Combustion has substantial impacts on NOx emissions as well as slagging and fouling. EFA understands how to balance NOx emissions with slagging and fouling targets. EFA’s technical director is a named inventor on multiple NOx control patents.
There are two primary methods for reducing NOx emissions. The first is to reduce NOx molecules to N2 and O2 by means of selective catalytic reduction (SCR) or selective non-catalytic reduction (SNCR). These technologies use a reducing agent such as ammonia or urea and elevated temperature (~1600-1800 °F SNCR) or a catalyst (SCR) to convert NO to N2 and O2.
Another method is to prevent NOx from forming in the first place. Combustion tuning and staged combustion can create a reducing rather than oxidizing atmosphere in the initial combustion process. This reduces the amount of fuel nitrogen in coal that is converted to NOx and thus reduces NOx emissions which must be controlled downstream by SCR or SNCR. In some cases, advanced combustion tuning and staging may result in a sufficiently low NOx emissions rate that SCR or SNCR are not needed providing a significant cost advantage to plant operations.
However, creating such a reducing environment in the combustion environment can reduce oxides in the ash to sub-oxides. For example, SiO2 may be reduced to SiO or Fe2O3 may be reduced to FeO. In some cases, sub-oxides can have a melting point several hundred degrees lower than the oxide. These molten ash constituents can then form slag and tenacious deposits which reduce the efficiency of boilers and can lead to output curtailments, excessive maintenance costs, and unplanned outages.
EFA understands the complex interplay between emissions controls, combustion conditions, and plant operations. We work with our customers to provide the most cost effective solutions for their individual needs and unique circumstances.