Simultaneous in situ measurement of temperature and size of burning char particles in a fluidized bed furnace by means of fiberoptic pyrometry

Abstract A pyrometric instrument for the measurement of the temperature of burning fuel particles in fluidized bed furnaces is presented. The instrument is equipped with a fiberoptic probe which is inserted into the fluidized bed. A theory based on radiative transfer and analysis of the statistics of fuel particles is developed, which allows for the extraction of statistical expectation values of the size of the fuel particle from the pyrometric signals along with the temperature. Experimental results obtained with the instrument in a pilot scale fluidized bed furnace of 500 kW thermal power are presented. The pyrometrically measured two-color ratio temperature of the fluidized bed is found to be in very close agreement with an independent thermocouple reading. The emissivity of the bed is found to be close to unity. The elevation of the fuel particle temperature above the bed temperature varies from about 50 up to about 600 degrees. The temperature elevation of the fuel particles is found to decrease with increasing particle size in all experiments.