Oxyfuel Combusting Boiler System and a Method of Generating Power By Using the Boiler System

A method of generating power by combusting carbonaceous fuel with an oxidant gas in a furnace of a boiler system, the method comprising the steps of:

• (a) feeding carbonaceous fuel into the furnace at a fuel feeding rate;
• (b) feeding oxidant gas into the furnace for combusting the fuel to produce exhaust gas;
• (c) discharging the exhaust gas from the furnace via an exhaust gas channel;
• (d) conveying a stream of feedwater at a feedwater conveying rate from a final economizer arranged in the exhaust gas channel to evaporating and superheating heat exchange surfaces arranged in the furnace and in the exhaust gas channel for converting the feedwater to superheated steam;
• (e) expanding the superheated steam in a high-pressure steam turbine for generating power;
• (f) extracting a first portion of steam from the high-pressure steam turbine for preheating the feedwater;
• (g) conveying a second portion of steam from the high-pressure steam turbine to reheating heat exchange surfaces arranged in the exhaust gas channel for generating reheated steam;
• and
• (h) expanding the reheated steam in an intermediate pressure steam turbine for generating power,
• wherein, in first operating conditions, the oxidant gas is a mixture of substantially pure oxygen and recycled exhaust gas and the ratio of the first and second portions of steam is controlled so as to obtain a desired flue gas temperature in the exhaust gas channel downstream of the final economizer.