| OCR Text |
Show Technical Background Flame fluctuations measured by burner flame sensors reflect flame turbulence in the ignition zone. In individual burner flames, the mixing rate of fuel and air dominates the combustionprocess. Each burner flame consists of a multitude of eddies contributing to flame flicker generation at various frequencies as a result of turbulent mixing at the edges of the fuel and air jets. Smaller eddies occur more often and generate higher frequencies and vice versa. The movement of eddies in turbulent flows affects the mixing rate of air and fuel in diffusion flames. The size of the eddy (.;ontrols the amount of fuel and air mixed. Since combustion kinetics are fast compared to these turbulent mixing times, the fuel and air are combusted essentially instantly. Because a large eddy may entrain more fuel than a smaller eddy, a larger eddy should give a larger emission intensity. Each flame characteristic (e.g., fuel to air ratio, swirl, mixing rate, or combustion efficiency) is associated with a dominant radiation segment in the observed flame fluctuations. Project Objectives The Burner Diagnostic System is based on a new method of signal processing (patent pending) in the frequency domain which allows the calculation of statistical variables characterizing various combustion parameters. The main objectives of the new combustion diagnostic system were to test and evaluate this new method (leading to improvement in combustion efficiency and reduction in Nox emissions), to finalize algorithm development, and to advance combustion optimization strategies. Practical applications of this method include: • Identification of out-of-tune bumer~ • Burner balancing • Burner optimization for ected cr: ria (e.g., minimum NOx or maximum efficiency) • NOx compliance and combustion optimization. Test Description The Fireye pilot-scale test boiler is equipped with a small l.O-MBtu gas burner of simple design with no special arrangements for low-NOx operation, such as air staging. The burner is equipped with basic automatic control and safety systems and allows broad changes of excess air. The boiler is the main testing facility for Fireye research and development efforts and has several scanner ports, flue gas analyzers, and a dat2 '1cquisition system (DAS). The gas analyzer used during our tests provided measurements of 02' CO, and NOx in the flue gas with the analog outputs connected to the DAS. Thermoane?mome~c transmitters measured fuel gas ~d air flows. A common electric actuator mechanIcally linked and modulated the fuel and aIr flow 2 |
