Carbon capture and storage|


CCS for gas turbines: a Siemens Energy perspective


A recent white paper published by Siemens Energy, CCUS technology landscape and infrastructure*, provides a valuable overview of carbon capture technologies, present and future


Today, chemical absorption using amine solvents represents the technology of choice for post combustion capture of CO2


gases. It is the most mature of currently available options, having been proven in the chemical processing and oil & gas industry for decades. Application of heat, typically in the form of steam at around 120°C, to separate carbon dioxide from the solvent in the stripper column, is the most energy intensive part of the process.


Amine-based systems are suitable for all scales of CCUS and can be applied to low CO2


such as gas turbine exhausts (~4% by vol). Whilst amine towers represent today’s mature technology, the white paper notes, many alternatives are being developed that seek to offer new value propositions.


For example, enhanced amine loading can be achieved by employing rotating packed beds (RPBs). Cryogenic de-sublimation of CO2


from flue gas


yields liquid CO2 such as NOx


and SOx


, and also co-captures pollutants .


The high technology readiness level (TRL 7–8) of cryogenic post combustion capture is reflected by projects already being implemented in the field. On the other hand, the currently available cryogenic capture systems have relatively high operating costs and require flue gas with a higher CO2


concentration (> 15% by vol) than other technologies, the white paper observes.


concentrations,


Potassium carbonates have been used by the gas processing industry to separate CO2


from power plant flue from gas


streams for more than 50 years. Whilst potassium carbonates are readily available and not a proprietary chemical (unlike tailored amines), technology providers may use special additives to speed up reactions within the absorber vessel. Similar to amine towers, potassium carbonate systems typically have large footprints and high energy demand, although in some systems the temperature of solvent desorption has been reduced to around 80°C, which allows hot water to be used as the source of heat rather than steam. Hot potassium carbonate (HPC) is a variation of the potassium carbonate concept that is capable of handling flue gas temperatures up to 700°C, making it applicable to open cycle gas turbines. Cryogenic and HPC-based CO2


capture


typically operate at 8–10 bar pressure. Therefore, compressors are needed to boost the pressure of flue gas at the inlet of the process.


Early-stage post combustion technologies


In addition to relatively mature post combustion capture technologies, several promising new concepts are being developed. The white paper lists the following:


Membrane contactor technology. This hybrid concept combines membranes, which by themselves are limited to high CO2


flue


gas applications, with an amine solvent. The large gas/solvent contact area reduces the contactor size and weight, and high solvent


loading expands the range of flue gas CO2 concentrations that can be treated. Adsorbents. Zeolites, carbon-based materials and amine impregnated chemicals are commonly used as adsorbents, although there is increasing interest in metal-organic frameworks (MOFs) for CO2


capture. Adsorption works best


at lower flue gas pressures and temperatures (40°C to 70°C). Sorbent regeneration typically requires slightly less energy and lower steam temperature than amine solvents. Electrochemical technologies. Electroswing adsorption and similar technologies rely on alternating electric fields, not heat, for CO2


separation – offering the possibility of increased operational flexibility. Molten carbonate fuel cells. These are characterised by relatively high temperature operation (up to ~600°C), eliminating the need for flue gas cooling and the provision of steam for CO2


desorption. However, further


development is needed to increase the purity of the captured CO2


at the anode of the fuel cell.


Gas turbine/CCS integration In future energy systems having a large majority share of power from renewables, the white paper suggests that decarbonised gas turbines will be required to ensure the uninterrupted supply of electricity, eg, to compensate for intermittency. It also notes that combined cycle power plants can load-follow very well due to their inherently high operational flexibility and can provide much needed grid ancillary services like inertia, short circuit power, voltage, and reactive power control. However, the CO2


concentration in a gas


turbine exhaust, as noted, is low compared to most other sources of carbon dioxide emissions, adding to the cost of CO2


capture.


The white paper points out that the CO2 concentration in a gas turbine exhaust can be


increased by exhaust gas recirculation (EGR) – a technology sometimes used on diesel engines to reduce NOx


emissions – whereby part of the (CO2 -


Schematic of gas power plant with EGR (exhaust gas recirculation) and PCC (post combustion capture). Source: Siemens Energy, CCUS technology landscape and infrastructure


enriched) exhaust is recirculated to the combustion air intake. Although it can be employed on any gas turbine, the impacts of EGR on gas turbine performance will vary on a model-by-model basis. The diagram, left, taken from the white paper, presents the basic concept of combined EGR and post combustion capture processes for a gas


* https://www.modernpowersystems.com/whitepapers/ccus-technology-landscape-and-infrastructure/?utm_campaign=40617182-BT 26 | September 2025| www.modernpowersystems.com


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