PURPOSE: To permit to remove carbon in a short time by a method wherein total heating values and reactor discharge heating values are obtained and estimated as the storage heating values of a reactor in accordance with difference between the total heating values and the discharge heating values, whereby, the set value of an air flow amount control is obtained.

CONSTITUTION: Air flow amount AF, diluted gas flow amount GF and others, density of carbon dioxide also are collected in a total heating values operation section 31. An efficiency ηused to obtain the total heating values due to the flow amount AF, GF or the like is multiplied them at a multiplication operation section 32, then the true total heating values are obtained, thereafter, it is performed subtraction treatment at a temperature difference operation section 41 and the temperature difference of an inlet.outlet at the reactor 10 is obtain to supply for the discharge heating value operation section 45. Respective flow amounts AF, GF are sent to the heating values operation sections 42, 43 and the heating values of the air flow amount and the heating values of the gas are obtained then it is supplied to the total heating value operation section 44 and the total sum of the heating values are obtained, thereafter, it is supplied to the discharge heating values operation section 45 and the temperature difference of the reactor 10 is multiplied with the total sum of the heating values to obtain the discharge heating values of the reactor 10. The discharge heating values are sent to the heating values difference operation section 51 and the deviation between the total heating values and the discharge heating values are obtained while the deviation is estimated as the storage heating values of the reactor 10. It is sent to the air flow amount set value operation section 52 and the set value of the air flow control section 17 may be obtained.