In-situ measurement of temperature and potassium concentration during the combustion of biomass pellets based on the emission spectrum

Here, a calibration method using the K concentration, temperature and the characteristic spectral line radiation intensity in flame is described. In addition, a radiation function model between these three variables, I-lambda 766 (T, C-K) = 0.821.I-b(lambda(766),T).C-K, was established. A Y-type optical fiber was used to connect the spectral signals from the same direction to two spectrometers. The continuous spectra in the 500-800 nm band were used for multi-spectral temperature measurements. The combination of the measured temperature and the K characteristic spectral line radiation intensity at 766 nm was used for measurements of K concentration. The temperature and equivalent ratio of the heating atmosphere were 1300 K (+/- 20 K) and 0.786, respectively. Compared with rice straw pellet, pine wood pellet had a lower K concentration and higher combustion temperature during the entire combustion process. The peak K release concentrations of the pine wood pellet and the rice straw pellet during the volatile combustion stage were 2.09 ppm and 10.03 ppm, respectively, and the peak flame temperatures were 1774 K and 1756 K, respectively. In the char combustion stage, the peak K release concentrations were 27.83 ppm and 110.43 ppm, respectively, and the peak surface temperatures were 1287 K and 1143 K, respectively. The established function model for measuring K concentration is also applicable to the combustion diagnosis of other K-rich fuels.

Automated summary

The method described uses K concentration, temperature, and characteristic spectral line radiation intensity in flame for calibration and establishes a radiation function model. It can be applied to measure K concentration and diagnose combustion processes, such as comparing K release concentrations and combustion temperatures of different fuels during volatile and char combustion stages.