Oxyfuel combustion boiler plant and operating method for the same

1. An oxyfuel combustion boiler plant having a first boiler and a second boiler for injecting gas including oxygen in higher concentration than that in the air, gas including carbon dioxide in higher concentration than that in the air, and fuel from a burner and generating steam by combustion gas in a furnace, a first CO2 capture unit for capturing carbon dioxide in an exhaust gas discharged from the first boiler, and a second CO2 capture unit for capturing carbon dioxide in the exhaust gas discharged from the second boiler, respectively, the oxyfuel combustion boiler plant further comprising:

an exhaust gas supply pipe for supplying exhaust gas discharged from the first boiler to a burner of the second boiler,

an exhaust gas circulation system for recirculating exhaust gas discharged from the second boiler to the burner of the second boiler,

a gas flow rate control apparatus for controlling an exhaust gas flow rate flowing into the second boiler, including supply of the exhaust gas of the first boiler to the second boiler when starting the second boiler and after arrival at a predetermined load condition of the second boiler, reducing an exhaust gas quantity of the first boiler and increasing a circulation exhaust gas quantity of the second boiler, and

a switching unit controlled by the gas flow rate control apparatus to permit the second boiler to use the exhaust gas of the first boiler supplied from the exhaust gas supply pipe when starting the second boiler and after arrival the predetermined load condition of the boiler, to reduce the exhaust gas quantity of the first boiler and increase the circulation exhaust gas quantity of the second boiler.

2. An oxyfuel combustion boiler plant having a first boiler and a second boiler for injecting gas including oxygen in higher concentration than that in the air, gas including carbon dioxide in higher concentration than that in the air, and fuel from a burner and generating steam by combustion gas in a furnace, a first CO2 capture unit for capturing carbon dioxide in an exhaust gas discharged from the first boiler, and a second CO2 capture unit for capturing carbon dioxide in the exhaust gas discharged from the second boiler respectively, the oxyfuel combustion boiler plant further comprising:

an air quality control system for removing harmful components from exhaust gas discharged from the first boiler,

an exhaust gas supply pipe for supplying exhaust gas discharged from the air quality control system to a burner of the second boiler,

an exhaust gas circulation system for recirculating exhaust gas discharged from the second boiler to the burner of the second boiler,

a gas flow rate control apparatus for controlling an exhaust gas flow rate flowing into the second boiler, a gas flow rate control apparatus for controlling an exhaust gas flow rate flowing into the second boiler, including supply of the exhaust gas of the first boiler to the second boiler when starting the second boiler and after arrival at a predetermined load condition of the second boiler, reducing an exhaust gas quantity of the first boiler and increasing a circulation exhaust gas quantity of the second boiler, and

a switching unit controlled by the gas flow rate control apparatus to permit the second boiler to use the exhaust gas of the first boiler supplied from the exhaust gas supply pipe when starting the second boiler and after arrival the predetermined load condition of the boiler, to reduce the exhaust gas quantity of the first boiler and increase the circulation exhaust gas quantity of the second boiler.

3. The oxyfuel combustion boiler plant according to claim 2 , wherein:

the gas flow rate control apparatus calculates a total exhaust gas quantity obtained by adding an exhaust gas quantity necessary for the operation condition of the second boiler to an exhaust gas quantity necessary for the load demand of the first boiler and controls an exhaust gas flow rate flowing into the second boiler on the basis of the total exhaust gas quantity.

4. The oxyfuel combustion boiler plant according to claim 2 , wherein:

the gas flow rate control apparatus calculates a total exhaust gas quantity obtained by adding an exhaust gas quantity necessary for the operation condition of the second boiler to an exhaust gas quantity necessary for the load demand of the first boiler and controls an exhaust gas flow rate flowing into the second boiler on the basis of the oxygen concentration in the mixed gas of the oxygen and exhaust gas injected from the burner of the second boiler.

5. An operating method of an oxyfuel combustion boiler plant having a first boiler and a second boiler for injecting gas including oxygen in higher concentration than that in the air, gas including carbon dioxide in higher concentration than that in the air, and fuel from a burner and generating steam by combustion gas in a furnace, a first CO2 capture unit for capturing carbon dioxide in an exhaust gas discharged from the first boiler, and a second CO2 capture unit for capturing carbon dioxide in the exhaust gas discharged from the second boiler, respectively, the oxyfuel combustion boiler plant further comprising:

an exhaust gas supply pipe for supplying exhaust gas discharged from the first boiler to a burner of the second boiler,

an exhaust gas circulation system for recirculating exhaust gas discharged from the second boiler to the burner of the second boiler, and

a gas flow rate control apparatus for controlling an exhaust gas flow rate flowing into the second boiler, wherein:

when starting the second boiler, the exhaust gas of the first boiler supplied from the exhaust gas supply pipe is used, and after arrival at a predetermined load condition of the boiler, an exhaust gas quantity of the first boiler is reduced, and a circulation exhaust gas quantity of the second boiler is increased.