A New Stable Operating Regime for Oxyfuel Combustion

TLDR: In this paper, the stability of the new oxyfuel combustion regime, termed as Intermediate temperature Diluted Oxygen Combustion (INDOCS), has been demonstrated theoretically, based on the well-established fact that the stability increases with preheating of the oxidant.

Abstract: In the present paper, the stability of the new oxyfuel combustion regime titled as Intermediate temperature Diluted Oxygen Combustion (INDOCS) has been demonstrated theoretically. The operating conditions for the INDOCS are different from those of conventional oxyfuel combustion: the concentration by mass of oxygen in the oxidant stream is between 16 to 20% by mass (as opposed to 24% by mass in conventional oxyfuel combustion) and the temperature of the oxidant at entry to the furnace is in the range of 600 to 850 K (as opposed to an ambient temperature of about 300 K in conventional oxyfuel combustion). The method relies on the well-established fact that the stability of the flame increases with preheating of the oxidant (as demonstrated in High Temperature Air Combustion (HITAC) and FLAMELESS combustion regimes). The attendant high peak temperature of the flame can be reduced, to minimize NOx formation, by diluting the oxygen concentration. The overall benefits of this method are stable combustion at diluted oxygen concentrations, lower NOx (if N2 is present due to incomplete separation of oxygen from air), higher concentration of carbondioxide in the flue gases for a more efficient carbon sequestration. Flame structure calculations using the flamelet model of combustion with 35-step methane-air simplified reaction mechanism are used to demonstrate the stability of the flame. Simulations have also been carried out for the geometry of the 300 kW IFRF burner test facility; these show that the decreasing concentration of H and OH radicals in the quarl zone with increasing dilution by CO2 is counteracted by increasing the temperature of the oxidant. One of the principal advantages of this method is that, unlike in the case of HiTAC, the preheat requirements are mild which can be achieved by mixing part of the flue gas with the oxygen separated from air. It can be therefore readily implemented as a retrofitting measure in existing coal-fired plants.Copyright © 2008 by ASME