Devolatilization of millimeter-sized biomass particles at high temperatures and heating rates. Part 1: Experimental methods and results

In the framework of a general research on biomass combustion, this paper presents and discusses the experimental techniques developed to analyze the heating, drying and devolatilization of biomass particles of few millimeters, a size range scarcely studied in the past. Individual particles were suspended in a stream of hot gases generated by a Flat Flame Burner, with controlled temperature and composition. The evolution of their morphology was monitored by time-lapse photography; additionally, an estimate of the instantaneous volatile release rate was derived from the picture series based on the size of the volatile shell flame. The temperature inside the particles (3-15 mm in diameter) was measured with pairs of fine wire thermocouples located at the particle's center and near its surface. The systematic error associated to this technique (deviations up to 300 K in relation to the actual particle temperature), due to the intense heat transfer along the metal wires, was evaluated experimentally and modeled; the agreement found in the comparison allowed for establishing a procedure to correct those signals and thus adequately evaluate the thermal gradients within the particles. A subsequent comparison of the experimental results (evolution of size, shape, internal temperature and temperature gradients, volatile release rate in a variety of conditions) with simulations performed with models which alternatively consider or neglect internal gradients is presented in a separate paper [21].