Knoxcheck checks NOx

A catalyst-activity testing tool developed with funding from the US Department of Energy offers a new way to manage the selective catalytic reduction systems that are used in power plants to control nitrogen oxides (NOx) emissions.

The commercially-available tool will help plant operators to more cost-effectively comply with NOx emissions regulations, including the new US Clean Air Interstate Rule.

Most of America's energy systems rely on combustion processes. A drawback of combustion is the formation of NOx - a group of highly reactive gases that form when fuel is burned at high temperatures and which contribute to smog, acid rain, and global warming. Selective catalytic reduction (SCR) systems control NOx emissions by injecting ammonia or urea into flue gas in the presence of a catalyst, converting NOx into nitrogen and water.

Over time, the ability of the SCR catalyst to convert NOx degrades, and the catalyst surface can also become clogged with fly ash. Additionally, SCR systems contain multiple catalyst layers, and each layer's activity can decay at different rates, requiring layer-specific maintenance. To restore SCR performance, power plant maintenance staff can either replace a layer of used catalyst with fresh catalyst, add an additional layer of fresh catalyst, or do both.