Flash Pyrolysis of Biomass for Liquid Fuels

Abstract

Conventional pyrolysis produces char, a crude organic liquid, sometimes referred to as "bio-oil", and gas in approximately equal proportions. However, if flash pyrolysis is used, very high yields of over 60 wt% (dry basis) of bio-oil are produced. This oil can be used as a low grade boiler fuel or can be upgraded to products such as gasoline and diesel. The principle of flash pyrolysis for liquids production is the combination of very high heating rates with moderate temperatures and rapid quenching of liquid intermediate pyrolysis products. Several techniques have been employed including fluid beds, entrained flow reactors, cyclone and vortex reactors; and the principles employed include gas-solid heat transfer as in entrained flow reactors and solid-solid heat transfer as in ablative pyrolysis. This thesis reviews the reaction mechanisms, pathways and kinetics of pyrolysis by reference to the flash pyrolysis technologies employed to date. A preliminary design of a 5 kg/h "bullet" shaped laboratory ablative pyrolysis unit was developed from specifications laid down for process performance by evaluating known theories of reaction pathways and mechanisms, and by examining the resultant technical requirements. In addition, simple empirical relationships were derived by fitting the data to a polynomial. Better relationships were obtained using data from Waterloo than using data from the various technologies described in the thesis.