The Status and Challenges of CO 2 Shipping Infrastructures

Efficient CCS at an industrial scale depends on CO2 capture from large point sources and transfer to secure geological storage sites. As this technology option expands, onshore pipeline networks will be necessary to deliver the volumes envisaged. However, this may not necessarily be the most favourable option offshore and shipping could offer a more flexible and economic alternative. Although liquefied CO2 is currently transported by sea tankers, it is a relatively modest trade and in comparatively small quantities of around 2,000 tonnes. A number of recent initiatives are developing CO2 shipping for CCS in Europe; however, shipping of CO2 at large scale requires consideration of regulatory, technical as well as economic conditions. This study presents a detailed assessment of the CO2 shipping supply chain, specifically considering the physical equipment, related handling infrastructure, operational constraints, projected costs and legal and regulatory issues that govern the marine shipment of CO2. The study included the onshore (at port) infrastructure requirements, CO2 carrying vessels and the unloading requirements. Both onshore unloading (for further transportation by pipeline) and offshore unloading (direct to storage site) are considered. CO2 capture conditions, onshore transport to the port and the final geological storage site are not included in the analysis. The infrastructure components of the CO2 shipping chain broadly consist of: • Liquefaction: CO2 is brought into the liquid state through a series of cooling and compression steps • Intermediate storage: buffer storage is used to bridge the gap between continuous CO2 capture and discrete (batch) transportation by ship • Loading/unloading equipment: Loading/unloading equipment consists of either conventional articulated loading arms or flexible cryogenic hoses and auxiliary equipment such as cryogenic pumps and pipelines for transfer from storage to loading arm and a return line for boil off gas • Ship: either a purpose-built CO2 tanker or converted ship may be used; however, repurposing of ships is challenging if the ship is not also originally designed for carrying CO2 • Conditioning: CO2 must be brought from the liquid state to a condition for further transportation or injection after shipping, typically by heating and pumping Both pressure and temperature affect a large number of the components of the supply chain including material choices, transport volumes and safety considerations. As such, trade-offs between cost and operational complexity must be considered in choosing the most appropriate transport condition. In addition, while processing and handling of pure CO2 streams is well-understood, the presence of water, oxygen and other impurities in CO2 from anthropogenic sources can also have a negative impact on transport and storage applications. Processes to purify the CO2 stream are therefore an integral part of the shipping chain. While the components and processes of onshore unloading are well understood from existing (small-scale) operations, offshore unloading is currently unproven and there is no clear consensus on the most appropriate solution. Whether the CO2 is unloaded by direct injection into the well or via intermediate platform with storage has implications for CO2 tanker design and costs of operation. Importantly, direct injection is necessarily batchwise which brings associated challenges at the storage site. Ship logistics scenarios for three possible future North Sea CCS projects have been defined and used as the basis for cost estimates. These scenarios compare two different pressure conditions for onshore unloading as well as the two different offshore unloading options. Considering only the shipping chain, unloading via a platform has the highest CAPEX and OPEX costs, and the highest overall undiscounted unit cost (€41/tCO2 transported). Direct injection has the lowest CAPEX and OPEX costs but stores the least CO2 for a fixed number of ships (unit cost €32/tCO2). Onshore unloading has the lowest overall unit cost, excluding transport beyond the port (€27/tCO2). Inclusion of a pipeline between the onshore unloading site and the final offshore unloading site is estimated to add a further €5/tCO2 to the total lifetime cost, bringing the costs of onshore unloading close to those of direct injection for the modelled transport conditions. However, it should be noted that an onshore-to-offshore pipeline is likely to be utilised by more than one project, improving the economic viability of this option Technoeconomic modelling based on these estimated costs shows that increasing the ship size and the unloading rate can reduce costs if the number of ships can be reduced. Shipping is more cost-effective than offshore pipelines under conditions of low flow rate and long transport distance. Legal instruments relevant for CO2 shipping are found in international, regional and national frameworks. The most relevant current legal instruments at each level have been reviewed and regulatory gaps and hurdles have been identified within a European-centric focus. Historically, the main regulatory hurdles to CO2 shipping for CCS have been the London Protocol, which prevents cross-border transport of CO2 for storage, and the EU ETS Directive, which excludes CO2 shipping from the greenhouse gas emissions trading scheme and therefore prevents CO2 shipping benefitting from financial incentives of CCS. A resolution to the London Protocol was adopted on 11th October 2019 which implies that this showstopper hurdle is effectively removed from an international perspective; however, it is now up to national declarations to implement the resolution. Contractual arrangements for large scale CO2 shipping have also been considered. An important issue for such contracts is the point of transfer of liability for CO2 leakage between supplier, transporter and storage operator, Such transfers require metering but this has been identified as a cost driver, representing a conflict between legal obligation and cost-effective operation. Resolving this conflict through alternative contractual arrangements may be possible or necessary to consider in future.