SELECTIVE CATALYTIC REDUCTION SYSTEM (SCR)
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The document discusses nitrogen oxides (NOx), their sources, health effects, and the selective catalytic reduction (SCR) technology that effectively reduces NOx emissions from exhaust gases. SCR systems can decrease NOx emissions by 70-95% and are increasingly used in commercial vehicles, marine vessels, and heavy-duty applications to meet stringent environmental regulations. It also highlights the importance of diesel exhaust fluid (DEF) for SCR operation and the need for periodic replenishment to maintain emission control efficiency.
![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.](https://image.slidesharecdn.com/scrppt-160927095249/85/SELECTIVE-CATALYTIC-REDUCTION-SYSTEM-SCR-18-320.jpg)
SELECTIVE CATALYTIC REDUCTION SYSTEM (SCR)
- 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)
- 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
- 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