Climate change has been attributed to greenhouse gases with carbon dioxide (CO2) being the major contributor. Most of these CO2 emissions originate from the burning of fossil fuels (e.g. power plants). Governments and industry worldwide are now proposing to capture CO2 from their power plants and either store it in depleted reservoirs or saline aquifers (‘Carbon Capture and Storage’, CCS), or use it for ‘Enhanced Oil Recovery’ (EOR) in depleting oil and gas fields. The capture of this anthropogenic (man made sources of CO2) CO2 will mitigate global warming, and possibly reduce the impact of climate change. The United States has over 30 years experience with the transportation of carbon dioxide by pipeline, mainly from naturally occurring, relatively pure CO2 sources for onshore EOR. CCS projects differ significantly from this past experience as they will be focusing on anthropogenic sources from major polluters such as fossil fuel power plants, and the necessary CO2 transport infrastructure will involve both long distance onshore and offshore pipelines. Also, the fossil fuel power plants will produce CO2 with varying combinations of impurities depending on the capture technology used. CO2 pipelines have never been designed for these differing conditions; therefore, CCS will introduce a new generation of CO2 for transport. Application of current design procedures to the new generation pipelines is likely to yield an over-designed pipeline facility, with excessive investment and operating cost. In particular, the presence of impurities has a significant impact on the physical properties of the transported CO2 which affects: pipeline design; compressor/pump power; repressurisation distance; pipeline capacity. These impurities could also have implications in the fracture control of the pipeline. All these effects have direct implications for both the technical and economic feasibility of developing a carbon dioxide transport infrastructure onshore and offshore. This paper compares and contrasts the current experience of transporting CO2 onshore with the proposed transport onshore and offshore for CCS. It covers studies on the effect of physical and transport properties (hydraulics) on key technical aspects of pipeline transportation, and the implications for designing and operating a pipeline for CO2 containing impurities. The studies reported in the paper have significant implications for future CO2 transportation, and highlight a number of knowledge gaps that will have to be filled to allow for the efficient and economic design of pipelines for this ‘next’ generation of anthropogenic CO2.

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Carbon Capture and Storage (CCS) is recognised as having a significant role to play in reducing carbon dioxide emissions and tackling climate change. In CCS schemes, carbon dioxide is captured from anthropogenic sources and transported to suitable sites either for EOR (Enhanced Oil Recovery) or storage. Globally, the largest source of CO2 is from power generation, therefore the initial projects proposed for CCS in the UK are from power plant. There are various technologies for capturing CO2 from power stations, however the captured CO2 can contain significant amounts of impurities. The presence of the impurities in the CO2 stream has an effect on the requirements for pipeline transportation and can change such factors as the flow properties, the decompression characteristics and the solubility of water in the mixture. Although transport of CO2 by pipeline is not new technology, and has been implemented in the USA for over 30 years, the effect of these impurities is not fully understood. The UK is in the advantageous position of having natural sinks for CO2 available offshore in the North and Irish Sea, which can be used for either EOR or storage. Therefore CCS implementation in the UK will involve transport of anthropogenic carbon dioxide from power stations to offshore sinks. All of the current experience with CO2 pipeline transport has been onshore, predominantly from near pure natural sources and therefore this is also a new challenge. This state-of the-art review paper will: • discuss the key technical factors presented by the transport of CO2 from power plant, including the effects of impurities on the design and operation of pipelines, • compare and contrast the current experience of transporting CO2 onshore with the proposed transport onshore and offshore in the UK and identify the technical and regulatory challenges, • present the results of initial modelling work to demonstrate the effects of the key variables on the development of a CO2 transport system in the UK.

Climate change has been attributed to green house gases, with carbon dioxide (CO2) being the main contributor. Sixty to seventy percent of carbon dioxide emissions originate from fossil fuel power plants. Power companies in the UK, along with oil and gas field operators, are proposing to capture this anthropogenic CO2 and either store it in depleted reservoirs or saline aquifers (carbon capture and storage, CCS), or use it for ‘Enhanced Oil Recovery’ (EOR) in depleting oil and gas fields. This would involve extensive onshore and offshore pipeline systems. The decline of oil and gas production of reservoirs beyond economic feasibility will require the decommissioning onshore and offshore facilities post-production. This creates a possible opportunity for using existing pipeline infrastructure. Conversions of pipelines from natural gas service to CO2 service for EOR have been done in the United States. However, the differing sources of CO2 and the differing requirements for EOR and CCS play a significant part in allowing the re-use of existing infrastructure. The effect of compositions, the phase of transportation, the original pipeline specifications, and also the pipeline route require major studies prior to allowing re-use. This paper will first review the requirements for specifying the purity of the CO2 for CCS and to highlight the implications that the presence of impurities and the current water specifications for pipelines has on the phase diagram and the associated physical properties of the CO2 stream. A ‘best’ and ‘worst’ case impurity specification will be identified. Then an analysis on the impact and subsequent validation, of equations of state based on available experimental data on the phase modelling of anthropogenic CO2 is presented. A case study involving an existing 300km gas pipeline in the National Transmission System (NTS) in the UK is then modelled, to demonstrate the feasibility of using this pipeline to transport anthropogenic CO2. The various issues involved for the selected ‘best’ and ‘worst’ case specification are also covered. This is then followed by an investigation of the options for transport in the ‘gas’ phase and ‘supercritical’ phases, and also identifying the limitations on re-using pipeline infrastructure for CCS.

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