of NOx from Exhaust Stack

Nitrogen OxideNitrogen oxide is typically any binary compound of

oxygen and nitrogen, or a mixture of such compounds:

Nitric oxide (NO), nitrogen(II) oxide - extremely toxic Nitrogen dioxide (NO2), nitrogen(IV) oxide - extremely toxic

Nitrous oxide (N2O), nitrogen (I) oxide - undesirable

Dinitrogen trioxide (N2O3), nitrogen(II,IV) oxide

Dinitrogen tetroxide (N2O4), nitrogen(IV) oxide

Dinitrogen pentoxide (N2O5), nitrogen(V) oxide

Source: Wikipedia

NOxNOx is a generic term for mono-nitrogen oxides (NO and NO2).

These oxides are produced during combustion, especially at high temperatures.

At ambient temperatures, the oxygen and nitrogen gases in air will not react with each other.

In atmospheric chemistry the term NOx is used to mean the total concentration of NO plus NO2.

Source: Wikipedia

Industrial SourcesThe three primary sources of NOx in combustion processes:

Thermal Nox - produced when nitrogen and oxygen in the combustion air supply combine at high flame temperatures.  Thermal NOx is generally produced during the combustion of both gases and fuel oils.

Fuel Nox - produced when nitrogen in the fuel combines with the excess oxygen in the combustion air and is only a problem with fuel oils containing fuel bound nitrogen.

Prompt NOx - Attributed to the reaction of atmospheric nitrogen, N2, with radicals such as C, CH, and CH2 fragments derived from fuel. Formed during the early, low temperature states of combustion and is insignificant.

Source: Wikipedia & http://www.bacharach-training.com/combustionzone/nox1.htm

Health EffectsNOx react with ammonia, moisture, and other compounds to

form nitric acid vapor and related particles.

Small particles can penetrate deeply into sensitive lung tissue and damage it, causing premature death in extreme cases.

Inhalation of such particles may cause or worsen respiratory diseases such as emphysema, bronchitis it may also aggravate existing heart disease.

Source: Wikipedia

NOx react with volatile organic compounds in the presence of heat and sunlight to form Ozone.

Ozone can cause adverse effects such as damage to lung tissue and reduction in lung function mostly in susceptible populations (children, elderly, asthmatics).

Ozone can be transported by wind currents and cause health impacts far from the original sources.

Health Effects

Source: Wikipedia

NOx (especially N2O) destroys ozone layer.

This layer absorbs ultraviolet light, which is potentially damaging to life on earth.

NOx also readily react with common organic chemicals, and even ozone, to form a wide variety of toxic products: nitroarenes, nitrosamines and also the nitrate radical some of which may cause biological mutations.

Health Effects

Source: Wikipedia

1999 National Emissions by Source: Nitrogen Oxides

1999 National Emissions by Source: Nitrogen Oxides (On-Road Mobile

Sources)

1999 National Emissions by Source: Nitrogen Oxides (Nonroad Mobile

Sources

Source: http://www.epa.gov/oms/invntory/overview/pollutants/nox.htm

Selective Catalytic ReductionMeans of converting nitrogen oxides, also referred to as NOx with the aid of

a catalyst into diatomic nitrogen, N2, and water, H2O.

known to reduce the NOx emissions by nearly 70-95%.

SCR provides emissions after-treatment well into the exhaust stack.

Commercial selective catalytic reduction systems are typically found on large utility boilers, industrial boilers, and municipal solid waste boilers and have been shown to reduce NOx by 70-95%.[1] More recent applications include diesel engines, such as those found on large ships, diesel locomotives, gas turbines, and even automobiles.

Source: Wikipedia.com About.com & Ezinearticles.com

SCR – The ProcessEngine: The NOx reduction process starts with an efficient CRD engine design that burns clean Ultra Low Sulfur Diesel (ULSD) and produces inherently lower exhaust emissions—exhaust that is already much cleaner due to leaner and more complete combustion.

Diesel Exhaust Fluid (DEF) tank and pump: Under the direction of the vehicle’s onboard computer, DEF is delivered in precisely metered spray patterns into the exhaust stream just ahead of the SCR converter.

Source: About.com

SCR – The ProcessSCR Catalytic Converter: This is where the conversion happens. Exhaust gases and an atomized mist of DEF enter the converter simultaneously. Together with the catalyst inside the converter, the mixture undergoes a chemical reaction that produces nitrogen gas and water vapor.

Control device: Exhaust gases are monitored via a sensor as they leave the SCR catalyst. Feedback is supplied to the main computer to alter the DEF flow if NOx levels fluctuate beyond acceptable parameters.

Source: About.com

SCR - ChemistryThe chemical equation for a stoichiometric reaction using either anhydrous or aqueous ammonia for a selective catalytic reduction process is:

4NO + 4NH3 + O2 → 4N2 + 6H2O

2NO2 + 4NH3 + O2 → 3N2 + 6H2O

NO + NO2 + 2NH3 → 2N2 + 3H2O

Source: Wikipedia

SCR - ChemistryWith several secondary reactions:

2SO2 + O2 → 2SO3

2NH3 + SO3 + H2O → (NH4)2SO4

NH3 + SO3 + H2O → NH4HSO4

Source: Wikipedia

The reaction for urea instead of either anhydrous or aqueous ammonia is:

4NO + 2(NH2)2CO + O2 → 4N2 + 4H2O + 2CO2

SCR - Chemistry

Source: Wikipedia

SCR - Catalyst

Manufactured from various ceramic materials used as a carrier, such as titanium oxide, and active catalytic components are usually either oxides of base metals (such as vanadium and tungsten), zeolites, and various precious metals.

Source: Wikipedia

SCR – Catalyst : Base Metal Catalyst

Examples: vanadium and tungsten

Lack high thermal durability

Less expensive and operate very well at the temperature ranges most commonly seen in industrial and utility boiler applications

high catalyzing potential to oxidize SO2 into SO3, which can be extremely damaging due to its acidic properties

Source: Wikipedia

SCR – Catalyst - Zeolitehave the potential to operate at substantially higher

temperature than base metal catalysts

can withstand prolonged operation at temperatures of 900 K and transient conditions of up to 1120 K

have a lower potential for potentially damaging SO2 oxidation.

Source: Wikipedia

SCR – Catalyst : Fe- & Cu-exchanged zeolite ureaApproximately equal performance to that of vanadium-

urea SCRs if the fraction of the NO2 is 20% to 50% of the total NOx

Two most common designs of SCR catalyst geometry used today are honeycomb and platePlate-type catalysts have lower pressure drops and are less

susceptible to plugging and fouling than the honeycomb types, but plate configurations are much larger and more expensive.

Honeycomb configurations are smaller than plate types, but have higher pressure drops and plug much more easily.

Source: Wikipedia

SCR - Reductants Remember: A reducing agent (also called a reductant or reducer) is the element or

compound in a redox (reduction-oxidation) reaction (see electrochemistry) that reduces another species. In doing so, it becomes oxidized, and is therefore the electron donor in the redox.

Several reductants are currently used in SCR applications including:Anhydrous ammonia

Extremely toxic and difficult to safely store, but needs no further conversion to operate within an SCR.

Typically favored by large industrial SCR operatorsAqueous 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.

Source: Wikipedia

SCR – The Process

SCR - LimitationIf unsuitable materials are used in the manufacture of the

units, ions can pass from the dispensing materials into the porous head on the SCR unit that spoils the SCR's efficacy and can reduce its lifespan by more than 60%.

Ammonia slip or release of unreacted ammoniaSlip can occur when catalyst temperatures are not in the

optimal range for the reaction or when too much ammonia is injected into the process.

Source: Wikipedia

NOx MonitoringThe purpose of the monitoring is to verify the company's

compliance with the air quality standards of the DENR Administrative Order DAO No. 2000-81 (Implementing Rules and Regulations of

the Philippine Clean Air Act of 1999) - for Stack Method of Sampling & Analysis : Grab Sampling –

Phenolsulfonic Method (US EPA Method 7)

DENR ADMINISTRATIVE ORDER No. 46 Series of 1998 – for motor vehicles Method of Sampling & Analysis : Direct Reading

Thank You!