Product distribution from pyrolysis of wood and agricultural residues

The pyrolysis characteristics of agricultural residues (wheat straw, olive husks, grape residues, and rice husks) and wood chips have been investigated on a bench scale. The experimental system establishes the conditions encountered by a thin (4 x 10(-2) m diameter) packed bed of biomass particles suddenly exposed in a high-temperature environment, simulated by a radiant furnace. Product yields: (gases, liquids, and char) and gas composition, measured for surface bed temperatures in the range 650-1000 K, reproduce trends already observed for wood. However, differences are quantitatively large. Pyrolysis of agricultural residues is always associated with much higher solid yields (up to a factor of 2) and lower liquid-yields. Differences are lower for the total gas,and approximate relationships:exist among the ratios of the main gas species yields, indicating comparable activation energies: for the corresponding apparent kinetics of formation, However, while the ratios are about the same for wood chips, rice husks, and straw, much lower values are shown by olive and grape residues. Large differences have also been found in the average values of the specific devolatilization rates. The fastest (up to factors of about 1.5 with respect to wood) have been observed for wheat straw and the slowest (up to factors of 2) for grape residues.