Measurement of char surface temperature in a fluidized bed combustor using pyrometry with digital camera

Artikel i vetenskaplig tidskrift, 2016

A method is presented to measure the char surface temperature during conversion in fluidized bed (FB) using a digital camera. The method applies one-color pyrometry (P1C) sequentially for the three wavelength bands (red, green, and blue) changing from one band to another automatically as a function of radiation intensity received by the sensor of the video camera. Experiments were made in a twodimensional FB combustor (0.18x0.50x0.018 m) equipped with a window for visual observation. It is shown that the new method improves the accuracy compared to two-color pyrometry (P2C), allowing the measurement of a wider range of temperature, including temperatures lower than the bed (background). The main limitation of P1C (compared to P2C) is that the char emissivity has to be known. However, a sensitivity analysis, assuming a char emissivity variation from 0.85 to 1, reveled that the relative error in temperature is lower than 1% when the surface temperature of the char is higher than that of the bed. Then an assumed value of emissivity within this range is sufficient. However, a more precise estimate of char emissivity is needed when measuring temperatures lower than the bed temperature. Furthermore, the method enables determination of details such as surface temperature gradients and size of the particle during combustion. Overall, the technique allows determination of precise data of the fuel conversion process in FB.