Controlling the Water Content of Biomass Fast Pyrolysis Oil

Abstract

Several methods to control the water content of pyrolysis oil from fast pyrolysis of biomass were evaluated experimentally. Parameters varied were the operating temperature of the condenser, the gas load of the condenser, and the moisture content of the feedstock. Experiments were performed in a continuous bench scale plant (1 kg/h intake) equipped with a fluidized bed reactor. Pine wood with moisture contents between 0 wt % and 20 wt % (as-received basis) was used as feedstock. The mass balance closure was between 94 wt % and 102 wt %, and the reproducibility of yields of identical experiments was good. Increasing the condenser temperature (15−90 °C) and increasing the gas load (2.0−4.1 kg of gases/kg of vapors in the condenser feed) of the condenser are both well suited to control the water content. However, decreasing the water content by these measures always results in a loss of organic vapors, leading to a lower oil yield in the condenser. Deep drying of the feedstock is beneficial; a lower moisture content of the feed results in less loss of organic vapors for the same water content of pyrolysis oil. Experimental results were compared with the predictions of an equilibrium flash condensation model. Predictions of this equilibrium model are in good agreement with the experimental results. All input parameters of the model (reactor yields and composition of the organics in pyrolysis oil) can be measured, or are known, with sufficient accuracy.

Relationships between Biomass Composition and Liquid Products Formed via Pyrolysis

“…Burhenne et al (2013) found that higher feedstock moisture content led to slightly lower char and gas yields upon pyrolysis with minimal changes to the elemental composition of the char. However, this is in disagreement with Westerhof et al (2007) who observed slightly higher char yields with increasing moisture content. The water weight fraction distribution of the feedstocks in the two studies were quite different, 2.4-55.4% in Beyond impacts to the yields, He et al (2009) studied the change in selectivity to the organic fraction produced upon pyrolysis of switchgrass with 5, 10, and 15% feedstock moisture contents.…”

“…Several investigations (Westerhof et al, 2007;He et al, 2009;Burhenne et al, 2013) suggest that feedstock moisture content can also play a role in the yield and product distribution of the organic fraction of the bio-oil. As previously discussed, the presence of water in bio-oil prohibits its direct use and creates challenges to catalytic valorization.…”

A CFD study of biomass pyrolysis in a downer reactor equipped with a novel gas–solid separator-II thermochemical performance and products

“…11a have given the exact fraction of water in the product oil, but a study by Westerhof [50] reported that typically water content in the pyrolysis bio-oil is in the range of 15-35 wt% water content. The low water content in the product predicted here is mainly due to the low moisture content in the feedstock.…”

Fast Pyrolysis of Biomass Residues in a Twin-screw Mixing Reactor

“…However, it should be pointed out that these calculated values from experiments with a specific moist feedstock do not necessarily reflect the behavior and yields of this specific feedstock if it was completely dried by physical means prior to the experiment. It is known that moisture affects the yield distribution of pyrolysis 23 and this should be kept in mind when evaluating and comparing 'dry' balances.…”