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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