An optical method of measuring the temperature in a fluidised bed combustor

The paper analyses the dynamic aspects of the temperature field in a fluidised bed of solids particles (e.g., sand) in which a gaseous fuel is being burned. Such a hot bed emits electromagnetic radiation within the visible range and this can be recorded using a digital video camera. This fact has been used to develop a method for measuring the bed’s temperature in the line of sight, through the quartz sides of the reactor. A solid probe is only used for calibration. Video recordings were obtained covering different regions of the bed over three wavelength bands, red, green and blue. In the course of an experiment, the mean temperature of the bed, measured with thermocouples, was raised from ambient to 1300 K, at a rate of ∼ 1 K/s. The data collected were used for calibration, with the brightness of individual pixels converted to a temperature scale. The calibration can then be used to investigate the dynamic temperature distribution within the field of view, in individual elements of the bed. This can also help the study of heat transfer in the bed, its distribution and dissipation. Using this method, it is possible to make direct observations of the intermittent combustion of gaseous fuels in a bubbling fluidised bed. The results provide direct proof that the temperature gradients observed within such beds are associated with exothermic processes within fast moving bubbles. The method could be adapted to studying, e.g., the combustion of solid fuels.