Circulating Fluidized Bed Combustor and a Method of Operating a Circulating Fluidized Bed Combustor

Abstract

A circulating fluidized bed combustor arrangement includes (a) a circulating fluidized bed reactor in which (i) a combustion chamber combusts a fuel material in a suspension of solid particles of a circulating fluidized bed, (ii) a first cyclone separator arrangement receives a mixture of gases and solid particles from the combustion chamber for separating a first fraction of the solid particles from the exhaust gases, and (iii) a solid particle return system connected to the first cyclone separator returns separated solid particles to the combustion chamber, (b) a heat transfer section including a water/steam heat exchanger section arranged after the first cyclone separator arrangement in the exhaust gas flow path, (c) a heat recovery device provided in connection with the combustion chamber, the first cyclone separator arrangement and the heat transfer section being arranged for recovering heat resulting from the combustion process in the combustion chamber, (d) a selective catalytic reduction system arranged in the exhaust gas flow path, after the heat transfer section, for removing NOx from the exhaust gas, (e) a device for injecting NOx reducing agent into the exhaust gases upstream of the selective catalytic reduction system, and (f) a second cyclone separator arrangement provided downstream of the first cyclone separator arrangement and upstream of the heat transfer section, in which a second fraction of the solid particles is separated form the exhaust gases.

1 . A circulating fluidized bed combustor arrangement comprising:
 (a) circulating fluidized bed reactor comprising:
 (i) a combustion chamber for combusting a fuel material in a suspension of solid particles of a circulating fluidized bed; 
 (ii) a first cyclone separator arrangement arranged to receive a mixture of gases and solid particles from the combustion chamber for separating a first fraction of the solid particles from the exhaust gases; and 
 (iii) a solid particle return system connected to the first cyclone separator for returning separated solid particles to the combustion chamber; 
   (b) a heat transfer section comprising a water/steam heat exchanger section arranged after the first cyclone separator arrangement in a flow path of the exhaust gases;   (c) heat recovery means, provided in connection with the combustion chamber, the first cyclone separator arrangement and the heat transfer section, being arranged for recovering heat resulting from the combustion process in the combustion chamber;   (d) a selective catalytic reduction system arranged in the flow path of the exhaust gases, after the heat transfer section, for removing NOx from the exhaust gas;   (e) means for injecting NOx reducing agent into the exhaust gases upstream of the selective catalytic reduction system; and   (f) a second cyclone separator arrangement provided downstream of the first cyclone separator arrangement and upstream of the heat transfer section, in which a second fraction of the solid particles is separated form the exhaust gases.   
     
     
         2 . A circulating fluidized bed combustor arrangement according to  claim 1 , wherein the second cyclone separator arrangement is provided immediately downstream of the first cyclone separator arrangement. 
     
     
         3 . A circulating fluidized bed combustor arrangement according to  claim 1 , wherein the first cyclone separator arrangement comprises at least one cyclone separator arranged to separate particles having a diameter primarily of greater than about 120 to about 140 μm and the second cyclone separator arrangement comprises at least one cyclone separator arranged to separate particles having a diameter of greater than about 20 to about 40 μm. 
     
     
         4 . A circulating fluidized bed combustor arrangement according to  claim 1 , wherein the second cyclone separator arrangement is connected to another system for processing solid particles. 
     
     
         5 . A circulating fluidized bed combustor arrangement according to  claim 1 , wherein the second cyclone separator arrangement is connected to the combustion chamber of the circulating fluidized bed combustor arrangement for recycling separated solid particles back to the combustion chamber. 
     
     
         6 . A circulating fluidized bed combustor arrangement according to  claim 4 , further comprising a desulfurization system in connection with the combustion chamber, the desulfurization system including means for injecting sulfur sorbent material into the combustion chamber, wherein the second cyclone separator arrangement is connected to the combustion chamber for recycling separated sulfur sorbent material back to the combustion chamber. 
     
     
         7 . A circulating fluidized bed combustor arrangement according to  claim 1 , wherein the means for injecting NOx reducing agent injects ammonia into the exhaust gases and is arranged immediately upstream of the selective catalytic reduction system. 
     
     
         8 . A circulating fluidized bed combustor arrangement according to  claim 1 , wherein the second cyclone separator arrangement is provided with heat recovery means. 
     
     
         9 . A circulating fluidized bed combustor arrangement according to  claim 1 , wherein the second cyclone separator is of an uncooled construction. 
     
     
         10 . A circulating fluidized bed combustor arrangement according to  claim 1 , wherein the first cyclone separator arrangement consists of one cyclone separator and the second cyclone separator arrangement connected to the first cyclone separator arrangement consists of two cyclone separators. 
     
     
         11 . A circulating fluidized bed combustor arrangement according to  claim 2 , wherein the selective catalytic reduction system for removing NOx comprises a group of parallel flow channels having a catalytic material on its respective surfaces. 
     
     
         12 . A method of operating a circulating fluidized bed combustor arrangement, the method comprising:
 combusting fuel material in a combustion chamber of a circulating fluidized bed reactor in a suspension of solid particles of a circulating fluidized bed;   passing a mixture of gases and solid particles from the combustion chamber to a first cyclone separator arrangement and separating a first fraction of the solid particles from the gases;   returning solid particles separated in the first cyclone separator arrangement via a solid particle return system from the first cyclone separator to the combustion chamber;   passing the gases from which the first fraction of the solid particles has been separated further in the process as exhaust gases;   recovering heat from the exhaust gases in a water/steam heat exchanger section arranged after the first cyclone separator arrangement in a flow path of the exhaust gases;   removing NOx from the exhaust gas by passing the exhaust gas through a selective catalytic reduction system arranged into the flow path of the exhaust gases after recovering heat from the exhaust gases;   injecting ammonia into the exhaust gases upstream of the selective catalytic reduction system; and   separating a second fraction of the solid particles from the exhaust gases in a second cyclone separator arrangement provided downstream of the first cyclone separator arrangement, prior to recovering heat from the exhaust gases.   
     
     
         13 . A method of operating a circulating fluidized bed combustor arrangement according to  claim 12 , wherein, in the first cyclone separator arrangement, particles having a diameter of greater than about 120 to about 140 μm are separated from the exhaust gases and, in the second cyclone separator arrangement, particles having a diameter of greater than about 20 to about 40 μm are separated from the exhaust gases. 
     
     
         14 . A method of operating a circulating fluidized bed combustor arrangement according to  claim 12 , wherein the solid particles separated in the second cyclone separator arrangement are at least partially passed to another system for processing solid particles. 
     
     
         15 . A method of operating a circulating fluidized bed combustor arrangement according to  claim 12 , wherein the solid particles separated in the second cyclone separator arrangement are at least partially recycled back to the combustion chamber of the circulating fluidized bed combustor. 
     
     
         16 . A method of operating a circulating fluidized bed combustor arrangement according to  claim 15 , further comprising injecting sulfur sorbent material into the combustion chamber of the circulating fluidizing bed combustor, separating unreacted sulfur sorbent material in the second cyclone separator arrangement and recycling at least a portion of the unreacted sulfur sorbent back to the combustor. 
     
     
         17 . A method of operating a circulating fluidized bed combustor arrangement according to  claim 12 , further comprising injecting ammonia into the exhaust gases immediately upstream of the selective catalytic reduction system. 
     
     
         18 . A method of operating a circulating fluidized bed combustor arrangement according to  claim 10 , further comprising recovering heat from the exhaust gases after passing the second cyclone separator arrangement. 
     
     
         19 . A method of operating a circulating fluidized bed combustor arrangement according to  claim 12 , further comprising passing the exhaust gases through the second cyclone separator without substantially cooling the exhaust gases. 
     
     
         20 . A method of operating a circulating fluidized bed combustor arrangement according to  claim 18 , wherein heat from the exhaust gases is recovered after passing the second cyclone separator so that the selective catalytic reduction system is operated at 450-500° C. 
     
     
         21 . A method of operating a circulating fluidized bed combustor according to  claim 19 , further comprising injecting ammonia or urea before the first cyclone in the temperature window of 760-950° C. to reduce NOx emission through a selective non-catalytic reduction process. 
     
     
         22 . A method of operating a circulating fluidized bed combustor according to  claim 19 , wherein both a selective non-catalytic reduction process system and a selective catalytic reduction process system are employed to achieve maximum NOx reduction efficiency. 
     
     
         23 . A method of operating a circulating fluidized bed combustor arrangement, the method comprising:
 combusting fuel material in a combustion chamber of a circulating fluidized bed reactor in a suspension of solid particles of a circulating fluidized bed;   passing a mixture of gases and solid particles from the combustion chamber to a first cyclone separator arrangement and separating a first fraction of the solid particles from the gases;   returning solid particles separated in the first cyclone separator arrangement via a solid particle return system from the first cyclone separator to the combustion chamber;   passing the gases from which the first fraction of the solid particles has been separated further in the process as exhaust gases;   recovering heat from the exhaust gases in a water/steam heat exchanger section arranged after the first cyclone separator arrangement in the exhaust gas flow path;   separating a second fraction of the solid particles from the exhaust gases in a second cyclone separator arrangement provided downstream of the first cyclone separator arrangement prior to recovering heat from the exhaust gases;   injecting ammonia into the exhaust gases upstream of the selective catalytic reduction system;   removing NOx from the exhaust gas in a selective non-catalytic reduction process by reacting a first portion of the ammonia injected;   removing NOx from the exhaust gas in a selective catalytic reduction process by passing the exhaust gas through a selective catalytic reduction system arranged into the exhaust gas flow path after recovering from the exhaust gases and reacting a second portion of the ammonia injected; and   injecting sulfur sorbent material into the combustion chamber of the circulating fluidized bed combustor, separating unreacted sulfur sorbent material is in the second cyclone separator arrangement and recycling at least a portion of the unreacted sulfur sorbent back to the combustor.