Circulating fluidized bed boiler having two external heat exchangers for hot solids flow

1. A circulating fluidized bed boiler comprising:

a furnace for combusting solid carbonaceous fuel in a fast fluidized bed, the furnace having (i) walls made of water/steam tube panels and used for evaporating water fed therein and (ii) an outlet channel for exhaust gas at an upper portion of the furnace;

a solids separator arranged adjacent to a sidewall of the furnace for separating solids entrained with exhaust gas discharged via the outlet channel from the upper portion of the furnace;

a gas seal for receiving at least a portion of the separated solids from the solids separator;

a first fluidized bed heat exchange chamber that is arranged downstream of the gas seal and has internal heat exchange surfaces, the first fluidized bed heat exchange chamber receiving the at least a portion of the separated solids from the solids separator via the gas seal;

at least one return channel connecting the first fluidized bed heat exchange chamber to the furnace, so that solids discharged from the first fluidized bed heat exchange chamber are only conveyed to a lower portion of the furnace via the at least one return channel;

a first lift channel having a lower end connected to a bottom portion of the first fluidized bed heat exchange chamber and an upper end connected to an upper end of a first the at least one return channel for discharging solids from the first fluidized bed heat exchange chamber to the at least one return channel;

a second fluidized bed heat exchange chamber being (i) arranged adjacent to a lower sidewall of the furnace and having internal heat exchange surfaces, (ii) positioned below the first fluidized bed heat exchange chamber, and (iii) narrower than the first fluidized bed heat exchanger;

a singular inlet channel for introducing hot solids from the furnace into the second fluidized bed heat exchange chamber, the singular inlet channel directly connecting the lower portion of the furnace to the second fluidized bed heat exchange chamber so that the second fluidized bed heat exchange chamber receives hot solids only directly from the lower portion of the furnace via the singular inlet channel; and

a second lift channel having a lower end connected to a bottom portion of the second fluidized bed heat exchange chamber and an upper end connected to the furnace for discharging solids from the second fluidized bed heat exchange chamber to the lower portion of the furnace,

wherein the first fluidized bed heat exchange chamber has two first lift channels and two return channels arranged at the lateral sides thereof such that the second fluidized bed heat exchange chamber is situated between the lower ends of the two return channels.

2. The circulating fluidized bed boiler according to claim 1 , further comprising at least one of a fuel feed, a bed material feed, a secondary gas feed, and a start up burner positioned between the first return channel and the second fluidized bed heat exchange chamber.

3. The circulating fluidized bed boiler according to claim 1 , wherein the first of the two return channels includes a receiver for receiving fuel to be introduced into the lower portion of the furnace.

4. The circulating fluidized bed boiler according to claim 1 , wherein the walls of each of the first and second fluidized bed heat exchange chambers are made of water tube panels.

5. The circulating fluidized bed boiler according to claim 4 , wherein the first of the two return channels has walls made of water tube panels.

6. The circulating fluidized bed boiler according to claim 4 , wherein the walls of at least one of the first fluidized bed heat exchange chamber, the second fluidized bed heat exchange chamber, and the first return channel are used for heating water to be introduced into the water/steam tube panels of the furnace.