Dynamics of physical characteristics of biowaste during pyrolysis

The changes in the weight,structural and morphological properties during pyrolytic treatment of pulp and paper biowaste were investigated. A thermogravimetric system Cahn TG 171 was applied. Residual ash samples were obtained at various maximum temperatures (150 degrees C, 400 degrees C, 600 degrees C, 900 degrees C, 1050 degrees C, 1200 degrees C, 1350 degrees C and 1500 degrees C). A heating rate of 40 degrees C min(-1) and a residence time at the maximum temperature of 10 min were used in all experiments. The reactor temperature and sample weight loss were recorded on-line by the TG. In this study the following were investigated: (1) the variation of the relative weight of a biowaste sample during the pyrolysis process, (2) the influence of the maximum temperature on the total weight loss of a sample, and (3) the structural evolution of the biowaste material during its pyrolysis. TG data showed that two inflection points identifying the limits of three stages of particle evolution characterize weight loss curves. These stages represent the devolatilization of the biowaste (stage 1), followed by the formation and escape of volatiles (stage 2) and the continuous gradual weight loss of the biowaste with increasing temperatures (stage 3). Scanning electron microscope images showed that the phenomenon of continuous gradual weight loss occurring in stage 3 is due to the formation of ash through the process of gradual peeling of the material from the surface of the fibers. With pyrolysis, a significant amount of weight is reduced (up to 75% at 1500 degrees C) with the fibrous structure of the original material still apparent. (C) 1998 Elsevier Science B.V. All rights reserved.