Fixed-bed pyrolysis of Cynara cardunculus L. - Product yields and compositions

The pyrolysis of Cynara cardunculus L. was studied with the aim of determin ing the main characteristics of the charcoal formed and the nature and quan tity of gases produced. Variables investigated were temperatures between 30 0 degreesC and 800 degreesC, particle sizes between 0.4 and 2 mm diameter, initial sample weights between 2.5 and 10 g, and nitrogen flow rates betwee n 100 and 300 cm(3)/min. Experiments were carried out isothermally. Under t he conditions of this study, particle size, nitrogen flow rate, and initial sample weight generally did not exert any influence, whereas temperature w as very significant. An increase in this variable led to an increase in the fixed carbon content, gases produced and, to a lesser extent, ash percenta ge. On the other hand, volatile matter and solid yields decreased with incr easing temperature. The principal gases generated were H-2, CH4, CO and CO2 . Heating values of both gas and solid phases were determined from gas comp osition and elemental analysis. The quality of charcoals and heating value allow the conclusion that the optimal temperature for pyrolysis should be b etween 600 degreesC and 700 degreesC. Finally, a kinetic study of the pyrol ysis, based on gas generation from thermal decomposition of the residue, wa s carried out. From this model, rate constants for the formation of each ga s and their corresponding activation energies were determined. (C) 2000 Els evier Science B.V. All rights reserved.