OCR Text |
Show Modification of the combustion process to allow natural gas to react initially under oxygen-deficient condition is one of the most effective methods of controlling thermal or fuel N O formation. Staged combustion could be accomplished by several different techniques. The combustion process will be staged either by physically separating the fuel rich zone from the burnout zone, or by using the burner to delay the mixing of the fuel with all of the combustion air. In this study, the combustion system was considered as a series of idealized reactors in which time / temperature history and stoichiometry could be controlled independently. The results obtained in bench scale studies define the optimum conditions for staged combustion, and the effects of other operating parameters on the formation and reduction of fuel N O are also studied. EXPERIMENTAL W O RK (1) Experimental System The experimental reactor used in this work in a refractory lined down-fired tunnel.it forms a vertical combustion chamber, 270 cm long and 15 cm diameter in cross section [4,5,12]. The furnace with six separate sections is made up of an outer steel shell and three layers of refractory insulation.the entry of the furnace consists of a 30 cm long refractory quarl which diverges gradually from 5 cm to the full 15 cm diameter. The long quarl helps to eliminate recirculation and improves the one-dimensionality of the flow field. The furnace sections include: (1) A removable radiation shield upstream of the staging/cooling position to minimize the effects of downstream parameters upon upstream conditions, (2) T w o refractory sections with removable coils to allow cooling of first or second stage combustion products, (3) A removable staging choke to insure isolation of the first stage, (4) A removable air ring for second stage air injection. Burner used in this study was an axial diffusion burner with swirling. A water jacket between furnace and burner was used to prevent the high temperature in furnace which would damage the burner. A gas mixer was used for mixing of fuel nitrogen (NO) and air. The mixing gas were separated by two streams and being injected into axial or radial direction of burner. Flue gas temperature in different positions were measured by thermocouples . Flue gas sampling was conducted with a stainless probe and in-flame gas sampling was taken with a stainless steel water cooled probe. The N O / N O x species were measured by chemilum-inescence method with Backman Model 951A . CO, CO2 species were using non-dispersive infrared method with Beckman Model 880. O2 species were using paramagnetism method with Beckman Model 755A. The whole experimental system is shown on Fig. 1. 3 in 4-7 |