Kotler V.R., Open JSC “VTI”
In technical literature of the most countries, these methods of nitrogen oxide emission reduction are commonly called "secondary” (secondary measures), as opposed to “primary”, which have been discussed in it. 1.1.2. This name comes from the fact that for economic reasons in boilers, firstly, technological methods of NOx reduction are realized (use of low-NOx burners, staged air or fuel supply, etc.) and only in case of ineffectiveness of the “primary” measures the more expensive “secondary” ones are usually introduced.