Effect of freeboard deflectors on the exergy in a fixed bed combustor

Document Type

Journal Article


Pergamon Press

Place of Publication

United Kingdom


School of Engineering




Originally published as: Rashidian, B., & Al-Abdeli, Y. M. (2017). Effect of freeboard deflectors on the exergy in a fixed bed combustor. Applied Thermal Engineering, 118, 62-72. Available here.


Deflectors have been employed in industrial combustors and boilers with an expectation they reduce both radiation heat losses from the fuel bed and impact particle emissions. Despite much research into lab-scale biomass combustion, there have been no systematic studies to investigate the effects of deflectors on the axially resolved and flue gas availability in laboratory scale fixed bed biomass combustors. This study includes experiments conducted on a continuous feed pellet combustor, with a freeboard deflector located at different axial locations. The aim is to characterize the relative impact of freeboard deflectors on the mechanical exergy profiles and exhaust gas total exergy, over a range of stoichiometry (primary and secondary air flow rates). Results indicate that deflectors affect the mechanical exergy in the downstream, however their influence depends on their relative (axial) position (H). Furthermore, results reveal that for the tests with and without deflector, both CO chemical exergy and total exergy decrease in a similar manner when the air-fuel equivalence ratio (λ) increases. It has been found that deflectors do not appear to affect the total and CO chemical exergy at the exhaust section of a lab-scale combustor, bearing in mind a ±3% variation in temperature, CO emissions as well as exergies is estimated based on the uncertainty analyses undertaken.