Steady State Flow Model for Impure CO2 Transportation in Industrial Processes

Carbon capture, utilization and storage, or CCUS, has been recognized as an accepted technology in the United Nations Framework Convention on Climate Change (UNFCCC) to achieve the Paris agreement commitments [1]. Within the CO₂ capture and utilization trend, the flow must be transported. The presence of impurities in the CO₂ stream affects thermo-dynamical fluid properties (density, critical point, triple point, viscosity, J-T coefficient, ect.), causing corrosion and modifying the CO₂ behavior during operational activities such as pipe depressurizations [2].

In order to prevent these negative effects, this paper describes one-dimensional steady-state flow model for impure CO₂ implemented in a rigorous process simulator, CHEMCAD 7.0. Focusing on the thermodynamical model selected in the process simulator, a benchmarking exercise was developed comparing Peng-Robinson equation of state (PR EoS) and Soave-Redlich-Kwong (SRK EoS). The model was validated with experimental data that were obtained in a demo transport plant (TRL 7) with a total length of 3.000 m (10 coils), 2” diameter and operation conditions that can be set within a range of 10-31 ºC and 80-110 bar(a); the facility includes a doping system to modify the composition of the processed CO₂, being the impurities selected SO2, O2 and moisture with a maximum composition of 500 ppmv that could be classified as low contaminant levels and water content below the solubility content.

The validation of the model for both thermodynamic models was really closed. The experimental results were matched with a maximum difference of 6,6 mbarg per linear meter of pipe in the pressure drop. Regarding the pressure drop behaviour, it is well known that one of the main parameters is the velocity (or volume flow rate) for a given diameter: the higher the velocity, the higher the pressure drop. Nevertheless, velocity is not the final analysis, but the CO₂ contaminants and the composition have also a crucial role in the pressure drop. To study this effect, a set of tests were done with constant flow rate (in the range of 14.600 l/h), obtaining that for the case of CO2 with 100 ppmv of SO2, an important increase in the pressure drop is produced whereas for CO2 with 500 ppmv of O2, a diminution of pressure drop was obtained.

References

[1]| IEA- International Energy Agency, «Global Energy & CO2 Status Report,» [En línea]. Available: https://www.iea.org/geco/electricity/. [Último acceso: 30 06 2019]

[2] S. Tollak, M. Hammer y S. Lovseth, «CO2 transport: Data and models - A review,» Applied Energy, pp. 499-523, 2016.