Materials for Next Generation CO2 Transport Systems

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BACKGROUND

The pipeline transport of CO₂ is a fundamental technology that will underpin a large proportion of future CCS (Carbon Capture and Storage) applications. The key problem is how to transport huge volumes of anthropogenic CO₂ in a safe and energy efficient manner from its source to its final storage point. This has never been attempted before anywhere in the world and the scale of the undertaking presents some key scientific challenges which need to be resolved immediately to allow timely implementation of CCS. So there is a real opportunity for the UK to take a lead.

The MATTRAN consortium has the interdisciplinary expertise from molecular level CO₂ to large scale fracture propagation which can deliver the science and engineering knowledge to address this problem. The current generation of CO₂ pipelines have been operational for over 30 years, mainly in the United States, transporting high pressure CO₂ for onshore EOR (Enhanced Oil Recovery) across sparsely populated terrain. The CO₂ stream in these pipelines is largely from natural sources of CO₂ and the purity is high as it is governed by the requirements of the EOR process. The next generation of CO₂ pipelines will be directed at climate change mitigation. In the UK this means designing and constructing a transport system for the collection of CO₂ from disparate anthropogenic sources, predominantly power plant, and transporting it under supercritical conditions through more densely populated areas for offshore storage.

Although there are many challenges to be tackled to enable the establishment of this CO₂ transport infrastructure, MATTRAN addresses the research needs required to define the CO₂ stream composition and the consequent impact of this composition on the pipe specification in terms of material choices and allowable operational envelopes. As the current generation of CO₂ pipelines are not operating under the same service conditions, the research base to enable these decisions to be made has not been established and the application of existing technology and understanding to these new conditions may not be appropriate. Consequently research is required immediately to ensure that any issues identified can be resolved rapidly and efficiently and to prevent transportation from becoming a bottleneck in the implementation of CCS.

THE MATTRAN PROJECT

It is recognised that there is currently no standard definition for the composition of the CO₂ stream expected from the different capture processes. Small levels of constituents can play a large role in the phase behaviour, thermodynamic properties and solubility of water in the supercritical CO₂ stream. The first tasks in the project are therefore to determine the expected ranges of compositional variation and conduct the necessary phase experiments in the supercritical range to characterise the behaviour of a selected subset of the CO₂ streams judged to have the biggest impact. This experimental data will be used to address another gap in the existing knowledge on supercritical CO₂ process streams, the prediction of the phase behaviour and thermodynamic properties using existing equations of state. Currently there is no consensus in the literature regarding which equation of state provides the most accurate predictions in the supercritical range. This presents a problem for pipeline engineers in modelling the hydraulic behaviour of the CO₂, both in the pipeline and in the event of an accidental or controlled release. In this project, the experimental data will be compared with existing equations of states and new models developed and provided to the hydraulic and fracture propagation models that will be used in the interconnected Work Packages.

The remaining Work Packages involve the specification of the pipeline and associated equipment materials to determine the conditions under which corrosion, stress corrosion cracking and fracture propagation will occur. Once the constituents in the CO₂ stream have been selected, experiments investigating corrosion, stress cracking and fracture propagation will be conducted. This database of experimental data does not currently exist and without this data, the operating conditions of the pipeline and the property requirements of the materials cannot be safely defined.

RELEVANCE TO BENEFICIARIES

In its widest sense, the Government and the general population of the UK and beyond are beneficiaries of the output from MATTRAN because CCS is playing an increasingly important role in UK energy policy and CO₂ transport plays an essential pivotal role in the process. CO₂ transport itself cannot be safely, effectively and economically implemented in an environmentally acceptable manner without resolving the issues raised by the MATTRAN research programme.

More explicitly, the project will benefit regulatory bodies, such as British Standard committees and the HSE who require knowledge of the material properties of the CO₂ stream and its interaction with the transport infrastructure and the environment to develop design codes and safety regulations. The resolution of such issues in close compliance with HSE’s requirements are key elements of the UK Government’s BERR competition for a full scale demonstration of post combustion CCS. In addition pipeline engineers and designers require MATTRAN output to develop a robust infrastructure constructed of appropriate materials transporting a CO₂ stream of known properties and characteristic behaviour in an operationally effective manner. These factors are a pre-requisite for public acceptability and so policy makers will also benefit. In the UK there is a shortage of the skills and knowledge required to implement a large scale CO₂ transportation infrastructure.

The MATTRAN dissemination work package is designed for rapid technology transfer targeted specifically at those bodies where such knowledge is most required. The programme also brings new academic members, over a range of disciplines, to the field of CCS and will benefit the academic community by an increase in activity in areas that have not previously been researched and a concomitant expansion of knowledge and data. The CO₂ transport community in general, both in academe and industry, will benefit from their interaction at MATTRAN conference/workshops and through the informal network to be established.