Selective non-catalytic reduction
- Selective non-catalytic reduction
Selective Non Catalytic Reduction (SNCR) is a method for reducing 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 1600 °F and 2100 °F (870 °C and 1150 °C) to react with the nitrogen oxides formed in the combustion process. The resulting product of the chemical reaction is elemental nitrogen (N2), carbon dioxide (CO2), and water (H2O).
Urea (NH2CONH2) is easier to handle and store than the more dangerous ammonia (NH3). In the process it reacts like ammonia:
:NH2CONH2 + H2O -> NH3 + CO2
The reduction happens according to (simplified) [Duo et al., 1992 Can. J. Chem. Engng, 70, 1014-1020]
:4 NO + 4 NH3 + O2 -> 4 N2 + 6 H2O
The reaction mechanism itself involves NH2 radicals that attach to NO and then decompose.
The reaction needs a certain minimum temperature to happen, otherwise the NO and the ammonia don't react. Ammonia that hasn't reacted is called ammonia slip and is undesirable.
At too high temperatures ammonia decomposes:
:4 NH3 + 5 O2 -> 4 NO + 6 H2O
In that case NO is formed instead of reduced. Thus the reaction needs a specific temperature window to be efficient. The reaction also needs sufficient reaction time in that temperature window.
A further complication is mixing. Generally more NO will form in the center and less near the walls, as the walls are cooler than the center. Thus optimally 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 can achieve the same efficiency of about 90 % as selective catalytic reduction, these practical constraints of temperature, time, and mixing often lead to worse results in practice. However, selective non-catalytic reduction has an economical advantage over selective catalytic reduction, as the cost of the catalyst isn't there.
References
Wikimedia Foundation.
2010.
Look at other dictionaries:
Selective Non Catalytic Reduction — Die Selektive nicht katalytische Reduktion (kurz SNCR von engl. Selective Non Catalytic Reduction) ist ein DeNOx Verfahren (Denitrifikations Verfahren, Rauchgasentstickung), um Stickoxide (NOx) in Rauchgasen abzubauen. Durch Thermolyse wird… … Deutsch Wikipedia
Selective Non Cat Reduction — Die Selektive nicht katalytische Reduktion (kurz SNCR von engl. Selective Non Catalytic Reduction) ist ein DeNOx Verfahren (Denitrifikations Verfahren, Rauchgasentstickung), um Stickoxide (NOx) in Rauchgasen abzubauen. Durch Thermolyse wird… … Deutsch Wikipedia
Catalytic converter — A catalytic converter (colloquially, cat or catcon ) is a device used to reduce the toxicity of emissions from an internal combustion engine. First widely introduced on series production automobiles in the US market for the 1975 model year to… … Wikipedia
Non-innocent ligand — In chemistry, a (redox) non innocent ligand is a ligand in a metal complex where the oxidation state is unclear. Typically, complexes containing non innocent ligands are redox active at mild potentials. The concept assumes that redox reactions in … Wikipedia
Corey-Itsuno reduction — The Corey Itsuno Reduction, also known as the Corey Bakshi Shibata (CBS) reduction, is a chemical reaction in which an achiral ketone is enantioselectively reduced to produce the corresponding chiral, non racemic alcohol. The oxazaborolidine… … Wikipedia
SNCR — Selective Non Catalytic Reduction (Governmental » Transportation) … Abbreviations dictionary
Incineration — For other forms of waste plant that produces energy, see waste to energy. Incinerator redirects here. For the fictional character, see Incinerator (Transformers). Incinerate redirects here. For the Sonic Youth song, see Incinerate (song). For the … Wikipedia
Air pollution — from World War II production Smog over … Wikipedia
NOx — Pour les articles homonymes, voir Nox. NOx, de N symbole de l azote, O celui de l oxygène et x représentant une stœchiométrie inconnue est une abréviation utilisée dans le domaine de la chimie, de la pollution et de la qualité de l air, qui… … Wikipédia en Français
NOx — This article is about nitrogen oxides produced during combustion. For other definitions see Nox See also: Nitrogen oxide NOx is a generic term for the mono nitrogen oxides NO and NO2 (nitric oxide and nitrogen dioxide). They are produced from the … Wikipedia
