Mazzoldi, Alberto
(2009)
Leakage and atmospheric dispersion of CO2 associated with carbon capture and storage projects.
PhD thesis, University of Nottingham.
Abstract
Climate change is affecting planet Earth. The main cause is anthropogenic emissions of greenhouse gases, the principal one being carbon dioxide, released in the atmosphere as a by-product of the combustion of hydrocarbons for the generation of energy. Carbon capture and storage (CCS) is a technology that would prevent carbon dioxide from being emitted into the atmosphere by safely sequestering it underground. For so doing, CO2 must be captured at large emission points and transported at high pressure to underground reservoirs, where the gas can be injected and stored for thousands of years to come. During surface transportation, leakages from high pressure facilities would pose a risk to the general public, for carbon dioxide is toxic at high concentrations.
In this study, atmospheric dispersion of carbon dioxide is studied by the usage of software that solves mathematical equations and algorithms simulating the pollutant dispersion. Dispersion models are used to estimate or predict downwind distances covered by toxic concentrations of the pollutant, emitted from sources such as high-pressure transportation facilities within CCS projects. Two modelling tools from two different classes (Gaussian ALOHA 5.4 and Computational Fluid Dynamics PANACHE 3.4.1) have been evaluated against release field experiments using the statistical model evaluation method proposed by Hanna et al. (1993,2004) and Hanna and Chang (2001), and applied for the consideration of the dense gas CO2, released in large amounts due to leakages.
Predictions from the two models have been compared and the limitations of both examined, when dealing with a gas that presents the distinctive physical characteristics of carbon dioxide. The models have been used and compared in simulating representative failure cases within CCS transportation with release parameters taken from the literature. The Computational Fluid Dynamics (CFD) model showed a much higher precision when describing the release of the gas from a HP facility, mainly when dealing with the jet release caused by leakages of any dimensions.
When dealing with the transportation of toxic gases, the magnitude of hazards posed by potential failure events within the transportation system is proportional to the extent of the area covered by toxic concentrations of the gas, when modelling representative leakages. Results of this investigation depict a lowering of the Risk involved in the transportation of CO2 by up to an order of magnitude, when modelling the same releases with CFD tools, instead of the more common Gaussian models.
The European Union recognizes that deployment of CCS for hydrocarbon power generation, in parallel with the production of renewable energies, is the only way to meet the target for temperature stabilization. For its Impact Assessment on CCS, the EU used results from a risk assessment compiled after the utilization of a Gaussian model. In this thesis, a criticism of this choice is put forward, considering that, when introducing the technology to the general public and regional scale administrators, a Risk Assessment derived using results from Gaussian models can over-estimate the risk in a way not favourable to the purpose.
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