Oscillating combustion technology currently being evaluated in the steel industry as a method to cost-effectively reduce NOx emissions from and increase productivity in high temperature, natural gas-fired furnaces.

Fig. 1 Schematic diagram of the oscillating combustion method as the fuel-rich, fuel-lean zones disperse within a furnace.
High temperature natural gas-fired furnaces, especially those fired with preheated air, produce large quantities of NOx per ton of material processed. As regulations on emissions from industrial furnaces become increasingly stringent, cooperative efforts between industry partners will be required to meet environmental regulations.
To help industries meet these more stringent emissions regulations, Columbia Energy Group-Energy Consulting Services, Gas Technology Canada, the Department of Energy, the Gas Research Institute, Southern California Gas Company, the Institute of Gas Technology, and their commercial development partners, Air Liquide and CeramPhysics are conducting a program to develop and commercialize a retrofit NOx-reducing technology for high temperature, natural gas-fired furnaces. Additional support is being provided by IGT's sustaining membership program.

Oscillating combustion (U.S. Patent No. 4,846,665; European Patent No. 0524880A1) involves the creation of successive, NOx-formation-retarding, fuel-rich and fuel-lean zones within the furnace (see Fig. 1). This is accomplished by installing a high-speed oscillating valve on the fuel line at the burner. Heat is removed from the zones before they mix to reduce overall peak flame temperature, thus reducing NOx formation. Heat transfer from the flame to the load (and, therefore, furnace productivity) increases due to the more luminous fuel-rich zones and the breakup of the thermal boundary layer.

Fig. 2 The results of bench-scale testing of the oscillating combustion process with an air-gas burner.
In the current program, during bench-scale testing with air-gas at IGT (see Fig. 2), NOx reductions of over 50% have been achieved, depending on burner design and oscillation parameters. Heat transfer increases of up to 10% have been simultaneously measured. In pilot-scale (2,000,000 BTU/h) testing with oxy-gas at Air Liquide, up to 70% reductions in NOx have been measured.
IGT developed an operational database for air-gas oscillating combustion by acquiring NOx and heat transfer data on a variety of industrial burners under controlled laboratory conditions. An air-gas test and an oxy-gas field test have also been completed. The air-gas field test was carried out on an indirect-fired steel annealing furnace showing up to 40% NOx reduction and 3 to 7% efficiency increase. The oxy-gas field test was completed recently on a 150-ton per day oxy-gas-fired borosilicate fiberglass furnace. Results show 55% NOx reduction, a 30 to 50¯F drop in furnace crown temperature, 3% fuel savings, and 7% oxygen savings with no impact on glass quality.

Following the completion of the field test, the host site decided to retain the system in continuous operation. The project team has recently initiated a project to scaleup and demonstrate this technology on a steel reheat furnace. IH