|Figure 1: CO₂ pipeline being laid in the US. Ogeechee River Keeper, 2015|
|Dispersion modelling techniques for CO₂ pipelines in Australia|
|By Dr David McManus, Research Investment Manager, BCIA|
|Effective deployment of carbon capture and storage (CCS) infrastructure in Australia will require pipelines to transport compressed CO₂ from the point of capture to the point of storage. While Australians are generally familiar and comfortable with the presence of natural gas pipelines, pipelines for CO₂ are less well known locally. David McManus outlines BCIA’s|
recent report on CO₂ dispersion modelling.
Although hundreds of miles of CO₂ pipelines have been built in the US, and planning for such infrastructure is well understood there, Australia has different regulations and to allow a pipeline to be built, strict risk assessments must be taken. The unplanned release of gas from a pipeline, and its subsequent dispersal into the atmosphere, is one of the major risks.
To assist in the planning of CO₂ pipelines in Australia, BCIA has supported the development of a report investigating the suitability of available gas dispersion modelling tools for use in Australian CO₂ pipeline permitting. Natural gas pipelines in Australia must conform to the design and risk management approach set out in Australian Standard 2885 ‘Pipelines – Gas and liquid petroleum’. Any new pipeline will also be designed using this Standard, but the methods for assessing the consequences of a gas release are not clearly specified.
One of the most important differences between natural gas and CO₂ is that natural gas is lighter than air, while CO₂ is heavier. In any event where gas is released from a pipeline, the dispersion of CO₂ into the atmosphere will be markedly different than the behaviour of natural gas.
Another important difference is that natural gas is highly flammable and explosive, while CO₂ is not. However, CO₂ is an acidic gas that can cause a pH imbalance in the bloodstream, with the physiological consequences depending on the dose and duration of the exposure. These two key differences mean that the consequence analysis tools used for natural gas pipeline design are not applicable to CO₂ pipelines. In order for a CO₂ pipeline to be designed in accordance with Australian Standard 2885, appropriate modelling tools need to be identified, especially for reliable simulation of release and dispersion of CO₂ into the atmosphere.
BCIA has supported a recently-completed project that investigated the application of CO₂ dispersion modelling in the context of new CO₂ pipeline infrastructure in Australia. The project was conducted in two stages, with the first led by Ramboll Environ Australia and the second by Sherpa Consulting.
Valuable international input was gained through technical contributions from Dr Stephen Hanna, an eminent expert in dense gas dispersion modelling, and through a critical review by Dr Simon Gant of the UK Health and Safety Laboratory, who was involved in recent European CO₂ release projects. Funding for the project was provided by the Victorian government through DEDJTR and by the Commonwealth through ANLEC R&D.
|The investigation considered a series of modelling tools that may be regarded as ‘fit for purpose’ for simulating the dispersion characteristics of CO₂ gas. The assessment was based on a number of criteria.|
- Availability, ease of use, access to technical support.
- Ability to calculate appropriate source terms for different CO₂ release scenarios.
- Validation history, particularly with CO₂.
- Ability to account for complex terrain and variable atmospheric conditions.
- Applicability to different stages of the design process.
- Acceptability to Australian regulators.
|Modelling of a release of dense phase CO₂ from a pipeline requires consideration of a number of aspects, including transient pipeline depressurisation, multi-phase jet release, and dispersion of both dense and neutral gas.|
|Figure 2: New CO₂ pipeline construction in US. BlackHawk Construction, 2014 (http://blackhawkus.com/pipeline- construction/).|
|Appropriate models that can be used for each of these aspects were identified.|
A range of dense gas dispersion models were investigated, including empirical correlations, integral models, Lagrangian particle and plume dispersion models and computational fluid dynamics (CFD) models. Selected models were reviewed and evaluated against the various criteria to determine if they could be considered ‘fit for purpose’.
One of the main conclusions from this project was that sufficient information and modelling tools are available to allow a new CO₂ pipeline to be designed in accordance with Australian Standard 2885. The project deliverable was a comprehensive report that provides guidance on the current international best practice in modelling CO₂ dispersion, and identifies appropriate, fit-for-purpose modelling tools that can be used at different stages in the pipeline design process.
The final report(1) has been made available to the public and is useful to both pipeline designers and regulatory authorities. The guidance provided in this report will allow the risks associated with new CO₂ pipelines to be reduced to as low as reasonably practicable, equivalent to the community expectations for natural gas pipelines.
(1) Sherpa Consulting, 2015. Report is available through the Global CCS Institute website. To download please click 'Download the document' on left of screen.