Publications

We numerically investigated high-pressure hydrogen leakage from facilities in storage and transportation phases. In storage phase assuming a tank placed in a hydrogen station we examined unsteady diffusion distance up to 100 ms after leakage. A series of simulations led us to develop an equation of unsteady hydrogen diffusion distance as a function of mass flow rate leakage opening diameter and tank pressure. These results helped us develop a safety standard for unsteady hydrogen diffusion. In transportation phase we simulated (in three dimensions) the dominant factor of steady mass flow rate from a square opening of a rectangular pipeline and the pressure distribution in the pipeline after leakage. The mass flow rate was smaller than the maximum mass flow rate and the pressure distribution converged to a steady state that was 16% higher than the pressure after the passage of expansion waves in a shock tube model. We introduced a theoretical model by dividing the flow with the leakage opening into two phases of the unsteady expansion waves’ propagation and acceleration. The simulation results showed good agreement with the modeling equation when the shrink coefficient was set to 0.8. When the leakage opening was rectangular the simulation results again showed good agreement with the modelling equation suggesting that our simulated results are independent of the leakage opening shape.

Proper management of hydrogen gas is very important for safety security of nuclear power plants. Hydrogen removal by water formation reaction on a catalyst is one of the candidates for creating hydrogen free system. We observed in situ and time-resolved structure change of palladium metal nanoparticle catalyst during the water formation reaction by using X-ray absorption spectroscopy technique. A poisoning effect by carbon monoxide on catalytic activity was also studied. We have found that the creation of oxidized surface layer on palladium metal nanoparticles plays an important role for the water formation reaction process.

This paper describes a series of numerical simulations with release and ignition of hydrogen. The objective of this work was to re-investigate the accidental explosion in an ammonia plant which happened in Norway in 1985 with modern CFD tools. The severe hydrogen-air explosion led to two fatalities and complete destruction of the factory building where the explosion occurred. A case history of the accident was presented at the 1.st ICHS in Pisa 2005.<br/>The numerical simulations have been performed with FLACS a commercial CFD simulation tool for gas dispersion and gas explosions. The code has in the recent years been validated in the area of hydrogen dispersion and explosions.<br/>The factory building was 100 m long 10 m wide and 7 m high. A blown-out gasket in a water pump led to release of hydrogen from a large reservoir storing gaseous hydrogen at 3.0 MPa. The accident report estimated a total mass of released hydrogen between 10 and 20 kg. The location of the faulty gasket is known but the direction of the accidental release is not well known and has been one of the topics of our investigations. Several simulations have been performed to investigate the mixing process of hydrogen-air clouds and the development of a flammable gas cloud inside the factory building resulting in a simulation matrix with dispersions in all axis directions. Simulations of ignition of the different gas clouds were carried out and resulting pressure examined. These results have been compared with the damages observed during the accident investigation.<br/>We have also performed FLACS simulations to study the effect of natural venting and level of congestion. The height of the longitudinal walls has been varied leading to different vent openings at floor level at the ceiling and a combination of the two. This was done to investigate the effects of congestion with regards to gas cloud formation.<br/>The base case simulation appears to be in good accordance to the observed damages from the accident. The simulations also show that the build up of the gas cloud strongly depends on the direction of the jet and degree of ventilation. The CFD study has given new insights to the accident and the results are a clear reminder of the importance of natural venting in hydrogen safety.

Computational fluid dynamics (CFD) is used to numerically solve the sudden release of hydrogen from a high pressure tank (up to 70MPa) into air. High pressure tanks increase the risk of failure of the joints and pipes connected to the tank which results in release of Hydrogen. The supersonic flow caused by high pressure ratio of reservoir to ambient generates a strong Mach disk. A three dimensional in-house code is developed to simulate the flow. High pressure Hydrogen requires a real gas law because it deviates from ideal gas law. Firstly Beattie-Bridgeman and Abel-Noble real gas equation of states are applied to simulate the release of hydrogen in hydrogen. Then Abel-Noble is implied to simulate the release of hydrogen in air. Beattie-Bridgeman has stability problems in the case of hydrogen in air. A transport equation is used to solve the concentration of Hydrogen-air mixture. The code is second order accurate in space and first order in time and uses a modified Van Leer limiter. The fast release of Hydrogen from a small rupture needs a very small mesh therefore parallel computation is applied to overcome memory problems and to decrease the solution time. The high pressure ratio of the reservoir to ambient causes a very fast release which is accurately modelled by the code and all the shocks and Mach disk happening are observed in the results. The results show that the difference between real gas and ideal gas models cannot be ignored.

Around 20% of the nation’s carbon emissions are generated by domestic heating. Analysis of the many ways the energy system might be adapted to meet carbon targets shows that the elimination of emissions from buildings is more cost effective than deeper cuts in other energy sectors such as transport. This effectively means that alternatives need to be found for domestic natural gas heating systems. Enhanced construction standards are ensuring that new buildings are increasingly energy efficient but the legacy building stock of around 26 million homes has relatively poor thermal performance and over 90% are expected to still be in use in 2050. Even if building replacement was seen as desirable the cost is unaffordable and the carbon emissions associated with the construction would be considerable.

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As the offshore energy landscape transitions to renewable energy useful decommissioned or abandoned oil and gas infrastructure can be repurposed in the context of the circular economy. Oil and gas platforms for example offer opportunity for hydrogen (H2) production by desalination and electrolysis of sea water using offshore wind power. However as H2 storage and transport may prove challenging this study proposes to react this H2 with the carbon dioxide (CO2) stored in depleted reservoirs. Thus producing a more transportable energy carriers like methane or methanol in the reservoir. This paper presents a novel thermodynamic analysis of the Goldeneye reservoir in the North Sea in Aspen Plus. For Goldeneye which can store 30 Mt of CO2 at full capacity if connected to a 4.45 GW wind farm it has the potential to produce 2.10 Mt of methane annually and abate 4.51 Mt of CO2 from wind energy in the grid.

For safety issues related to the storage of hydrogen under high pressure it is necessary to determine how the gas is released in the case of failure. In particular there exist limited quantitative information on the near-field properties of the gas jets which are important for establishing proper decay laws in the far-field. This paper reports recent CFD results for air and helium obtained in the near-field of the highly under-expanded jets. The gas jets are released from a 30-bar tank with the same opening (orifice). The Reynolds number based on the diameter of the orifice and corresponding gas conditions at the exit was well beyond 106 . The 3D Compressible Multi-Component Navier-Stokes equations were solved directly without relying on the compressibility-corrected turbulence models. The numerical model was initially tested on a one-component (air-air) case where a few aerospace-driven data sets are available for validation. The shock geometry is characterized through the Mach disk position and diameter. These are compared to the results known from the literature and to the scaling laws developed based on the dimensional analysis. In the second two-component (helium-air) jet scenario the density field was validated and examined together with other fields in the attempt to suggest potential initial conditions for the forthcoming far-field simulations.

An efficient production of hydrogen from a mixture of methanol and water is possible in a spark discharge. In this discharge there is a synergistic effect of high-energy electrons and high temperature interactions which enables an efficient course of endothermic processes such as the production of hydrogen from methanol. The water to methanol molar ratio of 1:1 was kept constant during the study. While the discharge power and feed flow rate were varied from 15 to 55 W and from 0.25 to 2 mol/h respectively which corresponded to the residence time of the reactants in the plasma zone from 58 to 7 ms. The cooled gas mixture contained 56 to 60% of H2. Other gaseous products of the process were CO CO2 and a small amount of CH4. The maximum energy yield was 16.2 mol(H2)/kWh which represents 20% of the theoretical energy yield when the substrates are in a liquid phase.

To advance hydrogen into the energy market it is necessary to consider risk assessment for scenarios that are complicated by accidental hydrogen release mixing with other combustible hydrocarbon fuels. The paper is aimed at examining the effect of mixing the hydrocarbon and inert gas into the hydrogen flame on the kinetic mechanisms the laminar burning velocity and the flame stability. The influences of hydrogen concentration on the flame burning velocity were determined for the hydrogen/propane (H2-C3H8) hydrogen/ethane (H2-C2H6) hydrogen/methane (H2-CH4) and hydrogen/carbon dioxide (H2-CO2) mixtures. Experimental tests were carried out to determine the lift-off blow-out and blowoff stability limits of H2 H2-C3H8 H2-C2H6 H2-CH4 and H2-CO2 jet flames in a 2 mm diameter burner. The kinetic mechanisms of hydrogen interacting with C3 C2 and C1 fuels is analysed using the kinetic mechanisms for hydrocarbon combustion.