof hydrogen gas is maintained at 0.12 MPa. However, we are not yet sure ofthe influence of pressure loss inside the tank under such a negativepressure region. So, at the moment the charging temperature is specified tobe below -10 degC with 0.12 MPa of charging pressure (See Table 1.).Then, you can see in the diagram (Fig. 2) that the MH alloy can dischargealmost all the hydrogen at +20 degC if the pressure is maintained at 0.17MPa. To be on the safer side, the discharging temperature is specified to be"above" +20 degC (See Table 1.). This means that the maximum internalpressure of the MH tank is likely to be reached during the hydrogen gasholding period if the water is stopped and the surrounding temperatureincreases. However, even at +30 degC, the expected internal pressure is notso high, approximately 1 MPa.

As a matter of fact, there will be an unknown factor, i.e., how accuratelywe could control the materials properties when we newly manufacture an MHalloy. Due to slight variations in the chemical composition and othermanufacturing parameters, the equilibrium temperature could vary by up to 5degC for the same pressure. This could cause further changes in thecharging/discharging temperatures and consequently the internal pressure.Since the relative plateau positions do not change, please assume that adifference of more than 30 degC is needed between the charging anddischarging temperatures for the given charging and discharging pressures.

What is known about metal hydride tank (4)

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Hydrogen R&D

Conceptual question: a small-scale rig vs. a full-scale prototype ?

Decision: go for a full-scale system which later will be used in MICE.

R&D goals:• Establish the working parameters of a hydride bed in the regimes of

storage, absorption and desorption of hydrogen.• Absorption and desorption rates and their dependence on various

parameters such as pressure, temperature etc.• Purity of hydrogen and effects of impurities.• Hydride bed heating/cooling power requirements.• What set of instrumentation is required for the operation of the system?• Safety aspects including what is the necessary set of safety relief valves,

sensors and interlocks.

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Tchill

Pressuregauge

Non-return valveP P VP Vacuum pumpBursting diskPressure

relief valveValvePressure

regulator

CoolantOut In

Test absorber assembly

Metal Hydride storage unit

(20m3 capacity)

Purge valve

0.5 bar

0.9 bar

H2 Detector

P

P

VP1

VP2

Purge valve

Chiller/Heater

Unit

1 bar

PP

0.5 bar

0.9 bar Helium supply

Hydrogen supply

High level vent

Buffer vessel

Vent outsideflame arrester

Extract hoodH2Detector

PP

Nitrogen supply

PP

PP

1 m3

Hydrogen zone 2

Vent manifold Vent manifold

P1

PV1

PV7

PV8

PV2

PV3

PV4

HV1

Fill valve

Tbed

HV2

HV3

P3

P

P2

PV6

High level vent

Non return valve

0.1 bar

Hydride system test rig

Mass spectrometer

M. F.M.

Mass flow meter

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Next steps

• Finish pressure rise rates calculations

• Select safety devices

• Control system diagram

• Instrumentation defined and implemented into design

• Hydrogen R&D:

- find suitable place for hydrogen test area (MICE hall ?);

- timetable depends on funding

but would like to setup test rig in 2005.