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The NO x reduction reaction takes place as the gases pass through the catalyst chamber. Before entering the catalyst chamber, ammonia, or other reductant (such as urea), is injected and mixed with the gases. The chemical equation for a stoichiometric reaction using either anhydrous or aqueous ammonia for a selective catalytic reduction process is:
Selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR) reduce post combustion NO x by reacting the exhaust with urea or ammonia to produce nitrogen and water. SCR is now being used in ships, [ 39 ] diesel trucks and in some diesel cars.
Two techniques have been developed for the catalytic reduction of NO x emissions under lean exhaust conditions, selective catalytic reduction (SCR) and the NO x adsorber. Instead of precious metal-containing NO x absorbers, most manufacturers selected base-metal SCR systems that use a reagent such as ammonia to reduce the NO x into nitrogen and ...
The NO x adsorber was designed to avoid the problems that EGR and SCR experienced. An adsorbent such as zeolite traps the NO and NO 2 molecules — acting as a molecular sponge. Once the trap is full (like a sponge full of water) no more NO x can be absorbed. Various schemes have been designed to "purge" or "regenerate" the trap.
The overall reduction of NO x by urea is then: 2 (NH 2) 2 CO + 4 NO + O 2 → 4 N 2 + 4 H 2 O + 2 CO 2 and 4 (NH 2) 2 CO + 6 NO 2 → 7 N 2 + 8 H 2 O + 4 CO 2 and (NH 2) 2 CO + NO + NO 2 → 2 N 2 + 2 H 2 O + CO 2. The ratio between NO 2 and NO determines which reactions take place and how fast. The highest conversion rates are achieved if ...
Catalytic reduction of NO x by adding NH 3 to the gas upstream of the SCR DeNO x reactor; Catalytic oxidation of SO 2 to SO 3 in the oxidation reactor; Cooling of the gas to about 100 °C whereby the H 2 SO 4 condenses and can be withdrawn as concentrated sulfuric acid
NO x (or NOx) refers to the sum of NO and NO 2. [1] [2] NO y (or NOy) refers to the sum of NO x and all oxidized atmospheric odd-nitrogen species (e.g. the sum of NO x, HNO 3, HNO 2, etc.) NO z (or NOz) = NO y − NO x; Mixed Oxides of Nitrogen ("MON"): solutions of nitric oxide in dinitrogen tetroxide/nitrogen dioxide.
Selective non-catalytic reduction (SNCR) 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 (760 and 1,090 °C) to react with the nitrogen oxides formed in the combustion process.