Air emissions management
Download July 21, 2022

Learn how EOS-CG helps improve the profitability of your CCS projects

What are equations of state used for?


Equations of State (EOS) are used to relate the densities of gases and liquids to temperatures and pressures. EOS are manipulated to calculate thermodynamic properties and predict fluid phase behaviours. 


The phase behaviours of fluids are applied within simulation software to model real-world processes. Hypothetical scenarios are created to determine a plant's most efficient settings to operate within. All modelled scenarios are dependent on the accuracy of the EOS.


Ultimately, using an accurate EOS when simulating your process can reduce energy usage or Green House Gas (GHG) emissions as it allows the optimal settings to be identified. This translates to either more money for the plant or environmental compliance.


Why you need a suitable EOS:


EOS focus only on a finite set of compounds for a specific range of conditions. The reality is that there are many different compounds out there with an infinite set of. There is no EOS that applies to everything. Some EOS are designed for generality, like Peng-Robinson or SRK. Others, are more specialized, designed for a small set of compounds, like EOS-CG.


Naturally, a highly specialized EOS can more accurately predict thermodynamic properties and phase behaviour and thus more effectively optimize the process being modelled. However, the more specific an EOS is, the more particular its use is. An EOS is only valid when used within its acceptable ranges.


Identifying the EOS most suitable for the set of conditions and fluids being tested is essential to accurately model the real-world process. The more accurate the EOS is at predicting the fluid’s thermodynamics and phase behavior, the more accurate the model is. Generally speaking, you would want the most specific EOS possible for your process to get the most accurate results. 


What is EOS-CG?


EOS-CG is a specialized Equation of State for Combustion Gases (and combustion gas-like mixtures). It is excellent for carbon capture and storage (CCS) technologies which are the most efficient interim solution for reducing CO2 released into the atmosphere from fossil-fuel energy production. EOS-CG mixture model improves the description of multicomponent mixtures when compared to its predecessor and accurately predicts phase boundaries across a wide range of temperatures and pressures. 


The predecessor to EOS-CG, GERG-2008, is a Helmholtz energy EOS based on state-of-the-art technology, but when it was developed, humid gas mixtures were not its focus. EOS-CG is developed from GERG-2008's mathematical approach but with a few changes because it falls short when describing the phase boundaries of CO2 mixtures and the solubility of gases in water.


With CO2 as the biggest contributor to hazardous GHG, separating it from the combustion gas before it enters the atmosphere is a powerful way to avoid hazardous climate conditions that higher concentrations of GHG may cause. Until renewable energy can replace fossil-fuelled power generation that accounts for 41% of CO2 emissions, efficient storage technologies will be in high demand.   


This is how EOS-CG/GERG-2008 compares to other common EOS:


Here's how EOS-CG compares to its predecessor GERG-2008:


Need help with modelling your CCS projects or help to choose the best EOS for your project?


Please get in touch with us.


Gernert, J. and Span, R., 2016. EOS–CG: A Helmholtz energy mixture model for humid gases and CCS mixtures. The Journal of Chemical Thermodynamics, 93, pp.274-293.


By Gabriel Mathias, B.Sc.

Gabriel joined Process Ecology in June 2020 as a Process E.I.T./Air Emissions Analyst. He started his career at Suncor as a Process Safety Engineer involved with the safe start-up of the Fort Hills mining operation. Gabriel has a BSc in Chemical Engineering from the University of Calgary and is pursuing an MSc in Software Engineering. His interest in both chemical and software engineering has been well utilized in the development of a new process simulation tool, NEXIM. He is also involved in air emission quantification and reporting for the oil and gas industry. When not behind a computer screen, Gabe enjoys bike riding in Fish Creek or a fun night of board games with friends.



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