Controlling the water content of biomass fast pyrolysis oil

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.