Patent ID: 8584604

Claim:
A method for controlling combustion in an oxygen fired boiler, comprising the steps of: separating air into oxygen and other nitrogen-prevailing gas by an air separation unit, burning the oxygen obtained by the air separation unit and fuel in a boiler body to heat feedwater to produce steam, partly recirculating combustion exhaust gas from the boiler body, at least after dust removal treatment, as recirculation gas to the boiler body, supplying oxygen to the boiler body in a setting amount in accordance with a boiler load demand, measuring a heat absorption amount of the boiler using an inlet temperature of the feedwater supplied to the boiler body and an outlet temperature of steam and/or a combustion exhaust gas temperature in the boiler, and controlling a recirculation flow rate of said recirculation gas to said boiler body to make the heat absorption amount equal to a targeted heat absorption amount to thereby control a concentration of oxygen in all gas guided to the boiler body, wherein the boiler is provided with a line for supply of said oxygen mixed with the recirculation gas to the boiler body and a line for supply of said oxygen directly to the boiler body, further comprising the steps of controlling an amount of all the oxygen supplied to the boiler body in accordance with a boiler load demand via said line for supply of said oxygen mixed with the recirculation gas to the boiler body and said line for supply of said oxygen directly to the boiler body, such that the amount of all the oxygen supplied to the boiler body becomes equal to a preliminarily obtained amount of all the oxygen supplied in an existing air fired boiler, controlling the recirculation flow rate of said recirculation gas such that the heat absorption amount becomes equal to a heat absorption amount of the existing air fired boiler, and changing flow rate ratios of the oxygen supplied to the boiler body via said line for supply of said oxygen mixed with the recirculation gas to the boiler body and said line for supply of said oxygen directly to the boiler body, thereby changing an ignition position of a burner flame to improve the heat absorption amount of the boiler body.