Depending on plant requirements (new plant, retrofit, space availability), NO_x reduction can be performed in a variety of configurations.

In a high dust configuration, the SCR reactor is installed directly downstream of the economizer and upstream of the air preheater. The main advantage of this arrangement is that preheating of the flue gas is not necessary. The flue gas temperature normally varies between 300°C and 430°C (570°F and 810°F). The principal advantages of the high dust system are lower capital investments and lower energy operating costs.