MICE Hydrogen System

MICE Collaboration Meeting, CERN, 29 March-2 April 2004

Elwyn Baynham, Tom Bradshaw , Yury Ivanyushenkov

Applied Science Division,RAL

Scope of the presentation

• Design changes arising from Safety Review Panel• Buffer volumes • Separation of vent systems• Vent system manifolding

• Ongoing design issues• Hydrogen vent pipe sizes• Liquid level control• Provisional hydrogen system control sequence

• R&D programme on metal hydride • Hydrogen system layout• Response to Review Panel – summary comments

Buffer Volumes

• Original Design• One evacuated buffer volume for both absorber and vacuum space venting• Separated from volumes by relief valves

•Assessment from the review•Buffer volume is more effective if directly connected•Vacuum space

•RAL safety does not require 52 x volume for vacuum space around absorber •Current design gives ~ 8 –10 x volume

•Absorber volume •Design includes buffer volume in the absorber line

•Window protection – response time •Simplification of control

Baseline layout

P P VP Vacuum pumpBursting diskPressure relief valveValve

Pressureregulator

Pressuregauge

18 K He14 K Hefrom Cold box

Liquid level gauge

LH2 Absorber

Vacuum

Vacuum vessel

LHe Heat exchanger

Internal Window

Safety window

Fill valve

Metal Hydride storage unit

(20m3 capacity)

Vent outside flame arrester

He Purge system

Non-return valve

Vent outsideflame arrester

Purge valve

1.6 bar

2.0 bar

H2 Detector

H2 Detector

P

P

P

Evacuated vent buffer tank

VP

P

VP

X 2X 2

VP

Version: 21/11/2003

H2 Detector

Ventilationsystem

Vent outsideflame arrester

Purge valve

H2 Gas bottle

PP

Chiller/Heater Unit

1 bar

PP

2.0 bar

1.6 bar 1.4 bar

Zone 2: An area within which any flammable or explosive substance whether gas, vapour or volatile liquid, although processed or stored, is so well under conditions of control that the production (or release) of an explosive or ignitable concentration in sufficient quantity to constitute a hazard is only likely under abnormal conditions.

P P VP Vacuum pumpBursting diskPressure relief valve

ValvePressureregulator

Pressuregauge

18 K Heout

14 K Hein

Safety window

Metal Hydride storage unit(20m3 capacity)

Non-return valve

Purge valve

0.5 bar

0.9 bar

H2 Detector

P

P

P

VP1

VP2

Purge valve

Chiller/Heater

Unit1 bar

PP

0.5 bar

0.9 bar Helium supply

Windows:

Design pressure 1.6 bar absTest pressure 2.0 bar absBurst pressure 6.4 bar diff

Hydrogen supply

High level vent

Buffer vessel

Vent outsideflame arrester

Extract hood

H2 Detector

PP

Nitrogen supply

P P

PP

1 m3

Hydrogen zone 2

Vent manifold Vent manifold

P1

PV1

PV7

PV8

PV2

PV3

PV4

HV1

Fill valve

TbedTchill

HV2

HV3

P3

P2

PV6

High level vent

Non return valve

0.1 bar

Absorber window

Hydrogen system - revised baseline layout

Tabs

Changes in MICE hydrogen system

AFC Safety Review Panel recommendations are implemented:

• Original buffer vessel is removed

• 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.

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

Hydrogen absorber - failure mode - vent system

Hydrogen must be vented out of the absorber module in two cases:

1) hydrogen window rupture (hydrogen spills out into the room temperature absorber vacuum chamber and floods the lowest points in the absorber vacuum chamber to a depth of 250 mm). Mass flow rate is 116 g/s. -> 150 g/s with margin (calculations by Mike Green)

2) catastrophic vacuum failure (leads to air being plated out on the inner window, this will put a heat load

on the hydrogen in the absorber leading to boil-off of the hydrogen).

Mass flow rate is ~12 g/s -> 24 g/s with factor 2 in safety. (calculations by Tom Bradshaw)

Pipe sizes –hydrogen vent(calculations by Tom Bradshaw)

40K 80K 300K

Length m 0.3 0.5 10

Diameter mm 15 25 40

Velocity m/s 109 154 227

Press drop Bar 0.0165 0.0104 0.0989

Total 0.1258

Mass flow kg/s 0.0228

Magnet

Mice vacuum space

40K

80K

300K

Specific load (W/cm2) 3.6

Load (W) 5089

Safety factor x2 (W) 10178

Pipe sizes for hydrogen vent systemSummary for direct venting to manifold

10m pipe run

LH2

ID=15 mmL=0.3 m

ID=25 mmL=0.5 m

ID=40 mmL=10 m

ID=60 mmL=10 m

Overallpressure

dropis 0.126 bar

for mass flow of 24 g/s

Pressure drop

is 0.367 barfor mass flow

of 150 g/s

Pipe sizes for hydrogen vent system30m pipe run

LH2

ID=15 mmL=0.3 m

ID=25 mmL=0.5 m

ID=40 mmL=30 m

ID=60 mmL=30 m

Overallpressure

dropis 0.307 bar

for mass flow of 22.8 g/s

Pressure drop

is 1.1 barfor mass flow

of 150 g/s

ID=100 mmL=30 m

Pressure drop

is 0.1 barfor mass flow

of 150 g/s

oror

Overallpressure

dropis 0.07 bar

for mass flow of 22.8 g/s

ID=15 mmL=0.3 m

ID=25 mmL=0.5 m

ID=60 mmL=30 m

Proposal

•Level Control – what variations do we need to respond to:

•Level will vary due to temperature changes in the absorber •Variation in density of LH2 could give ~ 1 – 2 litres volume change

•Such changes cannot be accommodated in small pipes•25mm dia = 2.2m/litre

•Such level changes will be relatively slow under normal operating conditions

•Energy to go from 14 – 18K ~ 50kJ for 20 litres•Nominal heat load /absorber is few W•Time 14 – 18K is ~ 5 – 10 hrs

•Most significant effect will be intermittent gas boil off due to changes in level – especially so for the horizontal pipe

Hydrogen level control – design considerations

•Level Control – Where is best place to monitor/control level•Absorber neck tube

•Insufficient volume •Horizontal pipe

•Not practical•Vertical pipe

•Need to thermalise the horizontal pipe •Small volume available

•Main absorber volume •Ullage - 2 litres is 10%•Temperature of absorber body will be uniform •Increase in volume will cause very little boil off •Less active role for control system – hydride bed

•External buffer volume 1m^3 could absorb ~ 0.5 –1 litre before activating the relief system – assuming no return to the hydride bed - need further work

Hydrogen level control – design considerations

Chiller onSet Tchill = Tchill_initial

Start PV1,2,3,4 closed

VP1 on, PV6 Open

Cooling system OnStart Pressure Control Loop

Start Vac MonitorOpen Pv1,Pv2

Tbed<Tbed1And

P3<1.e-5

P1Pset1

Close PV1,PV2Stop Pressure Control Loop

Set Tchill = Tchill_lowOpen PV3

Hlevel>Hlevel1

H2 System Ready

Increment/DecrementTchill

EmptySequence

P3<1.e-5

Vac monitor

Pressure Control

Yes

No

Yes

No Yes

No

Provisional Hydrogen System Control Sequence

Control logic – Fill Sequence

Open PV4Close PV1,PV2

Set Tchill = Tchill_low

Close PV1,PV2,PV3

P2<0.1barAND

Tabs>100K

H2 System Empty

EmptySequence

Yes

No

Provisional Hydrogen System Control Sequence

Empty Sequence

R&D programme on metal hydride storage system

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.•Status•Programme on hold pending funding approval for 2004/05

RF Zone

Hydrogen system layout

H2 H2 H2

3 hydrogen systems

•Hydrogen Gas Handling & Venting system•Remove buffer tank and vent the hydrogen out directly - implemented

•Remove relief valves in the hydrogen vent lines and have burst disks only – retained

• Completely separate vent system for the absorber and vacuum spaces -implemented

• Detail specification of the Relief valve – work in progress

•Is hydrogen detector appropriate in the vacuum line – still under consideration

•Hydrogen detectors are needed in the ventilation system and in the personnel space around the experiment – will be implemented

• Examine the level to which piping should be Argon jacketed – will be addressed

• Replacing the flame arrestor with a vent pipe with an inert atmosphere - implemented

• Adopt Fermilab requirement vacuum system volume 52x H2 liquid volume – not implemented

Safety Review Panel – Main Points – status review

• R & D on the Metal Hydride system

•The use of hydride system requires active control.

•The panel suggested an scaled model test.

• It also asked the group to examine the safety issues associated with this system

•R&D proposal defined and submitted

Safety Review Panel – Main Points

•Practicality of using intrinsically safe electrical equipment – response already drafted

•Pipe joints – will be as requested •Detection of Hydrogen in Personnel areas – agreed •Attention to Interlocks, alarms and control system - ongoing.• Continuation of HAZOP assessment – agreed • Response to Absorber system leak scenario - ongoing• Potential of liquid hydrogen sloshing in warmer part of the feed pipe – to be addressed in level control.• Leak between the helium and hydrogen compartment in Absorber unit - ongoing

Safety Review panel – Additional Points

•Agree level monitoring and control principles

•Range of parameters to control

•Control accuracy required

•Where to implement

•Design calculations required

•Engineering design required

•Define relief valves

•Pressure range confirmation

•Response speed required

•Identify supply availability

•Argon Jacketing

•H2 and He leaks

Hydrogen system next design steps