Investigating biomass pyrolysis through intra-particle gas measurements

Intra-particle gas sampling technique was effectively applied for the analysis of the pyrolysis process on birch wood spheres, aimed to provide more insight on decomposition mechanisms as well as the enthalpy changes occurring throughout the process. The collection and quantification of gaseous chemical species from the interior of the biomass spheres has provided new information related to the impact of gaseous diffusion on the final concentrations of the products. Different intra-particle gas sampling configurations were investigated to demonstrate this, referred to as "half-hole" and "through–hole" approaches. In the first case, the hole for inserting the sampling probe (a passivated stainless-steel tube directly connected to a micro gas-chromatographer device) was created only to the center of the sphere, while in the second case the hole penetrated across the entire diameter creating a channel through the sphere. In the half-hole configuration, the probe was inserted to the center, ensuring a correct positioning by means of stoppers installed on the sampling probe. In the through-hole configuration, a second passivated stainless-steel tube with the same external diameter of the sampling probe was inserted on the opposite side of the channel, ensuring that the sampled gases were only those evolved from the central area of the biomass sphere and not gases evolved from the surface of the particle. The main differences seen in the detected composition of gas evolved during pyrolysis and in the pressure profile at the center of birch wood particles, using the intra-particle gas sampling technique in the two different configurations, are here described and discussed, showing that the through-hole configuration, where the gases are expected not to diffuse along the porous matrix but being immediately extracted for sampling when released, likely provides a more representative sampling of the gasses that are released.