The Multi – Compartment FluoSolids® Reactor usually consists of a reaction bed and one or more heat exchange beds for heat recovery. In a typical 3 stage unit as illustrated here, hot gases from the main calcining compartment are used to dry and preheat calciner feed. Fuel is directly injected into the reaction compartment, where temperature and atmosphere are closely controlled. Finally, heat is recovered from hot product solids and used to preheat the fluidizing air. Auxiliary vessels, such as Fluid Bed Spray Coolers or Indirect Coolers may be used to further cool product solids for ease of handling.