Mono-nitrogen oxides (NO_x) including NO and NO₂ are byproducts of combustion where it occurs in the presence of nitrogen. Since the composition of the atmosphere is 78% nitrogen, this would include most places where this combustion occurs. These NOx gases:

…react to form smog and acid rain as well as being central to the formation of tropospheric ozone.

To control the level of NOx emissions to meet regulatory limits, ammonia (NH₃) can be used to react with these molecules at high temperatures to produce molecular nitrogen (N₂) and water vapor. DeNOx reactors take the combustion gas and vaporized ammonia over a solid catalyst to reduce the molecules to nitrogen and water. This process is known as selective catalytic reduction (SCR). When a catalyst is not used due to sufficient temperatures (1,400 and 2,000 °F [760 and 1,090 °C]) for the reaction to occur, the process is called selective non-catalytic reduction (SNCR).

In this short, 2:18 YouTube video, Optimization Solution for DeNOx Reactors, Emerson’s Amanda Gogates explains how Quantum Cascade Laser (QCL) analyzer technology can help to optimize the amount of ammonia used for this chemical reaction in both SCR and SNCR processes.

Amanda opens the video explaining ammonia slip—or the amount of unreacted ammonia in the process.

She notes that it’s critical to continuously monitor the level of ammonia slip, especially in high-dust, high-temperature applications.

https://www.youtube.com/watch?v=bP9fKD156PE

Using too little ammonia can lead to excessive NOx emissions beyond regulatory limits and inefficient use of the catalyzer materials. Using too much ammonia can lead to waste, ammonia salt formation and plugging, which can lead to downtime and higher maintenance costs. Quantum Cascade Laser Analyzers can provide real-time measurements of ammonia levels as low as 0.15 parts per million.

The QCL analyzer monitors two key areas including the feed to the reactor upstream of the ammonia injection grid to measure NO, NO2, carbon dioxide and oxygen as well as downstream of the reactor to measure for any ammonia slip. The QCL analyzer has no moving parts or consumables so the ongoing maintenance required is minimal.

You can connect and interact with other gas analysis and combustion experts in the Analytical group in the Emerson Exchange 365 community.