An integrated combustion chamber and fluidized bed pyrolysis reactor. In one embodiment, the combustion chamber is cylindrical and the pyrolysis reactor is provided annularly about the combustion chamber with an annular wall that provides a common surface for heat transfer. A lift tube in fluid communication with the pyrolysis reactor is provided within the combustion chamber for circulating biomass and an inert fluidizable media upwardly through the lift tube; this advantageously increases heat transfer and leads to more rapid pyrolysis. The media and biomass exit the lift tube into either a freeboard area of the pyrolysis reactor or into a low density region of the fluidized bed. A condensable gaseous product is produced during pyrolysis that has economic value. The apparatus and process are especially well suited to the pyrolysis of low density agricultural biomass. The apparatus is compact and particularly well suited to mobile operation.