Fast Pyrolysis

Fast pyrolysis is the process of rapid thermal decomposition of biomass in the absence of oxygen. This produces energy, liquids, gases, and char. Small particles, less than a quarter inch in size, are delivered to a high-heat reactor where essentially no combustion occurs. The fuel must be small in size to assure high heat transfer rates during the process. Around 500 degrees Celcius, the material is transformed into a vapor, which in turn is cooled, condensed, and recollected as a liquid bio-oil or converted to hydrogen through a reforming process (Day et al. 2003). Gases that are non-condensable are recycled for co-firing into the reactor while the char is removed for fuel, or as a commercial product. In order to ensure a high yield of bio-oil, the processing time from introducing the feedstock to quenching is typically less than two seconds. Thus the name fast pyrolysis. Prior to recent advancements, pyrolysis was a relatively slow cooking process of producing oils that were thick, low quality, tar-aqueous mixtures in low yields. Processing time took minutes to hours. This traditional slow pyrolysis had been used by industries to produce char and extracts such as turpentine, but has been displaced by fast pyrolysis for biorefining (Bridgewater 2002).

The primary products formed by fast pyrolysis are pyrolytic bio-oils, a combustible mixture of oxygenated hydrocarbons, and char. Reactor design and feedstock characteristics influence yield and quality. Assuming that the feedstock has been dried to less than 10 percent moisture, the process will yield approximately 150 gallons per ton (Brown 2003). Roughly 10 to 20 percent of the product will be in the form of a non-condensable combustible gas, mainly carbon monoxide, hydrogen, and methane and is recycled into the reactor for process heating (Agblevor et al. 1995).

The Ensyn Company announced a US$9 million plant to be built in Renfrew, Ontario. In 2003, Ensyn had 6 plants operating and reported producing 19 million liters of bio-oil per year. Other companies such as the DynaMotive Corporation and BTG Biomass are making great strides in pyrolysis technologies. PyNe, a global network of active researchers and developers, also exchange information and developements related to the production of liquid fuels, electricity, and chemicals.

Fast Pyrolysis