Pressurized internal circulating fluidized-bed boiler

Abstract

A pressurized internal circulating fluidized-bed boiler is incorporated in a combined-cycle electric generating system in which a fuel such as coal, petro coke or the like is combusted in a pressurized fluidized bed and an exhaust gas produced by the combusted fuel is introduced into a gas turbine. The pressurized internal circulating fluidized-bed boiler includes a pressure vessel, a combustor disposed in the pressure vessel and a main fluidized bed combustion chamber provided with an air diffusion device. A thermal energy recovery chamber is partitioned from the main combustion chamber by an inclined partition wall. A fluidized medium flows into and out of the main combustion chamber and the thermal energy recovery chamber. A free board is provided integrally above the main combustion chamber and the thermal energy recovery chamber so that combustion gas from the main combustion chamber and the thermal energy recovery chamber is mixed in the free board.

What is claimed is:  
     
       1. A pressurized internal circulating fluidized-bed boiler for use in a combined-cycle electric generating system, comprising: 
       a pressure vessel;  
       a combustor disposed in said pressure vessel;  
       a main fluidized bed combustion chamber having an air diffusion device provided at the bottom of said combustor and adapted to inject fluidizing air upwardly under a mass flow that is at least greater at one side than that at another side;  
       an inclined partition wall provided above a portion of said air diffusion device where the mass flow is greater so as to interfere with the upward flow of the fluidizing air and thereby to deflect the air towards a portion above said another side of said air diffusion device where the mass flow is smaller;  
       a thermal energy recovery chamber partitioned from said main combustion chamber by said inclined partition wall;  
       a heat transfer surface means provided in said thermal energy recovery chamber for a passage of a heat receiving fluid therethrough;  
       an air diffuser provided at a lower portion of said thermal energy recovery chamber; and  
       a free board provided integrally above said main combustion chamber and said thermal energy recovery chamber;  
       wherein said thermal energy recovery chamber is communicated at upper and lower portions thereof with said main fluidized bed combustion chamber, a moving bed is formed above the portion of said air diffusion device where the injected mass flow is smaller so that a fluidized medium descends and diffuses within the moving bed, and a circulating fluidized bed is formed above the portion of said air diffusion device where the mass flow of the fluidizing air is greater so that said fluidized medium is intensely fluidized and whirled towards a position above said moving bed and a part of said fluidized medium is introduced into said thermal energy recovery chamber beyond an upper portion of said inclined partition wall, the formation of said moving bed and said circulating fluidized bed is effected by regulation of the amount of air injected upwardly from said air diffusion device in said main combustion chamber and regulating of the fluidizing air injected from said air diffuser in said thermal energy recovery chamber causes the fluidized medium within said thermal energy recovery chamber to descend in a state of a moving bed for circulation to said main combustion chamber, and combustion gas from said main combustion chamber and said thermal energy recovery chamber is mixed in said free board.  
     
     
       2. The pressurized internal circulating fluidized-bed boiler according to claim  1 , further comprising at least one secondary air supplying nozzle for supplying a secondary air into said free board so that combustion gas from said main combustion chamber and said thermal energy recovery chamber is mixed and unburned combustible materials in said combustion gas is  are combusted. 
     
     
       3. The pressurized internal circulating fluidized-bed boiler according to claim  1 , further comprising screening means provided between said main combustion chamber and said thermal energy recovery chamber for preventing combustible materials having a large grain size from entering said thermal energy recovery chamber, and for allowing combustion gas from said thermal energy recovery chamber to pass therethrough while regulating a stream of said  the combustion gas and mixing with combustion gas from said main combustion chamber. 
     
     
       4. The pressurized internal circulating fluidized-bed boiler according to claim  2 , further comprising an air supplying system for controlling an amount of combustion air to combust fuel at a predetermined air ratio in accordance with an amount of said  the fuel to be supplied while maintaining oxygen concentration at a predetermined rate in exhaust gas discharged from said combustor, wherein by said air supplying system, the remaining amount of air is determined by subtracting an amount of air to be supplied to said air diffuser in said thermal energy recovery chamber from said  the amount of combustion air and said  the remaining amount of air is divided into an amount of air to be supplied to said air diffusion device in said main combustion chamber and an amount of air to be supplied to said free board as a  secondary air. 
     
     
       5. The pressurized internal circulating fluidized-bed boiler according to claim  4 , wherein said  the amount of air to be supplied to said main combustion chamber is controlled so as to be less than a stoichiometric air flow rate. 
     
     
       6. The pressurized internal circulating fluidized-bed boiler according to claim  1 , further comprising a baffle provided in said free board, wherein said baffle is positioned at an  upstream of a combustion gas outlet of said combustor to prevent a short-pass of combustion gas. 
     
     
       7. The pressurized internal circulating fluidized-bed boiler according to claim  1 , further comprising a gas turbine driven by combustion gas of said combustor, wherein exhaust gas discharged from said gas turbine is mixed with combustion air to be supplied to said combustor. 
     
     
       8. The pressurized internal circulating fluidized-bed boiler according to claim  1 , further comprising an equalizing nozzle for supplying a pressurized gas to a space between said pressure vessel and said combustor to balance the inner and the outer  pressures inwardly and outwardly of said combustor. 
     
     
       9. The pressurized internal circulating fluidized-bed boiler according to claim  1 , further comprising a dust collector provided in a passage of combustion gas discharged from said combustor, wherein flying ashes caught by said dust collector is  are classified into three groups of larger, medium and smaller particle diameters, and only flying ashes of medium particle diameter is  are returned to at least one of said main combustion chamber, said free board and a fuel supplying system for supplying fuel. 
     
     
       10. The pressurized internal circulating fluidized-bed boiler according to claim  1 , further comprising a dust collector provided in a passage of combustion gas discharged from said combustor, wherein flying ashes caught by said dust collector is  are returned to said thermal energy recovery chamber through an opening formed in said pressure vessel. 
     
     
       11. The pressurized internal circulating fluidized-bed boiler according to claim  1 , further comprising a dust collector provided in a passage of combustion gas discharged from said combustor, wherein flying ashes caught by said dust collector is  are returned to at least one of said main combustion chamber and said free board through an opening formed in said pressure vessel. 
     
     
       12. A pressurized internal circulating fluidized-bed boiler for use in a combined-cycle electric generating system, comprising: 
       a pressure vessel;  
       a combustor disposed in said pressure vessel and having a cylindrical outer wall;  
       a main fluidized bed combustion chamber having an air diffusion device provided at the bottom of said combustor and adapted to inject fluidizing air upwardly under a mass flow that is at least greater at an outer side than that at a central side;  
       a partition having a cylindrical partition and a conical partition formed at an upper portion of said cylindrical partition, said conical partition being provided above a portion of said air diffusion device where the mass flow is greater so as to interfere with the upward flow of the fluidizing air and thereby to deflect the air towards a portion above said central side of said air diffusion device where the mass flow is smaller;  
       an annular thermal energy recovery chamber partitioned from said main combustion chamber by said partition;  
       a heat transfer surface means provided in said thermal energy recovery chamber for a passage of a heat receiving fluid therethrough; and  
       an air diffuser provided at a lower portion of said thermal energy recovery chamber;  
       wherein said thermal energy recovery chamber is communicated at upper and lower portions thereof with said main fluidized bed combustion chamber, a moving bed is formed above the portion of said air diffusion device where the injected mass flow is smaller so that a fluidized medium descends and diffuses within the moving bed, and a circulating fluidized bed is formed above the portion of said air diffusion device where the mass flow of the fluidizing air is greater so that said fluidized medium is intensely fluidized and whirled towards a position above said moving bed and a part of said fluidized medium is introduced into said thermal energy recovery chamber beyond an upper portion of said conical partition, the formation of said moving bed and said circulating fluidized bed is effected by regulation of the amount of air injected upwardly from said air diffusion device in said main combustion chamber and regulating of the fluidizing air injected from said air diffuser in said thermal energy recovery chamber causes the fluidized medium within said thermal energy recovery chamber to descend in a state of a moving bed for circulation to said main combustion chamber.  
     
     
       13. The pressurized internal circulating fluidized-bed boiler according to claim  12 , wherein said air diffusion device is provided on a bottom face of said main combustion chamber, and said bottom face is conical in shape. 
     
     
       14. The pressurized internal circulating fluidized-bed boiler according to claim  12 , further comprising a free board provided integrally above said main combustion chamber and said thermal energy recovery chamber, wherein combustion gas from said main combustion chamber and said thermal energy recovery chamber is mixed in said free board. 
     
     
       15. The pressurized internal circulating fluidized-bed boiler according to claim  14 , further comprising at least one secondary air supplying nozzle for supplying a secondary air into said free board so that combustion gas from said main combustion chamber and said thermal energy recovery chamber is mixed and unburned combustible materials in said combustion gas is  are combusted. 
     
     
       16. The pressurized internal circulating fluidized-bed boiler according to claim  14 , further comprising screening means provided between said main combustion chamber and said thermal energy recovery chamber for preventing combustible materials having a large grain size from entering said thermal energy recovery chamber, and for allowing combustion gas from said thermal energy recovery chamber to pass therethrough while regulating a stream of said  the combustion gas and mixing with combustion gas from said main combustion chamber. 
     
     
       17. The pressurized internal circulating fluidized-bed boiler according to claim  15 , further comprising an air supplying system for controlling an amount of combustion air to combust fuel at a predetermined air ratio in accordance with an amount of said  the fuel to be supplied while maintaining oxygen concentration at a predetermined rate in exhaust gas discharged from said combustor, wherein by said air supplying system, the remaining amount of air is determined by subtracting an amount of air to be supplied to said air diffuser in said thermal energy recovery chamber from said  the amount of combustion and said  the remaining amount of air is divided into an amount of air to be supplied to said air diffusion device in said main combustion chamber and an amount of air to be supplied to said free board as a  secondary air. 
     
     
       18. The pressurized internal circulating fluidized-bed boiler according to claim  17 , wherein said  the amount of air to be supplied to said main combustion chamber is controlled so as to be less than a stoichiometric air flow rate. 
     
     
       19. The pressurized internal circulating fluidized-bed boiler according to claim  14 , further comprising a baffle provided in said free board, wherein said baffle is positioned at an  upstream of a combustion gas outlet of said combustor to prevent a short-pass of combustion gas. 
     
     
       20. The pressurized internal circulating fluidized-bed boiler according to claim  12 , further comprising an equalizing nozzle for supplying a pressurized gas to a space between said pressure vessel and said combustor to balance the inner and an outer  pressures inwardly and outwardly of said combustor. 
     
     
       21. The pressurized internal circulating fluidized-bed boiler according to claim  12 , wherein said air diffuser is provided on a bottom face of said thermal energy recovery chamber, said bottom face is inclined inwardly toward said main combustion chamber, and a lowermost bottom face of said thermal energy recovery chamber faces a connection opening for returning fluidized medium from said thermal energy recovery chamber to said main combustion chamber. 
     
     
       22. The pressurized internal circulating fluidized-bed boiler according to claim  21 , further comprising an air diffuser provided at said connection opening for enabling fluidized medium to be fluidized in said connecting opening. 
     
     
       23. The pressurized internal circulating fluidized-bed boiler according to claim  12 , wherein said heat transfer surface means comprises heat transfer tubes which are installed in a radial pattern, said heat transfer tubes are divided into a plurality of blocks for use as a block of evaporating tubes, a block of steam superheating tubes and a block of steam reheating tubes. 
     
     
       24. The pressurized internal circulating fluidized-bed boiler according to claim  13 , wherein a fuel inlet for supplying fuel to said main combustion chamber is provided in the vicinity of said bottom face of said main combustion chamber. 
     
     
       25. The pressurized internal circulating fluidized-bed boiler according to claim  12 , further comprising a dust collector provided in a passage of combustion gas discharged from said combustor, wherein flying ashes caught by said dust collector is  are returned to said thermal energy recovery chamber through an opening formed in said pressure vessel. 
     
     
       26. The pressurized internal circulating fluidized-bed boiler according to claim  14 , further comprising a dust collector provided in a passage of combustion gas discharged from said combustor, wherein flying ashes caught by said dust collector is  are returned to at least one of said main combustion chamber and said free board through an opening formed in said pressure vessel. 
     
     
       27. The pressurized internal circulating fluidized-bed boiler according to claim  14 , further comprising a dust collector provided in a passage of combustion gas discharged from said combustor, wherein flying ashes caught by said dust collector is  are mixed with a secondary air and a mixture of said  the flying ashes and said  secondary air is supplied to said free board through an opening formed in said pressure vessel. 
     
     
       28. The pressurized internal circulating fluidized-bed boiler according to claim  12 , further comprising a dust collector provided in a passage of combustion gas discharged from said combustor for collecting flying ashes and a classifier for recovering unreacted desulfurizing agent and unburned carbon from said  the ashes. 
     
     
       29. The pressurized internal circulating fluidized-bed boiler according to claim  28 , wherein unreacted desulfurizing agent and unburned carbon recovered by said classifier are returned to one of said main combustion chamber and a fuel supplying system for supplying fuel. 
     
     
       30. The pressurized internal circulating fluidized-bed boiler according to claim  12 , further comprising a dust collector provided in a passage of combustion gas discharged from said combustor, wherein flying ashes caught by said dust collector is  are classified into three groups of larger, medium and smaller particle diameters, and only flying ashes of medium particle diameter is  are returned to at least one of said main combustion chamber, said free board and a fuel supplying system for supplying fuel. 
     
     
       31. A topping-cycle combined electric generating system including a gasifier for generating a gas and char, an oxidizer for combusting said  the char to produce combustion gas, and a gas turbine which is driven by a high-temperature gas produced by combusting a mixture of said  the generated gas and said  the combustion gas, at least one of said gasifier and said oxidizer comprising a pressurized internal circulating fluidized-bed boiler which comprises: 
       a pressure vessel;  
       a combustor disposed in said pressure vessel and having a cylindrical outer wall;  
       a main fluidized bed combustion chamber having an air diffusion device provided at the bottom of said combustor and adapted to inject fluidizing air upwardly under a mass flow that is at least greater at an outer side than that at a central side;  
       a partition having a cylindrical partition and a conical partition formed at an upper portion of said cylindrical partition, said conical partition being provided above a portion of said air diffusion device where the mass flow is greater so as to interfere with the upward flow of the fluidizing air and thereby to deflect the air towards a portion above said central side of said air diffusion device where the mass flow is smaller;  
       an annular thermal energy recovery chamber partitioned from said main combustion chamber by said partition;  
       a heat transfer surface means provided in said thermal energy recovery chamber for a passage of a heat receiving fluid therethrough; and  
       an air diffuser provided at a lower portion of said thermal energy recovery chamber;  
       wherein said thermal energy recovery chamber is communicated at upper and lower portions thereof with said main fluidized bed combustion chamber, a moving bed is formed above the portion of said air diffusion device where the injected mass flow is smaller so that a fluidized medium descends and diffuses within the moving bed, and a circulating fluidized bed is formed above the portion of said air diffusion device where the mass flow of the fluidizing air is greater so that said fluidized medium is intensely fluidized and whirled towards a position above said moving bed and a part of said fluidized medium is introduced into said thermal energy recovery chamber beyond an upper portion of said conical partition, the formation of said moving bed and said circulating fluidized bed is effected by regulation of the amount of air injected upwardly from said air diffusion device in said main combustion chamber and regulating of the fluidizing air injected from said air diffuser in said thermal energy recovery chamber causes the fluidized medium within said thermal energy recovery chamber to descend in a state of a moving bed for circulation to said main combustion chamber.  
     
     
       32. The topping-cycle combined electric generating system according to claim  31 , wherein unburned char discharge  discharged from said gasifier is entrained, in its entirety, by said  the generated gas and cooled, and particles containing char, Na and K are collected by a downstream dust collector, and said  the particles are introduced into said oxidizer where they are completely combusted, and an exhaust gas produced in said oxidizer is discharged therefrom and cooled, and particles containing at least Na, K contained in said  the exhaust gas are collected by and discharged from a downstream dust collector, and purified exhaust gas and said  the generated gas which has been discharged from said gasifier and filtered to remove particles therefrom are mixed and combusted by a topping-combustor, and then a high-temperature exhaust gas produced by said combustor is introduced into said gas turbine. 
     
     
       33. An integral type of fluidized-bed furnace for use in a topping-cycle combined electric generating system, comprising: 
       a cylindrical outer wall;  
       a cylindrical partition provided concentrically with said cylindrical outer wall;  
       a gasifier formed inside said cylindrical partition;  
       an oxidizer formed between said cylindrical outer wall and said cylindrical partition;  
       an air diffusion device provided at the bottom of said gasifier and adapted to inject fluidizing air upwardly under a mass flow that is at least greater at an outer side than that at a central side;  
       a conical partition formed on said cylindrical partition, said conical partition being provided above a portion of said air diffusion device where the mass flow is greater so as to interfere with the upward flow of the fluidizing air and thereby to deflect the air towards a portion above said central side of said air diffusion device where the mass flow is smaller;  
       an air diffuser provided at a lower portion of said oxidizer; and  
       a first free board defined above said gasifier and a second free board defined above said oxidizer, said first and second free boards being separated from each other by said cylindrical partition so that a gas produced by said gasifier and combustion gas from said oxidizer are separately discharged towards the outside;  
       wherein said oxidizer is communicated at intermediate and lower portions thereof with said gasifier, a moving bed is formed above the portion of said air diffusion device where the injected mass flow is smaller so that a fluidized medium descends and diffuses within the moving bed, and a circulating fluidized bed is formed above the portion of said air diffusion device where the mass flow of the fluidizing air is greater so that said fluidized medium is intensely fluidized and whirled towards a position above said moving bed and a part of said fluidized medium is introduced into said oxidizer through an opening formed in an intermediate portion of said partition, the formation of said moving bed and said circulating fluidized bed is effected by regulating of the amount of air injected upwardly from said air diffusion device is said gasifier and regulating of the fluidizing air injected from said air diffuser in said oxidizer causes the fluidized medium within said oxidizer to descend in a state of a moving bed for circulation to said gasifier.  
     
     
       34. The fluidized-bed furnace according to claim  33 , further comprising a heat transfer surface means provided in said oxidizer for a passage of a heat receiving fluid therethrough. 
     
     
       35. The fluidized-bed furnace according to claim  33 , further comprising a pressure vessel for accommodating said fluidized-bed furnace, wherein said pressure vessel has a combustion gas outlet and a produced gas outlet, said combustion gas outlet is connected to said oxidizer and said produced gas outlet is connected to said gasifier. 
     
     
       36. The fluidized-bed furnace according to claim  33 , wherein unburned car discharged from said gasifier is entrained, in its entirety, by said  the generated gas and cooled, and particles containing char, Na and K are collected by a downstream dust collector, and said  the particles are introduced into said oxidizer where they are completely combusted, and an exhaust gas produced in said oxidizer is discharged therefrom and cooled, and particles containing at least Na, K in said  the exhaust gas are collected by and discharged from a downstream dust collector, and purified exhaust gas and said  the generated gas which has been discharged from said gasifier and filtered to remove particles therefrom are mixed and combusted by a topping-combustor, and then a high-temperature exhaust gas produced by said combustor is introduced into said gas turbine. 
     
     
       37. A pressurized cylindrical internal circulating fluidized- bed boiler for use in a combined cycle electric generating system, comprising:    
       
         a pressure vessel;  
       
       
         a combustor disposed in said pressure vessel;  
       
       
         a main fluidized bed combustion chamber having an air diffusion device provided at the bottom of said combustor and adapted to inject fluidizing air upwardly under a mass flow that is at least greater at one side than that at another side;  
       
       
         a partition wall provided above a portion of said air diffusion device;  
       
       
         a thermal energy recovery chamber partitioned from said main combustion chamber by said partition wall;  
       
       
         a heat transfer surface means provided in said thermal energy recovery chamber for a passage of a heat receiving fluid therethrough;  
       
       
         an air diffuser provided at a lower portion of said thermal energy recovery chamber; and  
       
       
         a free board provided above said main combustion chamber and said thermal energy recovery chamber;  
       
       
         wherein said thermal energy recovery chamber is communicated at upper and lower portions thereof with said main fluidized bed combustion chamber, a moving bed is formed above a portion of said air diffusion device where the injected mass flow is smaller so that a fluidized medium descends and diffuses within the moving bed, and a circulating fluidized bed is formed above a portion of said air diffusion device where the mass flow of the fluidizing air is greater so that said fluidized medium is intensely fluidized and whirled towards a position above said moving bed and a part of said fluidized medium is introduced into said thermal energy recovery chamber beyond an upper portion of said partition wall, the formation of said moving bed and said circulating fluidized bed is effected by regulation of the amount of air injected upwardly from said air diffusion device in said main combustion chamber and regulation of the fluidizing air injected from said air diffuser in said thermal energy recovery chamber causes the fluidized medium within said thermal energy recovery chamber to descend in a state of a moving bed for circulation to said main combustion chamber, and combustion gas from said main combustion chamber and said thermal energy recovery chamber is mixed in said free board. 
       
     
     
       38. The pressurized internal circulating fluidized- bed boiler according to claim  37 , further comprising at least one secondary air supplying nozzle for supplying a secondary air into said free board so that combustion gas from said main combustion chamber and said thermal energy recovery chamber is mixed and unburned combustible materials in said combustion gas are combusted.   
     
     
       39. The pressurized internal circulating fluidized- bed boiler according to claim  38 , further comprising an air supplying system for controlling an amount of combustion air to combust fuel at a predetermined air ratio in accordance with an amount of the fuel to be supplied while maintaining oxygen concentration at a predetermined rate in exhaust gas discharged from said combustor, wherein by said air supplying system, the remaining amount of air is determined by subtracting an amount of air to be supplied to said air diffuser in said thermal energy recovery chamber from the amount of combustion air and the remaining amount of air is divided into an amount of air to be supplied to said air diffusion device in said main combustion chamber and an amount of air to be supplied to said free board as secondary air.   
     
     
       40. The pressurized internal circulating fluidized- bed boiler according to claim  39 , wherein the amount of air to be supplied to said main combustion chamber is controlled so as to be less than a stoichiometric air flow rate.   
     
     
       41. The pressurized internal circulating fluidized- bed boiler according to claim  37 , further comprising screening means provided between said main combustion chamber and said thermal energy recovery chamber for preventing combustible materials having a large grain size from entering said thermal energy recovery chamber, and for allowing combustion gas from said thermal energy recovery chamber to pass therethrough while regulating a stream of the combustion gas and mixing with combustion gas from said main combustion chamber.   
     
     
       42. The pressurized internal circulating fluidized- bed boiler according to claim  37 , further comprising a baffle provided in said free board, wherein said baffle is positioned upstream of a combustion gas outlet of said combustor to prevent a short - pass of combustion gas.   
     
     
       43. The pressurized internal circulating fluidized- bed boiler according to claim  37 , further comprising a gas turbine driven by combustion gas of said combustor, wherein exhaust gas discharged from said gas turbine is mixed with combustion air to be supplied to said combustor.   
     
     
       44. The pressurized internal circulating fluidized- bed boiler according to claim  37 , further comprising an equalizing nozzle for supplying a pressurized gas to a space between said pressure vessel and said combustor to balance pressures inwardly and outwardly of said combustor.   
     
     
       45. The pressurized internal circulating fluidized- bed boiler according to claim  37 , further comprising a dust collector provided in a passage of combustion gas discharged from said combustor, wherein flying ashes caught by said dust collector are classified into three groups of larger, medium and smaller particle diameters, and only flying ashes of medium particle diameter are returned to at least one of said main combustion chamber, said free board and a fuel supplying system for supplying fuel.   
     
     
       46. The pressurized internal circulating fluidized- bed boiler according to claim  37 , further comprising a dust collector provided in a passage of combustion gas discharged from said combustor, wherein flying ashes caught by said dust collector are returned to said thermal energy recovery chamber through an opening formed in said pressure vessel.   
     
     
       47. The pressurized internal circulating fluidized- bed boiler according to claim  37 , further comprising a dust collector provided in a passage of combustion gas discharged from said combustor, wherein flying ashes caught by said dust collector are returned to at least one of said main combustion chamber and said free board through an opening formed in said pressure vessel.   
     
     
       48. A pressurized internal circulating fluidized- bed boiler according to claim  37 , wherein said partition has a cylindrical partition and a conical partition formed at an upper portion of said cylindrical partition, said conical partition being provided above a portion of said air diffusion device where the mass flow is greater so as to interfere with the upward flow of the fluidizing air and thereby to deflect the air towards a portion above a central part of said air diffusion device where the mass flow is smaller, and wherein said thermal energy recovery chamber partitioned from said main combustion chamber by said partition is annular.   
     
     
       49. The pressurized internal circulating fluidized- bed boiler according to claim  48 , wherein said air diffusion device is provided on a bottom face of said main combustion chamber, and said bottom face is conical in shape.   
     
     
       50. The pressurized internal circulating fluidized- bed boiler according to claim  49 , wherein a fuel inlet for supplying fuel to said main combustion chamber is provided in the vicinity of said bottom face of said main combustion chamber.   
     
     
       51. The pressurized internal circulating fluidized- bed boiler according to claim  48 , wherein said free board is provided integrally above said main combustion chamber and said thermal energy recovery chamber.   
     
     
       52. The pressurized internal circulating fluidized- bed boiler according to claim  51 , further comprising a dust collector provided in a passage of combustion gas discharged from said combustor, wherein flying ashes caught by said dust collector are mixed with secondary air, and a mixture of said flying ashes and said secondary air is supplied to said free board through an opening formed in said pressure vessel.   
     
     
       53. The pressurized internal circulating fluidized- bed boiler according to claim  48 , wherein said air diffuser is provided on a bottom face of said thermal energy recovery chamber, said bottom face is inclined inwardly toward said main combustion chamber, and a lowermost bottom face of said thermal energy recovery chamber faces a connection opening for returning fluidized medium from said thermal energy recovery chamber to said main combustion chamber.   
     
     
       54. The pressurized internal circulating fluidized- bed boiler according to claim  53 , further comprising an air diffuser provided at said connection opening for enabling fluidized medium to be fluidized in said connecting opening.   
     
     
       55. The pressurized internal circulating fluidized- bed boiler according to claim  48 , wherein said heat transfer surface means comprises heat transfer tubes which are installed in a radial pattern, said heat transfer tubes are divided into a plurality of blocks for use as a block of evaporating tubes, a block of steam superheating tubes and a block of steam reheating tubes.   
     
     
       56. The pressurized internal circulating fluidized- bed boiler according to claim  48 , further comprising a dust collector provided in a passage of combustion gas discharged from said combustor for collecting flying ashes, and a classifier for recovering unreacted desulfurizing agent and unburned carbon from said ashes.   
     
     
       57. The pressurized internal circulating fluidized- bed boiler according to claim  56 , wherein unreacted desulfurizing agent and unburned carbon recovered by said classifier are returned to one of said main combustion chamber and a fuel supplying system for supplying fuel.   
     
     
       58. The pressurized internal circulating fluidized- bed boiler according to claim  48 , further comprising a dust collector provided in a passage of combustion gas discharged from said combustor, wherein flying ashes caught by said dust collector are classified into three groups of larger, medium and smaller particle diameters, and only flying ashes of medium particle diameter are returned to at least one of said main combustion chamber, said free board and a fuel supplying system.   
     
     
       59. The pressurized internal circulating fluidized- bed boiler according to claim  37 , wherein said thermal energy recovery chamber substantially surrounds said main fluidized bed combustion chamber.   
     
     
       60. The pressurized internal circulating fluidized- bed boiler according to claim  37 , wherein the heat transfer surface means comprise heat transfer tubes immersed in the fluidized bed in said thermal energy recovery chamber and divided by function into blocks.   
     
     
       61. The pressurized internal circulating fluidized- bed boiler according to claim  60 , wherein the amount of air from said air diffuser in said thermal energy recovery chamber can be adjusted in each of said blocks.   
     
     
       62. The pressurized internal circulating fluidized- bed boiler according to claim  37 , wherein said heat transfer surface means comprise immersed heat transfer tubes installed in a radial pattern in plan view in said thermal energy recovery chamber.   
     
     
       63. The pressurized internal circulating fluidized- bed boiler according to claim  37 , wherein said partition wall is an inclined partition wall.   
     
     
       64. The pressurized internal circulating fluidized- bed boiler according to claim  37 , wherein said free board is provided integrally above said main combustion chamber and said thermal energy recovery chamber.   
     
     
       65. A pressurized cylindrical internal circulating fluidized- bed boiler comprising:    
       
         a pressure vessel;  
       
       
         a combustor disposed in said pressure vessel;  
       
       
         a main fluidized bed combustion chamber having an air diffusion device provided at the bottom of said combustor and adapted to inject fluidizing air upwardly under a mass flow that is at least greater at one side than that at another side;  
       
       
         a partition wall provided above a portion of said air diffusion device;  
       
       
         a thermal energy recovery chamber partitioned from said main combustion chamber by said partition wall;  
       
       
         a heat transfer surface means provided in said thermal energy recovery chamber for a passage of a heat receiving fluid therethrough;  
       
       
         an air diffuser provided at a lower portion of said thermal energy recovery chamber; and  
       
       
         a free board provided above said main combustion chamber and said thermal energy recovery chamber;  
       
       
         wherein said thermal energy recovery chamber is communicated at upper and lower portions thereof with said main fluidized bed combustion chamber, a moving bed is formed above a portion of said air diffusion device where the injected mass flow is smaller so that a fluidized medium descends and diffuses within the moving bed, and a circulating fluidized bed is formed above the portion of said air diffusion device where the mass flow of the fluidizing air is greater so that said fluidized medium is intensely fluidized and whirled towards a position above said moving bed and a part of said fluidized medium is introduced into said thermal energy recovery chamber beyond an upper portion of said partition wall, the formation of said moving bed and said circulating fluidized bed is effected by regulation of the amount of air injected upwardly from said air diffusion device in said main combustion chamber and regulation of the fluidizing air injected from said air diffuser in said thermal energy recovery chamber causes the fluidized medium within said thermal energy recovery chamber to descend in a state of a moving bed for circulation to said main combustion chamber, and combustion gas from said main combustion chamber and said thermal energy recovery chamber is mixed in said free board. 
       
     
     
       66. The pressurized internal circulating fluidized- bed boiler according to claim  65 , further comprising at least one secondary air supplying nozzle for supplying a secondary air into said free board so that combustion gas from said main combustion chamber and said thermal energy recovery chamber is mixed and unburned combustible materials in said combustion gas are combusted.   
     
     
       67. The pressurized internal circulating fluidized- bed boiler according to claim  66 , further comprising an air supplying system for controlling an amount of combustion air to combust fuel at a predetermined air ratio in accordance with an amount of the fuel to be supplied while maintaining oxygen concentration at a predetermined rate in exhaust gas discharged from said combustor, wherein by said air supplying system, the remaining amount of air is determined by subtracting an amount of air to be supplied to said air diffuser in said thermal energy recovery chamber from the amount of combustion air and the remaining amount of air is divided into an amount of air to be supplied to said air diffusion device in said main combustion chamber and an amount of air to be supplied to said free board as secondary air.   
     
     
       68. The pressurized internal circulating fluidized- bed boiler according to claim  67 , wherein the amount of air to be supplied to said main combustion chamber is controlled so as to be less than a stoichiometric air flow rate.   
     
     
       69. The pressurized internal circulating fluidized- bed boiler according to claim  65 , further comprising screening means provided between said main combustion chamber and said thermal energy recovery chamber for preventing combustible materials having a large grain size from entering said thermal energy recovery chamber, and for allowing combustion gas from said thermal energy recovery chamber to pass therethrough while regulating a stream of the combustion gas and mixing with combustion gas from said main combustion chamber.   
     
     
       70. The pressurized internal circulating fluidized- bed boiler according to claim  65 , further comprising a baffle provided in said free board, wherein said baffle is positioned upstream of a combustion gas outlet of said combustor to prevent a short - pass of combustion gas.   
     
     
       71. The pressurized internal circulating fluidized- bed boiler according to claim  65 , further comprising a gas turbine driven by combustion gas of said combustor, wherein exhaust gas discharged from said gas turbine is mixed with combustion air to be supplied to said combustor.   
     
     
       72. The pressurized internal circulating fluidized- bed boiler according to claim  65 , further comprising an equalizing nozzle for supplying a pressurized gas to a space between said pressure vessel and said combustor to balance inwardly and outwardly of said combustor.   
     
     
       73. The pressurized internal circulating fluidized- bed boiler according to claim  65 , further comprising a dust collector provided in a passage of combustion gas discharged from said combustor, wherein flying ashes caught by said dust collector are classified into three groups of larger, medium and smaller particle diameters, and only flying ashes of medium particle diameter are returned to at least one of said main combustion chamber, said free board and a fuel supplying system for supplying fuel.   
     
     
       74. The pressurized internal circulating fluidized- bed boiler according to claim  65 , further comprising a dust collector provided in a passage of combustion gas discharged from said combustor, wherein flying ashes caught by said dust collector are returned to said thermal energy recovery chamber through an opening formed in said pressure vessel.   
     
     
       75. The pressurized internal circulating fluidized- bed boiler according to claim  65 , further comprising a dust collector provided in a passage of combustion gas discharged from said combustor, wherein flying ashes caught by said dust collector are returned to at least one of said main combustion chamber and said free board through an opening formed in said pressure vessel.   
     
     
       76. A pressurized internal circulating fluidized- bed boiler according to claim  65 , wherein said partition has a cylindrical partition and a conical partition formed at an upper portion of said cylindrical partition, said conical partition being provided above a portion of said air diffusion device where the mass flow is greater so as to interfere with the upward flow of the fluidizing air and thereby to deflect the air towards a portion above a central part of said air diffusion device where the mass flow is smaller, and wherein said thermal energy recovery chamber partitioned from said main combustion chamber by said partition is annular.   
     
     
       77. The pressurized internal circulating fluidized- bed boiler according to claim  76 , wherein said air diffusion device is provided on a bottom face of said main combustion chamber, and said bottom face is conical in shape.   
     
     
       78. The pressurized internal circulating fluidized- bed boiler according to claim  77 , wherein a fuel inlet for supplying fuel to said main combustion chamber is provided in the vicinity of said bottom face of said main combustion chamber.   
     
     
       79. The pressurized internal circulating fluidized- bed boiler according to claim  76 , wherein said free board is provided integrally above said main combustion chamber and said thermal energy recovery chamber.   
     
     
       80. The pressurized internal circulating fluidized- bed boiler according to claim  79 , further comprising a dust collector provided in a passage of combustion gas discharged from said combustor, wherein flying ashes caught by said dust collector are mixed with secondary air, and a mixture of said flying ashes and said secondary air is supplied to said free board through an opening formed in said pressure vessel.   
     
     
       81. The pressurized internal circulating fluidized- bed boiler according to claim  76 , wherein said air diffuser is provided on a bottom face of said thermal energy recovery chamber, said bottom face is inclined inwardly toward said main combustion chamber, and a lowermost bottom face of said thermal energy recovery chamber faces a connection opening for returning fluidized medium from said thermal energy recovery chamber to said main combustion chamber.   
     
     
       82. The pressurized internal circulating fluidized- bed boiler according to claim  81 , further comprising an air diffuser provided at said connection opening for enabling fluidized medium to be fluidized in said connecting opening.   
     
     
       83. The pressurized internal circulating fluidized- bed boiler according to claim  76 , wherein said heat transfer surface means comprises heat transfer tubes which are installed in a radial pattern, said heat transfer tubes are divided into a plurality of blocks for use as a block of evaporating tubes, a block of steam superheating tubes and a block of steam reheating tubes.   
     
     
       84. The pressurized internal circulating fluidized- bed boiler according to claim  76 , further comprising a dust collector provided in a passage of combustion gas discharged from said combustor for collecting flying ashes, and a classifier for recovering unreacted desulfurizing agent and unburned carbon from said ashes.   
     
     
       85. The pressurized internal circulating fluidized- bed boiler according to claim  84 , wherein unreacted desulfurizing agent and unburned carbon recovered by said classifier are returned to one of said main combustion chamber and a fuel supplying system for supplying fuel.   
     
     
       86. The pressurized internal circulating fluidized- bed boiler according to claim  76 , further comprising a dust collector provided in a passage of combustion gas discharged from said combustor, wherein flying ashes caught by said dust collector are classified into three groups of larger, medium and smaller particle diameters, and only flying ashes of medium particle diameter are returned to at least one of said main combustion chamber, said free board and a fuel supplying system for supplying fuel.   
     
     
       87. The pressurized internal circulating fluidized- bed boiler according to claim  65 , wherein said thermal energy recovery chamber substantially surrounds said main fluidized bed combustion chamber.   
     
     
       88. The pressurized internal circulating fluidized- bed boiler according to claim  65 , wherein the heat transfer surface means comprise heat transfer tubes immersed in the fluidized bed in said thermal energy recovery chamber and divided by function into blocks.   
     
     
       89. The pressurized internal circulating fluidized- bed boiler according to claim  88 , wherein the amount of air from said air diffuser in said thermal energy recovery chamber can be adjusted in each of said blocks.   
     
     
       90. The pressurized internal circulating fluidized- bed boiler according to claim  65 , wherein said heat transfer surface means comprise immersed heat transfer tubes installed in a radial pattern in plan view in said thermal energy recovery chamber.   
     
     
       91. The pressurized internal circulating fluidized- bed boiler according to claim  65 , wherein said partition wall is an inclined partition wall.   
     
     
       92. The pressurized internal circulating fluidized- bed boiler according to claim  65 , wherein said free board is provided integrally above said main combustion chamber and said thermal energy recovery chamber.