FGD and DeNOx
NEWSLETTER       

                                                                                                         March 2005
                                                                                                             No. 323

Cogen Unit Reaches <10 ppm NO_x Without SCR

John Zink helped a natural gas-fired combined cycle cogeneration facility in Texas reach less than 10 ppm NO_x (corrected to 15 percent O₂) without using SCR. The company first installed aftermarket low-NO_x turbine combustors on its GE Frame 7EA gas turbines. Then John Zink’s modified fuel injection design was applied to the existing duct burners. The modification was accomplished by simply unscrewing the existing gas nozzles and replacing them with the new staged-gas tips. The new nozzles changed the way the fuel and turbine exhaust gases mixed prior to combustion by staging the fuel injection and thereby delaying fuel-air mixing. This resulted in a lower peak flame temperature and reduced NO_x, but did not increase flame length beyond acceptable levels. NO_x emissions from the duct burner were 25 percent lower than the original tip design emissions.

Because of the success with the first unit, the plant decided to proceed with the modification of a second unit. The team decided to increase the level of fuel staging to determine if the amount of NO_x reduction could be increased. The duct burners in the second unit were modified with John Zink’s Mark II, low-NO_x duct burner tips. These tips reduced NO_x emissions approximately 50 percent compared to the original tips. A third unit was also equipped with the Mark II tips.

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