Oscillating Combustion Increases Productivity and Decreases NOx Emissions from Industrial Furnaces

High-temperature, natural gas-fired furnaces, especially those fired with preheated air or industrial oxygen, produce large quantities of NOx per unit of material processed. Regulations on emissions from industrial furnaces are becoming increasingly more stringent. In addition, competition is forcing operators to make their furnaces more productive and/or energy efficient. Oscillating combustion involves the forced, out-of-phase oscillation of the fuel and/or oxidant flow rate(s) to a burner to create successive, fuel-rich and fuel-lean zones within the flame, thus increasing heat transfer (and therefore productivity) by enhancing flame luminosity and turbulence, and retarding NOx formation by avoiding stoichiometric combustion. In its simplest form, oscillating combustion can be accomplished by installing an oscillating valve package on the fuel supply line of each burner. Testing on standard 250,000- and 500,000-Btu/h commercial burners has shown that oscillating combustion can provide 2% - 13% increases in heat transfer and 50% - 75% reductions in NOx emissions using ambient air, preheated air, or even enriched air. Similar results have been obtained with oxy-gas combustion on a 2,000,000 Btu/h burner. Evaluation on several additional burners used in the steel, glass, non-ferrous metals, and ceramics industries is now underway. Two field evaluations have been conducted-one on an oxy-gas-fired iron melter and one on a steel ladle preheater. Both used the CeramPhysics SSP oscillating valve package, which has proven to be superior to other valve options. such as solenoid valves. These evaluations have confirmed that oscillating combustion provides productivity enhancement and NOx reduction, but does not affect the quality of the product. Additional field evaluations are underway on an air-gas-fired steel annealing furnace and an oxy-gas-fired glass melter.