Circulating fluidized bed reactor including external heat exchangers fed by internal recirculation

A circulating fluidized bed reactor, comprising:

• an enclosure (1) defining an interior space having a lower zone (3) extending from a bottom of said enclosure to an intermediate level in said interior space, said lower zone having a first cross-sectional area at said intermediate level and having a primary air inlet (12) near said bottom, a fluidization grid (11) above said air inlet and a secondary air inlet (13) above said fluidization grid, and an upper zone (2) extending from said intermediate level to a top of said enclosure and including solid matter exhausting means (6) for exhausting solid matter to a cyclone (7), said upper zone having a second cross-sectional area at said intermediate level, with a ratio of said second cross-sectional area to said first cross-sectional area at said intermediate level being in the range of 1.05 to 2;
• at least one internal bubbling bed (22) disposed in said interior space with its top substantially at said intermediate level, said internal bubbling bed including a further fluidization grid and a fluidization gas injection means beneath the further fluidization grid;
• means (10) for admitting fuel to said interior space;
• solid return means (9) for returning solid matter from the cyclone to said interior space;
• at least one external chamber (18) adjacent to and outside of said enclosure, disposed above the secondary air inlet (13) of said lower zone and above a point at which said solid return means (9) returns solid matter to said lower zone, said external chamber (18) comprising at least one external heat exchanger having means for exchanging heat with an external fluid to be heated, said at least one external heat exchanger of said external chamber controlling an operating temperature of the reactor;
• solid matter feed means (46) for feeding solid matter from said internal bubbling bed into said external chamber;
• means (28) for discharging solid matter from said internal bubbling bed into said lower zone;
• means (42) for discharging solid matter from said external chamber to said lower zone, said means (42) for discharging solid matter comprising an aperture which couples said external chamber to said interior space, said aperture being disposed in said enclosure at a level below the level of solid matter in said internal bubbling bed, whereby excess solid matter accumulating in said external chamber is permitted to overflow into said lower zone through said aperture;
• and
• means for controlling the flow of solid matter from said internal bubbling bed to said at least one external heat exchanger,
• wherein said at least one external heat exchanger is disposed at least partially below said internal bubbling bed, with a level of solid matter in said at least one external heat exchanger being below the level of solid matter in said internal bubbling bed, and
• further wherein the amount of solid matter falling into said internal bubbling bed is greater than the amount of solid matter supplied from said internal bubbling bed to said at least one external heat exchanger, whereby solid matter overflows from said internal bubbling bed into said lower zone.