Birch wood particle shrinkage during rapid pyrolysis

A study of the shrinkage of cubic (∼5 mm) birch wood particles during pyrolysis is presented. The particles were rapidly injected into a preheated furnace with a constant temperature in the range 350–900°C. The size of the particles in longitudinal, tangential and radial directions was measured until no further mass loss occurs. The volume shrinkage was found to be 45–70% and the shrinkage in the different directions 5–25, 25–40 and 15–40% for longitudinal, tangential and radial directions, respectively. Longitudinal shrinkage commenced after about 60% mass loss and is not strongly dependent on heating rate or on cellulose chain scission. A maximum shrinkage was found for tangential and radial directions at 400 and 500–700°C, respectively, and above these temperatures the shrinkage decreases. The char yield decreases and the char structure becomes more deranged with increasing temperature. Empirical models of shrinkage as a function of conversion are presented.