Transcript Document

MICE Hydrogen System
Elwyn Baynham, Tom Bradshaw , Yury Ivanyushenkov
Applied Science Division,
RAL
MICE Collaboration Meeting, CERN, 29 March-2 April 2004
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
Version: 21/11/2003
VP
P
He Purge system
Vent outside
flame arrester
Metal Hydride storage
unit
(20m3 capacity)
P
P
1 bar
18 K He
14 K He
from Cold box
Chiller/Heater
Unit
Fill valve
P
P
X2
X2
1.6 bar
P
2.0 bar
Purge valve
Liquid level gauge
H2 Detector
Vent outside
flame arrester
P
Vacuum
Ventilation
system
H2 Detector
Internal Window
LH2 Absorber
H2 Detector
Safety window
P
Purge valve
LHe Heat
exchanger
Vent outside
flame arrester
Evacuated vent
buffer tank
2.0 bar
Vacuum vessel
1.6 bar
1.4 bar
VP
VP
P
Pressure
gauge
P
Pressure
regulator
Valve
Pressure
relief valve
Non-return
valve
Bursting disk
VP
Vacuum pump
H2 Gas bottle
Hydrogen system - revised baseline layout
High level vent
High level vent
Non return
valve
0.1 bar
Vent manifold
Vent outside
flame arrester
Vent manifold
H2 Detector
Hydrogen zone 2
Extract hood
VP2
PV8
P
P1
Metal Hydride storage unit
(20m3 capacity)
PV7 P
P
PV2
PV1
PV3
Buffer 1 m3
vessel
P
Tbed
1
bar
PV4
Chiller/H
eater
Unit
Tchill
Fill valve
P
HV1
14 K He
in
18 K He
out
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.
0.5 bar
P2
P
Hydrogen supply
P
P
P
0.9 bar
Design pressure 1.6 bar abs
Test pressure
2.0 bar abs
Burst pressure 6.4 bar diff
Absorber window
Nitrogen
supply
H2 Detector
Purge valve
HV3
Tabs
Safety window
Helium
supply
HV2
Purge valve
P3
P
Windows:
P
PV6
0.9 bar
0.5 bar
VP1
P
Pressure
gauge
P
Pressure
regulator
Valve
Pressure
relief valve
Non-return
valve
Bursting disk
VP
Vacuum pump
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)
Mass flow kg/s
0.0228
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
300K
Total
80K
40K
Magnet
Mice vacuum
space
Specific load (W/cm2)
3.6
Load (W)
5089
Safety factor x2 (W)
10178
0.1258
Pipe sizes for hydrogen vent system
Summary for direct venting to manifold
10m pipe run
Overall
pressure
drop
is 0.126 bar
for mass flow
of 24 g/s
ID=40 mm
L=10 m
Pressure
ID=60 mm
drop
L=10 m
is 0.367 bar
for mass flow
of 150 g/s
ID=25 mm
L=0.5 m
ID=15 mm
L=0.3 m
LH2
Pipe sizes for hydrogen vent system
30m pipe run
Overall
pressure
drop
is 0.307 bar
for mass flow
of 22.8 g/s
ID=40 mm
L=30 m
Pressure
ID=60 mm
drop
L=30 m
is 1.1 bar
for mass flow
of 150 g/s
ID=25 mm
L=0.5 m
ID=15 mm
L=0.3 m
LH2
or
Overall
pressure
drop
is 0.07 bar
for mass flow
of 22.8 g/s
or
ID=60 mm
L=30 m
ID=25 mm
L=0.5 m
ID=15 mm
L=0.3 m
Proposal
Pressure
ID=100 mm
drop
L=30 m
is 0.1 bar
for mass flow
of 150 g/s
Hydrogen level control – design considerations
•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
Provisional Hydrogen System Control Sequence
Control logic – Fill Sequence
Increment/Decrement
Tchill
Chiller on
Set Tchill =
Tchill_initial
Start
PV1,2,3,4 closed
VP1 on, PV6 Open
No
No
Hlevel>Hlevel1
Yes
P1Pset1
Yes
Pressure
Control
Vac
monitor
P3<1.e-5
Yes
No
Empty
Sequence
Tbed<Tbed1
And
P3<1.e-5
Close PV1,PV2
Stop Pressure Control Loop
Set Tchill = Tchill_low
Open PV3
Cooling system On
Start Pressure Control Loop
Start Vac Monitor
Open Pv1,Pv2
H2
System
Ready
Provisional Hydrogen System Control Sequence
Empty Sequence
Open PV4
Close PV1,PV2
Set Tchill = Tchill_low
Empty
Sequence
No
P2<0.1bar
AND
Tabs>100K
Yes
Close PV1,PV2,PV3
H2
System
Empty
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
Hydrogen system layout
RF Zone
H2
H2
H2
3 hydrogen systems
Safety Review Panel – Main Points – status review
•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
• 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 – Additional 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
Hydrogen system next design steps
•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