SCR Catalyst Application Chart
		Minimum Temperature, 0F	Optimum Temperature, 0F	Maximum Temperature, 0F
Vanadia / Titania Catalyst (Middle Temperature Applications)		575 note 1	600 - 750	800
ETZ™ Catalyst (High Temperature Applications)		600	600 - 1000	1075 note 2
Vanadia / Titania Catalyst (High Temperature Applications)		600 note 3	800 - 850	875 note 4
Zeolite Catalyst		600 note 5	675 - 1075	1125
1.	Under 575 0F, NOx conversion efficiency is reduced with increased NH3 slip.
2.	Above 1000 0F, catalytic efficiency declines.  Selectivity declines: NH3 begins to oxidize to form NOx.  Catalyst does not degrade thermally (can operate up to 1200 0F without thermal damage).
3.	Below 600 0F, NOx conversion is reduced with increased NH3 slip.
4.	Above 875 0F, catalytic efficiency declines.  Selectivity declines: NH3 begins to oxidize to form NOx.  Catalyst activity decreases with time.
5.	Under 600 0F, NOx conversion efficiency is reduced with increased NH3 slip
	ETZ is a registered trademark of the Engelhard Corporation

A major factor for selecting a catalyst is the exhaust gas temperature.  Cooling systems can be included to lower the exhaust temperature, but there are practical limitations on the amount of cooling that can be added, and the potential failure of the cooling system must be considered.  The design temperature for the catalyst must take into consideration the highest temperature possible.  All turbines produce hotter exhaust gas with an increase in ambient temperature, and the exhaust temperature of the turbine may increase as the engine gets older.  Turbine operating temperatures tend to rise with continued operation.  Be sure this is understood before designing an SCR system. If a specification states 850 0F, this must be the highest operating temperature over the life of the turbine, not just first operation.

Turbine exhaust ductwork is typically insulated with ceramic fiber insulation.  Fibers tend to spall off the insulation unless the duct is lined with stainless steel to assure the fibers don't enter the catalyst.

Numerical and physical flow modeling is performed to achieve uniform distribution profiles at the SCR catalyst face with regard to NOx concentration, NH3/NOx molar ratio, velocity and temperature.  This is often complicated by physical space limitations, arrangement limitations and limits to process equipment modifications.  An example cfd model output is shown.

Among the criteria for selecting SCR catalyst for turbine exhaust are: The average and extreme temperatures of the turbine exhaust from winter to summer Allowable pressure drop (pressure drop is also influenced by the duct cross section area) Moisture content of the gas. Inlet NOx level and % conversion required. Resistance of the catalyst substrate to thermal shock Selectivity of the catalyst. Contaminants in the gas ( SO2 ,  SO3, dust, ash, soot, etc.) Allowable ammonia slip.