OCR Text |
Show where <L.(t)> denotes the time-averaged value. The function in EQ. 2 can be obtained by performing a calibration on a given combustion system over a range operating conditions. Once the function is defined the stoichiometry and/or firing rate can be determined from the specific spectral region being monitored. In addition to monitoring burner operating conditions, detection of abnormal variations in the observed emission intensity can be used to alert process operators of potential problems. In the simplest mode, the absence of an emission signal would indicate no flame being present, thus operating similar to conventional U V flame sensors. In a more sophisticated mode of operation detection of abnormal variations in the emission intensity could signify a burner malfunction, such as, deflection of the flame or refractory failure. m. STOICHIOMETRY MONITORING In the work presented, the OH band from 295nm to 325 nm was chosen for real-time monitoring2. The integrated O H signal was collected using the P C spectrometer, the burner configuration shown in FIG. 3, and data acquisition system software developed at Air Liquide. The acquisition software controls the P C spectrometer sampling frequency, calculates the integrated intensity of the O H band, and performs a background subtraction. Depending on the detector integration time and number of spectra being averaged the sampling frequency ranged from 12 to .001 Hz. For the work presented here the sampling frequency was 1 Hz. Prior to monitoring the burner stoichiometry a calibration is performed using calibrated flow meters and knowledge of the gas composition from G C analysis. Calibration points were obtained by operating the burner at a constant firing rate of 1.16 MMBtu/hr and varying the stoichiometry. In this case, E Q . 2 reduces to h °c f(S(t))V only. The simple calibration results in a linear expression relating the stoichiometry and integrated O H signal intensity, as shown below in FIG. 6. : The total integrated intensity observed is given by J w A (/) 9 |