(583ge) Energy Change Mechanisms Study During Biomass Pyrolysis By in-Particle Gas Sampling

For the optimal design of thermal treatment reactors, the knowledge of mechanisms and transformations occurring during the thermochemical conversion processes is fundamental. The aim of this paper is to provide better understanding of pyrolysis kinetics, through the correlation of pyrolysis gas composition with reaction heat. Some DTA/TG studies on reactions within biomass particles reported in the current literature conclude an overall exothermic reaction sequence while others report an endothermic process. In addition to weight changes, only in-particle temperature measurements have been reported and used to elucidate the reaction sequence. To obtain a better understanding of the process, chemical species gas sampling inside the particle was performed during controlled heating. To our knowledge, this is the first time gas sampling measurements inside of a sample have been made.
Birch spherical particles were chosen for these experiments, which were modeled using CFD analyses. The physical and chemical characterization of the wooden biomass has been performed. In addition, its thermal behavior has been characterized by means of TG/DTA coupled with FTIR, which allowed continuous analysis of the evolved gas.
The particles with 19.0 mm and 31.8 mm diameter have been subjected to flash pyrolysis in a stainless steel tubular reactor at operating temperatures of 500°C. The inert atmosphere was ensured by 350 cm³/min of Helium, injected into the reactor. Gas chromatographic analysis of the evolved gas has been performed, sampling from the center of the particle. Simultaneously, temperature measurements during the process were made at the surface and in the center of the wooden sphere. The GC detected CO₂, CO, CH₄, C₂H₆, C₂H₄ and H₂ as a function of center temperature, enabling a preliminary mechanistic understanding to develop. The temperature data revealed values of approximately 20°C to 50°C higher in the center compared to the surface of the particle.
Based on the primary analysis of the material and on the evolved gas composition, calculations of heat of reaction and theoretical adiabatic temperature were made combining the product gas measurements and the recorded temperatures. The time for the reactions happening inside of the particle is variable according to its dimensions and takes place at recorded center temperatures of 510°C. The presentation will show the details of the experimental technique as well as discuss the developed reaction sequence based on in-particle chemical species measurements coupled to CFD analyses.