Exhaust gas recirculation (EGR) and selective exhaust gas recirculation (S-EGR) are means of augmenting the flue gas CO2 concentration from gas turbines, with the aim of facilitating post-combustion CO2 capture. Gas turbines operate under lean conditions, resulting in flue gases with low CO2 and high O2 concentrations, in large volumetric flows. This negatively affects post- combustion capture and can lead to enhanced oxidative solvent degradation in amine-based systems. Making use of EGR/S-EGR could mitigate these impacts, resulting in energy and cost savings for capture, as well as efficiency improvements in the power plant. The experimental research herein considered various degrees of CO2 enhancement in the flue gas through CO2 injections to the compressor inlet of a highly-instrumented micro-gas turbine. Coupled with computational fluid dynamics (CFD) models, the impacts on turbine performance were assessed, in terms of emissions, temperatures and combustion stability. At low loads, the impacts of EGR/S-EGR were greater – with higher levels of incomplete combustion products (CO and unburned hydrocarbons). It would appear that the presence of more aromatics (unburned species) and, to a lesser degree, the reduced temperatures, also allowed for greater nanoparticle coagulation, significantly changing the size distribution of submicron and especially ultrafine particulates. Moreover, the greater heat capacity of the modified oxidiser (air+CO2) resulted in lower temperatures measured throughout the cycle, which reduced NOx formation. The CFD studies used a steady-state Reynolds-Averaged Navier-Stokes approach to corroborate these findings, with calculated in-flame temperatures up to ~100 K lower under EGR/S-EGR conditions and notable decreases in NOx levels.
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