The non-catalytic removal of NOx involves which additive?

The non-catalytic removal of NOx (nitrogen oxides) is primarily achieved through a process known as selective non-catalytic reduction (SNCR). In this process, ammonia is introduced into the combustion gases at high temperatures (typically between 900°C and 1,100°C). The ammonia reacts with the nitrogen oxides to form nitrogen and water, effectively reducing the NOx emissions.

Ammonia is favored for this application due to its effectiveness in facilitating the reduction reaction without the need for a catalyst. This means that, unlike other methods that may rely on catalytic processes, SNCR can perform at elevated temperatures where the presence of a catalyst isn't necessary. The reaction dynamics allow ammonia to react directly with NOx, leading to the desired decrease in these harmful emissions.

In contrast, the other additives listed do not serve this specific function in the non-catalytic removal of NOx. Water vapor can be a by-product of combustion processes but does not actively participate in NOx reduction. Nitrogen is typically inert under combustion conditions and would not contribute to the removal of NOx. Carbon dioxide, while a product of combustion, also does not engage in a reduction reaction with NOx. These characteristics highlight why ammonia is the correct