Embed Size (px)
Citation preview
Hydrogen R&D system HAZOP and failure analysis
Yury Ivanyushenkov, Elwyn Baynham, Tom Bradshaw, Mike Courthold, Matthew Hills and Tony Jones
2
Hydrogen Properties
The potential hazards of liquid hydrogen stem mainly from three important properties:
1. Its extremely low temperature
2. Its very large liquid to gas expansion ratio
3. Its wide range of flammable limits after vapourising to gas
3
Hydrogen Hazards
Consequences (hazards) of these properties:
1. => - severe burns can be produced upon contact with the skin; - some materials can become brittle and easily broken
2. => overpressure => - excessive deformation of a vessel; - rupture of the pressure vessel
3. => fire => - injury of personnel - damage to equipment / property
Fire is a primary hydrogen hazard !
4
Hydrogen Hazards (2)
Fire is a primary hydrogen hazard !
A fire can result from two scenarios [1]:
(1) - Hydrogen is released, - mixes with an oxidizer, - forms a combustible mixture, - the mixture contacts an ignition source, - and ignition occurs.
(2) - The hydrogen system is contaminated with an oxidizer (as a result of improper purging and/or in leakage of an oxidizer, such as air),
- the hydrogen and the oxidizer form a combustible mixture; - the combustible mixture contacts an ignition source; - and ignition occurs.
[1] Guide for Hydrogen Hazards Analysis on Components and Systems, NASA TP-WSTF-937
5
MICE Hydrogen R&D System
H
H H
H
H
Node 1
Node 4
Node 3
Node 2
Node 5
6
HAZOP: Nodes
Node 1: Metal hydride storage unit
Node 2: Hydrogen absorber vessel
Node 3: Hydrogen absorber vacuum jacket
Node 4: Buffer tank
Node 5: Hydrogen enclosure
7
HAZOP: Node 1
Node 1: Metal hydride storage unit
No Parameter Guide word
Cause Consequence Safeguards Recommendations
1 Pressure Higher Hydride bed is overheated.
Hydrogen goes back into the absorber rather then to be stored in the hydride bed.
Pressure in the absorber can exceed the max working pressure.
Pressure regulator to reduce the pressure on the line to the absorber.
Pressure relief valve to vent outside.
Active pressure gauge to trigger an alarm.
Consider implementation of an active pressure gauge.
Intent: To keep hydrogen gas in the storage unit - absorber vessel closed system.
8
HAZOP: Node 2
Node 2: Hydrogen absorber vessel
No Parameter Guide word
Cause Consequence Safeguards Recommendations
1 Temperature Lower Too much cooling power.
Pressure in the hydrogen system drops below atmospheric, the system is vulnerable for the ingress of air.
Active pressure gauge to trigger an alarm.
Temperature sensor to trigger an alarm.
Additional: Liquid hydrogen level meter to trigger an alarm.
The temperature and pressure to be continuously monitored.
Additional:Implement an active
liquid level meter.
2 Temperature Higher Not enough cooling power.
Power cut.
Liquid hydrogen evaporates and LH2 level eventually goes down.
Hydrogen pressure rises.
Temperature sensor to trigger an alarm
Additional: Liquid hydrogen level meter to trigger an alarm.
Pressure gauge to trigger an alarm.
As above.
3 Pressure Lower Absorber hydrogen vessel is leaking.
Absorber hydrogen vessel is over cooled.
Hydrogen leaks into vacuum vessel.
Pressure in the system drops and air might leak into the system if seals are faulty.
Active pressure gauge to trigger an alarm.
Temperature sensor to trigger an alarm.
As above.
Intent: To keep hydrogen liquid inside hydrogen absorber module.
9
HAZOP: Node 3
Node 3: Hydrogen absorber vacuum jacket
No Parameter Guide word Cause Consequence Safeguards Recommendations
1 Pressure Higher Hydrogen internal vessel leaks.
Vacuum jacket or seals are leaking
Hydrogen leaks into vacuum jacket
Air leaks into vacuum jacket.
Pressure in the vacuum jacket goes up
andheat load onto
hydrogen vessel increases.
Pressure relief valve to vent hydrogen outside in case of rapid pressure rise.
Pressure gauge to trigger an alarm.
Pressure to be continuously
monitored.
Intent: - To insulate thermally the internal hydrogen vessel.- To provide additional barrier for air.
10
HAZOP: Node 4
Node 4: Buffer tank
No Parameter Guide word Cause Consequence Safeguards Recommendations
1 Pressure Lower Hydrogen internal vessel is over-cooled.
Potential ingress of air into the buffer tank if it leaks.
Temperature control loop in the hydrogen vessel cooling system..
Active pressure gauge triggers an alarm.
Pressure to be continuously monitored.
Intent: To quickly relief pressure in the test absorber module in case of accidental rapid pressure rise.
11
HAZOP: Node 5
Node 5: Hydrogen enclosure
No Parameter Guide word Cause Consequence Safeguards Recommendations
1 Hydrogen concentration
Higher Hydrogen leaks out hydrogen pipes.
Hydrogen leaks out hydride bed.
Venting system stopped working due to power cut.
Explosive
oxygen-hydrogen mixture can be formed
Ventilation system to quickly vent hydrogen out.
Hydrogen detector to trigger an alarm and to start a high rate mode for the ventilation system.
Fans in the venting system are powered by UPS.
Consider installation of additional active hydrogen detector.
Intent: To localize and vent hydrogen off in case of hydrogen leakage.
12
HAZOP: Recommendations
Hydrogen storage unit: Consider implementation of active pressure gauge
Hydrogen absorber internal vessel: Implement monitoring of pressure temperature and liquid hydrogen level Hydrogen absorber vacuum jacket: Implement monitoring of pressure
Buffer tank Implement monitoring of pressure
Hydrogen module enclosure Consider implementation of more than one active hydrogen detectors.
13
No. Failure Mode Effect Criticality Comments
1 Failure of electricity supply
The temperature control of the hydride bed will be lost and the hydride will absorb hydrogen up to its equilibrium point. If there is liquid hydrogen in the system it will be evolved and absorbed by the hydride. The loss of vacuum will accelerate this process.
Need to ensure that the hydride bed can accommodate the evolution rate else hydrogen will be lost through the vent line. Normally loss of vacuum is gradual.
2 Failure of chiller/heater unit to hydride
Temperature control of the hydride will be lost and it will absorb up to its equilibrium pressure. When the pressure in the vessel riches the relief valve setting point, hydrogen venting starts.
Hydride bed vessel design pressure is about 30 bar.
Failure Mode Effect and Criticality Analysis (FMECA)
Preliminary FMECA
14
Preliminary FMECA (2)
No. Failure Mode Effect Criticality Comments
3 Rupture of line between hydride and absorber
Hydrogen will be lost and detected by hydrogen detectors in the vent line.
The hydrogen detectors are the only indication of system gas loss.
4 Fire in vicinity of hydride
This will cause a rise in temperature of the hydride bed leading to evolution of the hydrogen. The pressure will rise leading to venting as soon as the relief valve operates. The hydrogen will be vented at roof level away from the scene of the fire.
Is the hydride flammable ?
