Kinetic model of a CO2 recycling rotary adsorption wheel for gas turbine power plants with carbon capture
Palfi, Erika Alexandra
The selective recycling of carbon dioxide (CO2) upstream of post-combustion capture processes can greatly reduce both the size of equipment and capital costs by process intensification. For combined cycle gas turbine (CCGT) power plants, flue gas flow rates can be lowered by two thirds and CO2 concentration greatly increased from 4% to 14% v/v. Selective recycling of carbon dioxide (CO2) can be achieved in CCGT plants with a low pressure drop, regenerative rotary CO2 transfer device using physical adsorption. A newly developed kinetic model of this CO2 transfer device shows that, for an activated carbon material with suitable equilibrium properties, a mass requirement of circa 600 tonnes is necessary for a new build CCGT plant of 800 MW with 90% capture. This is 3.7 times higher than the mass previously reported, by means of an equilibrium model, for the best performing commercially available activated carbon material. A rigorous design shows that the mass of 600 tonnes of activated carbon can be distributed on a honeycomb structure on two CO2 transfer wheels of 30m diameter and 2.2m height, rotating at 1rpm, with a preferential direction of leakages towards the flue gas side. The design then provides the basis for an optimisation study of CO2 recovery rate and adsorbent mass by examining first kinetic properties of the CO2 adsorbent to inform material development and research; second, rotational speed; and, last, the partitioning of the wheel. Further, the selective recycling of CO2 is examined as a retrofit option for CCGTs with solvent based post-combustion capture. The aim is to explore the possibility to increase overall capture level beyond the initial design of 90% capture using an integrated model consisting of a gas turbine combined cycle, a rotary CO2 transfer device and a post-combustion capture unit and compression train. The operation of the absorber column at reduced gas velocity is, however, shown to be detrimental to retrofitting selective CO2 recycling to existing CCGT plants with solvent-based capture. Finally, a comparison between a new build CCGT with PCC and fully integrated regenerative selective CO2 transfer wheel to a new build CCGT with PCC without SEGR is performed. The results show a possible reduction in absorber total packing volume of 42% and a marginal increase of net power output of 0.3% relative to a new build CCGT with PCC without SEGR.