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

• A measurement method of K concentration is proposed based on the emission spectrum. • The temperature affected the radiation intensity of the K characteristic spectra. • The K concentration of biomass pellets was measured at different combustion stages. • The peak K release concentration of the rice straw was 110.43 ppm. 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 λ 766 T , C K = 0.821 · I b (λ 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. [ABSTRACT FROM AUTHOR]