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Overcoming uncertainties in sour natural gas dispersion modelling
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Nair, SreeRaj R. (2022) Overcoming uncertainties in sour natural gas dispersion modelling. PhD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b3944997
Abstract
The general area of the research lies in identifying the important source term characteristics of an accidental release of hydrogen sulphide containing natural gas (sour natural gas) and the key defining parameters in the sour gas dispersion modelling. This research study led to the development of a methodology for the selection of the consequence modelling for natural gas leaks from pipelines and the key modelling parameters to be subjected to the sensitivity analysis.
The research has evaluated the modelling tools and approaches for the three phases (i) discharge, (ii) expansion and (iii) dispersion following an accidental release. Release and dispersion of sour natural gas with a range of Methane and Hydrogen Sulphide compositions is evaluated in this study. A continuous high pressure dense natural gas leak from a transfer pipeline is the scenario of concern considered. Consequence modelling of this release scenario is carried out using different tools and approaches to estimate the downwind distance for the hazardous region of concern.
The first part of the research established that the depending on the gaseous mixture properties, and ambient conditions, the sour natural gas cloud from a release could be (i) dense (gravity slump), (ii) buoyant (rises over time), or (iii) neutrally buoyant (neither rises nor drops but disperses over time). The second part of the research determined the compositions of natural gas with shifts in buoyancy behaviours and identified the list of modelling parameters to be subjected to sensitivity analysis. The third part of the research developed a higher order Computational Fluid Dynamics (CFD) model for sour natural gas dispersion modelling and determined the appropriate solver and the modifications required on the model to take account of the effect of turbulence and the compositions. The first part used US EPA software ALOHA (CAMEO Suite by US EPA), the second part used commercially available and validated software packages commonly used in the Oil & Gas Industry – HYSYS and CANARY. The third part of the research used higher fidelity model OpenFOAM, an open-source CFD software.
The research findings concluded that the dispersion of the sour natural gas:
• Is sensitive to the release source terms hole size, release rate, and orientation of release.
• Is seriously affected by the terrain, obstructions and other the turbulence related parameters, stability class, wind speed and direction.
• Not significantly sensitive to the changes in humidity and ambient temperature.
The study also determined that the mass in a sour natural gas vapour cloud can increase or decrease depending on the buoyancy, turbulence, and the terrain. The Gaussian based modelling tools are quite suitable for emissions of pollutants whose density remains similar to that of air provided that the cloud does not move too far away from the ground, that there is no obstacle, no extreme meteorological conditions prevail, and there is a certain horizontal homogeneity. If parameters move away from these conditions, sophisticated models should be used.
The findings in this research (i) enables the risk analysts, project specialists, and local planners on hazardous substance transfer route selection, (ii) minimises the inconsistency in risk assessments and (iii) overcome the uncertainty in dispersion modelling whereby the right sized risk management can be deployed.
Item Type: | Thesis (PhD) | ||||
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Subjects: | Q Science > QC Physics T Technology > TN Mining engineering. Metallurgy T Technology > TP Chemical technology |
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Library of Congress Subject Headings (LCSH): | Natural gas, Natural gas -- Mathematical models, Dispersion -- Mathematical models, Atmospheric diffusion, Natural gas pipelines -- Safety regulations | ||||
Official Date: | December 2022 | ||||
Dates: |
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Institution: | University of Warwick | ||||
Theses Department: | School of Engineering | ||||
Thesis Type: | PhD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Wen, Jennifer ; Vendra, Madhav R. C. | ||||
Format of File: | |||||
Extent: | 297 pages : colour illustrations | ||||
Language: | eng |
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