Study of char morphology during biomass pyrolysis and gasification via micro-computed tomography

Chars produced by pyrolysis and gasification of almond shells to different peak temperatures have been imaged post-pyrolysis via x-ray micro-computed tomography (CT) in order to track the evolution of pores throughout the thermal processes. However, this technique cannot precisely resolve the process of pore evolution over time, and characteristics of the produced chars are affected by reactions that typically continue to occur as the reactor is cooled prior to char recovery. For this reason, a novel fixed-bed downdraft reactor has been developed to directly observe the processes of pore formation and evolution in different temperature regimes via in situ CT. Pulverised almond shells (<100 μm particle size) were pyrolysed or gasified via slow heating (1 °C s-1) n argon to peak temperatures between 300 °C and 1000 °C, followed by a 15-minute hold at peak temperature, either in argon (pyrolysis), or in CO2 to induce gasification at peak temperatures greater than 800 °C. From the acquired images, pathways to the evolution of porosity and pores morphology (3-4μm dia.) during slow pyrolysis and gasification of biomass have been proposed. Experiments employing direct observation of the solid state have been performed, and application of mechanisms confirmed by these experiments to pyrolysis and gasification models is planned.