O&M – Balance of Plant: Decatur Energy Center – Combined Cycle Journal

O&M – Balance of Plant: Decatur Energy Center

Ammonia injection air duct heater

Decatur Energy Center
Calpine Corp
800-MW, gas-fired, 3 x 1 combined-cycle cogeneration facility located in Decatur, Ala
Plant manager: Mike Gough
Key project participants: Joe Bogle, plant engineerScott Parker, operations manager


Decatur Energy Center (DEC) encountered decreased ammonia dilution- air flow as a result of moisture freezing and ammonia salt buildup in piping orifices during extreme cold-weather operations.


The site conducted a management of design change (MODC) procedure review since this was considered to be part of a process safety management (PSM) system. The decision was to install an ammonia dilution-air duct heater to preheat dilution air during winter operations.

The basic components included a control panel which contained a temperature controller with high-temperature shutoff and a power controller to regulate heater voltage and maintain the temperature set point of the controller.

Additionally, a temperature switch is used for automatic operation and is set to turn the system on at 40F ambient. An interlock from the blower starters will not allow the heater to energize if at least one of the two blowers is not running.


After system installation, the ammonia dilution-air temperature increased dramatically—from freezing ambient temperatures to approximately 90F. The warm air eliminated freezing and salt-buildup problems previously encountered at the piping orifices.

This has facilitated a return to normal air distribution and air flow rates in the SCR. The successful modification at DEC provided the incentive to install the same system at neighboring Morgan Energy Center.

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