Circulating Fluidized Bed Boiler

Abstract

A circulating fluidized bed boiler includes a furnace for combusting carbonaceous fuel, at least one outlet channel connected to the upper portion of the furnace for removing flue gas and solid particles generated in the combustion of the fuel, each outlet channel provided with a particle separator attached with a flue gas channel for transferring cleaned flue gas and a return duct for transferring separated solid particles to the lower portion of the furnace. The return duct is provided with a gas seal, a heat exchange chamber, a lift channel and an overflow conduit, in which solid particles exiting the gas seal are guided to the upper portion of the heat exchange chamber and from the lower portion of the heat exchange chamber through the lift channel to the furnace, or directly from the upper portion of the heat exchange chamber through the overflow conduit to the furnace. At least one downpipe is connected from the upper portion to flow connection with the upper portion of the lift channel and from the lower portion to flow connection with the lower portion of the furnace. Additionally, the overflow conduit is connected to the upper portion of the downpipe. The downpipe is also preferably connected to an inlet for fuel.

1 . A circulating fluidized bed boiler comprising:
 a furnace for combusting carbonaceous fuel; and   at least one outlet channel connected to the upper portion of the furnace for removing flue gas and solid particles generated in the combustion of the fuel from the furnace, each outlet channel being provided with a particle separator attached with a flue gas channel for transferring flue gas cleaned of solid particles out of the boiler and a return duct for transferring separated solid particles to the lower portion of the furnace, said return duct being provided with (i) a gas seal, (ii) a heat exchange chamber, (iii) a lift channel and (iv) an overflow conduit, wherein solid particles exiting the gas seal are guided to the upper portion of the heat exchange chamber and from the lower portion of the heat exchange chamber through the lift channel to the furnace or directly from the upper portion of the heat exchange chamber through the overflow conduit to the furnace,   wherein at least one downpipe is arranged in connection with the lift channel, the downpipe being connected at its upper portion to flow connection with the upper portion of the lift channel and at its lower portion to flow connection with the lower portion of the furnace, and the overflow conduit is in direct flow connection with the upper portion of the downpipe.   
     
     
         2 . A circulating fluidized bed boiler according to  claim 1 , further comprising downpipes arranged on two separate sides of the lift channel, said downpipes being provided with an overflow conduit in such a way that the lift channel and the upper portions of the downpipes are successively in the direction of the closest wall of the furnace. 
     
     
         3 . A circulating fluidized bed boiler according to  claim 1 , wherein two opposite sides of the heat exchange chamber are provided with a lift channel, said lift channels being connected with a respective downpipe and said downpipes being connected with an overflow conduit in such a way that the heat exchange chamber, the lift channels, and the upper portions of the downpipes are successively in the direction of the closest wall of the furnace. 
     
     
         4 . A circulating fluidized bed boiler according to  claim 1 , further comprising a lift channel and a downpipe arranged in connection with two side walls of the heat exchange chamber, said side walls being perpendicular to the closest wall of the furnace, and said sidewalls being provided with an overflow conduit. 
     
     
         5 . A circulating fluidized bed boiler according to  claim 1 , wherein the heat exchange chamber, the lift channel or lift channels, the upper portions of the downpipes and the overflow conduits form an integral entity. 
     
     
         6 . A circulating fluidized bed boiler according to  claim 5 , wherein the heat exchange chamber, the lift channel or lift channels, the upper portions of the downpipes and the overflow conduits are mainly made as water tube constructions. 
     
     
         7 . A circulating fluidized bed boiler according to  claim 1 , wherein the overflow conduit is connected to the downpipe at a higher level than the lift channel. 
     
     
         8 . A circulating fluidized bed boiler according to  claim 1 , wherein at least one downpipe is provided with an inlet for fuel. 
     
     
         9 . A circulating fluidized bed boiler according to  claim 8 , wherein the inlet for fuel is connected to a non-vertical portion of the downpipe. 
     
     
         10 . A circulating fluidized bed boiler according to  claim 9 , wherein the non-vertical portion forms a ceiling of the downpipe. 
     
     
         11 . A circulating fluidized bed boiler according to  claim 9 , wherein the non-vertical portion forms an inclined portion below the highest point of the downpipe. 
     
     
         12 . A circulating fluidized bed boiler according to  claim 8 , wherein the inlet for fuel is a drop leg. 
     
     
         13 . A circulating fluidized bed boiler according to  claim 8 , wherein the inlet for fuel is attached to a distributing conveyor for transferring fuel, said conveyor being directed alongside the heat exchange chamber directly towards the furnace. 
     
     
         14 . A circulating fluidized bed boiler according to  claim 13 , wherein the distributing conveyor is in connection with a common conveyor for transferring fuel, said common conveyor being aligned with the closest wall of the furnace, behind the heat exchange chamber, as viewed from the furnace.