Method and apparatus for reheat steam temperature control of oxy-fired boilers
View Patent ↗Method and system for adjusting a measured reheat outlet steam temperature (“R PV ”) to approximate a reheat outlet steam temperature setpoint (“R SP ”) in a boiler. An R PV is compared to an R SP . If the R PV is less than the R SP and a position of a fuel nozzle tilt (“TILT PV ”) is below a high limit of the fuel nozzle tilt (“TILT HIGH ”), the TILT PV is increased while a flow rate of a secondary flue gas recirculation (“SFGR PV ”) is kept constant. If the R PV is less than the R SP and the TILT PV is at the TILT HIGH , the SFGR PV is increased. If the R PV is greater than the R SP and the SFGR PV is greater than a low limit of flow rate of the SFGR (“SFGR LOW ”), the SFGR PV is decreased, while the TILT PV is kept constant. If the R PV is greater than the R SP and the SFGR PV is at the SFGR LOW , the TILT PV is decreased.
1. A method of adjusting a measured steam reheat outlet temperature (“R PV ”) to approximate a steam reheat outlet temperature setpoint (“R SP ”) 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 R PV to an R SP ;
if the R PV is less than the R SP and a position of the fuel nozzle tilt (“TILT PV ”) is below a high limit of the fuel nozzle tilt (“TILT HIGH ”) increasing the TILT PV to increase the R PV prior to changing a flow rate of a secondary flue gas recirculation (“SFGR PV ”) recirculated back to the furnace;
if the R PV is less than the R SP and the TILT PV is at the TILT HIGH after increasing the TILT PV , then increasing the SFGR PV to increase the R PV ;
if the R PV is greater than the R SP and the SFGR PV is greater than a low limit of flow rate of the SFGR (“SFGR LOW ”), decreasing the SFGR PV to decrease the R PV prior to changing the TILT PV ; and
if the if the R PV is still greater than the R SP and the SFGR PV is at the SFGR LOW after decreasing the SFGR PV , then decreasing the TILT PV to decrease the R PV .
2. The method of claim 1 , wherein the decreasing the SFGR PV causes a decrease in an amount of power consumed by a fan.
3. The method of claim 1 , further comprising prioritizing control of at least one of an attemperator spray water control, fuel nozzle tilts control, and SFGR control loop based on at least one closed-loop proportional-integral-derivative (“PID”) control.
4. A method of adjusting a measured steam reheat outlet temperature (“R PV ”) to approximate a steam reheat outlet temperature setpoint (“R SP ”) in a steam generating boiler having a furnace with a fuel nozzle which generates a flue gas, the method comprising:
comparing the R PV to the R SP ;
if the R PV is less than the R SP and a position of a fuel nozzle tilt (“TILT PV ”) is below a high limit of the fuel nozzle tilt (“TILT HIGH ”), then:
first increasing the TILT PV to increase the R PV while maintaining a flow rate of a secondary flue gas recirculation (“SFGR PV ”) recirculated back to the furnace constant;
if the R PV remains less than the R SP and the TILT PV is at the TILT HIGH after increasing the TILT PV , only then increasing the SFGR PV to increase the R PV ; and
if the R PV is greater than the R SP and the SFGR PV is greater than a low limit of flow rate of the SFGR (“SFGR LOW ”), then:
first decreasing the SFGR PV to decrease the R PV prior to changing the TILT PV ; and
if the if the R PV is still greater than the R SP and the SFGR PV is at the SFGR LOW after decreasing the SFGR PV , then decreasing the TILT PV to decrease the R PV .
5. The method of claim 4 , wherein the decreasing the SFGR PV causes a decrease in an amount of power consumed by a fan.
6. The method of claim 4 , further comprising prioritizing control of at least one of an attemperator spray water control, fuel nozzle tilts control, and SFGR control loop based on at least one closed-loop proportional-integral-derivative (“PID”) control.