Oxygen combustion system and method for operating same

1. An oxygen combustion system comprising:

a boiler adapted to burn fuel using combustion gas composed of a mixture of oxygen-rich gas and circulating flue gas containing 25% to 40% of water;

a dust remover disposed in a flue through which flue gas discharged from the boiler flows;

a combustion gas pipe adapted to lead the combustion gas to the boiler, the combustion gas being made by mixing the circulating flue gas extracted from the flue on a downstream side of the dust remover with the oxygen-rich gas;

a combustion gas heater adapted to exchange heat between the flue gas flowing through the flue between the boiler and the dust remover and the combustion gas flowing through the combustion gas pipe;

a flue gas cooler disposed in the flue between the combustion gas heater and the dust remover and adapted to cool the flue gas by exchanging heat between the flue gas running through the flue and a cooling medium; and

control means adapted to control at least one of a flow rate and temperature of the cooling medium of the flue gas cooler such that temperature of the flue gas introduced into the dust remover will be between and including 90° C. and 140° C., wherein SO 3 in the flue gas condenses on an inlet side of the dust remover, forming sulfuric acid mist, and is removed by the dust remover, sticking to soot particles in the flue gas, and temperature of the flue gas never falls below an acid dew-point temperature, and acid dew-point corrosion and clogging with soot particles of ducts are inhibited.

2. The oxygen combustion system according to claim 1 , further comprising:

an air separator adapted to produce the oxygen-rich gas by separating nitrogen from air; and

an oxygen introduction channel used to introduce the oxygen-rich gas produced by the air separator into the combustion gas pipe on an upstream side of the combustion gas heater, wherein

the oxygen introduction channel is provided with heating means adapted to heat oxygen flowing through the oxygen introduction channel.

3. The oxygen combustion system according to claim 1 , further comprising:

an air introduction port adapted to introduce air into the combustion gas pipe;

a first valve unit adapted to switch gas to be introduced into the combustion gas pipe between the circulating flue gas and air; wherein

the first valve unit comprises a damper disposed in a duct adapted to introduce the circulating flue gas into the combustion gas pipe, and a damper disposed in a duct being provided at one end of an air introduction port adapted to introduce air into the combustion gas pipe;

a condensate heater adapted to exchange heat between steam condensate obtained by a steam condenser of a steam system of the boiler and bleed steam, and to supply the steam condensate heated by the condensate heater to the boiler;

a bleed valve installed on a steam introduction conduit of the condensate heater and adapted to adjust an amount of the bleed steam introduced into the condensate heater;

a condensate bypass conduit adapted to bypass the condensate heater and to supply the steam condensate to the boiler bypassing the condensate heater;

a second valve unit adapted to switch a flow channel of the steam condensate supplied to the boiler by running through between the condensate heater and the condensate bypass conduit;

a flue gas bypass conduit adapted to allow the flue gas to run by bypassing a flow channel which links an output port disposed in the flue between the combustion gas heater and the dust remover with a return port on the downstream side of the output port; and

a third valve unit adapted to switch a flow channel of the flue gas between the flue and the flue gas bypass conduit, wherein

the flue gas cooler is configured to be able to exchange heat between the steam condensate running through the condensate bypass conduit and the flue gas running through the flue gas bypass conduit;

during oxygen combustion operation, the first valve unit is switched to the circulating flue gas, the bleed valve is closed, the second valve unit is switched to the condensate bypass conduit, the third valve unit is switched to the flue gas bypass conduit and then the flue gas is cooled by the condensate;

during air combustion operation, the first valve unit is switched to the air, the second valve unit is switched to the condensate heater, the bleed valve is opened, the third valve unit is switched to the flue and then the flue gas is able to stop cooling.

4. The oxygen combustion system according to claim 1 , further comprising:

a working gas supply device adapted to supply working gas which is used in an ancillary device of at least one of the boiler and a flue gas treatment system and intrudes into the flue gas, the flue gas treatment system being adapted to purify the flue gas discharged from the boiler, wherein

the working gas supply device uses the flue gas from which soot particles have been collected by the dust remover, as the working gas.

5. An oxygen combustion system comprising:

a boiler adapted to burn fuel using combustion gas composed of a mixture of oxygen-rich gas and circulating flue gas;

a dust remover disposed in a flue through which flue gas discharged from the boiler flows;

a combustion gas pipe adapted to lead the combustion gas to the boiler, the combustion gas being made by mixing the circulating flue gas extracted from the flue on a downstream side of the dust remover with the oxygen-rich gas;

a combustion gas heater adapted to exchange heat between the flue gas flowing through the flue between the boiler and the dust remover and the combustion gas flowing through the combustion gas pipe;

a flue gas cooler disposed in the flue between the combustion gas heater and the dust remover and adapted to cool the flue gas by exchanging heat between the flue gas running through the flue and a cooling medium;

control means adapted to control at least one of a flow rate and temperature of the cooling medium of the flue gas cooler such that temperature of the flue gas introduced into the dust remover will be between and including 90° C. and 140° C., wherein SO 3 in the flue gas condenses on an inlet side of the dust remover, forming sulfuric acid mist, and is removed by the dust remover, sticking to soot particles in the flue gas, and temperature of the flue gas never falls below an acid dew-point temperature, and acid dew-point corrosion and clogging with soot particles of ducts are inhibited;

an air separator adapted to produce the oxygen-rich gas by separating nitrogen from air;

an oxygen introduction channel used to introduce the oxygen-rich gas produced by the air separator into the combustion gas pipe on an upstream side of the combustion gas heater, the oxygen introduction channel being provided with heating means adapted to heat oxygen flowing through the oxygen introduction channel;

a first valve unit adapted to switch gas to be introduced into the combustion gas pipe between the circulating flue gas and air, wherein

the first valve unit comprises a damper disposed in a duct adapted to introduce the circulating flue gas into the combustion gas pipe, and a damper disposed in a duct being provided at one end of an air introduction port adapted to introduce air into the combustion gas pipe;

a condensate heater adapted to exchange heat between steam condensate obtained by a steam condenser of a steam system of the boiler and bleed steam, and to supply the steam condensate heated by the condensate heater to the boiler;

a bleed valve installed on a steam introduction conduit of the condensate heater and adapted to adjust an amount of the bleed steam introduced into the condensate heater;

a condensate bypass conduit adapted to bypass the condensate heater and to supply the steam condensate to the boiler bypassing the condensate heater;

a second valve unit adapted to switch a flow channel of the steam condensate supplied to the boiler by running through between the condensate heater and the condensate bypass conduit;

a flue gas bypass conduit adapted to allow the flue gas to run by bypassing a flow channel which links an output port disposed in the flue between the combustion gas heater and the dust remover with a return port on the downstream side of the output port; and

a third valve unit adapted to switch a flow channel of the flue gas between the flue and the flue gas bypass conduit, wherein

the flue gas cooler is configured to be able to exchange heat between the steam condensate running through the condensate bypass conduit and the flue gas running through the flue gas bypass conduit;

during oxygen combustion operation, the first valve unit is switched to the circulating flue gas, the bleed valve is closed, the second valve unit is switched to the condensate bypass conduit, the third valve unit is switched to the flue gas bypass conduit and then the flue gas is cooled by the condensate; and

during air combustion operation, the first valve unit is switched to the air, the second valve unit is switched to the condensate heater, the bleed valve is opened, the third valve unit is switched to the flue and then the flue gas is able to stop cooling.

6. The oxygen combustion system according to claim 1 , further comprising:

an air separator adapted to produce the oxygen-rich gas by separating nitrogen from air;

an oxygen introduction channel used to introduce the oxygen-rich gas produced by the air separator into the combustion gas pipe on an upstream side of the combustion gas heater, the oxygen introduction channel being provided with heating means adapted to heat oxygen flowing through the oxygen introduction channel; and

a working gas supply device adapted to supply working gas which is used in an ancillary device of at least one of the boiler and a flue gas treatment system and intrudes into the flue gas, the flue gas treatment system being adapted to purify the flue gas discharged from the boiler, wherein

the working gas supply device uses the flue gas from which soot particles have been collected by the dust remover, as the working gas.

7. An oxygen combustion system comprising:

a boiler adapted to burn fuel using combustion gas composed of a mixture of oxygen-rich gas and circulating flue gas;

a dust remover disposed in a flue through which flue gas discharged from the boiler flows;

a combustion gas pipe adapted to lead the combustion gas to the boiler, the combustion gas being made by mixing the circulating flue gas extracted from the flue on a downstream side of the dust remover with the oxygen-rich gas;

a combustion gas heater adapted to exchange heat between the flue gas flowing through the flue between the boiler and the dust remover and the combustion gas flowing through the combustion gas pipe;

a flue gas cooler disposed in the flue between the combustion gas heater and the dust remover and adapted to cool the flue gas by exchanging heat between the flue gas running through the flue and a cooling medium;

control means adapted to control at least one of a flow rate and temperature of the cooling medium of the flue gas cooler such that temperature of the flue gas introduced into the dust remover will be between and including 90° C. and 140° C., wherein SO 3 in the flue gas condenses on an inlet side of the dust remover, forming sulfuric acid mist, and is removed by the dust remover, sticking to soot particles in the flue gas, and temperature of the flue gas never falls below an acid dew-point temperature, and acid dew-point corrosion and clogging with soot particles of ducts are inhibited;

a first valve unit adapted to switch gas to be introduced into the combustion gas pipe between the circulating flue gas and air; wherein

the first valve unit comprises a damper disposed in a duct adapted to introduce the circulating flue gas into the combustion gas pipe, and a damper disposed in a duct being provided at one end of an air introduction port adapted to introduce air into the combustion gas pipe;

a condensate heater adapted to exchange heat between steam condensate obtained by a steam condenser of a steam system of the boiler and bleed steam, and to supply the steam condensate heated by the condensate heater to the boiler;

a bleed valve installed on a steam introduction conduit of the condensate heater and adapted to adjust an amount of the bleed steam introduced into the condensate heater;

a condensate bypass conduit adapted to bypass the condensate heater and to supply the steam condensate to the boiler bypassing the condensate heater;

a second valve unit adapted to switch a flow channel of the steam condensate supplied to the boiler by running through between the condensate heater and the condensate bypass conduit;

a flue gas bypass conduit adapted to allow the flue gas to run by bypassing a flow channel which links an output port disposed in the flue between the combustion gas heater and the dust remover with a return port on the downstream side of the output port;

a third valve unit adapted to switch a flow channel of the flue gas between the flue and the flue gas bypass conduit, wherein

the flue gas cooler is configured to be able to exchange heat between the steam condensate running through the condensate bypass conduit and the flue gas running through the flue gas bypass conduit;

during oxygen combustion operation, the first valve unit is switched to the circulating flue gas, the bleed valve is closed, the second valve unit is switched to the condensate bypass conduit, the third valve unit is switched to the flue gas bypass conduit and then the flue gas is cooled by the condensate;

during air combustion operation, the first valve unit is switched to the air, the second valve unit is switched to the condensate heater, the bleed valve is opened, the third valve unit is switched to the flue and the flue gas is able to stop cooling;

a working gas supply device adapted to supply working gas which is used in an ancillary device of at least one of the boiler and a flue gas treatment system and intrudes into the flue gas, the flue gas treatment system being adapted to purify the flue gas discharged from the boiler; and

wherein the working gas supply device uses the flue gas from which soot particles have been collected by the dust remover, as the working gas.

8. An oxygen combustion system comprising:

a boiler adapted to burn fuel using combustion gas composed of a mixture of oxygen-rich gas and circulating flue gas;

a dust remover disposed in a flue through which flue gas discharged from the boiler flows;

a combustion gas pipe adapted to lead the combustion gas to the boiler, the combustion gas being made by mixing the circulating flue gas extracted from the flue on a downstream side of the dust remover with the oxygen-rich gas;

a combustion gas heater adapted to exchange heat between the flue gas flowing through the flue between the boiler and the dust remover and the combustion gas flowing through the combustion gas pipe;

a flue gas cooler disposed in the flue between the combustion gas heater and the dust remover and adapted to cool the flue gas by exchanging heat between the flue gas running through the flue and a cooling medium;

control means adapted to control at least one of a flow rate and temperature of the cooling medium of the flue gas cooler such that temperature of the flue gas introduced into the dust remover will be between and including 90° C. and 140° C., wherein SO 3 in the flue gas condenses on an inlet side of the dust remover, forming sulfuric acid mist, and is removed by the dust remover, sticking to soot particles in the flue gas, and temperature of the flue gas never falls below an acid dew-point temperature, and acid dew-point corrosion and clogging with soot particles of ducts are inhibited;

an air separator adapted to produce the oxygen-rich gas by separating nitrogen from air;

an oxygen introduction channel used to introduce the oxygen-rich gas produced by the air separator into the combustion gas pipe on an upstream side of the combustion gas heater, the oxygen introduction channel being provided with heating means adapted to heat oxygen flowing through the oxygen introduction channel;

a first valve unit adapted to switch gas to be introduced into the combustion gas pipe between the circulating flue gas and air; wherein

the first valve unit comprises a damper disposed in a duct adapted to introduce the circulating flue gas in the combustion gas pipe, and a damper disposed in a duct being provided at one end of an air introduction port adapted to introduce air into the combustion gas pipe;

a condensate heater adapted to exchange heat between steam condensate obtained by a steam condenser of a steam system of the boiler and bleed steam, and to supply the steam condensate heated by the condensate heater to the boiler;

a bleed valve installed on a steam introduction conduit of the condensate heater and adapted to adjust an amount of the bleed steam introduced into the condensate heater;

a condensate bypass conduit adapted to bypass the condensate heater and to supply the steam condensate to the boiler bypassing the condensate heater;

a second valve unit adapted to switch a flow channel of the steam condensate supplied to the boiler by running through between the condensate heater and the condensate bypass conduit;

a flue gas bypass conduit adapted to allow the flue gas to run by bypassing a flow channel which links an output port disposed in the flue between the combustion gas heater and the dust remover with a return port on the downstream side of the output port;

a third valve unit adapted to switch a flow channel of the flue gas between the flue and the flue gas bypass conduit; wherein

the flue gas cooler is configured to be able to exchange heat between the steam condensate running through the condensate bypass conduit and the flue gas running through the flue gas bypass conduit;

during oxygen combustion operation, the first valve unit is switched to the circulating flue gas, the bleed valve is closed, the second valve unit is switched to the condensate bypass conduit, the third valve unit is switched to the flue gas bypass conduit and then the flue gas is cooled by the condensate;

during air combustion operation, the first valve unit is switched to the air, the second valve unit is switched to the condensate heater, the bleed valve is open, the third valve unit is switched to the flue and then the flue gas is able to stop cooling;

a working gas supply device adapted to supply working gas which is used in an ancillary device of at least one of the boiler and a flue gas treatment system and intrudes into the flue gas, the flue gas treatment system being adapted to purify the flue gas discharged from the boiler; and

the working gas supply device uses the flue gas from which soot particles have been collected by the dust remover, as the working gas.

9. An operating method for an oxygen combustion system which comprises: a boiler adapted to burn fuel using combustion gas composed of a mixture of oxygen-rich gas and circulating flue gas containing 25% to 40% of water; a dust remover disposed in a flue through which flue gas discharged from the boiler flows; a combustion gas pipe adapted to lead the combustion gas to the boiler, the combustion gas being made by mixing the circulating flue gas extracted from the flue on a downstream side of the dust remover with the oxygen-rich gas; a combustion gas heater adapted to exchange heat between the flue gas flowing through the flue between the boiler and the dust remover and the combustion gas flowing through the combustion gas pipe; and a flue gas cooler disposed in the flue between the combustion gas heater and the dust remover and adapted to cool the flue gas by exchanging heat between the flue gas running through the flue and a cooling medium, wherein

the operating method adjusts temperature of the flue gas passing through the flue gas cooler so as to keep the temperature of the flue gas introduced into the dust remover between and including 90° C. and 140° C. during oxygen combustion operation which involves burning the fuel by supplying combustion gas to the boiler, wherein SO 3 in the flue gas condenses on an inlet side of the dust remover, forming sulfuric acid mist, and is removed by the dust remover, sticking to soot particles in the flue gas, and temperature of the flue gas never falls below an acid dew-point temperature, and acid dew-point corrosion and clogging with soot particles of ducts are inhibited.

10. The oxygen combustion system according to claim 1 , wherein the control means is adapted to control the temperature of the flue gas introduced into the dust remover to a predetermined temperature between and including 90° C. and 140° C.