1 Hydrogen 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

2 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

3 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

4 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.

5 Pressure gauge Non-return valve PP VP Vacuum pump Bursting disk Pressure relief valve Valve Pressure regulator Pre-cooling Out In Metal Hydride storage unit (20m 3 capacity) Purge valve 0.5 bar 0.9 bar H 2 Detector P P VP1 VP2 Purge valve Chiller/He ater Unit 1 bar P P 0.5 bar 0.9 bar Helium supply Hydrogen supply High level vent Buffer vessel Vent outside flame arrester Extract hood H 2 Detector P P Nitrogen supply P P P P 1 m 3 Hydrogen zone 2 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 LH 2 absorber Safety windows Vacuum Vacuum vessel

6 Safety issues: Ongoing work Pressure rise rate calculations Valves Hydrogen sensors Control

7 Operation issues: Ongoing work Operation from cryocoolers Instrumentation and control

8 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

9 Point level sensors Continuous level sensor Hydrogen level sensors

10 The capacitance-based liquid level sensor, used in conjunction with the Model 185 and 186, is manufactured of stainless steel tubing. Upon request, special assembly techniques can be applied for sensors required for liquid oxygen or hydrogen measurement _ including minimization of oils during construction and no use of epoxies. Sensors can be supplied in single-section overall lengths of up to 30 feet. Multi-section lengths in excess of 50 feet are available upon request. Three standard sensor mounting configurations are available. The typical configuration includes a hermetically sealed BNC connector with an adjustable 3/8" male NPT nylon feed-through. For higher pressure or vacuum applications, a welded stainless steel 3/8" male NPT fitting or conflat flange fitting is available. Twelve feet of connecting coaxial cable and in-line oscillator/transmitter are included with the sensor. With additional cable the sensor can be remotely mounted over 500 feet from the instrument without effecting performance. Sensor options include: 1. Rugged service construction 1/2" or 3/4" OD 2. Miniature sensors of 3/16" and 1/4" OD 3. Radius bends up to 90° 4. Capacitance or RTD point sensing elements Custom sensors are available from AMI to meet your individual Cryogenic liquid level sensors from AMI

11 Continuous level sensor Connector required (Swagelok VCR Metal gasket face seal fittings ?) Level sensor implementation Can a sensor be manufactured to this shape ?

12 Table 1 The specification of the MH tank for RAL Hydrogen Storage Capacity 20 Nm 3 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

13 Fig.1 Schematics and dimensions of the MH tank What is known about metal hydride tank (2)

14 Fig.2 P-C-T curves of metal hydride for RAL What is known about metal hydride tank (3)

15 Annotation by JSW: Attached please find the temporary specification of a 20Nm3 metal hydride (MH) tank, its sketch and the pressure-composition-temperature diagram of the candidate MH alloy. It would be better to explain the temperatures and pressures on charging and discharging hydrogen, referring to the PCT diagram. As you can see in the diagram (Fig. 2), it is possible for the alloy to absorb hydrogen gas almost to its maximum capacity at 0 degC if the pressure of hydrogen gas is maintained at 0.12 MPa. However, we are not yet sure of the influence of pressure loss inside the tank under such a negative pressure region. So, at the moment the charging temperature is specified to be 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 discharge almost all the hydrogen at +20 degC if the pressure is maintained at 0.17 MPa. To be on the safer side, the discharging temperature is specified to be "above" +20 degC (See Table 1.). This means that the maximum internal pressure of the MH tank is likely to be reached during the hydrogen gas holding period if the water is stopped and the surrounding temperature increases. However, even at +30 degC, the expected internal pressure is not so high, approximately 1 MPa. As a matter of fact, there will be an unknown factor, i.e., how accurately we could control the materials properties when we newly manufacture an MH alloy. Due to slight variations in the chemical composition and other manufacturing parameters, the equilibrium temperature could vary by up to 5 degC for the same pressure. This could cause further changes in the charging/discharging temperatures and consequently the internal pressure. Since the relative plateau positions do not change, please assume that a difference of more than 30 degC is needed between the charging and discharging temperatures for the given charging and discharging pressures. What is known about metal hydride tank (4)

16 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.

17 Tchill

18 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.