Ammonia injection grid

FIGURE 17.21 Ammonia injection grid for circular duct in the FCCU SCR. (With permission from Haldor-Topsoe, Inc.)... 

An ammonia injection grid (to evenly disperse the NH3 across the duct)... 

The ammonia injection grid must be designed to evenly distribute the ammonia across the duct without restricting flow. Since NO concentrations vary across the duct, the ammonia injection grid must also be designed such that ammonia injection can be adjusted to match the NO concentrations across the duct of the exhaust system. 

Part of your assignment is to design the ammonia injection grid, catalyst and catalyst housing. Specify the number and arrangement of catalyst bricks and total catalyst volume. The ammonia... 

In the SCR process, ammonia, usually diluted with air or steam, is injected through a grid system into the flue/exhaust stream upstream of a catalyst bed (37). The effectiveness of the SCR process is also dependent on the NH to NO ratio. The ammonia injection rate and distribution must be controlled to yield an approximately 1 1 molar ratio. At a given temperature and space velocity, as the molar ratio increases to approximately 1 1, the NO reduction increases. At operations above 1 1, however, the amount of ammonia passing through the system increases (38). This ammonia sHp can be caused by catalyst deterioration, by poor velocity distribution, or inhomogeneous ammonia distribution in the bed. 

The ammonia injection is typically through a distribution grid (AIG) located upstream of the reactor. This distribution is critical to the performance of... 

The injection grid can be carbon steel, but near the injectors, stainless steel may be used due to the corrosive effects of the combination of atmnonia and fly-ash buildup (Cohen, 1993). The entire grid is sometimes made of stainless steel (Pritchard, 1994). Copper, galvanized steel, and viton should not be used in ammonia systems. 

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