Numerical simulations of the critical diameter and flame stability for hydrogen flames

This study focuses on development and validation of a CFD model to simulate the critical nozzle diameter and stability limits for hydrogen non-premixed flames. The critical diameter represents the minimum nozzle size through which a flame will remain stable at all driving pressures. Flames will not blow-out at diameters equal to or greater than the critical diameter. Accurate simulation of this parameter is important to assess performance of thermally activated pressure relief devices (TPRD) during blowdown from a storage tank. Flame stability is considered for diameters and overpressures ranging from 0.1 mm to 2 mm and from 0.06 MPa to 20 MPa, respectively. The impact of turbulent Schmidt number Sct, on predicted critical diameter is discussed. The model was applied for lower pressures (0.001–0.005 MPa) to understand the pressure at which the flame becomes attached. Simulations of a safer approach to TPRD design are discussed

CFD modelling of methane dispersion from buried pipeline leaks: experimental validation and hazard distance estimation

The safe operation of buried pipelines necessitates an understanding of potential leak dynamics and the subsequent formation of flammable clouds defining hazard distances. This paper presents a computational fluid dynamics (CFD) model and its validation against experimental data on the dispersion of methane through a sand layer of 100 mm thickness to the atmosphere. A leak orifice diameter of 4 mm was considered for pipeline gauge pressures in the range of 10 to 300 kPa. This study describes the methane propagation in time through the sand and the development of the flammable cloud in the atmosphere. The simulations demonstrate a high degree of accuracy in capturing the transient behaviour of methane propagation in the sand and dispersion in the atmosphere when compared with a 60 s experiment. The model was applied to predict the development and maximum spread of the flammable cloud and hazard distances are presented. The simulations provide insight into the development of the flammable cloud. The validated CFD model can serve as a predictive tool for hazard distance estimation in case of buried leaks, inform safer pipeline design and improve emergency response strategies for gas leaks

Hydrogen Jet Fire from a Thermally Activated Pressure Relief Device (TPRD) from Onboard Storage in a Naturally Ventilated Covered Car Park

Hydrogen jet fires from a thermally activated pressure relief device (TPRD) on onboard storage are considered for a vehicle in a naturally ventilated covered car park. Computational Fluid Dynamics was used to predict behaviour of ignited releases from a 70 MPa tank into a naturally ventilated covered car park. Releases through TPRD diameters 3.34, 2 and 0.5 mm were studied to understand effect on hazard distances from the vehicle. A vertical release, and downward releases at 0°, 30° and 45° for TPRD diameters 2 and 0.5 mm were considered, accounting for tank blowdown. direction of a downward release was found to significantly contribute to decrease of temperature in a hot cloud under the ceiling. Whilst the ceiling is reached by a jet exceeding 300 °C for a release through a TPRD of 2 mm for inclinations of either 0°, 30° or 45°, an ignited release through a TPRD of 0.5 mm and angle of 45° did not produce a cloud with a temperature above 300 °C at the ceiling during blowdown. The research findings, specifically regarding the extent of the cloud of hot gasses, have implications for the design of mechanical ventilation systems

Numerical modelling and validation for a methane leak from a buried pipeline

The release of methane from buried pipelines poses potential risks to humans and the environment. Prediction of the flammable methane-air envelope from a buried leak is important for safety recommendations and the estimation of hazard distances for pipelines. This work describes the development and validation of a computational fluid dynamics model capable of simulating an underground gas pipeline leak. Three-dimensional, unsteady, incompressible flow of methane through a sand layer to the atmosphere was simulated. The sand was considered as a porous medium. A species transport model was used for methane diffusion in sand. The dispersion of a buried methane, leak from a 4 mm and 2 mm diameter leak hole, and pipeline pressure of 300 kPa is presented. Validation of the model against experimental data for the initial stages of the leak is demonstrated. The numerical simulations of the first 60 s of the leak demonstrate a high degree of accuracy in capturing the transient behaviour of methane dispersion when compared with experiment. The model offers insights into the factors influencing the spread and dilution of the flammable cloud, thus serving as a reliable predictive tool for hazard distance estimation. The innovative aspect of this model lies in its unique portrayal of the flammable cloud development that is often overlooked in current modelling approaches. The model can be used to underpin inherently safer design of buried pipelines and devising emergency response procedures to gas leaks