A method of controlling a process of generating power in a power plant with a boiler by combusting carbonaceous fuel with substantially pure oxygen, the method comprising, at full load conditions, the steps of: introducing a first carbonaceous fuel feed stream into a furnace; introducing a first substantially pure oxygen feed stream into the furnace for combusting the first carbonaceous fuel feed stream with the oxygen so as to produce exhaust gas; discharging the exhaust gas via an exhaust gas channel from the furnace; recovering heat from the exhaust gas by a superheating heat exchange surface, arranged in an upstream portion of the exhaust gas channel; and recirculating a portion of the exhaust gas via an exhaust gas recirculating channel, at a first recirculation flow rate to the furnace, to form, together with the first substantially pure oxygen feed stream, a first inlet gas stream having a predetermined average oxygen content, whereby the exhaust gas is discharged from the furnace and flows through the superheating heat exchange surface at a first discharge flow rate, and, in second load conditions, corresponding to at most 90 % of the full load, the steps of: introducing a second carbonaceous fuel feed stream into the furnace; introducing a second substantially pure oxygen feed stream into the furnace for combusting the second carbonaceous fuel feed stream with the oxygen so as to produce exhaust gas; discharging the exhaust gas via the exhaust gas channel from the furnace; recovering heat from the exhaust gas by the superheating heat exchange surface arranged in the exhaust gas channel; and recirculating a portion of the exhaust gas via the exhaust gas recirculating channel at a second recirculation flow rate to the furnace, to form, together with the second substantially pure oxygen feed stream, a second inlet gas stream, so that the exhaust gas is discharged from the furnace and flows through the superheating heat exchange surface at a second discharge flow rate, and controlling the second recirculation flow rate to be from the first recirculation flow rate to a value providing the second discharge flow rate to be substantially as high as the first discharge flow rate. introducing a first carbonaceous fuel feed stream into a furnace; introducing a first substantially pure oxygen feed stream into the furnace for combusting the first carbonaceous fuel feed stream with the oxygen so as to produce exhaust gas; discharging the exhaust gas via an exhaust gas channel from the furnace; recovering heat from the exhaust gas by a superheating heat exchange surface, arranged in an upstream portion of the exhaust gas channel; and recirculating a portion of the exhaust gas via an exhaust gas recirculating channel, at a first recirculation flow rate to the furnace, to form, together with the first substantially pure oxygen feed stream, a first inlet gas stream having a predetermined average oxygen content, whereby the exhaust gas is discharged from the furnace and flows through the superheating heat exchange surface at a first discharge flow rate, introducing a second carbonaceous fuel feed stream into the furnace; introducing a second substantially pure oxygen feed stream into the furnace for combusting the second carbonaceous fuel feed stream with the oxygen so as to produce exhaust gas; discharging the exhaust gas via the exhaust gas channel from the furnace; recovering heat from the exhaust gas by the superheating heat exchange surface arranged in the exhaust gas channel; and recirculating a portion of the exhaust gas via the exhaust gas recirculating channel at a second recirculation flow rate to the furnace, to form, together with the second substantially pure oxygen feed stream, a second inlet gas stream, so that the exhaust gas is discharged from the furnace and flows through the superheating heat exchange surface at a second discharge flow rate, and controlling the second recirculation flow rate to be from the first recirculation flow rate to a value providing the second discharge flow rate to be substantially as high as the first discharge flow rate.