Pyrolysis of Cynara cardunculus L. samples – Effect of operating conditions and bed stage on the evolution of the conversion

Abstract

The effect of different parameters on the pyrolysis of Cynara cardunculus L. was studied through an innovative technique based on a precision scale, capable of measuring the time evolution of the biomass samples mass during their thermochemical conversion process while moving freely inside a fluidized bed. A silica sand bed reactor, operated under different values of excess gas velocity and reactor temperature, was employed to hold the pyrolysis reaction of cardoon particles of three different size ranges. The pyrolysis was accelerated for higher excess gas velocities, obtaining pyrolysis times as short as 17.3 s for experiments conducted under bubbling fluidized bed regimes, compared to 185.9 s required to complete the pyrolysis of the same sample in a fixed bed configuration. Similarly, the effect of increasing the reactor temperature promoted faster heating rates across the fuel samples, especially under fixed bed configurations, for which the pyrolysis time is reduced from 321.7 s to 132.0 s when increasing the bed temperature from 450 to 650 °C. Regarding the biomass particle size, small sizes are preferred to minimize the conduction thermal resistance inside the fuel particles and, thus, reduce pyrolysis times and increase volatile yields for the pyrolysis in a bubbling fluidized bed reactor. The opposite result was found when the pyrolysis took place in non-bubbling beds, where the use of larger particles is beneficial to accelerate the biomass pyrolysis reaction.