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;