(87f) Hazardous Flue Gas Mixtures in Furnaces Due to Fuel-Rich Combustion

Although most furnace incidents occur at light-off, it is also possible to create hazardous gas mixtures in an operating furnace. Fuel-rich combustion produces hot flue gases with residual combustibles that can burn or explode if mixed with fresh air too quickly. This is most likely to occur when a furnace transitions suddenly from rich combustion to lean combustion.

This paper describes the composition and behaviour of fuel-rich flue gases, as predicted by chemical equilibrium calculations. For furnaces that burn methane and hydrogen, it was found that above 700°C all unburned methane will be reduced to hydrogen and carbon monoxide. The relative hazard of the flue gases was estimated based on the amount of chemical energy that they can release as mechanical energy. Finally, a methodology was found to determine a safe rate of transition from rich combustion to lean combustion.