CO2 Dispersion Research Articles

Investigation of terrain effects on the consequence distance of CO2 released from high-pressure pipelines

As part of Carbon Capture and Storage (CCS) projects, Carbon Dioxide (CO2) is usually transported via pipelines from source to sequestration location. Ensuring the safety of the operation is of great importance, as CO2 is a hazardous substance and an accidental release may have catastrophic consequences. Therefore, a comprehensive understanding of the effects of a CO2 release from CCS facilities is essential to allow the appropriate safety precautions to be taken. The majority of prior studies that address this topic do so by simulating CO2 dispersion over a flat horizontal terrain. However, CO2 pipelines may be deployed near topographically complex locations such as congested industrial or urban areas. The extent to which the complexity of the terrain may affect the area affected by an accidental release has not been explored in detail. In this paper, we present Computational Fluid Dynamics (CFD) models for the prediction of atmospheric dispersion of CO2 over complex terrains, in order to evaluate the ‘consequence distance’ relating to accidental CO2 releases from high-pressure pipelines. The CFD model is validated against the results of a heavy gas dispersion experiment carried out at Thorney Island. Simulations of CO2 dispersion over seven types of complex terrain are carried out, considering ‘full-bore’ rupture of a pipeline carrying a pre-combustion CO2 mixture. The influence of different terrain features on the consequence distance is studied. In addition, the dispersion of a (CO2+H2S) mixture is simulated to investigate the threshold value of the fraction of Hydrogen Sulphide (H2S) for which the hazardous effects of H2S become significant for a release over complex terrains.

Formation and dispersion of CO2 after combustion in closed area

This study deals with the formation of carbon dioxide (CO2) after combustion process and dispersion in a closed area. The formation and dispersion of CO2 were numerically simulated and validated by experiment. Ethanol (C2H5OH) was chosen as a fuel for the combustion process. Numerical simulations were carried out by using Reynolds averaged Navier–Stokes (RANS) approach with k-e and k-ω turbulent models. The combustion process was simulated using two methods. Species transport with chemical reactions was the first method, and the second method was the nonpremix combustion model based on the mixture fraction theory. There were done some sensitivity studies on the influence of the time step size and a resolution of computational grid. Results from numerical simulations were validated by experimental measurements, where the CO2 concentration was measured by the non-dispersive infrared (NDIR) sensor at four points.

A new dispersion interferometer on HL-2A.

In order to avoid a fringe jump caused by high plasma density and pellet injection [Y. Zhou et al., Rev. Sci. Instrum. 87, 11E107 (2016)], a new CO2 dispersion interferometer is designed and commissioned on HL-2A for average line-density measurement and density feedback control. The second harmonic technology in this system eliminates the phase shift caused by mechanical vibration. Signals are processed by a digital phase comparator and can be monitored in real time. A series of experiments are conducted to study the characteristics of the system such as a second harmonic coefficient and long-term stability. The resolution of density measurement is less than 8 × 1017/m3, and the experiment result on HL-2A demonstrates the interferometer's capability to track plasma density evolution with rapid change. The system also shows good stability against mechanical vibrations.

The Influences of CO2 Injection Pressure on CO2 Dispersion and the Mechanism of CO2–CH4 Displacement in Shale

The effects of CO2 injection pressure (PCO2) on CO2 dispersion and the mechanism of CO2–CH4 displacement in a shale sampled from Changning of China were studied. Results indicated that Coats–Smith dispersion–capacitance model gave a reasonable simulated result to the breakthrough curves of CO2 under different injection pressures. The shapes of CO2 breakthrough curves became more asymmetrical with the increase of CO2 injection pressure. A higher CO2 injection pressure caused early CO2 breakthrough and reduced the recovery of CH4 at CO2 breakthrough (Rpipeline-CH4), but improved the ultimate displaced CH4 amount (Rultimate-CH4). With the increase of CO2 injection pressure, dispersion coefficient (Kd) increased nearly exponentially. A larger Kd led to a lower Rpipeline-CH4 and a longer transition zone. With the increase of CO2 injection pressure, the flowing fraction (F) in pore space decreased nearly linearly and more CO2 diffused into stagnant region to replace adsorbed CH4 in a shale, which resulted in a larger Rultimate-CH4. The mass transfer coefficient (Km) between the flowing and stagnant regions increased with the increase of CO2 injection pressure, which led to a smaller F and larger Rultimate-CH4. CO2 diffusion provided major contribution to CO2 dispersion at lower injection pressure, and mechanical mixing of CO2–CH4 offered predominant contribution to CO2 dispersion at higher injection pressure. Larger mechanical mixing accelerated the mixing of CO2–CH4, which was unfavorable for Rpipeline-CH4. Lower CO2 injection pressure was conductive to gain higher Rpipeline-CH4.

Modelling of source term from accidental release of pressurised CO2

Abstract Storage and transportation in carbon capture and sequestration (CCS) technology involve dealing with CO2 at high pressures, which can lead to accidental releases. To assess and control risks and to calculate the minimum safe distance from tanks and pipelines to populated areas, the source term model of the leakage is extremely important, as it serves as input to model the dispersion of CO2 into the atmosphere. The modelling of high pressurised CO2 releases is relatively complex due to its thermofluidynamics particularities. Its triple point pressure is higher than the atmospheric pressure and it has a relatively high Joule–Thomson coefficient depending on the temperature and pressure conditions. Hence, it might lead to a two-phase flow and to solid formation when the depressurisation to atmospheric pressure occurs. Also, the molecular vibration of CO2 might be important in some leakage scenarios. There are several approaches in the literature which address differently the aspects of the flow, specially regarding thermal and mechanical equilibrium or non-equilibrium. The present work provides an innovative approach for the discharge calculation in accidental high pressure releases. The Homogeneous Non-Equilibrium Model (HNM) is proposed, which accounts for non-equilibrium effects regarding not only metastability but also vibrational relaxation of the molecule. It considers the possible phase transitions and dry ice formation and it is applicable to steady-flow conditions. The model was tested with experimental data from CO2PIPETRANS project, HSE experiments and Cooltrans research programme. It was found that the model works well leading to results which agree with available experimental data. The proposed source model is relatively simple to implement and it does not demand numerical effort. The discussed discharge approach for CO2 releases emerges as a good alternative to existing models.

Shaped Co2+ doped TiO2 nanocrystals synthesized from nanotubular precursor: Structure and ferromagnetic behavior

Co2+ doped TiO2 nanocrystals were synthetized by a hydrothermal treatment procedure applied to precursor dispersion of titania nanotubes and Co2+ ions. Mixture of polygonal and prolate spheroid-like nanocrystals was obtained. The results of X-ray diffraction (XRD) analysis showed that resulted nanocrystals retain anatase crystal phase for both dopant concentrations (1.69 and 2.5 at%), but the crystal lattice parameters were affected. Reflection spectra revealed altered optical properties compared to bare TiO2. Room temperature ferromagnetic ordering with saturation magnetic moment in the range of 0.001–0.002 μB/Co was observed for both measured films made of Co2+ doped TiO2 nanocrystals.

CFD simulation of CO2 dispersion from urban thermal power plant: Analysis of turbulent Schmidt number and comparison with Gaussian plume model and measurements

This investigation presents computational fluid dynamics (CFD) simulations of carbon dioxide (CO2) dispersion from a natural gas-fueled thermal power plant in an urban environment. The results are compared with experimental measurements of column-averaged dry-air mole fraction (XCO2) on the site, obtaining a good agreement. Different turbulent Schmidt numbers are compared, and we suggest a value for being used in full-scale simulations. The particular characteristics, e.g. azimuth and elevation angles of the XCO2 measurement, are analyzed and taken into account for the comparison with simulation results. The conclusions from this comparison are useful not only for the XCO2 experimental data analysis, but also for the efficient and successful design of future measurement campaigns. The simulation results are also compared with the Gaussian plume model, and a new parametrization (i.e. vertical dispersion parameter) is suggested for being used in the urban environment. Additionally, CO2 concentration maps for an urban area are presented, and the spatial distribution is analyzed.

Potential for Very Deep Ocean Storage of CO2 Without Ocean Acidification: A Discussion Paper

Carbon Capture and Storage (CCS) is an essential contributor to the mitigation of climate change. CCS will require vast CO2 storage capacity. At present only geological storage is being considered. This paper revisits an alternative CO2 storage possibility in enclosed basins on the deep and very deep ocean floor.For example, the Indonesian Sunda trench, the Japanese Ryukyu trench and the Puerto Rico trench are more than 6km deep. If liquid CO2 were to be placed in such a trench, it would be 7% more dense than seawater and could remain permanently as a lake of liquid CO2 on the ocean floor, possibly becoming a solid hydrate over time which could inhibit mixing between the stored CO2 and ocean currents.At depths greater than about 4 to 5km metres, seawater is under-saturated in calcium carbonate, so ocean ecosystems are significantly different. Any impact on deep marine fauna would need to be investigated.The London Dumping Convention has provisions for disposal of material into the ocean provided the absence of adverse effects can be proven.Deep ocean CO2 entrapment is more certain than geological CO2 storage in deep aquifers. A CO2 delivery concept by ship and vertical pipe is suggested for exploratory trials, with subsea pipelines for permanent installations, which might be much cheaper than geological CO2 storage.There is vast capacity for storage of CO2 in the world's very deep ocean trenches. The Sunda trench below 6km has the capacity to accommodate 19,000 gigatonnes of liquid CO2, which is greater than the CO2 yield from all currently known global fossil fuel reserves. The Puerto Rico trench has capacity for 24,000 Gt of liquid CO2 deeper than 7km. Enclosed basins of limited area could easily accommodate captured CO2.China has the largest potential demand for CO2 storage from power generation and industrial sources, which could be 3 Gt per year by 2050. The Ryukyu trench, which is 700km from the Chinese coast and is in Japanese water, has two sections deeper than 7km. Those sections of the Ryukyu trench would have the capacity to accommodate all the CO2 captured in China at 3 Gt per year for over 200 years.In the event that very deep ocean storage of CO2 is found to be practicable and acceptable, the minimum practical depth would need to be determined as a criterions for acceptable additional storage locations. For consideration, there is an enclosed basin on the floor of the Mediterranean Sea 60km off Southern Greece, with capacity for 84 Gt of CO2 deeper than 4.5km. Also, there is an enclosed basin in the Arabian Sea, 320km south west of Karachi, with capacity for 86 Gt of CO2 deeper than 3.5km. The potential storage of CO2 in such locations would be temperature dependent.The global CCS community has previously considered ocean storage of CO2 on the basis of ultimate dissolution and dispersion of CO2 in ocean water. Those studies have dismissed ocean storage as environmentally unacceptable due to ocean acidification.This paper postulates that very deep ocean trenches (>6km) and deep ocean floor depressions (>4km) are environments for CO2 storage, where permanent storage without dissolution, acidification or adverse effects on fauna may be possible.The purpose of this paper is to pose the question “Why not?” to the CCS community and to suggest that active research is timely.

Coupled geomechanical and reactive geochemical model for fluid, heat flow and convective mixing: application for CO<SUB align="right">2 geological sequestration into saline aquifer with heterogeneity

The significance of thermal-hydrological-mechanical-chemical (THMC) processes is well-identified in the operation of CO2 geo-sequestration. Geomechanical and geochemical effects may significantly affect aqueous phase composition, porosity and permeability of the formation, which in turn influence fluid advection, convection and transport. A sequentially coupled mathematical algorithm is employed to simulate reactive transport of water, CO2 gas and species in subsurface formation with geomechanics, which is bale to model the THMC processes of the fluid advection and convection, heat and solute transport in aqueous and gaseous phase, mean stress, and geochemical reactions under both equilibrium and kinetic conditions. A 2D model with complex chemical compositions is presented to analyse the THMC processes quantitatively, including geomechamical effect due to CO2 injection, dispersion and convective mixing due to CO2 dissolution, mineral alteration due to chemical reaction of water, CO2 and rock minerals, coupled effects of geochemical reaction and geomechanics.

Coupled geomechanical and reactive geochemical model for fluid, heat flow and convective mixing: application for CO<SUB align="right">2 geological sequestration into saline aquifer with heterogeneity

The significance of thermal-hydrological-mechanical-chemical (THMC) processes is well-identified in the operation of CO2 geo-sequestration. Geomechanical and geochemical effects may significantly affect aqueous phase composition, porosity and permeability of the formation, which in turn influence fluid advection, convection and transport. A sequentially coupled mathematical algorithm is employed to simulate reactive transport of water, CO2 gas and species in subsurface formation with geomechanics, which is bale to model the THMC processes of the fluid advection and convection, heat and solute transport in aqueous and gaseous phase, mean stress, and geochemical reactions under both equilibrium and kinetic conditions. A 2D model with complex chemical compositions is presented to analyse the THMC processes quantitatively, including geomechamical effect due to CO2 injection, dispersion and convective mixing due to CO2 dissolution, mineral alteration due to chemical reaction of water, CO2 and rock minerals, coupled effects of geochemical reaction and geomechanics.

Under-expanded jets and dispersion in high pressure CO2 releases from an industrial scale pipeline

The widespread implementation of carbon capture and storage (CCS) in industry will require extensive long-distance CO2 pipeline networks to integrate the component technologies. The potential for pipeline rupture and leakage, possibly resulting in catastrophic accidents, will inevitably increase as networks become more extensive. The study of near-field source terms and dispersion behavior after pipeline rupture is an essential foundation of CO2 pipeline risk assessment and will provide effective technical support for the implementation of large-scale CCS projects and contribute to pipeline safety. In the CO2QUEST project under-expanded CO2 jets, cloud dispersion characteristics and the formation of dry ice particles in the near field were investigated during releases from a 258 m long, fully instrumented pipeline. Experimental data including cloud temperature, CO2 concentration and the visual evolution of the cloud (recorded on film), was gathered to investigate cloud behavior and to support future work in the field of CO2 pipeline safety. Experiments included the release of gaseous and dense phase CO2 through three orifice diameters: 15 mm, 50 mm and Full Bore Rupture (FBR). The lower limit of gaseous CO2 concentration for adverse effects in humans is 5% v/v. Safety distances from the release, based on this threshold concentration limit, are determined and reported for each experiment conducted.

Hazard investigation of dry–ice bank induced risks related to rapid depressurization of CCS pipelines: Analysis of different numerical modelling approaches

CO2 is recognized as one of the most important greenhouse gases. Many mitigating solutions to stabilize its atmospheric concentration are currently being investigated in order to control the so called Global Warming. Among these, the CCS (Carbon Capture and Storage) chain is one of the most promising solutions and is linked to the handling of large amounts of CO2 through dedicated buried pipelines. As a consequence of any accidental release, a dry ice bank may be formed on the ground acting as a delayed emission source.This study aims at investigating different modeling approaches to face hazards related to this source and the mechanisms related to the near field atmospheric dispersion of CO2. Moving from simplified approaches to more complex ones relying on Computational Fluid Dynamics, some danger distances are classified under different stability classes. The analysis shows some discrepancies concerning the predicted gas dispersion. The most simplified approaches are not able to give a near–field reliable description that is instead captured by the CFD along with stratification phenomena. On the contrary, the CFD applicability is strictly linked to the computational burden that is usually not compatible with emergency–related responses but only with planning issues.

Under-expanded jets and dispersion in supercritical CO2 releases from a large-scale pipeline

Long-distance CO2 pipelines will be widely applied to transport captured CO2 from fossil fuel fired power plants for subsequent sequestration. In the event of pipeline failure a large mass of the inventory may be discharged within a short time, this represents a significant hazard if leaks continue undetected. An important result of the risk assessment for a CO2 pipeline is the safety distance. At present the lack of knowledge concerning near-field source terms and the far-field dispersion behavior of CO2 leaking from pipelines can make the calculation of safety distances imprecise. Study of near-field source terms and dispersion behavior is therefore necessary and of paramount importance for assessing safety distances and the impact of CO2 pipeline releases on the surrounding environment. In order to study CO2 pipeline leakage, a large-scale pipeline set-up with a total length of 258m and an internal diameter of 233mm was constructed to study the near-field characteristics and dispersion behavior of supercritical CO2 during sudden releases. The dynamic pressure near the orifice and CO2 concentrations and temperatures within the downstream dispersion region were measured together with the pressures inside the pipeline. The under-expanded jet flow structure and phase transitions in the near-field were studied for supercritical CO2 released though different orifice diameters (15mm, 50mm and Full Bore Rupture). The formation of the visible cloud, the distribution of cloud temperatures and CO2 concentrations in the far-field were analyzed using the measured data, photographs and video recordings. The safety distances along the horizontal direction for 5% CO2 concentration for each of the three orifice diameters were determined from the lower limit for adverse human effects.

High pressure CO2 CCS pipelines: Comparing dispersion models with multiple experimental datasets

Carbon capture and storage (CCS) presents the short-term option for significantly reducing the amount of carbon dioxide (CO2) released into the atmosphere from the combustion of fossil fuels, thereby mitigating the effects of climate change. Enabling CCS requires the development of capture, storage and transport methodologies. The safe transport of CO2 in CCS scenarios can be achieved through pipelines or by shipping. Either way, transport and temporary storage of pressurised liquid CO2 will be required and subject to quantitative risk assessment, which includes the consideration of the low-risk, low-probability puncture or rupture scenario of such a pipeline, ship or storage facility. In this work, we combine multiple experimental datasets all concerned with the atmospheric free release of pure and impure liquid CO2 from CCS-transport-chain-relevant high pressure reservoirs and perform the first multiple dataset comparison to numerical models for both pure and impure CO2 jets in dry ambient air with no water vapour. The results validate the numerical approach adopted and for the prediction of such releases, highlight the significance of the mixture fraction at the release point, over the mixture composition itself. A new method for impure CO2 dispersion modelling is introduced and limited preliminary comparisons of impure CO2 data and predictions are performed. No clear difference between pure and impure releases is found for the cases considered.

The conceptual design of interferometer/polarimeter system on HL-2M.

HL-2M is a new medium-sized tokamak with major radius of 1.78 m, minor radius of 0.65 m, and aspect ratio of 2.8 and will be finished soon. In the conceptual design, a double-pass, horizontal view, multi-channel far-infrared (FIR) laser interferometer/polarimeter system (at 432 μm) is proposed to simultaneously measure the phase change and the Faraday rotation for density and current profile reconstruction. A vertical CO2 dispersion interferometer system (with wavelength of 10.6 μm and 5.3 μm) is designed to measure the line density, which will mainly be used for density feedback. The performance of the system is expected to meet the requirement of the measurements on HL-2M, with phase accuracy ∼0.1°, time resolution ∼1 μs, spatial resolution ∼7.2 cm, and density measurement range of 1 × 10 18-1 ×1021 m-3.

Further development and validation of CO2FOAM for the atmospheric dispersion of accidental releases from carbon dioxide pipelines

This paper reports on the further development and validation of CO2FOAM, a dedicated computational fluid dynamics solver for the atmospheric dispersion of Carbon Dioxide (CO2) from accidental pipeline releases. The code has been developed within the framework of the open source CFD code OpenFOAM® (OpenCFD, 2014). Its earlier version used the homogeneous equilibrium method for fully compressible two-phase flow. Validation of the code against CO2 releases through vertical vent pipes and horizontal shock tubes was previously reported by Wen et al. (2013). In the present study, the homogeneous relaxation model has been implemented as it is more suited to account for the presence of solid CO2 within the releases. For validation, the enhanced CO2FOAM has been used to predict CO2 dispersion in a range of full scale tests within the dense phase CO2 PipeLine TRANSportation (COOLTRANS) research programme (Cooper, 2012) funded by National Grid. The test case used in the present study involved a puncture in a buried pipe. The experimental measurements were supplied to the authors after the predictions were completed and submitted to National Grid. Hence, the validation reported here is indeed ‘blind’. The validated model has also been used to study the effect of a commercial building located downstream from the release location.

CFD Simulation of CO<sub>2</sub> Dispersion in a Real Terrain

A deeper understanding of CO2 dispersion resulting from accidental releases is essential to evaluate the risk associated with the Carbon Capture and Storage (CCS) technology. The dispersion patterns of CO2, which is a heave gas, may vary according to local conditions. In this study the possibility of simulating the dispersion of CO2 clouds over a real topographically complex area in Australia by a general purpose Computational Fluid Dynamics (CFD) code is investigated. The study may offer a viable method for assessment of risks associated with CCS.

Fast estimation of dense gas dispersion from multiple continuous CO2 surface leakage sources for risk assessment

Surface leakage of CO2, and associated potential impacts on health, safety, and the environment (HSE) are considered hazards of geologic carbon sequestration (GCS). There are two challenges associated with impact assessment of CO2 surface dispersion. First, the fact that CO2 is a dense gas makes its dispersion in air a complex process. Rigorous numerical solutions for modeling concentration distributions are relatively time-consuming. Second, impact assessment requires consideration of uncertainty, e.g., quantification of how much uncertainty is propagated through input parameters to model outputs by carrying out large numbers of model runs. In order to assess the potential consequences of surface leakage of CO2, it is useful to have a model that executes very quickly for repeated model calculations (e.g., in Monte Carlo mode) of the atmospheric dispersion of CO2 (concentrations as a function of space and time). In addition, the model should be able to handle multiple surface leakage sources. In this study, we have extended the nomograph approach of Britter and McQuaid (1988) for estimating dense gas plume length from single leakage source to multiple leakage sources. The method is very fast and therefore amenable to general system-level GCS risk assessment including uncertainty quantification within the framework of the National Risk Assessment Partnership (NRAP) Integrated Assessment Model (IAM). The method is conservative in that it assumes the wind could be from any direction, and it handles multiple sources by a simple superposition approach. The method produces results in reasonable agreement with a sophisticated computational fluid dynamics (CFD) code, but runs in a small fraction of the time.

Experimental data and CFD performance for CO2 cloud dispersion analysis

Dispersion of hazardous gas releases represents a major threat to health and to the environment; therefore, the prediction of the dispersion features raises great interest. In recent years, with the increase in computational capacity, the interest in Computational Fluid Dynamics (CFD) tools to evaluate dispersion analysis has increased. With the growing use of CFD tools to perform dispersion analysis in different scenarios, it is imperative to amplify the availability of experimental data in order to allow validations studies to contribute to understanding the real capacity of CFD tools to properly represent real cases. The second stage of the field tests conducted by a joint venture between the University of São Paulo and the Universitat Politecnica de Catalunya was established to investigate the performance of CFD tools when analyzing cloud dispersion of hazardous substances by means of ad-hoc experimentation. The experiments consisted of CO2 clouds formation and dispersion tracking of releases of up to 0.85 kg s−1 of about 40 s of duration in a 600-m2discharge area. We provide a description of the tests and the main results of the simulation using the FLACS software; the peak concentrations for 51 sensors placed at the dispersion cloud path are provided here and compared with CFD simulations. In general terms, the CFD simulator presented good performance; all the statistical performance measures were well within the acceptable range. However, the simulator performance presented sensitivity to the wind profile, especially when cross wind occurs.

Computational fluid dynamics simulation of carbon dioxide dispersion in a complex environment

In order to quantitatively evaluate the risk associated with the Carbon Capture and Storage (CCS) technology, a deeper understanding of CO2 dispersion resulting from accidental releases is essential. CO2 is a heavier-than-air gas. Its dispersion patterns may vary according to local conditions. This study focuses on CO2 dispersion over complex terrains. Computational Fluid Dynamics (CFD) models were developed to simulate the CO2 dispersion over two hypothetical topographies: (1) a flat terrain with an axisymmetric hill and (2) a simplified model of an urban area with buildings. The source strength, wind velocity and height of the buildings were varied to investigate their effects on the dispersion profile. The study may offer a viable method for assessment of risks associated with CCS.