MICE Hydrogen System

1. MICE Hydrogen System Elwyn Baynham, Tom Bradshaw , Yury Ivanyushenkov Applied Science Division, RAL MICE Collaboration Meeting, CERN, 29 March-2 April 2004

2. 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

3. 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

4. P P P P P P H2 Gas bottle H2 Detector H2 Detector H2 Detector P P P P VP VP VP VP Version: 21/11/2003 Baseline layout Vent outside flame arrester He Purge system Metal Hydride storage unit (20m3 capacity) 1 bar Chiller/Heater Unit 18 K He 14 K He from Cold box Fill valve X 2 X 2 1.6 bar 2.0 bar Purge valve Liquid level gauge Vent outside flame arrester Vacuum Ventilation system Internal Window LH2 Absorber Safety window Purge valve LHe Heat exchanger Vent outside flame arrester Evacuated vent buffer tank 2.0 bar Vacuum vessel 1.6 bar 1.4 bar Pressure relief valve Pressure regulator Non-return valve Pressure gauge Vacuum pump Valve Bursting disk

5. Hydrogen system - revised baseline layout P P P P H2 Detector H2 Detector P P P P P P P P P High level vent High level vent Vent outside flame arrester Non return valve Vent manifold Vent manifold 0.1 bar Hydrogen zone 2 Extract hood VP2 PV8 P1 Metal Hydride storage unit (20m3 capacity) PV7 Chiller/Heater Unit PV2 PV1 Tbed PV3 1 bar Tchill Buffer vessel PV4 1 m3 Fill valve HV1 18 K He out 14 K He in 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 0.9 bar Hydrogen supply HV2 Purge valve P3 Windows: Design pressure 1.6 bar abs Test pressure 2.0 bar abs Burst pressure 6.4 bar diff Purge valve Absorber window HV3 Tabs 0.9 bar Safety window Nitrogen supply PV6 Helium supply 0.5 bar VP1 Pressure relief valve Non-return valve Pressure gauge Pressure regulator VP Vacuum pump Valve Bursting disk

6. 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.

7. 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)

8. 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 Total 0.1258 300K 80K 40K Magnet Specific load (W/cm2) 3.6 Load (W) 5089 Safety factor x2 (W) 10178 Mice vacuum space

9. Pipe sizes for hydrogen vent system Summary for direct venting to manifold 10m pipe run ID=40 mm L=10 m Overall pressure drop is 0.126 bar for mass flow of 24 g/s Pressure drop is 0.367 bar for mass flow of 150 g/s ID=60 mm L=10 m ID=25 mm L=0.5 m ID=15 mm L=0.3 m LH2

10. Pipe sizes for hydrogen vent system 30m pipe run ID=40 mm L=30 m Overall pressure drop is 0.307 bar for mass flow of 22.8 g/s Pressure drop is 1.1 bar for mass flow of 150 g/s ID=60 mm L=30 m ID=25 mm L=0.5 m ID=15 mm L=0.3 m LH2 or or ID=60 mm L=30 m Overall pressure drop is 0.07 bar for mass flow of 22.8 g/s Pressure drop is 0.1 bar for mass flow of 150 g/s ID=100 mm L=30 m ID=25 mm L=0.5 m Proposal ID=15 mm L=0.3 m

11. 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

12. 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

13. Provisional Hydrogen System Control Sequence Control logic – Fill Sequence Chiller on Set Tchill = Tchill_initial Start PV1,2,3,4 closed VP1 on, PV6 Open Hlevel>Hlevel1 Increment/Decrement Tchill No P1Pset1 No Yes Tbed<Tbed1 And P3<1.e-5 Pressure Control Close PV1,PV2 Stop Pressure Control Loop Set Tchill = Tchill_low Open PV3 Yes Cooling system On Start Pressure Control Loop Start Vac Monitor Open Pv1,Pv2 Vac monitor P3<1.e-5 H2 System Ready No Empty Sequence Yes

14. Provisional Hydrogen System Control Sequence Empty Sequence Open PV4 Close PV1,PV2 Set Tchill = Tchill_low Empty Sequence P2<0.1bar AND Tabs>100K No Yes Close PV1,PV2,PV3 H2 System Empty

15. 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

16. Hydrogen system layout RF Zone H2 H2 H2 3 hydrogen systems

17. 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

18. 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

19. 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 Absorberunit - ongoing

20. 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