A feedstock conversion system including an integrated two-stage fluid bed thermochemical reaction apparatus (50) has first and second reaction chambers (110, 120) side-by-side and physically separated from one another in one vessel (100) by a partition (130). One or more clusters of heat pipes (400) pass through the partition (130) between the first and second chambers (110, 120) for efficient indirect heat transfer between first and second fluid bed reaction stages (200, 300) and materials therein. The system includes devices for solids transfer between the two reaction chambers (110, 120) to enhance feedstock conversion.