Status Report on the Development of the VIStA Combustor for Very Low NOx Emissions in Furnaces and Boilers

The objective of this development program is to bring to the market an economically attractive ultra-low emissions combustor with NOx production of less than 9 ppmv with CO emissions of less than 50 ppmv (both at 3% 02) while maintaining high efficiency and ease of operation and maintenance. The technology called the Vortex Inertial Staged Air (VIStA) combustor addresses both prompt and thermal NOx production in an air-staged combustor design. It reduces prompt NOx by partially reforming thoroughly pre-mixed natural gas fuel and air in the first stage of the combustor to CO and H2. By operating the first stage of the combustor at optimum conditions, natural gas can be reformed to species that will not contribute to the formation of prompt NOx The inertial combustion system is ideal for this purpose because it promotes very stable combustion over a wide range of stoichiometry and firing rates and aids in the reformation of the fuel. The VIStA combustor reduces thermal NOx production by utilizing advanced aerodynamic principles to provide high internal flue gas recirculation in each of the combustion stages without resorting to conventional external flue gas recirculation (FGD) approaches. This translates into improved efficiency and reduced maintenance and operating expenses. Laboratory testing of three prototype VIStA combustors with nominal thermal inputs of 0.25, 3.0, and 6.0 MMBtu/hr has demonstrated the technical viability of the VIStA concept to be capable of achieving the desired NOx and CO emission levels. As scale-up has progressed with each of these combustors, design modifications have been implemented with the aid of computational fluid dynamic (CFD) modeling using Fluent, a product of Fluent, Inc Through this parallel effort, verification of the computational model with actual performance test data is providing the technology understanding necessary for future scale-up to 30-60 MMBtu/hr levels. This paper describes the results of recent testing of the 6.0 MMBTU/hr VIStA combustor towards meeting the design goals.