Evaluation of a Wire-Mesh Duct Burner Premixer Using LSI Techniques

Abstract

The mixing of fuel and oxidizer is critical for the reduction of NOx emissions from premixed combustion burners. The mixing process in a pre-mixer of a natural gas-fired conical wire-mesh duct burner (DB) was studied experimentally using the laser sheet illumination (LSI) technique. A quasi-quantitative technique was used to rank the relative mixing performance of the different geometrical and flow combinations tested (mixer geometry, fuel injection angle and fuel air momentum ratio). The present paper presents some of the results used in the design and analysis of the burner. This burner was integrated and tested with a micro-turbine cogeneration system (MT70 kW Ingersoll Rand (IR) CHP unit). The DB provides supplementary firing in the exhaust gas stream of the microturbine to increase and control the thermal output of the micro-cogeneration system. The combination provided near perfect premixing and low emissions. The DB successfully raised the micro-turbine exhaust gas temperature from about 227°C to as high as 700°C with NOx and CO emissions of less than 5 ppm and 10 ppmv (corrected to 15 percent O2) respectively. The DB also displayed stable, low emissions operation throughout the surface firing rate range of 148 kW to 328 kW (1574 kW/m2 to 3489 kw/m2). The results show that LSI technique can provide invaluable information about the overall flow field structure. Many important observations are discussed such as mixing, fuel spread, and fuel jet penetration. Samples of the LSI images and 3D plots for selected cases are presented. The two best geometrical combinations ranked during the LSI test were used in the actual combustion test of the DB. Some of the combustion results which prove the effectiveness of the LSI technique are presented.