Experimental investigation on the effect of O 2 and CO 2 on burning rates during oxyfuel combustion of methane

Abstract

For combustion in an CO 2/O 2 atmosphere, known as oxy-combustion, altered combustion rates have to be expected. Previous investigations reported that this can be explained not only with the different thermophysical and radiative properties, but also by the fact that CO 2 participates directly in the chemical reactions. This paper presents an experimental study on oxyfuel methane combustion with the aim to investigate the importance of the chemical effects of high CO 2 concentrations. Experiments have been carried out in a 25 kW furnace for flameless combustion which provides the possibilities to achieve stable combustion of methane within a wide range of oxygen concentrations in the CO 2/O 2 mixture at constant reactor temperature. This allows to focus on the chemical effects of CO 2 by keeping the remaining factors affecting the combustion rate constant. Four different oxidizer mixtures (CO 2/O 2 and N 2/O 2 both with 21 vol% and 18 vol% O 2) have been studied by detailed in-furnace measurements for flue gas compositions and temperature. In case of combustion in N 2/O 2 atmosphere, the CO profiles obtained for different O 2 concentrations overlap thus demonstrating that changing the O 2 concentration did not affect combustion rates, with keeping the temperature constant. In case of combustion in CO 2/O 2 atmosphere, the CO concentrations obtained were much higher than those in N 2/O 2 atmosphere. In contrast to N 2/O 2, the O 2 concentrations had a significant impact on the production and consumption rates of CO in oxyfuel combustion. The results obtained in this work demonstrated that by elimination of the influence of: molar heat capacity, CO 2 dissociation, and thermal radiation, it can be estimated that the observed effects of high CO 2 concentrations on combustion rates can be attributed to its participation in the chemical reactions. An increase of O 2 in oxyfuel led to a reduction of this impact, however, further investigations on the exact mechanism are necessary.