Carbon capture and storage |


fuelled power plant. Without additional actions, the EGR rate is limited to around 30–50% since flame instability tends to occur when the oxygen concentration at the inlet of the gas turbine combustor falls below ~14% by vol.


The temperature of the recirculated gas is a key factor that determines the performance of the gas turbine: the closer the recirculated exhaust gas is to ambient temperature, the lower the impact on performance. If the EGR stream is cooled to ambient temperature then operating with a constant turbine entry temperature can increase power output (due to higher mass flow), whereas constant speed control reduces the power output. The white paper emphasises that several considerations must be taken into account when EGR is implemented on a gas turbine: correct mixing with the combustion air is critical, as is the cleanliness of the recirculated gas. Condensibles and any particulates that could block cooling air passages need to be removed, while CO2


in seal


content to around 6% by vol, which is enough to achieve CAPEX and footprint reduction


air may impact the viscosity of the lubricating oil. The EGR loop pressure drop and control of EGR under transient conditions have to be considered, as do potential issues surrounding compressor fouling, hot section corrosion, hot section component cooling and material fatigue – none of which are yet well-known. An EGR rate up to 30–40% can be achieved without modification of the gas turbine core for most models, but at this level EGR only boosts the CO2


for amine-based post conbustion capture plant but not enough to move into the range of simpler, lower cost CO2


For high CO2 capture technologies like


molecular sieves, the white paper says. It is possible to achieve stable combustion at higher rates of EGR, eg via injection of supplemental oxygen, but according to the white paper this introduces new complexities and challenges. Although a 70% EGR rate yields an exhaust concentration of only 10.5–11.5% by


gas CO2


vol, EGR rates of 80% or higher can boost CO2 concentration to over 15% by vol.


is worth considering ‘CO2


concentrations in the exhaust, it -enriched EGR’, where a


capture technologies are undergoing rapid development, the white paper observes, and Siemens Energy’s partnering strategy provides access to state-of-the-art technologies from leading suppliers, allowing it to focus on its strength of “integrating the power side with the capture side.”


membrane is placed in the EGR loop to remove nitrogen from the recirculated gas stream, the white paper recommends. CO2


CCUS in the US, positives and negatives


The US government has reaffirmed its support for carbon capture and storage by preserving – and in some cases increasing – the federal Section 45Q tax credit, as set out in the One Big Beautiful Bill Act (OBBBA), signed into law by President Trump on 4 July, 2025. The Global CCS Institute said it welcomed this continued support, recognising the 45Q tax credit as a “cornerstone policy crucial for


accelerating deployment across the country”, and suggesting that “extending it is key to maintaining industrial competitiveness, energy security, and economic resilience.”


The bill maintains the 45Q tax credit for point- source capture at $85/ton and direct air capture (DAC) at $180/ton with dedicated geologic storage, preserves transferability, and keeps the inflation adjustment date of 2027 with a base index year of 2025.


The tax credit now includes parity for the utilisation of carbon dioxide. In the new bill, CO2


used or converted into useful products or injected and geologically stored in a qualified enhanced oil recovery or natural gas recovery project site will qualify for the same dollar value credit as CO2


that is permanently sequestered


in a dedicated geologic storage site. The bill also introduces new restrictions on “foreign entities of concern”, primarily China.


The Institute says it applauds US policymakers for preserving and strengthening this crucial policy for CCS deployment and points out that it is not alone: “Many US organisations have issued statements or conducted analysis that highlights the importance of the 45Q tax credits for accelerating the deployment of carbon management technologies within the US.” These organisations include the Carbon Capture Coalition, Carbon Utilization Research Council, Clean Air Task Force, Clear Path and Rocky Mountain Institute.


Although the OBBBA is supportive of carbon capture, it is worth noting that on 30 May the


28 | September 2025| www.modernpowersystems.com


US Department of Energy, under its new Secretary of Energy, Chris Wright, announced the cancellation of awards to 24 decarbonisation and CCS projects, totalling about $3.7 billion (see MPS, June 2025, p 29). The awards were handed out under the previous administration by the DoE Office of Clean Energy Demonstrations, with, interestingly, 16 of the 24 awards signed between election day and


20 January (Trump inauguration). Among the cancelled awards are those to four key power generation CCS demo projects, three at natural gas fuelled combined cycle sites (Sutter, Baytown, and Cane Run) and one at a coal fuelled power plant site (Dry Fork). It remains to be seen what if anything can be salvaged of these capture technology demo projects. The Global CCS Institute says, as of June 2025, it was tracking 70 operational CCS projects globally, with a combined capture capacity of 61 million tons per annum and the USA remained “the global leader in CCS deployment, with 33 operational projects, 19 under construction, and over 300 in various stages of development.”*


*Global CCS Institute, CO2RE database Pre- vs post-combustion CO2


The economics of decarbonising gas power plants depends largely on their operational profiles. The graph shows the opportunity window for gas turbine based power plants using precombustion CCS, ie running on 100% blue hydrogen (produced


via steam methane reforming, with CO2 captured during the process), versus post combustion CCS. Hydrogen based pre-combustion capture suits flexible power plants operating for relatively fewer hours. Since operational hours are limited, the hydrogen price is a relatively insignificant factor in the overall economics.


capture for gas turbines On the other hand, for plants operating


at baseload or semi-baseload, post combustion capture becomes more economic – as it becomes easier to achieve return on the relatively high initial cost.


Source: Siemens Energy white paper CCUS technology landscape and infrastructure


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