Carbon capture research has blossomed in recent years as interest in achieving net zero stepped up.
Most net-zero projections include carbon capture, utilization, and storage (CCUS) as a critical decarbonization strategy; there is little chance of achieving these lofty goals without it. Hence, an early session at this year’s Turbomachinery Exposition featured papers on the latest research in this dynamic field.
Majed Sammak, Carbon Capture System Integration Leader at GE Vernova, laid out a variety of integration concepts such as steam integration and application of exhaust gas recirculation (EGR) technology to concentrate CO2 in the exhaust.
With EGR, a portion of the turbine exhaust gases is recirculated back into the compressor stage and then into the combustion chamber. Low pressure steam is required in the carbon capture stripper reboiler, he said, to release high-purity carbon dioxide from the capture solvent. This steam might come either from an auxiliary boiler or a combined cycle plant.
“EGR reintroduces part of the exhaust into the gas turbine’s inlet after appropriate cleaning and conditioning,” said Sammak. “By recirculating part of the flue gas, you increase the concentration of CO2 in the flue gas, hence flow of flue gas to the carbon capture plant is reduced.”
Exhaust gas recirculation addresses a real need in the CCUS field – reduce high costs. CCUS technology has lingered in the shadows for decades due to its price tag. Other than a few demonstration and government-funded research projects, few operators would engage in it.
This has changed since net-zero became such a big issue along with a host of incentives being offered for those implementing it. Sammak noted that EGR decreases the size of major carbon capture plant components — resulting in a smaller footprint, lower CAPEX, and improved performance.
Antoine Verhaeghe, a PhD student at Belgium’s University of Mons, discussed how solvent selection might affect performance when retrofitting an existing combined cycle gas turbine with post-combustion carbon capture technology.
Amine-based post-combustion carbon capture is the most mature and applicable technology to transform combined cycle facilities into low-carbon power plants, he said. “However, its deployment is hindered by high CAPEX as well as high OPEX linked with the energy requirement for the solvent regeneration process.
His research delved into how to lower the carbon capture energy penalty from such processes. He stressed efficient heat integration as a key strategy, involving the extraction of steam from the most suitable location in the steam cycle to supply the reboiler. The choice of extraction location, he said, depends on the required steam quality.
Verhaeghe evaluated different solvents, analyzing their influence on plant performance. He compared monoethanolamine (MEA), which is the conventional solvent choice, against a blend of methyldiethanolamione (MDEA) and piperazine (PZ) at full and part-load operations.
Reboiler duty is lower when using MDEA/PZ, due to its lower regeneration energy, he said. However, the efficiency gain is constrained by the higher steam quality requirements, which notably impacts steam turbine power production.”
In addition, MDEA/PZ allows a broader range of regeneration pressure adjustments. This enables better alignment with steam cycle operating conditions during partial-load operations , thereby reduces the energy penalty.
The combined cycle efficiency penalty can be reduced by 6.3% by replacing MEA with MDEA/PZ, concluded Verhaeghe.
Elettra Vantaggiato, a Master of Science Researcher at SINTEF Energy in Trondheim, Norway, reported on hydrogen piloting as an alternative way to deal with EGR. She expects that H2-assisted EGR, with CO2capture, will be a key solution in different applications in a carbon-constrained energy system and for low-carbon electrical power generation.”
Increasing the CO2 content of the exhaust gas has a favorable impact on the energy requirements and size of the CO2 capture unit. However, a 35% to 40% EGR rate cannot be exceeded without impeding combustion behavior severely.
She suggested hydrogen piloting in the combustor as a solution that improves the kinetics, stabilizes the flame, and allows higher EGR levels. Her research used a Baker Hughes Frame 9 gas turbine operating at base load conditions and integrated with an absorption-based CO2 capture process using MEA as the solvent.
A final presentation dealt with semi-closed oxy-combustion (SCOC) combined cycle (CC) arrangement for gas-fired combined heat and power plants using the Allam cycle to net over 50% electric efficiency.
SCOC-CC enables the adoption of a CHP configuration, for the heat recovery steam cycle, coupled with either a backpressure steam turbine or an extraction-condensing arrangement.
As steam is not required for solvent regeneration, all steam generated is available for cogeneration.
