Method and apparatus for reheat steam temperature control of oxy-fired boilers

A method of adjusting a measured steam reheat outlet temperature (“RPV”) to approximate a steam reheat outlet temperature setpoint (“RSP”) in a dual-mode air and oxy-fired steam generating boiler having a furnace with a fuel nozzle which generates a flue gas, comprising:

• operating a furnace in one of an air-fired mode and an oxy-fired mode;
• comparing an RPV to an RSP;
• if the RPV is less than the RSP and a position of the fuel nozzle tilt (“TILTPV”) is below a high limit of the fuel nozzle tilt (“TILTHIGH”) increasing the TILTPV to increase the RPV prior to changing a flow rate of a secondary flue gas recirculation (“SFGRPV”) recirculated back to the furnace;
• if the RPV is less than the RSP and the TILTPV is at the TILTHIGH after increasing the TILTPV, then increasing the SFGRPV to increase the RPV;
• if the RPV is greater than the RSP and the SFGRPV is greater than a low limit of flow rate of the SFGR (“SFGRLOW”), decreasing the SFGRPV to decrease the RPV prior to changing the TILTPV;
• and
• if the if the RPV is still greater than the RSP and the SFGRPV is at the SFGRLOW after decreasing the SFGRPV, then decreasing the TILTPV to decrease the RPV.