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6| CO 2 transport options between sources and storage sites
Successful implementation of CCS in Scotland will require a suitable transport network for CO 2.
This study examined options for transporting CO 2 between the sources and storage sites identified. Various onshore and offshore routes and technologies were examined. The latest UK and international codes and standards applicable to CO 2 pipelines were used.
Table 11
Source categories defined as Tiers with examples.
Tier | Source category | Source size (Tonnes CO 2/year) | Examples |
|---|
0 | Large | > 1 million | Coal fired power station, hydrocarbon refinery, major chemical works |
1 | Medium | 50,000 to 1 million | Chemicals, glass, food manufacturers, large Combined Heat & Power ( CHP) & Combined Cycle Gas Turbines ( CCGT's) |
2 | Small | 1,000 to 50,000 | CHP units, incinerators, small to medium industrial works |
Sources were categorised according to their output per year (Table 11). The tiers provide some indication of the potential for applying a CCS solution at each level and are linked to emission allowances allocated under the European Union Emissions Trading Scheme. Large (Tier 0) sources are recognised as the primary focus for any CCS scheme as the cost of allowances under European Union Emissions Trading Scheme should make it more economical to store the carbon than to pay for or trade any excess over the emission allowance. The CO 2 transportation network will be built around these centres. Medium (Tier 1) sources may be less economically suited to a CCS solution. Their location is likely to determine whether they are included in the network. For instance, offshore installations (Medium (Tier 1) sources that produce in total 23.7 Mt/year of CO 2) are not included in the example network discussed below. It is unlikely to prove either practical or economic to include most small (Tier 2) sources in a CCS scheme.
All large Scottish sources are located along the Firth of Forth except the gas-fired power station at Peterhead. Several medium sized (Tier 1) clusters could feasibly be associated with the large sources. For example, St Fergus Gas Terminal naturally links to the large Peterhead source and plants at Stirling and Mossmorran to the large Longannet power station (Figure 4). Future projects, such as replacement of power generation at the Hunterston Nuclear site, were not added to CO 2 volumes but network access was modelled, and replacement of existing plant was included.
6.1 Network design
A well-developed oil and gas pipeline transport infrastructure is present throughout the onshore UK and the offshore UK Continental Shelf. Parts of this infrastructure may become available for re-use and potentially could be used to transport CO 2. For example, a previous proposal demonstrated that the pipeline from the vicinity of Peterhead to the Miller field is technically capable of carrying a substantial volume of CO 2. It could well form a key element in any future offshore CO 2 pipeline network and the potential for its use in this context should be examined in detail as a priority. However, re-use of onshore and offshore pipelines raises major issues related to change of use in areas of planning, capacity and safety, in addition to various technical questions. Assessing the possibility of re-using each pipeline for CO 2 transport would require a line by line analysis and is beyond the scope of this study. However, in broad terms, and dependant upon pipelines becoming available, offshore pipelines are more likely to be suitable for re-use, whereas onshore, the potential for re-use will be more restricted. Importantly, sections of the onshore National Transmission System ( NTS) could be used as part of a start up or phased approach while gas flow is low. Thus, taken together, use of existing onshore and offshore pipelines may be viable for the small volumes (~3Mt/year) of CO 2 required for a demonstration project.
The design of a network for Scotland's CCS system therefore reflects the location of the key large (Tier 0) emitters, all but one clustered around the Firth of Forth, and the various CO 2 storage options in the Scottish defined offshore area. These groupings and the distances between them naturally suggest an approach consisting of source hubs connected by a transport spine to storage hubs. The presence of a hub near several storage sites allows a variety of storage technologies (saline aquifer, depleted hydrocarbon field or CO 2- EOR) to be pursued as opportunities permit, thereby lowering risk. Four storage hub locations were chosen to permit examination of relative transport costs between various areas and the effect of various assumptions about the re-use of existing infrastructure. The storage hubs are named after local oil fields (Captain, Dunbar, Brae and Gannet; Figure 16) and are not necessarily optimal.
6.2 Transport options
The viability of transport by pipeline and ship were both assessed. Pipeline design is a complex issue with many factors affecting the building of this infrastructure. A CO 2 pipeline system must be able to accommodate the full range of conditions from fast ramp up rates and shut-downs of power stations and the closure of geological storage sites. It must accommodate varying flows, surges and variations in composition of the CO 2 fluid itself. Key issues unique to CCS are:
- chemical and physical properties of the CO 2 including any impurities within the CO 2 stream;
- consideration of pressures, to maintain the CO 2 in the required phase throughout the network without exceeding safe levels at other points;
- legislation specific to CO 2 including UK Health and Safety requirements and international codes of practice.
A pipeline operating pressure above 100 bar is desirable with a minimum pressure of 90 bar in order to prevent phase change within the pipe. This maintains the CO 2 well above its critical point pressure of 73.9 bar. This pressure margin also allows for a degree of contamination of the CO 2 stream.
Although elements within the National Transmission System onshore pipeline system may be available and suitable for use within a CO 2 pipeline network, this possibility was not considered within the economic assessment discussed below.
In terms of the technical and economic viability of transporting CO 2 by ship, this study focussed on transport of captured CO 2 from a location in the Firth of Forth to the Peterhead area (Figure 16). The assessment was limited to vessel access, berthing and ship support services only. No account was taken of any specialist storage tanks, pressure and cooling systems necessary for loading and discharge of the CO 2. Note that, to minimise disruption to the capture process, storage tanks should be sufficient to allow 50% redundancy over and above the ship's cargo capacity.
The model for costs of transport by ship assumes newly designed vessels of 18,000 m 3 capacity, total cargo pumping rate of 1,500 m 3/hr, no waiting on tides, and that discharge occurs in Peterhead Harbour (although discharge at an offshore location would considerably reduce overall harbour costs). A fleet of four vessels would allow in excess of 13.5 Mt of CO 2 to be transported per year. Transportation cost would be in region of £4.57 per tonne. The capital cost for the vessels, whether new build or converted, has not been included in the cost model. In the final analysis, five possible transport options, each with the same offshore storage hubs, were identified and costed. Options for transporting CO 2 from the Tees/Tyne area were also assessed (Table 12).
Table 12
Summary of possible transport options identified through consideration of the locations of CO 2 sources and potential storage sites.
Network Option
1-Peterhead to Forth (Longannet) onshore pipeline
2-Forth to Peterhead onshore pipeline
3-Forth (Longannet) with offshore pipeline route to Peterhead
4-Full network
5-Shipping from Forth to Peterhead hub
6-Tyne/Tees direct to offshore storage hubs
Assessment of transport options
Assessment of the five pipeline and shipping options for transportation of CO 2 shows that they are within the scope of costs for a major infrastructure project.
The option using ship transport, a 'floating pipeline', is feasible and may be comparable to pipeline options in terms of capital cost, but with up to four times higher operating expense.
A more detailed examination would be required to accurately differentiate between the onshore and offshore routes from the Forth to Peterhead (options 2 and 3).
This appraisal does not consider a phasing of the construction of the network but assumes a relatively quick build-up to full capacity due to the small number of large sources.
Figure 16
Summary of proposed CO 2 transportation routes.
The implications of importing CO 2 from areas outside Scotland were investigated by examining the route from the Tees-Tyne area to storage sites offshore Scotland (Option 6). Linking directly into a pre-existing network within Scotland would be costly in terms of both capital and operating costs, not least because pipelines are complex systems. This study suggests that multiple feeder pipelines from the onshore clusters to the offshore storage sites is likely to offer a more cost-effective solution with CAPEX ranging from £1.4 to £2.3 billion and OPEX ranging between £27.5 to £53.5 million depending on storage hub destination. Whilst this introduces complexity into storage management, it allows for much more flexibility in phasing construction and operations.
Figures 17 & 18 show the costs of the various options. Option 2 (onshore pipeline) forms the lowest cost option in terms of capital expense ( CAPEX) for all offshore hubs and the lowest cost option in terms of operating expense ( OPEX) for all except the Gannet hub where Option 3 (offshore pipeline) is slightly less. Captain is the lowest cost target for Option 2. The overall costs of Options 2 and 3 are comparable. Option 3 is slightly more expensive, but constitutes a viable alternative to an extensive onshore pipeline. Option 1 (principal pipeline from the Forth to the offshore hubs) and Option 4 (full network) are more costly than either Option 2 or Option 3. The capital costs of shipping Option 5, are comparable with those of the other options, but the high operating costs and risks suggest that it is unlikely to prove a viable long term solution.
Figure 17
Capital expenditure for the five CCS network options investigated for each offshore hub (in £ Billion).
Figure 18
Operational expenditure for the five CCS network options investigated for each offshore hub (in £ Million per year).
CO 2 transport options between sources and storage sites - key conclusions
- Five network options, linking CO 2 source and storage hubs have been identified and a technical and economic assessment undertaken.
- A sixth option, importing CO 2 from NE England was also investigated. Here, multiple feeder pipelines to offshore hubs are likely to form a more appropriate means of accepting additional CO 2 from NE England rather than attempting the technically complex option of connecting directly into a pipeline network within Scotland.
- Some re-use of facilities is possible, especially in the early stages of CCS projects.
- The potential for using the Peterhead to Miller pipeline and the National Transmission System infrastructure as a key element of a Scottish CO 2 pipeline network should be examined in detail.
- A pipeline network used to transport 20 million tonnes/year of CO 2 from sources to the storage hub at CAPEX costs of £0.7 to £1.67 billion and OPEX costs of £38 to £74 million depending on hub location and excluding the shipping option. OPEX for shipping ranges from £148 to £171 million depending on hub location.
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