Characterization of Products From High-Pressure Biomass Pyrolysis in an Entrained-Flow Reactor
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Pyrolysis experiments on pine and switchgrass (sieved to 180-250 µm) were performed in entrained flow reactor at high temperatures (600-1000 °C) and high pressures (1-20 bar). Heating rates as high as 104 K/s were achieved with solids residence time from 3-10 s. Char, gases and condensable tars were characterized using SEM, N2 physisorption, GC and MS respectively.
SEM was used to study the influence of pyrolysis temperature and pressure on char morphology. The results show that with increase in pyrolysis temperature and pressure the particles melted and gained more spherical features. At ambient pressures, a significant fraction of particles burst at higher temperatures. At high pressures, pyrolysis gases tend to be trapped in char particles forming distinct gas filled pockets. Char structure and surface area, is strongly impacted by the increased temperature and pressure during pyrolysis, and is likely to affect char gasification activity.
The yields of light gases such as CO, CO2, H2, CH4, C2H4 and C2H2 were quantified using GC analysis. The condensable organics from pyrolysis were extracted and analyzed using MS. A variety of tar species from phenolics to polynuclear aromatic hydrocarbons (PAHs) were identified and their relative abundance rated as a function of temperature and pressure.
The present study will provide the basis for improved mathematical model for char gasification based on meaningful descriptors.