The aim of this paper is to provide a non-technical summary of a selected number of publicly released and peer-reviewed studies on carbon dioxide (CO2) distribution infrastructure (networks) as applied to carbon capture and storage (CCS).
CCS consists of four components:
- emissions sources (where CO2 emissions are produced);
- CO2 capture (where a physical or chemical separation process isolates CO2 from other components in the exhaust gas – for which CO2 streams are often differentiated by costs, pressure and purity);
- CO2 transport (moving the captured CO2 from point source to a sink); and
- CO2 storage (where CO2 is injected into a geological formation and subsequently isolated from the atmosphere).
CCS is recognised by the United Nations Framework Convention on Climate Change (UNFCCC) as a technically-legitimate mitigation option, capable of delivering permanent abatement outcomes. It is also recognised as an eligible project level activity in the(CDM). This demonstrates that CCS activities can be readily and systematically institutionalised (and rewarded) in market-based mechanisms, and is internationally accepted as being consistent with the sustainability development requirements of developing countries.
CCS has the potential to deliver one of the largest emissions abatement outcomes of all possible mitigation options in the global challenge of avoiding dangerous levels of climate change. The International Energy Agency (IEA) estimates that CCS could contribute about 20 per cent of the required abatement to hold atmospheric concentrations of 1.to 450 parts per million (ppm) by 2050. The Intergovernmental Panel on Climate Change (IPCC) estimates that CCS could contribute between 15 and 55 per cent of the required abatement by 2100
CCS can also drive negative emissions (removing greenhouse gas emissions from the atmosphere) when combined with carbon neutral energy(such as sustainable biomass) and permanently storing the captured emissions deep in the geological sub-surface.
The primary focus of this paper is on the transport of CO2 by pipeline. Much of the publicly available literature concurs that pipelines will be the most likely option used for transporting a large majority of the gigatonnes of CO2 (GtCO2) that will potentially be required to be captured and stored in the decades to come. This scale of mitigation is considered to be imperative within the context of the global community preserving a carbon budget (the allowable volume of greenhouse gas emissions to be released) that may avoid dangerous levels of climate change.
The paper does not specifically focus on CO2 capture or storage solutions. It recognises however that CO2 will not be transported at scale unless there is a sufficient and reliable source of CO2 as well as sufficient, secure, safe and available long term storage options. These activities will consequently require the establishment of property rights, appropriate regulations governing the long term liability, monitoring, measurement and verification (MMV) of sites, as well as effective compliance regimes across the CCS chain.
In practice, least cost development of an integrated CCS project will depend on the optimal design of all CCS components including:
- capture (number of CO2 sources, volume of CO2, quality of CO2 stream),
- transport (pipeline sizes, flow rates, pipeline siting and distances); and
- storage (the number, type and location of injection wells and the and of the supporting geology).
While the main drivers for investing in CCS can differ across the various components, the decisions of all actors mobilised across the CCS chain (CO2 emitters/capture; CO2 transport operators, and geological storage operators) will necessarily impact on each other.
Pipelines can transport large volumes of CO2 at high pressures and through relatively small diameter pipes. The CO2 gas being moved must first be transformed to a Diagram 1). The transition to a dense phase also reduces the volume of CO2 by many orders of magnitude (see Diagram 2).– also referred to as a supercritical fluid – where it behaves like a compressible liquid (see
Diagram 1: Dense phase of CO2
Diagram 2: Volume of CO2
The resulting CO2 stream lends itself to being easily transported by pipelines over long distances due to its relatively low friction on a per unit mass of CO2 basis, with a density of between 500~900kg/m3.
CO2 can also be transported by the use of trucks, ships and barges similar to those used for Liquefied Natural Gas (LNG) and Liquefied Petroleum Gas (LPG). While literature generally views these options as viable, they are considered to be relatively costly for large-scale movements of CO2. This may have as much to do with their limited transport capacity relative to the amount of CO2 needing to be moved, as it does the accessibility of transport options linking the CO2 needing to be captured to the sinks being targeted.
Box 1 provides a hypothetical example of the scale of the commercial volume of CO2 that may need to be moved between CO2 sources to permanent storage sites in 2050. The daily volume of CO2 needing to be handled could be some 2.5 times the current volume of oil being produced and transported. An important consideration is however the average distance required to move the CO2 relative to oil, which some surveys suggest could be much shorter.
Box 1 – Volume of CO2 versus oil
Assuming that supercritical CO2 has a density of 700 kg/m3, 8.27 GtCO2 a year needs to be captured and permanently stored (as per IEA Blue Map scenario), and the global daily oil production is 80 million barrels, then the following calculations hold true:
Calculation: M Bonner, Global CCS Institute.
While the design and operation of CO2 pipelines is often considered similar to that of natural gas pipelines, there are differences between them. A major difference is that CO2 is normally transported as a supercritical fluid. To maintain its supercritical state, the CO2 is transported at very high pressures ranging from 1,800 to 2,700 pounds per square inch (psi) or equivalently about 12,400 to 18,600 kilopascals (kPa). These pressures tend to be higher than the operating pressures used in most natural gas pipelines, which can typically range between 200 to 1,500 psi (or 1,380 to 10,340 kPa). This means that booster stations (pumps) are needed along the pipeline route to maintain the necessary pipeline pressure. The increase in pressure of these CO2 pipelines also typically requires thicker walled pipes than that used for natural gas transportation.
It is clear that the development of CO2 networks can build upon already extensive technical, operational and regulatory experiences of the natural gas and CO2 pipelines used for EOR. As illustrated, the scale of the CO2 needing to be transported for geological storage projects will however be very much larger.
When compared to the literature available on CO2 capture and storage, there is less analytical work available on CO2 pipelines including an examination of size, configuration, commercial structures and regulations of national pipeline systems. This could reflect a general perception among the CCS community that CO2 transport-related issues are not considered major barriers to a critical deployment path for CCS at this time.
Outside of the US,and Norway, existing worldwide experience of CO2 pipelines is relatively limited. In the US, there is over 6,000 km of dedicated pipelines transporting between 45 MtCO2 and 55 MtCO2 per year from natural and anthropogenic sources.
A recent study states for CO2 pipelines that there is “... no need for innovation on a component level, [and as such] the assessment of CO2 transport will have a different character than that of the capture and compression parts of CCS.”2
In 2005, the IPCC’s Special Report on CCS concluded that “there is no indication that the problems for CO2 pipelines are any more challenging than those set by hydrocarbon pipelines in similar areas or that cannot be resolved.”3
While it may be generally true that CO2 distribution networks present fewer hurdles to the wide-scale deployment of CCS than capture processes and/or storage solutions, this component is far from simple and lends itself to many complex considerations of design, planning, and operation.
There are four major challenges affecting the development of CO2 pipeline infrastructure.
- Engineering design, including:
- an increasing need to transport CO2 over longer distances for storage purposes and across ever more challenging terrains (e.g. closer to urban centres and offshore);
- the physico-chemical properties of CO2 streams derived from capture processes — CO2 streams from pre and post-combustion capture plants will likely have varying levels of impurities such as solid sulphur or liquid water that not only affect behaviour, but may also require an increasing complexity of design compared to existing CO2 pipelines for (EOR) purposes;
- matching CO2 supply (capture) with demand (storage) – the amount and quality of CO2 supplied from power and industrial sources are likely to be highly variable at any point in time, which will necessitate careful operational management of CO2 flows to avoid phase changes within the pipeline; and
- pipeline operations will, by their very nature, involve dynamic flows over irregular periods (from seconds to weeks) for reasons like routine start-up or maintenance and seasonal variations – this requires balancing and coordinating the technical specifications across the CCS chain.
- Policy and regulatory issues:
- economic regulation and supporting complementary policies;
- optimised network design to meet short and long-term policy objectives, including issues such as financing, increasing capacity over time and flexibility;
- legal barriers, such as restrictions on CO2 transport across jurisdictional borders; and
- regulatory models and variations in regimes between jurisdictions.
- The evolution of fit-for-purpose standards, where common entry specifications for CO2 pressures, temperatures and concentrations of impurities may be required where multiple CO2 sources connect to the same pipeline network, and this may subsequently impact on CO2 capture technology choices (including costs of capture, compression and drying technologies needing to be employed).
- Overall cost and capacity of pipeline investments and financing options:
- levelised costs of pipelines; and
- business and finance models consistent with uncertainties in CO2 demand, high capital expenditures, long payback periods, oversized pipes; and limited visibility of future CO2 prices.
This paper is formatted into five chapters:
- Chapter 1 introduces networks and some of the issues affecting their design, construction and operation;
- Chapter 2 explores policy related issues including ownership structures, markets, incentives and other forms of government interventions;
- Chapter 2 also identifies important standards that may guide network design and construction;
- Chapter 3 looks at the economics of networks, including levelised costs, relative cost components, network optimisation, and financing arrangements;
- Chapter 4 examines key regulatory elements that can affect the social licence to construct and operate a network; and
- Chapter 5 consolidates areas of agreement.