Method of controlling a process of generating power by oxyfuel combustion

Abstract

A method of controlling a process of generating power in a power plant with a boiler by combusting carbonaceous fuel with substantially pure oxygen. At full load conditions, the method includes 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, and recirculating a portion of the exhaust gas discharged from the furnace 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, thereby discharging exhaust gas from the furnace at a first discharge flow rate. In second load conditions, corresponding to at most 90% load, the method includes 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, and recirculating a portion of the exhaust gas discharged from the furnace 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 as to discharge exhaust gas from the furnace 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.

1 . 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:
 (a1) introducing a first carbonaceous fuel feed stream into a furnace;   (b1) introducing a first substantially pure oxygen feed stream into the furnace for combusting the first carbonaceous fuel feed stream with the oxygen;   (c1) discharging exhaust gas via an exhaust gas channel from the furnace;   (d1) recovering heat from the exhaust gas by heat exchange surfaces arranged in the exhaust gas channel; and   (e1) 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, thereby discharging exhaust gas from the furnace at a first discharge flow rate,   and, in second load conditions, corresponding to at most 90% of the full load, the steps of:   (a2) introducing a second carbonaceous fuel feed stream into the furnace;   (b2) introducing a second substantially pure oxygen feed stream into the furnace for combusting the second carbonaceous fuel feed stream with the oxygen;   (c2) discharging exhaust gas via the exhaust gas channel from the furnace;   (d2) recovering heat from the exhaust gas by the heat exchange surfaces arranged in the exhaust gas channel; and   (e2) 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 as to discharge exhaust gas from the furnace 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.   
     
     
         2 . The method according to  claim 1 , wherein the second load conditions corresponds to at most 80% of the full load. 
     
     
         3 . The method according to  claim 2 , wherein the second load conditions correspond to at most 70% of the full load. 
     
     
         4 . The method according to  claim 3 , wherein the average oxygen content of the first inlet gas stream is, by volume, from about 20% to about 25%, and the average oxygen content of the second inlet gas stream is 0.70 to 0.78 times the average oxygen content of the first inlet gas stream. 
     
     
         5 . The method according to  claim 3 , wherein the average oxygen content of the first inlet gas stream is, by volume, from about 20% to about 25%, and the average oxygen content of the second inlet gas stream is 0.72 to 0.75 times the average oxygen content of the first inlet gas stream. 
     
     
         6 . The method according to  claim 3 , wherein the average oxygen content of the first inlet gas stream is, by volume, from about 40% to about 60%, and the average oxygen content of the second inlet gas stream is 0.73 to 0.82 times the average oxygen content of the first inlet gas stream. 
     
     
         7 . The method according to  claim 3 , wherein the average oxygen content of the first inlet gas stream is, by volume, from about 40% to about 60%, and the average oxygen content of the second inlet gas stream is 0.77 to 0.81 times the average oxygen content of the first inlet gas stream. 
     
     
         8 . The method according to  claim 1 , further comprising a step of measuring the discharge flow rate. 
     
     
         9 . The method according to  claim 1 , further comprising a step of measuring the recirculation flow rate. 
     
     
         10 . The method according to  claim 1 , further comprising controlling the second recirculation flow rate by a fan.