Safety challenges in view of the upcoming hydrogen economy: An overview

Transcription

1 Safety challenges in view of the upcoming hydrogen economy: An overview Hans Pasman and William Rogers Mary Kay O Connor Process Safety Center, Texas A&M University, College Station, TX 7784 Contents : Hydrogen economy and H 2 properties as an energy carrier Knowledge gaps regarding safety Risk assessments Conclusions MKOPSC Symp Oct 27-28, 2009

2 The Hydrogen Economy Car driving and house heating (fuel cells) The quest for more sustainable energy has really started Storage of electrical energy has its limitations; range of cars too restrictive With air oxygen omnipresent: 142 MJ/kg H 2 versus 45 MJ/kg gasoline H 2 by nuclear hydrogen initiative, coal, natural gas, waste, directly solar 1974 IEA; 1977 HIA; 2004 Task 19 Hydrogen Safety 1993 Japan WE NET 2003 President Bush: Hydrogen Initiative 2003 Int l Partnership for the H 2 Economy: IPHE (17 partners) European Commission FP6 established HYdrogen PERmitting (HYPER) and HySafe programs. (Latter revamped into Int l Association HySafe Brussels) Current FP7 Joint Technology Initiative fuel cell and H 2 application: emphasis on PPPs.; hydrogen hi ways refueling stations. 2005, 07 and 09: 3 Int l Conferences on H Safety, ICHS

3 Hydrogen refuelling stations are spreading rapidly (ca. 400) Hydrogen Hi-ways: California; Norway Denmark, Hamburg; Amsterdam-Munich

4 Hydrogen fuel cells for household electricity and heating Electronics Vent Fuel cell Storage tank Risk informed Standards & Codes; ATEX requirements; skilled work force; leak detection

5 Hydrogen properties Storage: compressed up to 1000 bar, liquefied 20 K, as a hydride (research) Liquefied currently most effective : but boil-off (e.g. in trunk BMW cars) Flammable range 4% ( 7.2%; 9.5%) -75% (hydrocarbons roughly 2-10%) Low MIE 0.02 mj; self-ignition after pin hole jet leak possible Low viscosity, high diffusivity, more prone to leakage, permeation In open space easily dispersion; in confined space filling from the top down with explosive mixture Minimum requirements of venting garage boxes Codes, standards, best practices needed for use of H 2 on large scale In the US and elsewhere: NFPA 2 draft available for public review; NFPA 52 and 55 adaptation to H 2 Sandia Labs is doing supporting studies and risk assessments EU HYPER Installation Permitting Guide completed ASME, ISO, EIGA, SAE, EN etc.

6 Knowledge gaps, research needs All IPHE countries made inventory. Hydrogen Research Advisory Council of Fire Protection Research Foundation of NFPA: 2008 document: 27 items identified for NFPA 2, 11 most pressing: 1. Hydrogen explosion modeling refinement blast waves, flame speeds, etc 2. Development and evaluation of wide area hydrogen sensing technology 3. Hydrogen effects on materials, specifically fatigue loading 4. Hydrogen gas cabinets 5. Hydrogen deflagrations in partially enclosed areas 6. Pressure relief device reliability 7. Confined release mitigation strategies 8. Design, installation, testing, and maintenance of hydrogen detection systems 9. Ignition limits/criteria for large leak (dynamic) scenarios 10. Hydrogen safety study on infrastructure 11. Fire barrier effectiveness Int l Energy Agcy, IEA-HIA, Task 19, White Paper on Knowledge Gaps: 1. Gaps in connection with Codes & Standards 2. Gaps in existing risk assessment methods and tools 3. Gaps in fundamental knowledge ( e.g. CFD modeling)

7 Risk assessments: LaChance et al. rpt. SAND Hazards of hydrogen: Materials (metals) may embrittle: a long-term effect, and containment may fail. When compressed in case of leak, jet of gas can self-ignite immediately, or after a short delay, and produce a jet flame, or in case it ignites at a source a certain distance from the leak (delayed ignition) in the open, a flash fire occurs and within a confinement a deflagration or even detonation. Liquefied H 2, the vessel may fail and liquid hydrogen spilled. It will immediately start to evaporate, in principle in a pool, which can be ignited. A cloud will disperse and can produce a vapor Conditions? cloud explosion. Vessel containing liquid Delayed hydrogen may not be able to cope Cloud explosion with the boil-off due Ignition? to heat influx, especially in case of fire, and the hydrogen may BLEVE: Boiling Yes Liquid Expanding Vapor Explosion producing blast, fragments, Flash fire and / jet fire a fireball Finally hydrogen asphyxiates like nitrogen and other gases when a person Leak Jet fire suddenly enters a hydrogen Immediate filled space, while contact with cryogenic hydrogen direct or via metal results in cold burns or frost bite injuries. No Simplified H 2 leak event tree Congestion/confinement Open back to leak Cloud disperses Properties of H 2 cannot be changed: Therefore appropriate measures/distances for inherently safer system

8 Risk assessment cont. (2): Leak frequencies (problem) UK HSE offshore data: Spouge relationship pipes: F(d) = f(d) d m + F rup F(d) = leak frequency of holes exceeding diameter d (minimum 1 mm) f(d) = specific leak frequency with size D d m = pipe diameter influence (exponential law) on this frequency F rup = (small) component rupture frequency Prior distribution + few H 2 data in Bayesian approach to posterior distribution: Cumulative probabilities for different leak sizes based on Bayesian analysis:

9 Risk assessment cont. (3): Hydrogen jets in the open: jet flames, flash fires Schefer et al. concentration measurements jets: H 2 jets penetrate in air further than CH 4 U j = 134 m/s; Re = 2348

10 Risk assessment cont. (4): Models for cloud dispersion and explosion in confined space ICHSs : Standard Benchmark Exercise Problems (6 14 teams; SBEP Vs > 20) checking CFD models: SBEP V1 : subsonic vertical release in vessel SBEP V3 : subsonic vertical release in garage SBEP V4 : horizontal under expanded jet SBEP V5 : subsonic horizontal jet release in a multi compartment room NaturalHy (mixtures of H2 and CH4): Explosion tests by HSL and Shell in UK in congestion rig 3 x 3 x 2 m Blockage 20% 50 mj ignition spark

11 Tests by Shell and HSL in UK with methane and hydrogen 2 nd frame after ignition H 2 CH 4

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13 Risk assessment cont. (5): Liquid H 2 pool and vapor dispersion Experiments NASA 80s, BAM 90s, Juelich LAUV model of Verfondern and Dienhart, 2005 Predictive calculation with LAUV code of A310 Airbus simulated fuel spill in a crash situation on the ground: Pool radius as function of time

14 Risk assessment cont. (6): Preventive and Protective measures; Harm distances, Risk criteria and guidelines Improved engineering, suitable sensors, blocking valves, adequate ventilation, catalytic recombiners Flame barriers against radiation, torch effect Emergency response: scenario analysis, guideline drafting, SOPs Hydrogen Executive s Leadership (HELP) initiative: safest possible transition Harm distances review heat radiation: borderline lethality 4.7 kw/m 2 during 3 min Overpressure: NL Purple Book 0.3 bar 100% lethality indoors UK: 1 bar for 100% lethality, 0.05 bar for 1% lethality. LaChance et al. most acceptance criteria ca /yr as individual risk to be killed; some go as low as 10 6 /yr, e.g. the Netherlands. (For comparison: Gasoline spill fatality risk in the US is /yr, while fires in general is /yr)

15 Risk assessment cont. (7): Hypothetical case safety distances Cryogenic tank rail car, 30,000 gallons, 90% filled = 100 m 3 at 71 kg/m 3 = 7000 kg When stored it means the US RMP rule and EU Seveso threshold quantity for hydrogen has been exceeded, hence safety report

16 Safe distances according to various national systems Country Criterion Prob. of Fatality Overpressure bar TNT eq. or MEM distance Distance m US kg 1 psi TNT eq.10% kg 1 psi TNT eq.10% kg 1 psi MEM UK Dangerous dose MEM IZ MZ OZ France SELS Très grave SEL Grave SEI Irreversible Indirect Indirect Germany Distance If no details available 126 Netherlands Individual 1 outdoors Risk 10-6 /yr new Bevi idem 1 outdoors 0.3 TNT eq.20% regulation 1% lethality 0.01 indoors 0.1 TNT eq. 20%

17 Conclusions H 2 safety Hydrogen is an attractive fuel (energy carrier), producible by renewable sources. Mass and volume storage efficiency + safety can be improved by absorption in a solid matrix (nanotechnology). When mixed with air explosion and fire. Knowledge gaps to perform risk assessments, e.g. ignition probability, component failure rates. To enable a smooth introduction of the technology, risk studies will be essential. Risk informed Codes and Standards has to be further developed. Distribution system has to be built with inherently safer features to cope with hydrogen s properties. Further international coordination/cooperation with respect to risk analysis and acceptance is highly desirable.