Understanding CO2 flow measurement for carbon capture and storage (CCS) transport applications

Abstract

Carbon Capture and Storage (CCS) is a decarbonization solution, particularly suited to industries with hard-to-abate emissions such as cement, iron & steel, and fertilizer production. However, as a prerequisite for commercialisation of CCS, accurate measurement is required for quantifying CO2 streams across the CCS value chain and to comply with a range of environmental legislation and regulations. Unlike other industrial process fluids such as water, oil, and natural gas, it is still unclear whether current commercially available metering technologies can meet the requisite accuracy levels, specifically the ±2.5% accuracy recommended within the EU/UK European Trading Scheme for CO2 mass transfer. Therefore, this research is aimed towards gaining a comprehensive understanding of flow measurement of CO2 under relevant CCS transport conditions. This understanding is crucial for examining the capabilities of both Coriolis and orifice meters under more realistic CCS transport conditions, specifically assessing whether these CCS metering technologies meet the MRR Tier 4 MPE requirement. The experimental study predominantly focuses on evaluating the performance of two distinct designs of Coriolis meters and an orifice meter, across gas, liquid, and supercritical conditions, using both pure CO2 and CO2-rich mixture samples. In order to understand the influence of non-condensable gas impurities in CCS flow operations, a review of relevant thermodynamic modelling equations was conducted. These models play a relevant role in predicting the optimal transport conditions for the CO2-rich mixtures. Moreover, a dedicated laboratory-scale gravimetric flow facility was designed for conducting CO2 flow measurement tests. Using this facility, flow measurement tests were conducted to evaluate the performance of the selected meters under gas, liquid, and supercritical flow conditions. Additional tests were conducted to assess the performance of one of the Coriolis meters with light energy carrier gases (hydrogen-methane blend). The findings from these flow experiments indicate that the non-condensable impurities, such as N2, H2, O2, Ar, and CH4 have a relatively minor impact on Coriolis meters, with maximum mean absolute errors of 0.51%, 0.26%, and 0.56% observed in gas, liquid, and supercritical CO2 flow conditions, respectively. However, the impact of these impurities, which is often associated with an increase in the compressibility of the fluid and reduction in density or homogeneity of the fluid, tends to become apparent with different Coriolis designs or quality of flow operation (flow rates and regions). In the case of the test orifice meters, impurities also have a less noticeable impact during gaseous flow conditions, with the highest recorded mean absolute error reaching approximately 1%. However, the impact of these impurities becomes more noticeable in liquid and supercritical flow conditions, resulting in maximum mean absolute errors of 2.84% and 11.14%, respectively. It is worth noting that although impurities seem to have a more pronounced effect in these dense phases (high density liquid and supercritical phases), a substantial component of these errors can be attributed to uncertainty in the density measurements. These results conclude that Coriolis metering technology as a robust choice for CCS metering, underscoring its suitability for accurate measurements in single phase CO2 transport conditions, as well as in handling other relevant low-carbon fluids. Meanwhile, the performance of orifice meters in gaseous flow conditions emphasizes their effectiveness and potential applicability in repurposed gas pipeline infrastructures for CCS transport applications. The overall outcome of this study helps contribute towards understanding flow measurement capabilities of specific commercially available CCS metering technologies. The assessment of these meters offers crucial insights and measurement data to understand how well some existing flow metering technologies, currently employed in the oil and gas industry, can be adapted for CCS transport metering applications. The study also helps understand the impacts of non-condensable gas impurities in CCS flow operations, showing how well these impacts can be handled to improve flow activities