NOx Control (SNCR)

Selective Non-Catalytic Reduction is a post-combustion technology that is designed to control nitrogen oxides (NOx) emissions from boilers by the injection of ammonia or urea reagents into the flue gas.

Hamon Research-Cottrell is licensed by Exxon Mobil for the application of ammonia based Thermal DeNox™ (TDN).

The key to the SNCR process is optimization of reagent injection with the flue gas within a specific temperature window. For urea this window is approximately 1800°F-2100°F (982°C-1149°C). For ammonia the window is slightly lower at 1600°F-1800°F (871°C-982°C). The temperature window can be effectively shifted to a lower range by the co-injection of hydrogen with ammonia.

Temperature mapping using HVT (high velocity temperature) probes, at different operating loads is critical to determine the locations of the desired temperature windows. The HVT mapping and system geometry is used along with computer combustion CFD modeling to characterize the system. The temperatures and gas streamlines are then predicted for a range of loads.

In addition to the temperature mapping and boiler/furnace modeling, a computer chemical kinetic reaction model is also utilized which provides a solution for the competing gas phase reactions and predicts NOx removal.

Spray patterns and dispersion are also critical to achieving proper reduction levels. Typically, there are two types of reagent injectors placed in the system to achieve reagent coverage.

• Retractable multiple port lances are used to inject the reagent over the width of the system. Lances are steam, water or glycol cooled.
• Retractable wall injectors are short, small lances designed to get reagent coverage near the wall of the boiler.

The SNCR reaction requires ammonia as the primary reducing agent. The ammonia may be provided based on anhydrous, aqueous or U2A product gas ammonia or from urea solution injection. The reagent is be piped to distribution and mixing modules for metering to each of the injectors.

Selective Non-Catalytic Reduction offers lower capital equipment cost and is extremely versatile for medium levels of NOx control. SNCR can be combined with other upstream and downstream NOx control technologies. SNCR is applied in many industries including, Power, Steel, Pulp and Paper, Petrochemical, Waste to Energy, Glass and others.