Development of safe and reliable operations in large-scale CO₂ shipping: an experimental approach.

A successful worldwide implementation of Carbon Capture, Utilisation and Storage largely relies on the establishment of a safe and reliable CO₂ transmission network. CO₂ shipping hereby represents a promising transport option, characterised by a high degree of flexibility in sink-source matching. This study addressed some key knowledge gaps that currently pose a limitation on large-scale commercialisation of this technology by providing information on operational and maintenance challenges in the chain. Firstly, an extensive review of technological advancements and future projections in large scale CO₂ shipping drew the attention to the fact that key technical challenges still need to be addressed in both pipeline and sea vessel systems in order to establish a worldwide network of CO₂ transport infrastructure. In particular, significant dearth concerns the adoption of appropriate safety protocols during accidental scenarios and selection of suitable materials to ensure integrity of transport infrastructure throughout real operations. Thus, an experimental lab scale rig was built and commissioned, capable of handling refrigerated carbon dioxide batches (up to 2.25 L) at conditions typical of sea vessel transport (~0.7 - 2.7 MPa, 223 - 259 K); the facility was designed to permit investigation of accidental leakage behaviour and to determine the qualification assessment of elastomer materials exposed under real shipping conditions. A technical qualification of elastomer materials for CO₂ transport systems was then performed with the aim of assessing their suitability in the intended systems and propensity for degradation. Such elastomers are used as seals in pressure- relief valves, providing elastomer-to-metal shutoff and eliminating leakage around stem during relief mode. Samples previously tested under pipeline conditions (9.5 MPa, 318 K) at exposure times of 50 – 400 h were characterised for a visual inspection, mechanical and thermo-analytical properties. Based on the suitable performance of the elastomers under such pipeline conditions, Ethylene Propylene Diene Monomer was selected for testing under operations typical of CO₂ shipping; constrained (25% compression) samples thereby underwent 20 – 100 CO₂ loading and offloading cycles at average decompression rates of 1.6 MPa/min; tested materials were then qualified through the aforementioned characterisation methodology, demonstrating a satisfactory resistance to rapid gas decompression and mechanical stability. A detailed experimental campaign was considered to assess the accidental leakage behaviour of CO₂ under shipping conditions; the main risks associated with CO₂ are asphyxiation due to displacement of oxygen to critically low levels, and exposure to concentrations of 15% or above in air are deemed life threating due to toxicological impacts on humans. The study highlighted that selection of initial fluid conditions significantly affects the propensity for solid formation in the vessel and blockages in the pipe section, thus resulting in significantly diverse leakage behaviours. Low-pressure decompression tests (0.7 – 0.94 MPa) resulted in the highest amount of inventory solidification (36 – 39 wt%) while high- pressure decompression scenarios (1.8 – 2.65 MPa) demonstrated the lowest (17 – 22 wt%). Lastly, a real-scale investigation on liquid CO₂ discharge from the coupler of an emergency release system was undertaken in order to scrutinise the applicability of such spillage containment measure to CO₂ shipping operations. The study focused on two refrigerated states, namely low- (0.87 – 0.94 MPa, 227 – 231 K) and medium-pressure conditions (1.62 – 1.65 MPa, 239 – 240 K) typical of shipping transport; findings demonstrated the presence of an abrupt outflow behaviour, characterised by full inventory discharge form the coupler in less than 1 s and achievement of peak depressurisation rates of 6 MPa/s. Moreover, the discharge behaviour showed considerable variations in relation to the selected initial conditions.PhD in Energy and Powe

A review of large-scale CO2 shipping and marine emissions management for carbon capture, utilisation and storage

Carbon Capture, Utilisation and Storage (CCUS) can reduce greenhouse gas emissions for a range of technologies which capture CO2 from a variety of sources and transport it to permanent storage locations such as depleted oil fields or saline aquifers or supply it for use. CO2 transport is the intermediate step in the CCUS chain and can use pipeline systems or sea carriers depending on the geographical location and the size of the emitter. In this paper, CO2 shipping is critically reviewed in order to explore its techno-economic feasibility in comparison to other transportation options. This review provides an overview of CO2 shipping for CCUS and scrutinise its potential role for global CO2 transport. It also provides insights into the technological advances in marine carrier CO2 transportation for CCUS, including preparation for shipping, and in addition investigates existing experience and discusses relevant transport properties and optimum conditions. Thus far, liquefied CO2 transportation by ship has been mainly used in the food and brewery industries for capacities varying between 800 m3 and 1000 m3. However, CCUS requires much greater capacities and only limited work is available on the large-scale transportation needs for the marine environment. Despite most literature suggesting conditions near the triple-point, in-depth analysis shows optimal transport conditions to be case sensitive and related to project variables. Ship-based transport of CO2 is a better option to decarbonise dislocated emitters over long distances and for relatively smaller quantities in comparison to offshore pipeline, as pipelines require a continuous flow of compressed gas and have a high cost-dependency on distance. Finally, this work explores the potential environmental footprint of marine chains, with particular reference to the energy implications and emissions from ships and their management. A careful scrutiny of potential future developments highlights the fact, that despite some existing challenges, implementation of CO2 shipping is crucial to support CCUS both in the UK and worldwid

Corrosion of potential first stage blade materials in simulated supercritical CO2

Global power consumption is predicted to double by 2050, notably driven by the transportation and energy sectors necessitating limitations of emissions. Due to its compact turbomachinery, better thermal efficiency, and simpler layout, supercritical-CO2 cycles have received attention, with numerous variations proposed (either indirect-fired/closed cycles or direct-fired-open cycles). One technical challenge is degradation pathway quantification of turbine materials in sCO2 as selection is crucial to successfully and economically operate new plants. This requires degradation assessment in representative environments simulating the Allam cycle. Laboratory tests were conducted on a first stage turbine blade alloy, CM247, with either an environmentally resistant coating or bond coat/thermal barrier coat at one atmosphere and 800°C, with potential exposure including (O2, H2O, N2, SO2) for up to 1000 h. Weight change and metallographic measurements tracked scale development. Scanning electron microscopy/energy dispersive X-ray spectroscopy studied scales and internal precipitates. Locations of contaminant element in the CO2-rich environment were investigated

Experimental study of accidental leakage behaviour of liquid CO2 under shipping conditions

CO2 shipping is a viable transport alternative when pipelines are impractical. Lack of experience in large-scale CO2 shipping projects implies uncertainty in selecting optimal cargo conditions and operational safety procedures. The risk of uncontrolled release of CO2 arises in case of mechanical failure of storage or cargo vessels, and a thorough understanding of the discharge phenomena, including the propensity for solid formation, is necessary to develop safety protocols. A refrigerated experimental setup is established in this study to investigate the release phenomena of liquid CO2 under shipping conditions. The rig features a dome-ended cylindrical pressure vessel, a discharge pipe section and a liquid nitrogen refrigeration system that enables conditioning near the triple point – at ∼0.7 MPa, 223 K - and higher liquid pressures (∼2.6 MPa, 263 K). Pressure, temperature and mass monitoring were considered to enable an extensive observation of the leakage behaviour under typical operation scenarios. Three different sets of experiments were considered to inform the designer in the selection of optimal process conditions, with low-pressure (0.7 – 0.94 MPa, 223–228 K), medium-pressure (1.34–1.67 MPa, 234–245 K) and high-pressure tests (1.83–2.65 MPa, 249–259 K) demonstrating distinct behaviours relative to phase transitions, leakage duration and solidification of inventory

Real-scale investigation of liquid CO2 discharge from the emergency release coupler of a marine loading arm

Carbon capture, utilisation and storage has been recognised as a necessary measure to reduce greenhouse gas emissions. CO2 shipping represents a promising transportation option that offers flexible sink-source matching to enable decarbonisation at a global scale. In order to implement safe and reliable loading and offloading operations at the terminal, marine loading arms require the integration of emergency release systems in the event of sudden movement of the ship away from the berthing line. In this study, a cryogenic test facility was constructed to handle CO2 in proximity of the triple point (∼0.9 MPa[abs] – 1.7 MPa[abs], 227 K - 239 K) and replicate the principles of an emergency release coupler during a shutdown, with the aim of investigating the CO2 discharge and dispersion behaviour, and determining the implications on coupler design and safety protocols. Findings show that separation of the test vessel leads to an abrupt discharge of the liquefied CO2 inventory and several phase transitions within 0.6 s of the start of the discharge in all tests. The clouds disperse in a ‘tulip’ shape that could be clearly observed from afar, and generation of carbon dioxide solids was observed on the vessel surface in all performed tests, bringing the temperature inside the vessel to approximately 190 K. The implementation of protective barriers is expected to reduce the impact of the release, though the risk of asphyxiation or cryogenic burns to surrounding personnel cannot be ruled out given the magnitude of the discharge process