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Liu X.,University of Wollongong | Godbole A.,University of Wollongong | Lu C.,University of Wollongong | Michal G.,University of Wollongong | Venton P.,Venton and Associates Pty Ltd
Applied Energy | Year: 2014

Transportation of CO2 in high-pressure pipelines forms a crucial link in the ever-increasing application of Carbon Capture and Storage (CCS) technologies. An unplanned release of CO2 from a pipeline presents a risk to human and animal populations and the environment. Therefore it is very important to develop a deeper understanding of the atmospheric dispersion of CO2 before the deployment of CO2 pipelines, to allow the appropriate safety precautions to be taken. This paper presents a two-stage Computational Fluid Dynamics (CFD) study developed (1) to estimate the source strength, and (2) to simulate the subsequent dispersion of CO2 in the atmosphere, using the source strength estimated in stage (1). The Peng-Robinson (PR) EOS was incorporated into the CFD code. This enabled accurate modelling of the CO2 jet to achieve more precise source strength estimates. The two-stage simulation approach also resulted in a reduction in the overall computing time. The CFD models were validated against experimental results from the British Petroleum (BP) CO2 dispersion trials, and also against results produced by the risk management package Phast. Compared with the measurements, the CFD simulation results showed good agreement in both source strength and dispersion profile predictions. Furthermore, the effect of release direction on the dispersion was studied. The presented research provides a viable method for the assessment of risks associated with CCS. © 2014 Elsevier Ltd. Source

Botros K.K.,Nova Chemicals Corporation | Geerligs J.,Nova Chemicals Corporation | Rothwell B.,Brian Rothwell Consulting Inc. | Carlson L.,Alliance Pipeline Ltd. | And 2 more authors.
Proceedings of the Biennial International Pipeline Conference, IPC | Year: 2010

The control of propagating ductile (or tearing) fracture is a fundamental requirement in the fracture control design of pipelines. The Battelle two-curve method developed in the early 1970s still forms the basis of the analytical framework used throughout the industry. GASDECOM is typically used for calculating decompression speed, and idealizes the decompression process as isentropic and one-dimensional, taking no account of frictional effects. While this approximation appears not to have been a major issue for large-diameter pipes and for moderate pressures (up to 12 MPa), there have been several recent full-scale burst tests at higher pressures and smaller diameters for which the measured decompression velocity has deviated progressively from the predicted values, in general towards lower velocities. The present research was focused on determining whether pipe diameter was a major factor that could limit the applicability of frictionless models such as GASDECOM. Since potential diameter effects are primarily related to wall friction, which in turn is related to the ratio of surface roughness to diameter, an experimental approach was developed based on keeping the diameter constant, at a sufficiently small value to allow for an economical experimental arrangement, and varying the internal roughness. A series of tests covering a range of nominal initial pressures from 10 to 21 MPa, and involving a very lean gas and three progressively richer compositions, were conducted using two specialized high pressure shock tubes (42 m long, I.D. = 38.1 mm). The first is honed to an extremely smooth surface finish, in order to minimize frictional effects and better simulate the behaviour of largerdiameter pipelines, while the second has a higher internal surface roughness. The results show that decompression wave speeds in the rough tube are consistently slower than those in the smooth tube under the same conditions of mixture composition and initial pressure & temperature. Preliminary analysis based on perturbation theory and the fundamental momentum equation indicates that the primary reason for the slower decompression wave speed in the rough tube is the higher spatial gradient of pressure pertaining to the decompression wave dynamics, particularly at lower pressure ratios and higher gas velocities. The magnitude of the effect of the slower decompression speed on arrest toughness was then evaluated by a comparison involving several hypothetical pipeline designs, and was found to be potentially significant for pipe sizes DN450 and smaller. Copyright © 2010 by ASME. Source

Godbole A.,University of Wollongong | Michal G.,University of Wollongong | Lu C.,University of Wollongong | Liu X.,University of Wollongong | And 2 more authors.
Proceedings of the Biennial International Pipeline Conference, IPC | Year: 2014

This paper describes two separate field experiments involving the venting of natural gas pipelines. The pipelines were 32 km and 60 km in length respectively. The studies were carried out as part of an investigation of the phenomenon of Low Temperature Excursions (LTE) under the aegis of the Energy Pipelines Cooperative Research Centre (EPCRC), Australia. When a highly compressed gas is allowed to escape from a pipeline, the large drop in pressure is accompanied by a significant drop in the temperature of the gas. The general impression is that the pipeline material is also cooled to a comparable extent. This has often led to over-specification of the properties of the pipeline material. Theoretical and CFD studies have shown that although the gas undergoing severe decompression can indeed attain very low temperatures, the adjacent pipe wall does not experience cooling to a comparable extent. This appears to be in part due to the short time scales involved, and due to frictional effects at the gas-pipe wall interface [1]. In the field experiments described, in-situ measurements of gas pressure and pipe wall temperature were carried out. One of the field experiments also involved thermal imaging of the vent pipe surface. The measurements showed that even the most susceptible parts of the vent pipe were not excessively cooled during the event, i.e. much less than the cooling experienced by the gas at the corresponding location. CFD simulations of the highly transient flow in one of the field studies suggest that this may be due to a combination of the time scales involved, and frictional dissipation in severe pipeline decompression, i.e. rapid decompression from an initially high pressure level. Based on the above findings, work is in progress to improve the temperature calculations in computer applications. Copyright © 2014 by ASME. Source

Liu X.,University of Wollongong | Godbole A.,University of Wollongong | Lu C.,University of Wollongong | Michal G.,University of Wollongong | Venton P.,Venton and Associates Pty Ltd
Environmental Science and Pollution Research | Year: 2015

The carbon capture and storage (CCS) and enhanced oil recovery (EOR) projects entail the possibility of accidental release of carbon dioxide (CO2) into the atmosphere. To quantify the spread of CO2 following such release, the ‘Gaussian’ dispersion model is often used to estimate the resulting CO2 concentration levels in the surroundings. The Gaussian model enables quick estimates of the concentration levels. However, the traditionally recommended values of the ‘dispersion parameters’ in the Gaussian model may not be directly applicable to CO2 dispersion. This paper presents an optimisation technique to obtain the dispersion parameters in order to achieve a quick estimation of CO2 concentration levels in the atmosphere following CO2 blowouts. The optimised dispersion parameters enable the Gaussian model to produce quick estimates of CO2 concentration levels, precluding the necessity to set up and run much more complicated models. Computational fluid dynamics (CFD) models were employed to produce reference CO2 dispersion profiles in various atmospheric stability classes (ASC), different ‘source strengths’ and degrees of ground roughness. The performance of the CFD models was validated against the ‘Kit Fox’ field measurements, involving dispersion over a flat horizontal terrain, both with low and high roughness regions. An optimisation model employing a genetic algorithm (GA) to determine the best dispersion parameters in the Gaussian plume model was set up. Optimum values of the dispersion parameters for different ASCs that can be used in the Gaussian plume model for predicting CO2 dispersion were obtained. © 2015, Springer-Verlag Berlin Heidelberg. Source

Liu X.,University of Wollongong | Godbole A.,University of Wollongong | Lu C.,University of Wollongong | Michal G.,University of Wollongong | Venton P.,Venton and Associates Pty Ltd
Atmospheric Environment | Year: 2015

The development of the Carbon Capture and Storage (CCS) technique requires an understanding of the hazards posed by the operation of high-pressure CO2 pipelines. To allow the appropriate safety precautions to be taken, a comprehensive understanding of the consequences of unplanned CO2 releases is essential before the deployment of CO2 pipelines. In this paper, we present models for the predictions of discharge rate, atmospheric expansion and dispersion due to accidental CO2 releases from high-pressure pipelines. The GERG-2008 Equation of State (EOS) was used in the discharge and expansion models. This enabled more precise 'source strength' predictions. The performance of the discharge and dispersion models was validated against experimental data. Full-bore ruptures of pipelines carrying CO2 mixtures were simulated using the proposed discharge model. The propagation of the decompression wave in the pipeline and its influence on the release rate are discussed. The effects of major impurities in the CO2 mixture on the discharge rate were also investigated. Considering typical CO2 mixtures in the CCS applications, consequence distances for CO2 pipelines of various sizes at different stagnation pressures were obtained using the dispersion model. In addition, the impact of H2S in a CO2 mixture was studied and the threshold value of the fraction of H2S at the source for which the hazardous effects of H2S become significant was obtained. © 2015 Elsevier Ltd. Source

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