Parametric optimization study of a multi-burner flameless combustion furnace

A parametric study on a 300 kWth furnace equipped with three pairs of regenerative flameless combustion burners has been performed. Each burner pair has a rated thermal power of 100 kWth firing Dutch natural gas. The objective of the study was to optimize the furnace performance, i.e., to maximize the cooling tube efficiency and minimize the CO and NO emissions. In the study the following parameters were varied: the positions of the burners in the furnace (burner configuration), the firing mode (parallel and staggered), the excess air ratio (λ) and the cycle time (tcycle). Also, the influence on the furnace performance of the jet momentum of the combustion air and the temperature uniformity in the furnace were studied.It was concluded that staggered firing mode is disadvantageous, since it results in significantly higher NO emissions than parallel firing mode. Also, out of the five investigated burner configurations one has been exempted, since its cooling tube efficiency was significantly lower compared to the other configurations. Furthermore, a horizontal setup of the firing burners improves the cooling tube efficiency at a fixed temperature uniformity. Also, for the burner configurations with the firing burners positioned closer to the regenerating burners and further from the stack, the temperatures in the regenerators are higher, leading to higher combustion air preheat temperatures. The temperature in the regenerators was also influenced by the cycle time; higher cycle times leading to higher (peak) temperatures in the regenerators. Finally, this temperature in the regenerators was shown to be more decisive for the final amount of CO emitted than the excess air ratio or the jet momentum. In all experiments, due to differences in path length of the mean flow, higher CO emissions were measured in the flue gas from the regenerators compared to in the flue gas from the stack. These two trends in the CO emissions were not observed for the NO emissions.

► Burner positioning effects in a multi-burner flameless combustion furnace.
► Horizontal burner setup improves efficiency at constant temperature uniformity.
► Burner positions influence combustion air preheat temperature.
► Combustion air preheat temperature decisive for carbon monoxide emissions.