Publications

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Overall objectives of the project are: Develop a science & engineering basis for the release, ignition, and combustion behavior of hydrogen across its range of use (including high pressure and cryogenic); and, Facilitate the assessment of the safety (risk) of hydrogen systems and enable use of that information for revising regulations, codes, and standards (RCS), and permitting hydrogen fueling stations.

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DOE has identified consistent safety, codes, and standards as a critical need for the deployment of hydrogen technologies, with key barriers related to the availability and implementation of technical information in the development of regulations, codes, and standards. Advances in codes and standards have been enabled by risk-informed approaches to create and implement revisions to codes, such as National Fire Protection Association (NFPA) 2, NFPA 55, and International Organization for Standardization (ISO) Technical Specification (TS)-19880-1. This project provides the technical basis for these revisions, enabling the assessment of the safety of hydrogen fuel cell systems and infrastructure using QRA and physics-based models of hydrogen behavior. The risk and behavior tools that are developed in this project are motivated by, shared directly with, and used by the committees revising relevant codes and standards, thus forming the scientific basis to ensure that code requirements are consistent, logical, and defensible.

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The Overall Objectives of this study are: 1).Create compact gaseous and delivered liquid hydrogen reference station designs appropriate for urban locations, enabled by hazard/harm mitigations, near-term technology improvements, and layouts informed by risk (performance-based design). 2) Disseminate results and obtain feedback through reports and a workshop with stakeholders representing code/standard development organization, station developers, code officials, and equipment suppliers. 3) Identify and provide designs for compact station concepts which enable siting on 3-times the number of stations in the dense urban example of San Francisco.

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Apparent char kinetic rates are commonly used to predict pulverized coal char burning rates. These kinetic rates quantify the char burning rate based on the temperature of the particle and the oxygen concentration at the particle surface, thereby inherently neglecting the impact of variations in the penetration of oxygen into the char on the predicted burning rate. To investigate the impact of variable extents of penetration during Zone II burning conditions, experimental measurements were performed of char particle combustion temperature and burnout for a common U.S. subbituminous coal burning in an optical laminar entrained flow reactor with either helium or nitrogen diluents. The combination of much higher thermal conductivity and mass diffusivity in the helium environments resulted in substantially cooler char combustion temperatures than in equivalent N2 environments. Measured char burnout was similar in the two environments for a given bulk oxygen concentration but was approximately 60% higher in helium environments for a given char combustion temperature. Detailed particle simulations of the experimental conditions confirmed a 60% higher burning rate in the helium environments as a function of char temperature, whereas catalyst theory predicts that the burning rate in helium could be as high as 90% greater than in nitrogen, in the limit of large Thiele modulus (i.e. near the diffusion limit). For application combustion in CO2 environments (e.g. for oxy-fuel combustion), these results demonstrate that due to differences in oxygen diffusivity the apparent char oxidation rates will be lower, but by no more than 9% relative to burning rates measured in nitrogen environments.

Apparent char kinetic rates are commonly used to predict pulverized coal char burning rates. These kinetic rates quantify the char burning rate based on the temperature of the particle and the oxygen concentration at the particle surface, thereby inherently neglecting the impact of variations in the penetration of oxygen into the char on the predicted burning rate. To investigate the impact of variable extents of penetration during Zone II burning conditions, experimental measurements were performed of char particle combustion temperature and burnout for a common U.S. subbituminous coal burning in an optical laminar entrained flow reactor with either helium or nitrogen diluents. The combination of much higher thermal conductivity and mass diffusivity in the helium environments resulted in substantially cooler char combustion temperatures than in equivalent N2 environments. Measured char burnout was similar in the two environments for a given bulk oxygen concentration but was approximately 60% higher in helium environments for a given char combustion temperature. Detailed particle simulations of the experimental conditions confirmed a 60% higher burning rate in the helium environments as a function of char temperature, whereas catalyst theory predicts that the burning rate in helium could be as high as 90% greater than in nitrogen, in the limit of large Thiele modulus (i.e. near the diffusion limit). For application combustion in CO2 environments (e.g. for oxy-fuel combustion), these results demonstrate that due to differences in oxygen diffusivity the apparent char oxidation rates will be lower, but by no more than 9% relative to burning rates measured in nitrogen environments.

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To meet the needs of public and private stakeholders involved in the development, construction, and operation of hydrogen fueling stations needed to support the widespread roll-out of hydrogen fuel cell electric vehicles, this work presents publicly available station templates and analyses. These ‘Reference Stations’ help reduce the cost and speed the deployment of hydrogen stations by providing a common baseline with which to start a design, enable quick assessment of potential sites for a hydrogen station, identify contributors to poor economics, and suggest areas of research. This work presents layouts, bills of materials, piping and instrumentation diagrams, and detailed analyses of five new station designs. In the near term, delivered hydrogen results in a lower cost of hydrogen compared to on-site production via steam methane reforming or electrolysis, although the on-site production methods have other advantages. Modular station concepts including on-site production can reduce lot sizes from conventional assemble-on-site stations.

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To meet the needs of public and private stakeholders involved in the development, construction, and operation of hydrogen fueling stations needed to support the widespread roll-out of hydrogen fuel cell electric vehicles, this work presents publicly available station templates and analyses. These 'Reference Stations' help reduce the cost and speed the deployment of hydrogen stations by providing a common baseline with which to start a design, enable quick assessment of potential sites for a hydrogen station, identify contributors to poor economics, and suggest areas of research. This work presents layouts, bills of materials, piping and instrumentation diagrams, and detailed analyses of five new station designs. In the near term, delivered hydrogen results in a lower cost of hydrogen compared to on-site production via steam methane reforming or electrolysis, although the on-site production methods have other advantages. Modular station concepts including on-site production can reduce lot sizes from conventional assemble-on-site stations.

The HyRAM software toolkit provides a basis for conducting quantitative risk assessment and consequence modeling for hydrogen infrastructure and transportation systems. HyRAM is designed to facilitate the use of state-of-the-art science and engineering models to conduct robust, repeatable assessments of hydrogen safety, hazards, and risk. HyRAM is envisioned as a unifying platform combining validated, analytical models of hydrogen behavior, a stan- dardized, transparent QRA approach, and engineering models and generic data for hydrogen installations. HyRAM is being developed at Sandia National Laboratories for the U. S. De- partment of Energy to increase access to technical data about hydrogen safety and to enable the use of that data to support development and revision of national and international codes and standards. This document provides a description of the methodology and models contained in the HyRAM version 1.1. HyRAM 1.1 includes generic probabilities for hydrogen equipment fail- ures, probabilistic models for the impact of heat flux on humans and structures, and computa- tionally and experimentally validated analytical and first order models of hydrogen release and flame physics. HyRAM 1.1 integrates deterministic and probabilistic models for quantifying accident scenarios, predicting physical effects, and characterizing hydrogen hazards (thermal effects from jet fires, overpressure effects from deflagrations), and assessing impact on people and structures. HyRAM is a prototype software in active development and thus the models and data may change. This report will be updated at appropriate developmental intervals.

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In this work, under-expanded cryogenic hydrogen jets were investigated experimentally for their ignition and flame characteristics. The test facility described herein, was designed and constructed to release hydrogen at a constant temperature and pressure, to study the dispersion and thermo-physical properties of cryogenic hydrogen releases and flames. In this study, a non-intrusive laser spark focused on the jet axis was used to measure the maximum ignition distance. The radiative power emitted by the corresponding jet flames was also measured for a range of release scenarios from 37 K to 295 K, 2–6 barabsthrough nozzles with diameters from 0.75 to 1.25 mm. The maximum ignition distance scales linearly with the effective jet diameter (which scales as the square root of the stagnant fluid density). A 1-dimensional (stream-wise) cryogenic hydrogen release model developed previously at Sandia National Laboratories (although this model is not yet validated for cryogenic hydrogen) was exercised to predict that the mean mole fraction at the maximum ignition distance is approximately 0.14, and is not dependent on the release conditions. The flame length and width were extracted from visible and infra-red flame images for several test cases. The flame length and width both scale as the square root of jet exit Reynolds number, as reported in the literature for flames from atmospheric temperature hydrogen. As shown in previous studies for ignited atmospheric temperature hydrogen, the radiative power from the jet flames of cold hydrogen scales as a logarithmic function of the global flame residence time. The radiative heat flux from jet flames of cold hydrogen is higher than the jet flames of atmospheric temperature hydrogen, for a given mass flow rate, due to the lower choked flow velocity of low-temperature hydrogen. This study provides critical information with regard to the development of models to inform the safety codes and standards of hydrogen infrastructure.

The Reacting Particle and Boundary Layer (RPBL) model computes the transient-state conditions for a spherical, reacting, porous char particle and its reacting boundary layer. RPBL computes the transport of gaseous species with a Maxwell-Stefan multicomponent approach. Mass transfer diffusion coefficients are corrected to account for a non-stagnant bulk flow condition using a factor based on the Sherwood number. The homogeneous gas phase reactions are modeled with a syngas mechanism, and the heterogeneous reactions are calculated with a six-step reaction mechanism. Both homogeneous and heterogeneous reaction mechanisms are implemented in Cantera. Carbon density (burnout) is computed using the Bhatia and Perlmutter model to estimate the evolution of the specific surface area. Energy equations are solved for the gas temperature and the particle temperature. The physical properties of the particle are computed from the fractions of ash, carbon, and voids in the particle. The void fraction is computed assuming a constant diameter particle during the reaction process. RPBL solves a particle momentum equation in order to estimate the position of the particle in a specific reactor. We performed a validation and uncertainty quantification study with RPBL using experimental char oxidation data obtained in an optically accessible, laminar, entrained flow reactor at Sandia National Laboratories. We used a consistency analysis to compare RPBL and experimental data (with its associated uncertainty) for three coal chars over a range of particle sizes. We found consistency for particle temperature and velocity across all experiments.

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The HySafe research priorities workshop is held on the even years between the International Conference on Hydrogen Safety (ICHS) which is held on the odd years. The research priorities workshop is intended to identify the state-of-the-art in understanding of the physical behavior of hydrogen and hydrogen systems with a focus on safety. Typical issues addressed include behavior of unintended hydrogen releases, transient combustion phenomena, effectiveness of mitigation measures, and hydrogen effects in materials. In the workshop critical knowledge gaps are identified. Areas of research and coordinated actions for the near and medium term are derived and prioritized from these knowledge gaps. The stimulated research helps pave the way for the rapid and safe deployment of hydrogen technologies on a global scale. To support the idea of delivering globally accepted research priorities for hydrogen safety the workshop is organized as an internationally open meeting. In attendance are stakeholders from the academic community (universities, national laboratories), funding agencies, and industry. The industry participation is critically important to ensure that the research priorities align with the current needs of the industry responsible for the deployment of hydrogen technologies. This report presents the results of the HySafe Research Priorities Workshop held in Washing ton, D.C. on November 10-11, 2014. At the workshop the participants presented updates (since the previous workshop organized two years before in Berlin, Germany) of their research and development work on hydrogen safety. Following the workshop, participants were asked to provide feedback on high-priority topics for each of the research areas discussed and to rank research area categories and individual research topics within these categories.

Much effort has been made to model hydrogen releases from leaks during potential failures of hydrogen storage systems. A reduced-order jet model can be used to quickly characterize these flows, with low computational cost. Notional nozzle models are often used to avoid modeling the complex shock structures produced by the underexpanded jets by determining an "effective" source to produce the observed downstream trends. In this work, the mean hydrogen concentration fields were measured in a series of subsonic and underexpanded jets using a planar laser Rayleigh scattering system. The experimental data was compared to a reduced order jet model for subsonic flows and a notional nozzle model coupled to the jet model for underexpanded jets. The values of some key model parameters were determined by comparisons with the experimental data. The coupled model was also validated against hydrogen concentrations measurements for 100 and 200 bar hydrogen jets with the predictions agreeing well with data in the literature.

Much effort has been made to model hydrogen releases from leaks during potential failures of hydrogen storage systems. A reduced-order jet model can be used to quickly characterize these flows, with low computational cost. Notional nozzle models are often used to avoid modeling the complex shock structures produced by the underexpanded jets by determining an "effective" source to produce the observed downstream trends. In this work, the mean hydrogen concentration fields were measured in a series of subsonic and underexpanded jets using a planar laser Rayleigh scattering system. The experimental data was compared to a reduced order jet model for subsonic flows and a notional nozzle model coupled to the jet model for underexpanded jets. The values of some key model parameters were determined by comparisons with the experimental data. The coupled model was also validated against hydrogen concentrations measurements for 100 and 200 bar hydrogen jets with the predictions agreeing well with data in the literature.

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The HyRAM software toolkit provides a basis for conducting quantitative risk assessment and consequence modeling for hydrogen infrastructure and transportation systems. HyRAM is designed to facilitate the use of state-of-the-art science and engineering models to conduct robust, repeatable assessments of hydrogen safety, hazards, and risk. HyRAM is envisioned as a unifying platform combining validated, analytical models of hydrogen behavior, a standardized, transparent QRA approach, and engineering models and generic data for hydrogen installations. HyRAM is being developed at Sandia National Laboratories for the U. S. Department of Energy to increase access to technical data about hydrogen safety and to enable the use of that data to support development and revision of national and international codes and standards. This document provides a description of the methodology and models contained in the HyRAM version 1.0. HyRAM 1.0 includes generic probabilities for hydrogen equipment failures, probabilistic models for the impact of heat flux on humans and structures, and computationally and experimentally validated analytical and first order models of hydrogen release and flame physics. HyRAM 1.0 integrates deterministic and probabilistic models for quantifying accident scenarios, predicting physical effects, and characterizing hydrogen hazards (thermal effects from jet fires, overpressure effects from deflagrations), and assessing impact on people and structures. HyRAM is a prototype software in active development and thus the models and data may change. This report will be updated at appropriate developmental intervals.

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A cooperative research and development agreement was made between Linde, LLC and Sandia to develop a plan for modifying the Turbulent Combustion Laboratory (TCL) with the necessary infrastructure to produce a cold (near liquid temperature) hydrogen jet. A three-stage heat exchanger will be used to cool gaseous hydrogen using liquid nitrogen, gaseous helium, and liquid helium. A cryogenic line from the heat exchanger into the lab will allow high-fidelity diagnostics already in place in the lab to be applied to cold hydrogen jets. Data from these experiments will be used to develop and validate models that inform codes and standards which specify protection criteria for unintended releases from liquid hydrogen storage, transport, and delivery infrastructure.

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Oxy-fuel combustion technology with carbon capture and storage could significantly reduce global CO₂ emissions, a greenhouse gas. Implementation can be aided by computational fluid dynamics (CFD) simulations, which require an accurate understanding of coal particle kinetics as they go through combustion in a range of environments. To understand the kinetics of pulverized coal char combustion, a heated flow reactor was operated under a wide range of experimental conditions. We varied the environment for combustion by modifying the diluent gas, oxygen concentration, gas flow rate, and temperature of the reactor/reacting gases. Measurements of reacting particle temperatures were made for a sub-bituminous and bituminous coal char, in environments with CO₂ or N₂ as the diluent gas, with 12, 24, and 36 vol-% oxygen concentration, at 50, 80, 100, and 200 standard liters per minute flowing through the reactor, reactor temperatures of 1200, 1400 K, at pressures slightly above atmospheric. The data shows consistent increasing particle temperature with increased oxygen concentration, reactor temperature and higher particle temperatures for N₂ diluent than CO₂. We also see the effects of CO₂ gasification when different ranks of coal are used, and how the reduction in the temperature due to the CO₂ diluent is greater for the coal char that has higher reactivity. Quantitative measurements for temperature are not yet complete due to ongoing calibration of detection systems.

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This report describes an FY13 effort to develop the latest version of the Sandia Cooler, a breakthrough technology for air-cooled heat exchangers that was developed at Sandia National Laboratories. The project was focused on fabrication, assembly and demonstration of ten prototype systems for the cooling of high power density electronics, specifically high performance desktop computers (CPUs). In addition, computational simulation and experimentation was carried out to fully understand the performance characteristics of each of the key design aspects. This work culminated in a parameter and scaling study that now provides a design framework, including a number of design and analysis tools, for Sandia Cooler development for applications beyond CPU cooling.

In CFD models of pulverized coal combustion, which often have complex, turbulent flows with millions of coal particles reacting, the char combustion sub-model needs to be computationally efficient. There are several common assumptions that are made in char combustion models that allow for a compact, computationally efficient model. In this work, oft used single- and double-film simplified models are described, and the temperature and carbon combustion rates predicted from these models are compared against a more accurate continuous-film model. Both the single- and double-film models include a description of the heterogeneous reactions of carbon with O2, CO2, and H2O, along with a Thiele based description of reactant penetration. As compared to the continuous-film model, the double-film model predicts higher temperatures and carbon consumption rates, while the single-film model gives more accurate results. A single-film model is therefore preferred to a double-film model for a simplified, yet fairly accurate description of char combustion. For particles from 65 to 135μm, in O2 concentrations ranging from 12 to 60vol.%, with either CO2 or N2 as a diluent, particle temperatures from the single-film model are expected to be accurate within 270K, and carbon consumption rate predictions should be within 16%, with greater accuracies for a CO2 diluent and at lower bulk oxygen concentrations. A single-film model that accounts for reactant penetration and both oxidation and gasification reactions is suggested as a computationally efficient sub-model for coal char combustion that is reasonably accurate over a wide range of gas environments. © 2013 The Combustion Institute.

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The effects of hydrogen on the mechanics (e.g. strength, ductility, and fatigue resistance) of polymer materials are outlined in this report. There are a small number of studies reported in the literature on this topic, and even fewer at the extreme temperatures to which hydrogen service materials will be exposed. Several studies found little evidence that hydrogen affects the static tensile properties, long term creep, or ductile fracture of high density polyethylene or polyamide. However, there has been a report that a recoverable drop in the modulus of high density polyethylene is observable under high hydrogen pressure. A research need exists on the mechanical effects of hydrogen on the wide range of polymers used or considered for use in the hydrogen economy, due to the lack of data in the literature.

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Cellulosic ethanol, generated from lignocellulosic biomass sources such as grasses and trees, is a promising alternative to conventional starch- and sugar-based ethanol production in terms of potential production quantities, CO{sub 2} impact, and economic competitiveness. In addition, cellulosic ethanol can be generated (at least in principle) without competing with food production. However, approximately 1/3 of the lignocellulosic biomass material (including all of the lignin) cannot be converted to ethanol through biochemical means and must be extracted at some point in the biochemical process. In this project we gathered basic information on the prospects for utilizing this lignin residue material in thermochemical conversion processes to improve the overall energy efficiency or liquid fuel production capacity of cellulosic biorefineries. Two existing pretreatment approaches, soaking in aqueous ammonia (SAA) and the Arkenol (strong sulfuric acid) process, were implemented at Sandia and used to generated suitable quantities of residue material from corn stover and eucalyptus feedstocks for subsequent thermochemical research. A third, novel technique, using ionic liquids (IL) was investigated by Sandia researchers at the Joint Bioenergy Institute (JBEI), but was not successful in isolating sufficient lignin residue. Additional residue material for thermochemical research was supplied from the dilute-acid simultaneous saccharification/fermentation (SSF) pilot-scale process at the National Renewable Energy Laboratory (NREL). The high-temperature volatiles yields of the different residues were measured, as were the char combustion reactivities. The residue chars showed slightly lower reactivity than raw biomass char, except for the SSF residue, which had substantially lower reactivity. Exergy analysis was applied to the NREL standard process design model for thermochemical ethanol production and from a prototypical dedicated biochemical process, with process data supplied by a recent report from the National Research Council (NRC). The thermochemical system analysis revealed that most of the system inefficiency is associated with the gasification process and subsequent tar reforming step. For the biochemical process, the steam generation from residue combustion, providing the requisite heating for the conventional pretreatment and alcohol distillation processes, was shown to dominate the exergy loss. An overall energy balance with different potential distillation energy requirements shows that as much as 30% of the biomass energy content may be available in the future as a feedstock for thermochemical production of liquid fuels.

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