Circulating fluidized bed reactor and method of operating the same

A circulating fluidized bed reactor has substantially vertical walls with cooling elements, defining the interior of the reactor chamber, and a device for introducing fluidization gas at the bottom of the fluidized bed reactor. Particulate material is introduced into the reactor. A separator separates particulate material from the exhaust gases, the separator being in connection with the reactor chamber. A return duct is connected to the separator. A bubbling fluidized bed is adjacent the reactor and provided with a heat exchanger for cooling particulate material, and side walls, rear and front walls having cooling elements in fluid communication with the cooling elements of the reactor chamber; and a discharge channel with a separate fluidizing gas source for discharging particles from the bottom of the bubbling bed to adjacent the top of the bubbling bed in the reactor chamber. A method of operating a circulating fluidized bed reactor, comprises the steps of maintaining a circulating fluidized bed in the reactor; separating particulate material from the gas in the separator and returning separated material back to the reactor; introducing particulate material into the bubbling fluidized bed above the upper surface of the bubbling fluidized bed; fluidizing the particulate material in the bubbling fluidized bed and recovering heat from the fluidized particulate material by the heat exchanger; discharging cooled particulate material from the bubbling fluidized bed at its lower section into the lower section of the discharge channel; fluidizing the discharged particulate material in the discharge channel; and introducing particulate material from the upper section of the discharge channel into the reactor chamber.