A fast pyrolysis heat exchanger system for economically and efficiently converting biomass and other combustible materials into bio-oil. The system employs multiple closed loop tubes situated inside the heat exchanger. As a granular solid heat carrier is deposited at the top of the heat exchanger and caused to move downwardly therethrough, heat is transferred from the tubes to the heat carrier which is then transferred to a reactor where it is placed in contact with the combustible materials.