MODELING OF SUDDEN HYDROGEN EXPANSION FROM CRYOGENIC PRESSURE VESSEL FAILURE

Guillaume Petitpas and Salvador M. Aceves

Lawrence Livermore National Laboratory7000 East Avenue, L-792Livermore, CA 94550USA

ID#: 253

September 12-14, 2011SAN FRANCISCO, USA

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Cryogenic pressure vessels can store hydrogen at low temperatures with minimum evaporative losses

Low heat transfer obtained with “vessel within a vessel” design

•Conduction: composite supports•Convection: vacuum pressure < 1mTorr•Radiation: MLI

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Thermodynamic advantages of cryogenic pressure vessels drive superior weight, volume and cost

Source: TIAXSource: Argonne National Lab (Ahluwalia et al.),AMR 2011

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Cryogenic pressure vessels’ low operating temperature reduces expansion energy

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High Pressure VesselMOP: 350 bar

Operating T: 20.3 to 300 K

Scenario: sudden hydrogen expansion resulting from accidental pressure vessel failure

Vacuum shell

Rupture DiscsBurst pressure: 1.5 bar (relative)

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High Pressure Vessel

Scenario: sudden hydrogen expansion resulting from accidental pressure vessel failure

Vacuum shell

Rupture Discs

Pressure vessel initially full (H2 density between 28 and 70 g/L)

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High Pressure Vessel

Scenario: sudden hydrogen expansion resulting from accidental pressure vessel failure

Vacuum shell

Rupture Discs

At t=0 s, an accidental failure happens

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High Pressure Vessel

Scenario: sudden hydrogen expansion resulting from accidental pressure vessel failure

Vacuum shell

Rupture Discs

Hydrogen starts flowing into the vacuum shell through a 7.62 mm diameter opening (penetration test FMVSS 304)

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High Pressure Vessel

Scenario: sudden hydrogen expansion resulting from accidental pressure vessel failure

Vacuum shell

Rupture Discs

When the pressure in the vacuum shell reaches 1.5 bar, the rupture discs break and H2 flows in the atmosphere

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Governing equations

• Adiabatic release: no heat transfer between gas and containers

• Orifices at choked condition throughout the process, no slip

• Expansion takes place in small region near the orifice, modeled by a quasi 1D isentropic flow

• Real gas behavior, using REFPROP Version 8.0

• Calculation ends when vacuum shell reaches atmospheric pressure

We have developed a transient H2 release model

11Initial conditions in the vessel : 350 bar, 300 K

Choked flow for a single vessel is determined using initial stagnation state, assuming isentropic flow

ThroatPt, Tt, st=s

VesselP,T,s

At maximum flow rate, M=1 (velocity=

local speed of sound)

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Thermodynamic state at the throat can be “mapped” for different initial vessel conditions

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Step 1: Determine choked conditions at the throat for stagnation state down to 0.7*Tc

14Hydrogen release from 350 bar, 300 K

Step 2: Apply those calculations to the accidental release of H2 in a cryogenic pressure vessel

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Results indicate that a vessel initially at room temperature does not experience phase change

Hydrogen release from 350 bar, 300 K

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H2 initially at cryogenic temperature depressurizes faster, phase change occurs in the pressure vessel

Hydrogen release from 350 bar, 62 K (70 g/L)

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Vent pressure is ~10X lower for cryogenic vessels vs. room temperature compressed gas vessel

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Vent energy is 10X lower for cryogenic vesselsvs. room temperature compressed gas vessel

Energy released in 1 second:

Room Temp150 Wh/kgH2

Cryogenic15 Wh/kgH2

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SummaryWe have modeled 2-phase

choking states down to 0.7*Tc

Choked flow model has been applied to accidental release from “vessel within a vessel” cryogenic storage

Vent energy and pressure from cryogenic pressure vessel failure is 10 times lower than for compressed gas tanks, reducing hazards to surrounding people and property