Pressurized fluidized bed boiler

A pressurized fluidized bed boiler comprising

• furnace means having an evaporator, a superheater, and reheater disposed therein and divided into at least two separate furnaces:
• a furnace with an evaporator disposed therethrough, and a furnace with a reheater disposed therethrough,
• at least two pressure vessels which separately accommodate the furnaces, respectively,
• control means for controlling the temperature of steam in each of outlets of the superheater and the reheater by varying the level of the fluidized bed in each of the separate furnaces,
• air pipes connected to the pressure vessels to introduce a combustion air into said furnaces and a compressed air into said pressure vessels, respectively,
• air flow rate adjusting means mounted in said air pipes connected to said pressure vessels for independently controlling the flow rate of air introduced into each of said furnaces,
• oxygen concentration detecting means mounted in an exhaust gas pipe from each of said furnaces for detecting the concentration of oxygen in an exhaust gas in an outlet of each of said furnaces,
• fuel supply amount detecting means for detecting the amount of fuel supplied into each of said furnaces, and
• air-fuel ratio control means for allowing said air flow rate adjusting means to perform an air flow rate control on the basis of a detection value detected by at least one of said oxygen concentration detecting means and said fuel supply amount detecting means.

A method for operating a pressurized fluidized bed boiler comprising furnace means having an evaporator, a superheater, and reheater disposed therein and divided into at least two separate furnaces:

• a furnace with an evaporator disposed therethrough, and a furnace with a reheater disposed therethrough, at least two pressure vessels which separately accommodate the furnaces, respectively, control means for controlling the temperature of steam in each of outlets of the superheater and the reheater by varying the level of the fluidized bed in each of the separate furnaces, air pipes connected to the pressure vessels to introduce a combustion air into said furnaces and a compressed air into said pressure vessels, respectively, air flow rate adjusting means mounted in said air pipes connected to said pressure vessels for independently controlling the flow rate of air introduced into each of said furnaces, oxygen concentration detecting means mounted in an exhaust gas pipe from each of said furnaces for detecting the concentration of oxygen in an exhaust gas in an outlet of each of said furnaces, fuel supply amount detecting means for detecting the amount of fuel supplied into each of said furnaces, and air-fuel ratio control means for allowing said air flow rate adjusting means to perform an air flow rate control on the basis of a detection value detected by at least one of said oxygen concentration detecting means and said fuel supply amount detecting means, wherein
• only said furnace having the evaporator disposed therein is started at an initial stage of starting of said boiler, and
• said furnace having the reheater disposed therein is started only when a condition permitting steam to be sufficiently insured in said reheater has been reached.