Carbon dioxide transport pipeline systems: overview of technical characteristics, safety, integrity and cost, and potential application of digital twin

Carbon dioxide transport from capture to utilization or storage locations plays key functions in carbon capture and storage systems. In this study a comprehensive overview and technical guidelines are provided for CO2 pipeline transport systems. Design specifications, construction procedures, cost, safety regulations, environmental and risk aspects are presented and discussed. Furthermore, challenges and future research directions associated with CO2 transport are sorted out including the large capital and operational costs, integrity, flow assurance, and safety issues. A holistic assessment of the impurities' impacts on corrosion rate and phase change of the transported stream is required to improve pipeline integrity. The influence of impurities and the changes in elevation on the pressure drop along the pipeline need to be further investigated to ensure continuous flow via accurate positioning of pumping stations. Although the long-experience in oil and gas pipeline industry forms powerful reference, it is necessary to develop particular standards and techno-economic frameworks to mitigate the barriers facing CO2 transport systems. Digital twins (DT) have potential to transform CO2 transport sector to achieve high reliability, availability and maintainability at lower cost. Herein, an integrated 5-component robust DT framework is proposed for CO2 pipeline transport systems and the future directions for DT development are insinuated. Data-driven-algorithms capable of predicting system's dynamic behavior still need to be developed. The data-driven approach alone is not sufficient and low-order physics based models should operate in tandem with the updated system parameters to allow interpretation and result's enhancing. Discrepancies between dynamic-system-models, anomaly-detection and deep-learning require in-depth localized off-line simulations.

Impact of CO2 Specifications on Design and Operation Challenges of CO2 Transport and Storage Systems in CCUS

The presence of impurities in captured CO2 plays a vital role in the safe and effective CO2 transport and storage in the CCUS chain. Impurities can significantly increase the cost of processing, transport, and storage and moreover add additional challenges to the design, operation, health and safety and integrity aspects. The effects of various impurities on the aforementioned challenges have been addressed in this work. Despite the importance of this area, there are still some knowledge gaps in terms of assessing the impact of CO2 specification on CCUS design and operations. International standards address different elements of the CCS chain, but none cover the full chain or consider the full chain economics. There are also differences between industry and leading CO2 authorities regarding the potential issues and challenges of implementing those standards. This paper reviews available standards and references which provide specifications/limitations for impurities for the purpose of transport and storage. In this work, the modified cubic EoSs and GERG EoS have been used to predict the thermodynamic properties and tuned viscosity models have been used for the prediction of transport properties. The required specifications for the quality of CO2 streams have been investigated using the above methodology for fluid properties, followed by the use of commercial software packages for thermohydraulic analysis of CO2 pipelines. Additionally, the storage capacity and geochemistry of fluids under high-pressure and high-temperature (HPHT) storage conditions were investigated. The impact of impurities has been assessed based on various CO2 sources using commercial capturing technologies. The assessment considered the impact of impurities on thermodynamic, thermohydraulic, integrity and operation of CO2 transport, injection, and storage system. This would include the effects of various types of components and their typical concentrations, e.g., water content, non-condensable gases (N2, O2, CH4, Ar, H2and CO), toxic gases (H2S and SO2), and hydrocarbons, on the thermophysical properties including density, viscosity, phase envelope and hydraulic parameters. A comparison of modelling results against the available experimental data measured at elevated pressure and temperature conditions have also been presented. This paper has mainly focused on the lessons learned from past CO2 transport design and operational experiences in order to identify the areas where it could lead to an optimised system in terms of design, costs, and operation. Additionally, past experience in the design of CO2 pipelines and operation of CO2 injection has been used to identify opportunities where CO2 specifications and guidelines could potentially be modified in order to achieve an optimised and cost-effective CO2 transport and injection system. Keywords: CO2 Specification; CO2 Transport Pipelines; Design and Operation Challenges; CO2 impurities; CCUS;

New insights into the allosteric effects of CO2 and bicarbonate on crocodilian hemoglobin

Crocodilians are unique among vertebrates in that their hemoglobin (Hb) O2 binding is allosterically regulated by bicarbonate, which forms in the red blood cell upon hydration of CO2. Although known for decades, this remarkable mode of allosteric control has not yet been experimentally verified with direct evidence of bicarbonate binding to crocodilian Hb, probably because of confounding CO2-mediated effects. Here we provide the first quantitative analysis of the separate allosteric effects of CO2 and bicarbonate on purified Hb of the spectacled caiman (Caiman crocodilus). Using thin-layer gas diffusion chamber and Tucker chamber techniques, we demonstrate that both CO2 and bicarbonate bind to Hb with high affinity and strongly decrease Hb-O2 saturation. We propose that both effectors bind to an unidentified positively charged site containing a reactive amino group in the low-O2 affinity T conformation of the Hb. These results provide the first experimental evidence that bicarbonate binds directly to crocodilian Hb and promotes O2 delivery independently of CO2. Using the gas-diffusion chamber, we observed similar effects in Hbs of a phylogenetically diverse set of other caiman, alligator, and crocodile species, suggesting that the unique mode of allosteric regulation by CO2 and bicarbonate evolved >80-100 million years ago in the common ancestor of crocodilians.Our results show a tight and unusual linkage between O2 and CO2 transport in the blood of crocodilians, where build-up of erytrocytic CO2 and bicarbonate ions during breath-hold diving or digestion facilitates O2 delivery, while Hb desaturation facilitates CO2 transport as protein-bound CO2 and bicarbonate.

Effect of Mobile Carrier on the Performance of PVAm–Nanocellulose Facilitated Transport Membranes for CO2 Capture

Facilitated transport membranes obtained by coupling polyvinylamine with highly charged carboxymethylated nanocellulose fibers were studied considering both water sorption and gas permeation experiments. In particular, the effect of the L-arginine as a mobile carrier was investigated to understand possible improvements in CO2 transport across the membranes. The results show that L-arginine addition decreases the water uptake of the membrane, due to the lower polyvinylamine content, but was able to improve the CO2 transport. Tests carried on at 35 °C and high relative humidity indeed showed an increase of both CO2 permeability and selectivity with respect to nitrogen and methane. In particular, the CO2 permeability increased from 160 to about 340 Barrer when arginine loading was increased from 0 to 45 wt%. In the same conditions, selectivity with respect to nitrogen was more than doubled, increasing from 20 to 45. Minor improvements were instead obtained with respect to methane; CO2/CH4 selectivity, indeed, even in presence of the mobile carrier, was limited to about 20.