Selective Catalytic Reduction (SCR) is an advanced active emissions control technology system that injects a liquid-reductant agent through a special catalyst into the exhaust stream of a diesel engine. The reductant source is usually automotive-grade urea, otherwise known as Diesel Exhaust Fluid (DEF). The DEF sets off a chemical reaction that converts nitrogen oxides into nitrogen, water and tiny amounts of carbon dioxide (CO2), natural components of the air we breathe, which is then expelled through the vehicle tailpipe. SCR technology is designed to permit nitrogen oxide (NOx) reduction reactions to take place in an oxidizing atmosphere. It is called "selective" because it reduces levels of NOx using ammonia as a reductant within a catalyst system. The chemical reaction is known as "reduction" where the DEF is the reducing agent that reacts with NOx to convert the pollutants into nitrogen, water and tiny amounts of CO2. The DEF can be rapidly broken down to produce the oxidizing ammonia in the exhaust stream. SCR technology alone can achieve NOx reductions up to 90 percent

1. Prepared by: Engr. Mohammad Imam Hossain (Rubel),
Skype: mdimam, Email: rubelduet04@gmail.com

3. 1.Ozone
2.Particulate Matters
3.Carbon Monoxides
4.Sulfur Dioxide
5.Lead
6.Nitrogen Dioxide
According to EPA six common air pollutants are:

5. WHAT IS NOx?
 NOx 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.

6.  Nitrogen 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
WHAT IS NOx?

7. INDUSTRIAL SOURCES
The 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.

8.  Inhalation of NOX particles causes respiratory diseases such as Bronchitis and
Emphysema.
 NOX particles causes depletion of Ozone layer.
 It reacts with organic chemicals to form harmful compounds which causes biological
mutations.
 It is the main reason for the occurrence of Acid rains.
EFFECT OF NOx?

9. EFFECTS OF HEALTH
 NOx 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.

10. EFFECTS OF HEALTH
 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.

11. EFFECTS OF HEALTH
 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.

12. SELECTIVE CATALYTIC REDUCTION (SCR)

14. SCR-S SYSTEM OVERVIEW

15. SCR-S SYSTEM OVERVIEW

16. SCR-S SYSTEM DIAGRAM

17. WHAT IS SCR
The reduction of pollutant emissions is an important challenge in automotive technology.
The SCR system is a new exhaust gas after treatment system. It is used to reduce the nitrogen
oxides contained in exhaust gas. The abbreviation SCR stands for Selective Catalytic Reduction.
With this technology, the chemical reaction of reduction is selective. This means that, out of all
exhaust gas, only the nitrogen oxides are specifically reduced.
In the reduction catalytic converter, the nitrogen oxides (NOX) contained in the exhaust gas are
converted into nitrogen (N2) and water (H20). To achieve this, a reducing agent is continuously
injected into the exhaust gas flow upstream of the reduction catalytic converter. The reducing
agent is contained in a separate, additional tank.
In the automotive industry, SCR technology has already been in use for some time in
commercial vehicles and buses.

18. SCR
 Means 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.

19. Arrangement of a high-pressure SCR solution on a 6S46MC-C engine (Source: MAN)
SCR SYSTEM IN ENGINE

23. BASIC CHEMISTRY OF SCR

24. BASIC CHEMISTRY OF SCR

25. BASIC CHEMISTRY OF SCR

26. SELECTIVE CATALYTIC REDUCTION SYSTEM NOX
SWITCHING OVER PROCESS

27. BASIC CHEMISTRY OF SCR

28. WHY SCR IS IMPORTANT?
SCR technology is one of the most cost-effective and fuel-efficient technologies available to
help reduce emissions. SCR can reduce NOx emissions up to 90 percent while
simultaneously reducing HC and CO emissions by 50-90 percent, and PM emissions by 30-50
percent. SCR systems can also be combined with a diesel particulate filter to achieve even
greater emission reductions for PM. SCR technology may play a key role in achieving
emissions reductions that allow light-duty diesel vehicles to meet the new, lower EPA
emissions regulations to be phased in through 2009 and potentially expand the diesel
vehicle sales market to all 50 states.

29. OPTIONS
The SCR-S system can be prepared as an In-line or Compact model. The In-line model has a
partially integrated urea mixing pipe. The Compact model has a fully integrated urea mixing
pipe. Several standard height/width configurations are possible for all system models.
A customized solution, of course, is possible for very tight or complex engine rooms.
Examples of deliverable options are:
 In-line or Compact model
 Separate reactor housing with dummy elements (SCR prepared)
 Without an integrated silencer (only the reactor housing)
 With an integrated spark arrester
 With 45 dB(A) noise reduction
 Stainless steel reactor housing
 Intake and exhaust at alternative positions
 Alternative catalyst types
 Motor load signal through J1939 or analogue
 External communication through Mod or CAN bus.

30. WHERE IS SCR USED?
SCR has been used to reduce stationary source emissions since the 1980s. In addition,
more than 100 marine vessels worldwide have been equipped with SCR technology,
including cargo vessels, ferries and tugboats. While SCR has been installed on both
highway and non-road engines in diesel retrofit demonstration projects throughout the
U.S., SCR systems have become the technology of choice for many of Europe’s heavy-duty
diesel truck and bus manufacturers where the urea agent is commonly known as AdBlue.
SCR technology may become more prevalent in the United States as both light- and heavy
duty engine manufacturers work to meet future emissions reduction standards starting in
2009. In fact, several light duty diesel manufacturers have already indicated that they are
considering the use of SCR in
future products.

31. OPERATING PRINCIPLE OF THE SCR SYSTEM
The reduction catalytic converter has reached its operating temperature at approximately 200 ‘C.
Information on the reduction catalytic converter’s exhaust gas temperature is received by the
engine control unit from exhaust gas temperature sender.
The AdBlue° reducing agent is sucked out of the reducing agent tank by the reducing agent pump
and send through the heated supply line to the injector for reducing agent at a pressure of approx.
5 bar.
The injector for reducing agent is actuated by the engine control unit and injects the metered
reducing agent into the exhaust system. The injected reducing agent is carried along by the
exhaust gas flow and is evenly distributed in the exhaust gas by the mixer. On the route to the
reduction catalytic converter, which is called the hydrolysis section, the reducing agent is broken
down into ammonia (NH3) and carbon dioxide (CO2).
In the reduction catalytic converters, the ammonia (NH3) reacts with the nitrogen oxides (NOX) to
form nitrogen (N2) and water (H20). The SCR system’s efficiency is registered by NOX sender.

32. OPERATING PRINCIPLE OF THE SCR SYSTEM

33. ACHIEVABLE EMISSION REDUCTIONS

34. WHAT ARE THE TECHNOLOGY CHALLENGES OF USING SCR?
A major challenge of the SCR system is the replenishment of the urea solution. The urea solution is
carried in an onboard tank which must be periodically replenished based on vehicle operation. For
light-duty vehicles, urea refill intervals will occur around the time of a recommended oil change, while
urea replenishment for heavy-duty vehicles will vary depending on the vehicle specifics and application
requirements.
While vehicles could continue to function normally even without the urea solution, the emissions system
will not meet NOx reduction requirements. Manufacturers are currently working with the EPA to address
these technology and emissions performance challenges. One concept is to establish a nationwide urea
distribution infrastructure for consumers, while another option links the replenishment of urea with
pre-existing scheduled maintenance intervals (i.e. oil changes).
Other issues include the availability of space on vehicles to provide user-friendly access to the urea tank
and other SCR components. In addition, proper storage of urea is required to prevent the liquid from
freezing at temperatures below 12 degrees Fahrenheit.

35. WHEN COMPARED WITH OTHER TECHNOLOGIES, SCR IS THE
EFFECTIVE ONE TO REDUCE NOX.

36. DIFFERENCE IN NOX LEVELS BEFORE AND AFTER SCR

37. •This does not require any modifications to the
combustion unit.
•Higher NOX reduction is possible.
Advantages:
Disadvantages:
•In SCR systems, Ammonia slip may occur.
•Large volumes of reductant and catalyst are
required.

38. WHAT ARE THE SPECIAL CONSIDERATIONS OF USING SCR?
One unique aspect of a vehicle or machine with an SCR system is the need for replenishing Diesel Exhaust
Fluid (DEF) on a periodic basis. DEF is carried in an onboard tank which must be periodically replenished by
the operator based on vehicle operation. For light-duty vehicles, DEF refill intervals typically occur around the
time of a recommended oil change, while DEF replenishment for heavy-duty vehicles and off-road machines
and equipment will vary depending on the operating conditions, hours used, miles traveled, load factors and
other considerations.
DEF is an integral part of the emissions control system and must be present in the tank at all times to assure
continued operation of the vehicle or equipment. Low DEF supply triggers a series of escalating visual and
audible indicators to the driver or operator. Once the tank reaches a certain level near empty, the starting
system may be locked out the next time the vehicle is used, preventing the vehicle from being started without
adequate DEF. A nationwide DEF distribution infrastructure has rapidly expanded to meet the needs of a
growing SCR technology marketplace.
On-board tanks to store DEF are typically located in the spare tire area of passenger vehicles, while tractor
trailers typically have a DEF tank alongside the diesel fuel saddle tank. Proper storage of DEF is required to
prevent the liquid from freezing at temperature below 12 degrees Fahrenheit, and most vehicle DEF
dispensing systems have warming devices.

39. WHAT IS DEF?
Diesel Exhaust Fluid (DEF) is a non-toxic fluid composed of purified water and automotive grade
aqueous urea. DEF is available with a variety of storage and dispensing methods. Storage
options consist of various size containers such as bulk, totes and bottles or jugs. The American
Petroleum Institute rigorously tests DEF to ensure that it meets industry-wide quality standards.
DEF is available for purchasing at various locations like truck stops, truck dealerships and engine
distributors which can be located using one of the below links. DEF tanks range in size from 6 to
23 gallons depending on the truck's application. The DEF tank fill opening is designed to
accommodate a DEF fill nozzle to ensure only DEF is put into the tank. A diesel fuel nozzle will
not fit into the DEF tank opening.

40. The SCR technology is the dominating deNOX technology to meet the current
and future NOX emission regulations. To meet the current US 2010 and EURO
VI regulations, Zeolite based SCR catalysts are required.
With the increasing more and more stringent emission standards, it is very
much necessary to improve and implement such technologies.
CONCLUSION

41. THANKS A LOT…………..