MECHANISTIC SAFETY ANALYSIS OF HYDROGEN BASED ENERGY SYSTEMS W. Breitung Institute for Nuclear and Energy Technologies Karlsruhe Research Center Germany Second European Summer School on Hydrogen Safety, University of Ulster, Belfast, 30 July- 8 August 2007 KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH 1 und Universität Karlsruhe (TH)
CONTENT OF PRESENTATION • Presentation consists of two topics which are treated in parallel Analysis tools and Analysis of hydrogen release in a private garage related physics Mixture generation Gas transport and mixing Hazard potential Combustion regimes Turbulent deflagration Combustion Detonation Consequences Structural response Sequence of analysis steps KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH 2 und Universität Karlsruhe (TH)
OUR EXAMPLE FOR HYDROGEN ANALYSIS • Oil peak behind us, hydrogen fueled cars in widespread use • Returned from a trip late at night • There was some small collision but apperently no domage to LH 2 -system • Park car in private garage • But at night the questions come …. What could be the consequences? What would happen in case of a hydrogen leak? What would be the pressure Could they be How fast could loads? flammable? the burn be? What mixtures could develop? KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH 3 und Universität Karlsruhe (TH)
GENERIC ARCHITECTURE OF AN LH 2 -TANK SYSTEM CRACK! Source: EU-Project EIHP-2, Final Report 2004 KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH 4 und Universität Karlsruhe (TH)
INVESTIGATED GARAGE SCENARIOS • A thermal energy deposition of 1 Watt into a cryogenic LH 2 -tank leads to a boil-off of 170 g of gaseous hydrogen per day • Assume here 5 release pulses per day, 34 g H 2 each, with two different release rates GEOMETRY GEOMETRY HYDROGEN SOURCE HYDROGEN SOURCE CASE CASE Garage Garage Total Total Release Release Vent Vent H 2 -Rate H 2 -Rate Duration Duration Release Release Volume Volume Mass Mass Temp. Temp. Nr. Nr. Openings Openings (g/s) (g/s) (s) (s) Location Location (m³) (m³) (g) (g) (K) (K) 3.40 3.40 10 10 34 34 22.3 22.3 1 1 under-neath under-neath Two times Two times 70.2 70.2 10 x 20 10 x 20 cm² cm² trunk trunk 0.34 0.34 100 100 34 34 22.3 22.3 2 2 KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH 5 und Universität Karlsruhe (TH)
WHAT ARE THE IMPORTANT RISK DETERMINING PARAMETERS? • Large spectrum of events possible, ranging from zero risk to destruction of garage • What are the parameters influencing the outcome of such a leak scenario? …. …. …. …. …. …. …. …. …. …. …. …. …. …. …. …. • Obvious first step is to understand mixture generation, defines initial and boundary conditions for further accident development KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH 6 und Universität Karlsruhe (TH)
Analysis tools and Analysis of a hydrogen release related physics scenario in a private garage Gas transport and mixing Sequence of analysis steps KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH 8 und Universität Karlsruhe (TH)
AN INITIAL ESTIMATE ON HYDROGEN CONCENTRATION • We can make a first estimate on the hydrogen concentration in the garage by using a single volume approach ⋅ volume H released 34 g H 22.4 l /2 g H 2 2 2 ≈ = ≈ volume fraction H 0.5 % 2 3 volume of garage 70 m • Any risk? • Why is result independent of release rate? • Obviously the real situation is more complex • Next approach is a CFD model KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH 9 und Universität Karlsruhe (TH)
Physical models of 3d code GASFLOW (1) Rekos • Conservation equations of fluid flow (fully compressible, 3-dim. Navier- Stokes) • Thermophysical properties of components (JANAF) (internal energy, specific heats, 25 components including two-phase water) • Molecular transport coefficients (CHEMKIN) (thermal conductivity, dynamic viscosity, binary diffusion coefficients) • Convective and radiative heat transfer between gas and structure • Heat conduction within structures • Condensation and vaporization of water (film, droplets, sump) IRWST T>1000K KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH 10 und Universität Karlsruhe (TH)
Physical models of 3d code GASFLOW (2) Rekos • Lumped- parameter sump model • Boundary layer model for wall shear stress • Turbulence modeling (algebraic, k- ε ) (effects on molecular transport coefficients) • Accident mitigation measures (Recombiner and igniter models, containment inertisation) • Ventilation systems (1-dim. ducts, pipes, junctions, blowers, dampers, valves, filters, etc) IRWST T>1000K KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH 11 und Universität Karlsruhe (TH)
GASFLOW EQUATIONS Fully compressible Navier-Stokes, expressed in integral form for finite volume discretisation Mass conservation Internal energy conservation ∂ ⎛ ⎞ ∂ ( ) p V ∫ ∫ ∫ ∫ ρ = ρ − ⎜ Total mass: HO ⎟ edV e u A dS - p uA S dV d 2 ⎝ ⎠ ∂ ∂ t V t ∂ S S V V ∫ ∫ ∫ ρ ρ + convection pV work pV work due to phase change dV = uA dS S dV ρ ∂ t S V V + ∫ = ∑ ( ) ∫ convection sources (inflow, droplet depletion) e x e α : - qA S dV dS α α Component e α S V ∂ ( ) energy flux energy sources ∫ ∫ ∫ ∫ ρ = ρ + dV uA dS - J A dS S dV (thermal, (combustion, α α α ρ α ∂ t , conductivity, phase change, S S V V ........) heat transfer) convection diffusion chem. reaction two-phase change Vertical He- jet into Vertical He- jet into air (42 m/s) for 200 s air (42 m/s) for 200 s Momentum conservation 20 20 10 Vol % He 10 Vol % He 80 80 FZK/GASFLOW FZK/GASFLOW 15 15 Isosurface Isosurface ∂ 6kp270M18 6kp270M18 ( ) ∫ ∫ ∫ ∫ ∫ ρ = ρ + ρ − τ 9KP000K76 9KP000K76 10 10 2 u dV u A dS - pd S g dV A dS FZK/GASFLOW FZK/GASFLOW 40 40 ∂ t 5 5 V S S V S 0 0 0 0 6 6 0 0 200 200 400 400 600 600 800 800 0 0 2 2 4 4 momentum pressure gravity viscous Time (s) Time (s) Vertical distance from injection location (m) Vertical distance from injection location (m) flux gradient stresses R5 R5 + ∫ ( ) ∫ - D A dS S dV 15 15 EXPERIMENT EXPERIMENT d m x x 80 80 x x FZK/GASFLOW FZK/GASFLOW 6KP270M18 6KP270M18 FZK/GASFLOW FZK/GASFLOW S 10 10 R6 R6 V x x drag from momentum 40 40 x x 5 5 x x internal surfaces sources x x 0 0 Ring Ring & flow restrictions He- Source He- Source x x x x x x 0 0 0 0 200 200 600 600 800 800 -2 -2 0 0 1 1 2 2 400 400 Room R9 Room R9 -1 -1 Time (s) Time (s) Distance from jet axis (m) Distance from jet axis (m) x J.R. Travis et al, Report FZKA-5994 (1998) KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH 12 und Universität Karlsruhe (TH)
GASFLOW VERIFICATION • 3d code GASFLOW used and developed at FZK for hydrogen distribution simulation. Large verification matrix: Report FZKA-7085 (2005), www.fzk.de/hbm KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH 13 und Universität Karlsruhe (TH)
EXAMPLE FOR RECENT GASFLOW VERIFICATION • German national benchmark, test TH7 in Thai facility with condensation • Blind pressure prediction of CFD codes lower inj 1 lower inj 2 upper inj 35 g/s 5 g/s 1.8 35 g/s steam T wall > STAR-CD 330K 1.6 Inj. points CFX [bar] 1.4 GASFLOW Experiment 1.2 Gothic Fluent T wall < lower 1.0 300K source [sec] P. Royl, IKET KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH 14 und Universität Karlsruhe (TH)
Analysis tools and Analysis of a hydrogen release in a private garage related physics Mixture generation Gas transport and mixing Sequence of analysis steps KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH 15 und Universität Karlsruhe (TH)
GASFLOW SIMULATION OF GARAGE SCENARIO • Case 1: release rate 3.4 g H 2 / s for 10 seconds volume fraction H 2 Isosurface with 4 vol% H 2 , depicts flammable mixture in garage KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH 16 und Universität Karlsruhe (TH)
GASFLOW SIMULATION OF GARAGE SCENARIO • Case 2: release rate 0.34 g H 2 / s for 100 seconds volume fraction H 2 Isosurface with 4 vol% H 2 , depicts flammable mixture in garage KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH 17 und Universität Karlsruhe (TH)
RESULTING HYDROGEN CLOUD IN GARAGE 180 d (cm) 160 3.4 g H 2 /s for 10 s cc 140 • Computed dimension of combustible Case 1 120 H 2 -air cloud in garage (4…75% H 2 ) stable 100 80 60 40 • Characteristic size of combustible cloud 20 0 expressed as d CC = (V cc ) 1/3 0 10 20 30 40 50 60 Time (s) 90 • Combustible cloud size strongly dependent d (cm) 80 cc on release rate, is result of balance between 0.34 g H 2 /s for 100s 70 60 source strength and sinks, or release Case 2 50 rate and mixing mechanisms transient 40 30 20 10 0 0 50 100 150 200 250 Time (s) KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH 18 und Universität Karlsruhe (TH)
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