| 1. In combination with a fossil fuel combustion system including a boiler, an exhaust duct communicating with the boiler to
receive the combustion products laden gases therefrom, a selective catalytic reduction chamber located within the exhaust
duct, an air heater, an air duct for supplying substantially unadulterated heated combustion air from the air heater to the
boiler, and improved apparatus for the removal of nitrogen oxides from the combustion gases including a heat exchanger and
comprising an arrangement whose function is to improve the operation and extend the service life of the heat exchanger by
placing said heat exchanger within the combustion products free environment of the air duct, an ammonia tank, a first duct
for delivering dilution air to be heated by the heat exchanger, a second duct for receiving the heated dilution air and delivering
it to the tank to vaporize the ammonia, an ammonia injection grid located within the exhaust duct upstream of the selective
catalytic reduction chamber, a third duct for delivering the vaporized ammonia to the injection grid, and whereby the vaporized
ammonia is injected into the combustion gases to react with the catalyst in the catalytic reduction chamber to dissociate
the nitrogen oxides to molecular nitrogen and water vapor.
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