Expanded bed height determination in a tapered fluidised bed reactor

Fluidised bed coating is a commonly applied technique to microencapsulate food powder ingredients. Particularly for the food industry, the use of a top-spray configuration in a tapered reactor is considered to be most appropriate. Good particle-droplet contacting can be established by controlling the air flow rate and by adjusting the distance between the nozzle and the particle bed. In this paper, the determination of bed height in a tapered expansion chamber of fluidised bed equipment was investigated using static pressure measurements along the wall. As an alternative to this traditional approach, the use of wall surface temperature measurements was proposed as a non-invasive routine method. The experiments were performed in a Glatt GPCG-1 top-spray fluidised bed unit in which a polycarbonate expansion chamber was mounted. This allowed comparison of the results of the pressure and temperature measurements with visual observations.