Jaypar:
You haven't told us how much ammonia your waste gas contains. Nor have you told us the operating conditions for the thermal oxidizer (i.e., combustion temperature, excess air percentage, whether or not a catalyst is used, etc).
However, in general, ammonia combustion does produce NO and NO2. Depending upon the location of your plant and the environmental regulations that you must satisfy, you may have to consider removal of those gases from your oxidizer flue gas.
Milton Beychok
(Contact me at www.air-dispersion.com)
.