ⓘ Selective non-catalytic reduction


ⓘ Selective non-catalytic reduction

Selective non-catalytic reduction is a method to lessen nitrogen oxide emissions in conventional power plants that burn biomass, waste and coal. The process involves injecting either ammonia or urea into the firebox of the boiler at a location where the flue gas is between 1.400 and 2.000 °F to react with the nitrogen oxides formed in the combustion process. The resulting product of the chemical redox reaction is molecular nitrogen, carbon dioxide, and water.

Urea, NH 2 CONH 2 easier to process and store more dangerous ammonia пн3. In the process, he reacts like ammonia:

NH 2 CONH 2 + H 2 O ->, 2NH 3 + CO2

The reduction occurs according to the simplified

4 NO + 4 NH 3 + O 2 ->, 4 N 2 + 6 H 2 O

The reaction mechanism includes the NH 2 radicals, which attach to no, and then decompose.

The reaction requires a sufficient reaction time within a certain temperature range, usually to 1400 and 2000 °C and 760 1.090 °C to be effective. At lower temperatures the no and the ammonia dont react. Ammonia that is not reacted is called ammonia slip and is undesirable, as the ammonia can react with other types of combustion, such as sulfur trioxide ѕо3, in the form of ammonium salts.

At temperatures above 1093 °C ammonia decomposes:

4 NH 3 + 5 O 2 ->, 4 NO + 6 H 2 O

In this case, is not created instead of removed.

Another difficulty lies in the mixing. In General, will no longer form in the center and less near the walls as the walls are colder than the center. Thus, more ammonia must find its way to the center and less near the walls, otherwise no in the center meets insufficient ammonia for reduction and excess ammonia near the walls slips through.

Though in theory selective non-catalytic reduction recovery can achieve the same efficiency of about 90% as selective catalytic reduction of SLE, these practical constraints of temperature, time and mixing often lead to worse results in practice. However, selective non-catalytic reduction has an economic advantage over selective catalytic reduction, as the cost of the catalyst no.

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