Carbon capture and storage |


Figure 2. Basic flow scheme for a combined cycle power plant equipped with carbon capture. With steam integration an external auxiliary boiler is not needed (Image: GE Vernova)


Exhaust gas


Further treatment if required


Blower Stack Decarbonised exhaust gas


Direct contact cooler (DCC)


CO2 to compressor/pipeline


Inlet air


HRSG


GT inlet house


GT Blower Cooling water Reboiler ST Flue gas Cooling water


Low pressure steam Rich amine solution Lean amine solution


Auxiliary boiler


Low pressure steam


Exhaust gas DCC


The exhaust gas from large land-based gas turbines contains 3-4.5% mol CO2


at near-


atmospheric pressure, depending on the gas turbine frame (E, F, or HA class). When compared to sources that have a high concentration of CO2


, carbon capture is


more challenging and requires more energy to remove the CO2


a low concentration of CO2


from sources that have , such as natural


gas fuelled combined cycle power plants.


Exhaust gas recirculation elevates the CO2 concentration in gas turbine exhaust to approximately 6-7% mol, dependent upon the exhaust gas recirculation ratio. Exhaust gas recirculation enhances the performance of carbon capture plants, lowers overall capital expenditure, and mitigates solvent losses by lowering the degradation rate.


Amine based carbon capture Amine based solvent post-combustion carbon capture technology (Figure 2) depends on the chemical properties of the amine–CO2


-H2 O


at low temperatures and release it at higher temperatures. Carbon dioxide and water react to produce carbonic acid, which subsequently undergoes a reaction with an amine solution in the absorption column. This reaction results in the creation of a solution that absorbs carbon dioxide from the gaseous stream.


system and the ability of amine solution to trap CO2


The flue gas is diverted from the existing HRSG plant stack in a way that does not impact the operation of the power plant. Shutoff dampers are installed to isolate the ducts from the main HRSG stacks. During normal operation, the shutdown dampers of


the capture plant will be fully open. The flue gas is cooled by introducing water into the top of the DCC (direct contact cooler), with gas entering from the bottom section of the DCC. The DCC operates as a quenching tower, where water undergoes condensation from the flue gas and gets driven out from the loop as water blowdown. The cooled and cleaned flue gas is introduced into the CO2


absorber


in a temperature range of 40°C to 50°C and at normal atmospheric pressure. Variable- frequency blowers are employed to move the flue gases from the DCC to the absorber and to overcome the drop in pressure in the main ducts and the absorber column. The CO2


absorber is constructed as a


in the flue gas is chemically absorbed as it moves upwards in a counter-current direction with the spraying CO2


-lean amine solution


that is flowing from the upper part of the absorber. The exiting solution at the bottom of the absorber, the CO2


-rich amine solution, is


-rich amine solution is pumped through the lean/rich amine cross heat exchanger and heated before being sent to the top of the regeneration column. The regenerator column is a distillation column with packing. There, the rich solution flows down the column counter-current to steam generated by boiling


14 | November/December 2024| www.modernpowersystems.com


subsequently circulated via a cross-flow heat exchanger and heated to a higher temperature by the lean solution that is being returned from the amine regenerator column.The CO2


packed tower, with a design that ensures the flue gas is equally distributed throughout the column. High-performance packing is installed to ensure efficient mass transfer and to reduce the column diameter and pressure drop. The CO2


a portion of the lean solution that exits the bottom of the regeneration column. The stripper receives heat through the stripper reboiler which is situated at the bottom of the stripper. The reboiler is a kettle heat exchanger where steam flows through the tube bundle and exits as condensate and the solvent is heated against the steam. The lean solution in the amine regenerator is fed back to the absorber via the lean/rich amine cross heat exchanger. The heated lean solution is cooled, and the heat recovered heats the rich CO2


solution from the absorber. The generated gas at the top of the stripper, consisting primarily of carbon dioxide and water vapour, is directed through a series of compressors, coolers, and dryers to eliminate the water vapour from the CO2


and increase its pressure to required pressure at the storage location.


Cost savings from steam integration


Consider a (1x1) HA-class gas turbine natural gas combined cycle plant with a post-combustion carbon capture plant. The steam turbine is configured with an IP-LP crossover for steam extraction (see Figure 3) while the heat recovery steam generator consists of a 3-pressure level HRSG with reheat. The carbon capture plant is an aqueous amine-based capture system. Two sources of steam can be used to power the reboiler: an external auxiliary boiler (bolt- on solution) or the existing combined cycle plant’s steam turbine. The required steam quality for a combined cycle power plant depends on the reboiler temperature, which is determined by the selected solvent/ solvent mixture.


Lean amine solution


Stack


Rich amine solution


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