Oxyfuel boiler and a method of controlling the same

1. An oxyfuel boiler having a furnace configured such that oxygen separated from air is mixed with a portion of combustion flue gas branched from combustion flue gas discharged from the boiler, which burns fuel coal to generate steam to be supplied to a steam demand equipment, so as to form oxidizing gas for burning coal, and the oxidizing gas is supplied to the boiler,

characterized in that

the oxyfuel boiler is further comprising:

an oxygen separation apparatus to produce oxygen by separating oxygen from the air,

a recirculation fan to supply a portion of combustion flue gas branched from the combustion flue gas discharged from the boiler to the oxyfuel boiler,

a temperature sensor disposed at a boiler outlet in the oxyfuel boiler to detect gas temperature of the combustion flue gas, and

a control apparatus to calculate gas temperature of the combustion flue gas at the furnace outlet in the boiler from the gas temperature of the combustion flue gas at the boiler outlet detected by the temperature sensor and control the operating condition of the recirculation fan so that the calculated gas temperature of the combustion flue gas at the furnace outlet becomes a desired preset gas temperature.

2. The oxyfuel boiler according to claim 1 , wherein

an oxygen sensor to detect oxygen concentration of the combustion flue gas is disposed at a boiler outlet in the oxyfuel boiler, and the control apparatus controls the operating condition of the oxygen separation apparatus so that oxygen concentration at the boiler outlet detected by the oxygen sensor becomes a desired preset oxygen concentration.

3. A control apparatus of an oxyfuel boiler according to claim 1 , wherein

the desired preset gas temperature at the furnace outlet in the boiler is determined so that the balance of the heat storage quantity in each heat exchanger located on the rear heat transfer surface in the boiler operating to perform oxygen combustion is almost equivalent to the balance of the heat storage quantity in the each heat exchanger in the boiler operating to perform air combustion.

4. A control apparatus of an oxyfuel boiler according to claim 2 , wherein

the desired preset gas temperature at the furnace outlet in the boiler is determined so that the balance of the heat storage quantity in each heat exchanger located on the rear heat transfer surface in the boiler operating to perform oxygen combustion is almost equivalent to the balance of the heat storage quantity in the each heat exchanger in the boiler operating to perform air combustion.

5. A method of controlling an oxyfuel boiler having a furnace configured such that oxygen separated from the air is mixed with a portion of combustion flue gas branched from the combustion flue gas discharged from a boiler, which burns fuel coal to generate steam to be supplied to a steam demand equipment, so as to form oxidizing gas for burning coal, and the oxidizing gas is supplied to the boiler,

characterized in that

the method of controlling the oxyfuel boiler is further comprising the steps of:

oxygen mixed into as oxidizing gas supplied to the boiler is produced by separating oxygen from the air by an oxygen separation apparatus,

combustion flue gas mixed into as the oxidizing gas supplied to the boiler is a portion of the combustion flue gas discharged from the boiler and supplied by a recirculation fan,

the oxidizing gas which is a mixture of the oxygen produced by the oxygen separation apparatus and the combustion flue gas supplied by the recirculation fan is supplied to the oxyfuel boiler to be used for burning coal in the oxyfuel boiler,

gas temperature of the combustion flue gas at a furnace outlet in the boiler is calculated by a control apparatus from the gas temperature of the combustion flue gas at the boiler outlet detected by a temperature sensor disposed at the boiler outlet in the oxyfuel boiler,

the quantity of the combustion flue gas supplied from the recirculation fan is regulated by the control apparatus so that the calculated gas temperature of the combustion flue gas at the furnace outlet becomes a desired preset gas temperature.

6. The method of controlling an oxyfuel boiler according to claim 5 , wherein

the quantity of oxygen supplied from the oxygen separation apparatus is regulated by the control apparatus so that the oxygen concentration at the boiler outlet detected by the oxygen sensor disposed at the boiler outlet in the oxyfuel boiler becomes a desired preset oxygen concentration.

7. The method of controlling an oxyfuel boiler according to claim 5 , wherein

the desired preset gas temperature at the furnace outlet of the boiler is determined so that the balance of the heat storage quantity in each heat exchanger located on the rear heat transfer surface in the boiler operating to perform oxygen combustion is almost equivalent to the balance of the heat storage quantity in the each heat exchanger in the boiler operating to perform air combustion.

8. The method of controlling an oxyfuel boiler according to claim 6 , wherein

the desired preset gas temperature at the furnace outlet of the boiler is determined so that the balance of the heat storage quantity in each heat exchanger located on the rear heat transfer surface in the boiler operating to perform oxygen combustion is almost equivalent to the balance of the heat storage quantity in the each heat exchanger in the boiler operating to perform air combustion.