EFFECT OF CO2 INJECTION IN THE COMBUSTION AIR ON THE PERFORMANCE OF A HOT WATER DOMESTIC FUEL OIL BOILER

In order to investigate the effect of CO2 addition in the combustion air of a yellow flame burner, tests have been performed during which different volume flow rates of CO2 have been injected. For all the tests performed, the burner consumption and the oxygen mole fraction in the flue gas have been kept quite constant, say at about 240 kW and 1.8 % (on dry basis) respectively. For the interpretation of the flame radiation results, tests have also been performed with N2 injection. The results gathered (for CO2 and N2 addition up to 4.8 % and 7.4 % in volume respectively) show that the thermal efficiency and the CO emission of the boiler are not affected. For small amounts of CO2 or N2 volume flow rates, there is a slight decrease of the NOx emission and the flame radiation. If the quantity of the additive is increased above a critical value, the flame becomes unstable and one observes first a sudden increase of the NOx emission and the flame radiation and then a decrease. That sudden increase is explained by the change of the flame shape and geometry