TEMPERATURE PROFILES IN A WOOD PACKED-BED HEATED BY HOT INERT-GASES

Presented in this paper are temperature profiles in a green-wood packe d bed heated by hot inert gases for the sensible heating stage of wood carbonization. They give insight into the heat transfer during the in itial carbonization stage and hence are useful for carbonization retor t design. Gas temperatures within a cylindrical bed, packed with green wood particles, were measured at different heights across the diamete r by means of thermocouples. The wood bed was heated by inert hot gase s from a charcoal combustion chamber. There was a high temperature dro p which happened mostly in the first one third of the bed. This was at tributed to the high moisture content of the wood. The measured radial temperature variations showed a symmetrical profile between each side of the bed; the centre being the highest with strong local horizontal variations. This uneven heat distribution could affect the quality an d uniformity of the charcoal produced. It was deduced that for uniform charcoal production, a short and wide bed was more appropriate. An at tempt was made to predict the axial temperatures profiles using the on e-dimensional axial mathematical model, initially proposed by Schumann (6) and extended by Rosen(10) and Jeffreson(11). The bed was physicall y modelled as thin independent elements similar to that proposed by Pa rti(5). The predictions were within 14% of the measured values. Using the axial temperatures at every measurement height, an empirical relat ionship for radial temperatures was suggested.