In this study, a novel aerosol-based method has been further developed and applied for on-line investigating of steam gasification kinetics of suspended biomass char particles. By combining the aerosol method with thermogravimetric analysis, the gasification kinetics were established in steam (33 vol%)-N₂ atmosphere from 800°C to 1300°C for char samples produced from pelletized wood, straw, and miscanthus. The aerosol method includes steps for generating, suspending, and gasifying char particles. The conversion of the char particles was established by measuring the change in particle size distributions and mass concentrations using an aerodynamic particle sizer (APS) spectrometer and a tapered element oscillating microbalance (TEOM), respectively. The reactivity of three char samples could be ranked as wood > miscanthus > straw. The activation energy was 155 kJ·mol^-1 for wood char, 199 kJ·mol^-1 for miscanthus char, and 222 kJ·mol^-1 for straw char. Results interpreted from TEOM and APS measurements indicated that the effective density of char particles initially decreased until a certain level of conversion was reached, and then remained constant. 

In total eight char samples from pelletized wood, miscanthus, and straw were prepared under various pyrolysis conditions. The CO₂ gasification kinetics for each sample was established in the temperature range from 800 °C to 1300 °C by the combination of thermogravimetric analysis (TGA) and a novel aerosol-based method. The aerosol-based method was used for the high temperature range between 1100 °C and 1300 °C, by gasifying suspended char particles (0.5–10 μm) in an oxidizing carrier gas. A tapered element oscillating microbalance (TEOM) was used to measure the change of mass concentrations of particles in the carrier gas, before and after gasification. The results showed that the aerosol-based method could be used to investigate the intrinsic gasification kinetics of biomass char, at least up to 1300 °C. All char samples showed similar reactivity in the low temperature range. However, above 1000 °C there were significant differences in reactivity, and at 1300 °C the conversion of the wood was in the order of 10 times faster than that of straw. The general char reactivity order in this study was wood > miscanthus > straw.

An aerosol-based method was proposed and developed to characterize particles fragmented from biomass chars during oxidation. The chars were prepared from both wood and miscanthus pellets under various pyrolysis conditions. Char fragments with aerodynamic diameters in the range of 0.5–10 μm were suspended and transported in a reactive gas through an aerosol reactor, which was heated by an electric oven. The oxidation of char particles in the reactor was investigated by determining on-line the particle size distributions before and after passage through the reactor using an aerodynamic particle sizer (APS) spectrometer. The interpretation of APS data was evaluated by both experiments and models in which the fine char particles were assumed to keep either constant density or constant diameter during the oxidation process. The results indicate that the aerosol-based method can be used to determine reaction kinetics of char particles in the high temperature range, where oxidation is normally controlled by diffusion limitation if measuring with the conventional techniques. The application of the aerosol method indicated that high pyrolysis temperature and prolonged retention time will reduce the char reactivity.

This study compares the characteristics of particulate matter (PM) in the hot product gas from three different atmospheric fluidized bed biomass gasifiers: a bubbling fluidized bed (BFB) gasifier, a circulating fluidized bed (CFB) gasifier, and an indirect BFB gasifier (the latter integrated with a CFB boiler). All gasifiers displayed a bimodal particle mass size distribution with a fine mode in the <0.5 μm size range and a coarse mode in the >0.5 μm size range. Compared with the mass concentration of the coarse mode the mass concentration of the fine mode was low in all gasifiers. For both the BFB and CFB gasifiers the fine-mode PM had a similar inorganic composition, indicating an origin from the ash and the magnesite bed material used in both gasifiers. In the indirect BFB gasifier the fine-mode PM was instead dominated by potassium and chlorine, and the tar fraction properties evoked tar condensation in the sampling system that affected mainly the fine-mode PM. The coarse-mode PM in the BFB gasifier was dominated by char fragments abraded from the pyrolyzed wood pellets. In the CFB gasifier the coarse-mode PM was mainly ash and magnesite bed material that passed through the process cyclone. In the indirect BFB gasifier the coarse-mode PM was mainly ash, probably originating both from the BFB gasifier and the CFB boiler.

This study characterized the particulate matter (PM) formed during the indirect steam bubbling fluidized bed gasification of wood pellets at atmospheric pressure. A system including a dilution probe, a bed of granular activated carbon, and a thermodenuder was used to sample the PM at high temperature with the aim of separating it from condensing inorganic vapors and tars. The particle mass size distribution was bimodal with a fine mode in the <0.5-μm size range and a dominating coarse mode in the >0.5-μm size range. The coarse mode was representatively characterized while condensing inorganic vapors and tars complicated the evaluation of the results for the fine-mode PM. Morphological analysis of the PM indicated that the char content was low. The inorganic fraction was dominated by potassium and chlorine for fine-mode PM and calcium and silicon for coarse-mode PM.