An Exergy Analysis of a Laboratory Scale Fast Pyrolysis Process Design

An exergy analysis is carried out on a laboratory scale fast pyrolysis process. Mass balance and key compositional data are obtained from a lab scale plant operating at a biomass feed rate of approximately 1 kg/h. Exergy flows and losses are determined for the overall system, as well as the main subsystems, and the sensitivity of the exergy efficiency to reactor temperature and biomass feed moisture content is investigated. The optimal operating temperature for the reactor is within the approximate range 426–457 °C, providing a rational exergy efficiency of approximately 30%. The main exergy losses are found to be associated with the combination of the fluidised bed reactor and the char separation cyclone. The water-chilled condensers used to quench pyrolysis gases and to separate bio-oil are found to be the second largest source of exergy loss, primarily through irreversible exergy destruction and via noncondensable gas products. It is also estimated that increasing the moisture content of the feedstock will decrease the exergy efficiency of the overall system by about 2% for every weight percentage increase in feedstock moisture content.