Bio-oil from Sawdust: Design, Operation, and Performance of a Bench-Scale Fluidized-Bed Pyrolysis Plant

To test the viability of converting sawdust to bio-oil, an experimental fluidized-bed reactor was designed, constructed, and operated. The design was for a sawdust feed rate of 100 g/h at a temperature of 500 °C. The gas residence time in the reactor was less than 1 s to achieve fast pyrolysis. Experimental repeatability and operational stability were evaluated, and the yields of various products, including char and bio-oil, were determined. Results showed a consistent bio-oil yield of about 62%. Bio-oil samples from the liquid collection system were taken and examined separately using gas chromatography/mass spectrometry (GC/MS). Detectable components with a sizable concentration belonged to the acid, ketone, and phenol groups. The heavier fraction of bio-oil had a lower water content and higher percentage of phenolic compounds. Elemental analyses of the bio-oils and chars were determined and compared to that of the sawdust. A low ash content in the produced bio-oils proved that the char separation system was very efficient. The heating value of the produced char, the byproduct of pyrolysis, was high, and therefore, it has potential for use as a source of process heat. The composition of the non-condensable gas produced was characterized by a micro-gas chromatograph. Results prove that fast pyrolysis is a promising technique to convert sawdust into liquid that can be more easily transported than low-density biomass.