Influence of feedstock variability on thermal decomposition of forest residue in a screw feeder for high temperature conversion

Abstract

Thermochemical conversion of biomass uses high temperatures to break down the feedstock into products. Feeding the reactor, however, can be a challenge that impedes smooth operation of the thermochemical process. The aim of this study was to investigate the effect of feedstock compositional variability on the material deposition on the screw feeder during pyrolysis reactor feeding. Four different sample sets derived from pine (Pinus Taeda), 1st (rich in stem wood), 2nd (rich in bark and needles), 3rd (rich in stem wood), and 4th (whole residues), were used in this study while the reactor was operated at 500 °C. Results showed that the sample set consisted with cleaner feedstock experienced relatively less solid material and tar deposition on the screw feeder. For example, the lowest pseudo accumulation rate was 0.5 pitch/kg-feed for the 3rd set while the highest was 6.7 pitch/kg-feed for the 2nd set showing strong material dependance. Simulations on the temperature prediction inside the auger explored the surface of the auger exposed inside the reactor (ΔTavg = 93 °C) and outlet of the purge gas region (ΔTavg = 126 °C). This temperature drop would likely reduce the formation of deposits on the auger allowing the system for longer periods of continuous operation.