selective catalytic reduction
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Transcript of selective catalytic reduction
KUSHAGRA ABHISHEK 11/CH/25
Selective catalytic reduction
of NOx
WHAT IS NOX
NOX - Family of SEVEN Nitrogen compound (NO,NO2,N2O2,N2O3,N2O,N204,N2O5)Of these NO2 is surrogate of this family of compound as it is most prevalent form of NOx in the atmosphere generated by anthropogenic activities.
Combustion sources• Automobiles• Boilers• Incinerators
High-temperature industrial operations• Metallurgical furnaces• Blast furnaces• Plasma furnaces• Kilns
Other sources• Nitric acid plants• Industrial processes that use nitric acid
Sources of Nox
NOX EFFECTS: formation of ozone Acid rain Toxic chemicals Global warming Causes visibility impairment. Deteriorates water quality
NO – Nitric oxide• Colorless and odorless gas• Insoluble in water• Toxic
NO2 – Nitrogen dioxide• Usually exists as a dimer compound
(N2O4) at low 0C• Has distinct reddish-brown color• Moderately soluble in aqueous liquids• Toxic• Contributes to brown haze that occurs
with smog
Characteristics of NOx compounds
NOX CONTROL TECHNOLOGIES
Selective Catalytic Reduction (SCR)Reaction
With several secondary reactions:2SO2 + O2 → 2SO3 2NH3 + SO3 + H2O → (NH4)2SO4 NH3 + SO3 + H2O → NH4HSO4
The reaction for urea instead of either anhydrous oraqueous ammonia is:4NO + 2(NH2)2CO + O2 → 4N2 + 4H2O + 2CO2
OHNONHNO
OHNONHNO
22catalyst supported OVor TiO
232
22catalyst supported OVor TiO
23
6342
6444522
522
Temperature ~ 300 - 400 oC
Selective catalytic reduction (SCR) 1)Beds of NH3 or urea.
2)Catalysts (Ti and V ) are embedded in following design:
• Plate configuration – lower pressure drop, less prone to
Plugging and fouling , much larger and more expensive.
• Honeycomb configurations- smaller than plate, high pressure drop and plug much more easily.
3)Efficiency Up to 95 %.
SCR – THE PROCESS
Catalyst used in SCR for reduction of NOx
Titanium oxideOxide of base metals like vanadium and tungstenZeolitesEtc…
Several reductant are currently used in SCR applications: Anhydrous ammonia Extremely toxic and difficult to safely store, but needs no further
conversion to operate within an SCR. Typically favoured by large industrial SCR operators
Aqueous ammonia must be hydrolyzed in order to be used, but it is substantially safer to
store and transport than anhydrous ammonia.
Urea the safest to store, but requires conversion to ammonia through
thermal decomposition in order to be used as an effective reductant
Ap
plica
tion
Limitations of SCR:The most common limitation of SCR in power plants is the ammonia slipemission of ammonium sulfate and ammonium bisulfateVery high capital costHigh operating costCatalyst bed increases pressure dropPossible water wash RequiredHigh Space requirements
Conclusion: SCR technology is one of most simple clean and reliable technology present today.
It is a flue gas treatment method which is successfully operating in various field like automobile, industry etc.. It is most effective as it is easily operated after proper installation, have better efficiency than other available technology for Nox reduction.
THANK YOU!!!!