Swirl assisted distributed combustion behavior using hydrogen-rich gaseous fuels

Abstract

Controlled entrainment of hot reactive gases into the fresh oxidizer mixture prior to ignition is critical for achieving colorless distributed combustion (CDC) condition that results in a uniform thermal field, ultra-low emissions, enhanced flame stability, low noise and mitigation of combustion instability. This paper examines the fuel flexibility of colorless distributed combustion in a swirl-stabilized burner using hydrogen enriched methane gas. Distributed combustion condition was achieved by reducing the oxygen concentration in the oxidizer through addition of either N2 or CO2. Three different gas fuel compositions were investigated. Hydrogen enriched methane in various concentrations in the presence of CO2 and N2 represented coke oven gas. Results on the effect of fuel properties on global flame structure and emissions are reported here. The effect of equivalence ratio on flame stability and emissions was also investigated to determine the impact of air dilution with no change in oxygen concentration. The results showed that for the different gas compositions investigated, transition to distributed combustion conditions occurred at oxygen concentrations of 10–12% with N2 and 13–15% with CO2 as the diluent gas. Increase in hydrogen concentration (or decrease in methane concentration) in the gas mixture resulted in transition to distributed condition at reduced oxygen concentration. The NO emission decreased considerably (to less than 1 ppm) as compared to normal air combustion under the distributed combustion condition for all the gas compositions examined using the different diluents. The emission of CO decreased gradually when approaching distributed conditions, and then increased slightly when the condition moved toward the lower flammability limit. Single digit ppm CO levels were achieved with CDC under nitrogen dilution while carbon dioxide dilution resulted in slightly higher CO emission that was attributed to the dissociation of CO2 at high temperatures. The propensity for flashback with high hydrogen content gas was eliminated under distributed condition and provide wider flame stability limits. These results demonstrate fuel flexibility of diluted hydrogen rich methane gas (akin to coke oven gas) under distributed combustion that provided enhanced stability and ultra-low emissions.