Low NOx, high efficiency multistaged burner: Gaseous fuel results

Abstract

AbstractA multistaged combustion burner design is being evaluated on a 0.6 MW package boiler simulator for in‐furnace NOx control and high combustion efficiency. A low NOx precombustion chamber burner has been reduced in size by approximately a factor of two (from a 600 ms first‐stage residence time to 250 ms), and, for additional NOx control, coupled with [1] air staging, resulting in a three‐stage configuration, and [2] natural gas fuel staging, yielding up to four stoichiometric zones. Natural gas, doped with ammonia to yield a 5.8 percent fuel nitrogen content, was used to simulate a high nitrogen content fuel/waste mixture. In low NOx burner baseline tests, without advanced staging, a 315 ppm NO emission (measured dry, corrected to zero percent O2) was measured, compared with an emission of 1000 ppm measured using a conventional, unstaged burner. Both of the multistaged combustion modifications for additional NOx control reduced NO emissions by an additional 50 percent, to 160 ppm meeting the program goal. However, air staging application resulted in the entire front end of the boiler being fuel‐rich, whereas fuel staging, or reburning, in the boiler required only a small fuel‐rich flame core in the boiler. Further, no boiler penetrations were necessary with reburning modification, as staged fuel and air were injected through the boiler front wall; access for burnout air injection deep into the boiler was necessary for the air staging modification. Thus, the four‐stage configuration, combining the precombustion chamber burner and reburning, appears to be the most promising approach for minimizing NO emissions and maximizing primary fuel/waste destruction.