Apparatus for carrying out a physical and/or chemical process, such as a heat exchanger

An apparatus for carrying out a physical and/or chemical process, such as a heat exchanger, comprising a reservoir provided with upwardly-directed tubes accommodated, at top and bottom ends thereof, in tube plates, the tubes being in open communication with a top box and a bottom box, at least one distribution plate arranged in said bottom box for supporting a fluidized bed of granular material capable of being held in a quasi-stationary, fluidized condition by a medium to be treated or heated which is supplied via the bottom box and which flows through the tubes, means for feeding fluidized bed particles back from the top box to the bottom box including a downcomer arranged outside the reservoir and connected, at a top end thereof, to the top box by a separating device, and at a bottom end thereof, through a valve, to the bottom box of the reservoir,

• wherein the bottom end of the downcomer opens into a collecting reservoir which is divided into a top and a bottom section by a distribution plate, the bottom section being closably connected by a conduit to a feed line feeding the medium to be treated, and the bottom end of the downcomer opens into the top section, the top section being connected, via a conduit, to the bottom box of the reservoir.