Publications

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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 external particle surface, inherently neglecting the impact of variations in the internal diffusion rate and penetration of oxygen. To investigate the impact of bulk gas diffusivity on these phenomena during Zone II burning conditions, experimental measurements were performed of char particle combustion temperature and burnout for a subbituminous coal burning in an optical entrained flow reactor with helium and nitrogen diluents. The combination of much higher thermal conductivity and mass diffusivity in the helium environments resulted in 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. To augment the experimental measurements, detailed particle simulations of the experimental conditions were conducted with the SKIPPY code. These simulations also showed a 60% higher burning rate in the helium environments for a given char particle combustion temperature. To differentiate the effect of enhanced diffusion through the external boundary layer from the effect of enhanced diffusion through the particle, additional SKIPPY simulations were conducted under selected conditions in N2 and He environments for which the temperature and concentrations of reactants (oxygen and steam) were identical on the external char surface. Under these conditions, which yield matching apparent char burning rates, the computed char burning rate for He was 50% larger, demonstrating the potential for significant errors with the apparent kinetics approach. However, for specific application to oxy-fuel combustion in CO2 environments, these results suggest the error to be as low as 3% when applying apparent char burning rates from nitrogen environments.

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Spontaneous Raman scattering images of liquid and near liquid methane released through 1 and 1.25 mm diameter orifices were taken using a pulsed planar laser sheet. The methane back pressure was varied between 2 and 6 bar_abs with methane temperatures between 130 and 220 K. Analysis of the Raman images resulted in the planar concentration and temperature fields of the methane jets. The measured methane concentration was compared with empirical relationships for warm gas releases and found to be in agreement in terms of centerline concentration decay rate, self-similarity, and half-width decay rate. Comparisons were then made for anticipated real-world CNG and LNG releases showing similar extents of flammable mass for the two fuel options. Measured images were compared to a cold gas release model, which showed good agreement over the range of methane release temperatures, pressures, and nozzle sizes. The collected measurements provide validation of this cold release model which will be used to model additional scenarios and inform LNG safety codes and standards.

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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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