Impact of CCUS Impurities on Dense Phase CO2 Pipeline Surface Engineering Design
Authors: Ali, MEng, CEng, MIChemE Sawsan M. , Thyagarajan Santhanam , Kataria Ashwani , Al Ankar Sami , Al Marzooqi Amal 
Published: December 2021

Numerous CO2 injection pipeline applications have been developed and implemented in the past decades in the UAE and all around the globe. Transporting the CO2 in dense phase, rather than in gas or liquid phases, is well recognized of being techno-economically attractive with respect to its major CAPEX benefits of optimized pipeline material of construction; which is driven by the high water solubility in dense phase CO2 as well as the optimized pipeline size which is greatly influenced by the density and viscosity characteristics of supercritical/dense phase CO2.

In light of the active deployment of dense phase CO2 injection EOR pipeline transportation across the various existing and future CO2 capture facilities across the UAE, ADNOC onshore technical expertise team has been conducting intensive research analysis on the unique thermodynamic aspects of dense phase CO2 pipeline systems. The focus was directed towards understanding the transient characteristics, which directly influence crucial design strategies including and not limited to CO2 purity specifications, CO2 pipeline pressure and temperature operating envelopes as well as the developed operating philosophy which involves start-up, shutdown and depressurization.

While optimizing the economics of the carbon capture units (CCUS) is a pivotal strategy mandating rationalizing the dictated purity level of the captured CO2 and valorizing the projects. However, such thrifty initiatives to moderate the costs of the selected CO2 removal technologies can lead to underlying cascading effects of the lower purity recovered CO2 on systems design and its operation.

As part of the nation's strategic objective to reduce carbon footprint, CO2 has been recovered for EOR re-injection applications. Relaxing the purity specification met by the CO2 capture units can positively improve the cost of the recovery plant while may potentially have adverse impacts on CO2 pipeline integrity.

This paper provides a comprehensive analysis of the impact of the CO2 purity specification on the flow assurance safety performance of dense phase CO2 pipeline. It is worth highlighting that the design of CO2 systems is challenged by the paucity of the available reference design guidelines since domain of CO2 itself is still evolving under an active area of research.

Although some previous publications have demonstrated the latent underlying effects of imputiries such as (N2, H2, SO2, NO2, CH4, C2H6, and Argon) on the physical and thermodynamic behavior of CO2 systems, however, this was supported by literature experimental modelling without transient analysis. In this paper, the behavior of varying CO2 purity levels on the design and operational aspects of CO2 pipeline is substantiated and both steady state and transient flow assurance modelling are presented. Gauging the system's design integrity cannot be solely assured from the perspective of steady state behavior and hence this paper's findings provide additional information to that previously published with the detailed modelling applied for varying purity scenarios of captured CO2 streams employed in EOR applications across the UAE. The findings of the analysis are benchmarked against plausible worldwide CO2 compositions with a wide range of impurity levels with further in depth demonstration of the transient effects which are usually absent in the available literature.