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Determination of Hazardous Zones Case study: Generic Hydrogen Refuelling Station

Determination of Hazardous Zones Case study: Generic Hydrogen Refuelling Station. Background. Kommentarer: legg inn et bilde her. Aim of zone classification Central requirements outlined in 1999/92/EC Safety and health protection of workers potentially at risk from explosive atmospheres

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Determination of Hazardous Zones Case study: Generic Hydrogen Refuelling Station

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  1. Determination of Hazardous ZonesCase study: Generic Hydrogen Refuelling Station

  2. Background Kommentarer: legg inn et bilde her • Aim of zone classification • Central requirements outlined in • 1999/92/EC Safety and health protection of workers potentially at risk from explosive atmospheres • IEC/EN 60079-10 …Part 10 Classification of hazardous areas • IEC standard opens for ventilation to avoid zone classification when volume of explosive atmosphere is negligible • Conclusions from HySafe work – Italian Guidelines recommended

  3. Definitions

  4. Italian Guide 31 – 35 and Guide 31-35/A • Stepwise process, giving guidelines on • Leak size dependent on component • Flow rates for continuous releases as a function of component • Reference formulas for calculation of flow/leak rates • Evaluation of the extent of the hazardous zone as a function of release flow rate, ventilation and flammable substance • Gas dispersion calculations to determine the extent of the hazardous zones

  5. Italian Guidelines - Risk Based Approach

  6. Assumptions Delivery 60 Nm3/h Pressure:15/460 bar 3 pressure banks - 8 storage vessels Max storage volume 200 kg Gas in process eqipment in building: 300 g Valve/piping dimensions: 5 – 15 mm Generic Hydrogen Refuelling Station Simplified process drawing Horisontal view

  7. Scenarios considered for zone classification • Valve leak inside dispenser enclosure • Opening of safety valve - vent line for the safety valves • Outdoor valves at storage vessels • Refuelling nozzle • Valve at buffer tank • Shutoff valve outside gas processing building • Releases inside the gas processing building

  8. Relevant leak frequency and leak size • Relevant leak frequencies for this type of technology/installation not available • Considered 3 different leaks sizes (release diameter) for valves • 0,56 mm (from Italian met.) -> release rate 5.7 g/s • 0,2 mm -> release rate 0.7 g/s • 0,1 mm -> release rate 0.2 g/s

  9. Gas processing building Ventilation capacity: • Natural: 0.5 m/s • Mechanical: 10, 150, 300, 800 ACH Ventilation Design 1 Ventilation Design 2: Fan location in the middle of the roof, 2 louvers at lower part of long walls 6 x 0.5 m Inside gas processing building

  10. Results – Gas Processing Building • Results for ventilation Design 2 • Based on LFL assumed as basis for the determination of the zones

  11. Gas processing building Importance of risk reducing measures • ESD activated by gas detection • Reliable non-return valves downstream compressor - outdoors …if not leak from the non-return valve itself will be the representative leak scenario - backflow from 460 bar

  12. Outdoor valve at storage vessels • Significant difference in zones dependent on LFL or ½ LFL • Experimental data indicate that ignition might be difficult between 4 and 8 vol%

  13. Summary • Italian method recommended • Systematic analytical method, verification of zones based on a risk based approach • Hazardous zones at generic hydrogen station based on 0.56 mm leak diameter: • Zone 2 inside gas processing building • More than 300 ACH and prevention of back flow -> no hazardous area • Zone 2 radius 5 or 3.5 m around outdoor HP valves

  14. Needs for improvement • Obtaining relevant leak frequency and leak sizes coupled to new technology and new user groups • Experimental studies on ignition probability in realistic release conditions • Verification of CFD tools tools for prediction of gas dispersion in confined and obstructed areas

  15. hydro.com

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