Publications

Abatement of greenhouse gas emissions and diversification of energy sources will probably lead to an economy based on hydrogen. In order to evaluate safety conditions during transport and distribution experimental data is needed on the detonation of Hydrogen/Natural gas blend mixtures. The aim of this study is to constitute detonation and deflagration to detonation transition (DDT) database of H2/CH4-air mixtures. More precisely the detonability of such mixtures is evaluated by the detonation cell size and the DDT run up distance measurements. Large experimental conditions are investigated (i) various equivalence ratios from 0.6 to 3 (ii) various H2 molar fraction x ( ( )2 2 4x H H CH= + ) from 0.5 to 1 (iii) different initial pressure P0 from 0.2 to 2 bar at fixed ambient temperature T0=293 K. Detonation pressures P velocities D and cell sizes ? were measured in two smooth tubes with different i.d. d (52 and 106 mm). For DDT data minimum DDT run up distances LDDT were determined in the d=52 mm tube containing a 2.8 m long Schelkin spiral with a blockage ratio BR = 0.5 and a pitch equal to the diameter. Measured detonation velocities D are very close to the Chapman Jouguet values (DCJ). Concerning the effect of detonation cell size ? follows a classical U shaped- curve with a minimum close to =1 and concerning the effect of x ? decreases when x increases. The ratio ik L?= obtained from different chemical kinetics (Li being the ZND induction length) is well approximated by the value 40 in the range 0.5 < x < 0.9 and 50 for x 0.9. Minimum DDT run up distance LDDT varies from 0.36 to 1.1m when x varies from 1 to 0.8. The results show that LDDT obeys the linear law LDDT ~ 30-40? previously validated in H2/Air mixtures. Adding Hydrogen in Natural Gas promotes the detonability of the mixtures and for x 0.65 these mixtures are considered more sensitive than common heavy Alkane-Air mixtures.

This paper discusses the preliminary results of the Risk Management subtask efforts within the International Energy Agency (IEA) Hydrogen Implementing Agreement (HIA) Task 19 on Hydrogen Safety to develop uniform harm criteria for use in the Quantitative Risk Assessments (QRAs) of hydrogen facilities. The IEA HIA Task 19 efforts are focused on developing guidelines and criteria for performing QRAs of hydrogen facilities. The performance of QRAs requires that the level of harm that is represented in the risk evaluation be established using deterministic models. The level of harm is a function of the type and level of hazard. The principle hazard associated with hydrogen facilities is uncontrolled accumulation of hydrogen in (semi) confined spaces and consecutive ignition. Another significant hazard is combustion of accidentally released hydrogen gas or liquid which may or may not happen instantaneously. The primary consequences from fire hazards consist of personnel injuries or fatalities or facility and equipment damage due to high air temperatures radiant heat fluxes or direct contact with hydrogen flames. The possible consequences of explosions on humans and structures or equipment include blast wave overpressure effects impact from fragments generated by the explosion the collapse of buildings and the heat effects from subsequent fire balls. A harm criterion is used to translate the consequences of an accident evaluated from deterministic models to a probability of harm to people structures or components. Different methods can be used to establish harm criteria including the use of threshold consequence levels and continuous functions that relate the level of a hazard to a probability of damage. This paper presents a survey of harm criteria that can be utilized in QRAs and makes recommendations on the criteria that should be utilized for hydrogen-related hazards.

A series of experiments are described in which helium was released at a constant rate into a 1.5 m × 1.5 m × 0.75 m enclosure designed as a ¼-scale model of a two car garage. The purpose was to provide reference data sets for testing and validating computational fluid dynamics (CFD) models and to experimentally characterize the effects of a number of variables on the mixing behaviour within an enclosure and the exchange of helium with the surroundings. Helium was used as a surrogate for hydrogen and the total volume released was scaled as the amount that would be released by a typical hydrogen fuelled automobile with a full tank. Temporal profiles of helium were measured at seven vertical locations within the enclosure during and following one hour and four hour releases. Idealized vents in one wall sized to provide air exchange rates typical of actual garages were used. The effects of vent size number and location were investigated using three different vent combinations. The dependence on leak location was considered by releasing helium from three different points within the enclosure. It is shown that the National Institute of Standards and Technology (NIST) CFD code Fire Dynamics Simulator (FDS) provides time resolved predictions for helium concentrations that agree well with the experimental measurements.

Computational fluid dynamics is used to simulate the release of high pressure Hydrogen from a reservoir with an exit of increasing diameter. Abel-Noble real gas equation of state is used to accurately simulate this high pressure release. Parallel processing based on Message Passing Interface for domain decomposition is employed to decrease the solution time. The release exit boundary is increased in time to simulate a scenario when the exit area increases during the release. All nodes and elements are moved accordingly at each time step to maintain the quality of the mesh. Different speeds of increasing diameter are investigated to see the impact on this unsteady flow.

High resolution numerical simulations used to study the mechanism of deflagration-to-detonation transition (DDT). The computations solved two-dimensional time-dependent reactive Navier-Stokes equations including the effects of compressibility molecular diffusion thermal conduction viscosity and detailed chemical kinetics for the reactive species with subsequent chain branching production of radicals and energy release. It is shown that from the beginning the flame accelerates exponentially producing shock waves far ahead. On the next stage the flame acceleration decreases and the shocks are formed close ahead of the flame front. The final stage is the actual transition to detonation. During the second stage a compressed unreacted mixture of increased density enters the flame producing a high pressure pulse which enhances reaction rate and the heat release in the reaction zone with a positive feedback coupling between the pressure pulse and the reaction rate. As a result the peak of the pressure pulse grows exponentially steepens into a strong shock which is coupled with the reaction zone forming the overdriven detonation. This new mechanism of DDT is different from the Zel’dovich’s gradient mechanism. The temperature gradients which appear in the form of hot spots and the like are not suitable to initiate detonation.

Hydrogen can be produced in undesired ways such as a high temperature metal oxidation during an accident. In this case the hydrogen must be carefully managed. A hydrogen mitigation system (HMS) should be installed to protect a containment of a nuclear power plant (NPP) from hazards of hydrogen produced by an oxidation of the fuel cladding during a severe accident in an NPP. Among hydrogen removal devices passive auto-catalytic recombiners (PARs) are currently applied to many NPPs because of passive characteristics such as not requiring a power supply nor an operators’ manipulations. However they offer several disadvantages resulting in issues related to hydrogen control by PARs. One of the issues is a hydrogen stratification in which hydrogen is not well-mixed in a compartment due to the high temperature exhaust gas of PARs and accumulation in the lower part. Therefore experimental simulation on hydrogen stratification phenomenon by PARs is required. When the hydrogen stratification by PARs is observed in the experiment the verification and improvement of a PAR analysis model using the experimental results can be performed and the hydrogen removal characteristics by PARs installed in an NPP can be evaluated using the improved PAR model. View Full-Text

A crucial problem of new hydrogen technologies is the lightweight and also safe storage of acceptable amounts of hydrogen for portable or mobile applications. A new and innovative technology based on capillary arrays has been developed. These systems ensure safe infusion storage and controlled release of hydrogen gas although storage pressures up to 1200 bar are applied. This technology enables the storage of a significantly greater amount of hydrogen than other approaches. In storage tests with first capillary arrays a gravimetric storage capacity of about 33% and a volumetric capacity of 28% was determined at a comparative low pressure of only 400 bar. This is much more than the actual published storage capacities which are to find for other storage systems. This result already surpassed the US Department of Energy's 2010 target and it is expected to meet the DOE's 2015 target in the near future.<br/>Different safety aspects have been evaluated. On the one hand experiments with single capillaries or arrays of them have been carried out. The capillaries are made of quartz and other glasses. Especially quartz has a three times higher strength than steel. At the same time the density is about three times lower which means that much less material is necessary to reach the same pressure resistance. The pressure resistance of single capillaries has been determined in dependence of capillary materials and dimensions wall thickness etc. in order to find out optimal parameters for the “final” capillaries. In these tests also the sudden release of hydrogen was tested in order to observe possible spontaneous ignitions. On the other hand a theoretical evaluation of explosion hazards was done. Different situations were analyzed e.g. release of hydrogen by diffusion or sudden rupture.

The International Energy Agency’s Hydrogen Implementing Agreement (www.ieahia.org) initiated a collaborative task on hydrogen safety in 1994 and this has proved to an effective method of pooling expert knowledge to address the most significant problems associated with the barriers to the commercial adoption of hydrogen energy. Presently there are approximately 10 countries participating in the task and it has proven a valuable method of efficiently combining efforts and resources. The task is now in the fifth year of a six year term and will end in October 2010. This paper will describe the scope of the task the progress made and plans for future work. There are also a number of other tasks underway and this paper will give a brief summary of those activities. Because of the nature of the International Energy Agency which is an international agreement between governments it is intended that such collaboration will complement other efforts to help build the technology base around which codes and standards can be developed. This paper describes the specific scope and work plan for the collaboration that has been developed to date.

Decarbonization of the heating sector is essential to meet the ambitious goals of the Paris Climate Agreement for 2050. However poorly insulated buildings and industrial processes with high and intermittent heating demand will still require traditional boilers that burn fuel to avoid excessive burden on electrical networks. Therefore it is important to assess the impact of residential commercial and industrial heat decarbonization strategies on the distribution and transmission gas networks. Using building energy models in EnergyPlus the progressive decarbonization of gas-fueled heating was investigated by increasing insulation in buildings and increasing the efficiency of gas boilers. Industrial heat decarbonization was evaluated through a progressive move to lowercarbon fuel sources using MATLAB. The results indicated a maximum decrease of 19.9% in natural gas utilization due to the buildings’ thermal retrofits. This coupled with a move toward the electrification of heat will reduce volumes of gas being transported through the distribution gas network. However the decarbonization of the industrial heat demand with hydrogen could result in up to a 380% increase in volumetric flow rate through the transmission network. A comparison between the decarbonization of domestic heating through gas and electrical heating is also carried out. The results indicated that gas networks can continue to play an essential role in the decarbonized energy systems of the future.

The use of hydrogen as an energy carrier is going to widen exponentially in the next years. In order to ensure the public acceptance of the new fuel not only the environmental impact has to be excellent but also the risk management of its handling and storage must be improved. As a part of modern risk assessment procedure CFD modeling of the accident scenario development must provide reliable data on the possible pressure loads resulted from explosion processes. The expected combustion regimes can be ranged from slow flames to deflagration-to-detonation transition and even to detonation. In the last case the importance of the reliability of simulation results is particularly high since detonation is usually considered as a worst case state of affairs. A set of large-scale detonation experiments performed in Kurchatov Institute at RUT facility was selected as benchmark. RUT has typical industry-relevant characteristic dimensions. The CFD codes possibilities to correctly describe detonation in mixtures with different initial and boundary conditions were surveyed. For the modeling two detonation tests HYD05 and HYD09 were chosen; both tests were carried out in uniform hydrogen/air mixtures; first one with concentration of 20.0% vol. and the second one with 25.5% vol. In the present exercise three CFD codes using a number of different models were used to simulate these experiments. A thorough inter-comparison between the CFD results including codes models and obtained pressure predictions was carried out and reported. The results of this inter comparison should provide a solid basis for the further code development and detonation models’ validation thus improving CFD predictive capabilities.