Staged combustion is a method used to reduce the emission of nitrogen oxides (NOx) during combustion. There are two methods for staged combustion: air staged supply and fuel staged supply. Applications of staged combustion include boilers[1] and rocket engines.[2]
Air staging, or two-stage combustion, is generally described as the introduction of over-fire air into a boiler or furnace. Staging the air in the burner (internal air staging) is generally a design feature of low NOx burners.
Furnace over-fire air (OFA) technology requires the introduction of combustion air to then be separated into primary and secondary flow sections. This achieves complete burnout and encourages the formation of nitrogen gas (N2) rather than NOx.
Primary air (70-90%) is mixed with the fuel, producing a relatively low temperature, oxygen-deficient, fuel-rich zone, leading to only moderate amounts of NOx being formed.
The secondary (10-30%) combustion air is injected above the combustion zone through a special wind-box with air-introducing ports and/or nozzles, which are mounted above the burners.
Combustion is completed at this increased flame volume. Hence, the relatively low-temperature secondary stage limits the production of thermal NOx. The location of the injection ports and the mixing of over-fire air is critical to maintaining efficient combustion.
Retrofitting over-fire air on an existing boiler involves water-wall tube modifications to create the ports for the secondary air nozzles and the addition of ducts, dampers, and the wind-box. This technique is currently used in 116 pulverized coal-fired units on a total capacity of 50 gigawatt electrical (GWe) as a standalone measure.
It is used in combination with other primary measures for NOx control in 175 coal-fired units on a total capacity of 53 GWe.[3]
Via air staged supply, a NOx reduction rate from 50-75% is possible. Air staged supply also leverages a simple configuration and is applicable in small-scale combustion.
Fuel staged supplyedit
This section needs expansion. You can help by adding to it. (February 2012)
One form of fuel staged combustion is the procedure known as burner out of service (BOOS).[4] The technique involves shutting off the fuel flow from one burner or more to create fuel-rich and fuel-lean zones, achieving some NOx emission control (10%). The technique is not widely used in pulverized coal-fired plants (2 units, 350 MWe).
Another method of fuel staged combustion is fuel biasing. In fuel biasing, combustion is staged by diverting fuel from the upper-level burners to the lower ones or from the center to the side burners. The aim is to create a fuel-rich lower or central zone and a fuel-lean upper or side zone in order to achieve complete burnout. The technology lowers the flame temperature and improves the balance of the oxygen concentration in the furnace. NOx emissions may be reduced by up to 30% using this technology. This technique is used in 13 pulverized coal-fired units on a total capacity of 2.7 GWe.[5]
Via fuel staged supply, a NOx reduction rate from 50-75% is also possible, though minor temperature instabilities at the reduction zone can occur and a lower temperature is necessary. While applicable in large-scale combustion, fuel staged combustion uses a more complex constructive configuration.
Staged combustion dates back to the hot bulb engine of the 1890s. The first stage of combustion occurred inside a hot bulb, where the hot gases were forced out into the cylinder. Then, when mixed with additional air, the second stage of combustion took place. During those times, staged combustion was used because it was a convenient method of ignition, and, likely, there was not much concern about air pollution. A modern application of the principle is the Stratified charge engine, in which a spark ignites a rich mixture and the resulting flame-front ignites the weaker mixture elsewhere in the cylinder.
^(PDF). Archived from the original (PDF) on 8 March 2012. Retrieved 3 February 2012.{{cite web}}: CS1 maint: archived copy as title (link)
^"ESA - Launchers Home - First hot firing of European staged-combustion demonstration engine". Esa.int. 26 February 2008. Retrieved 3 February 2012.
^"Air staging for NOx control (overfire air and two-stage combustion)". IEA Clean Coal Centre. 20 January 2018. Retrieved 26 June 2020.
^"Fuel staging (burner out of service (boos), fuel biasing, reburning, or three-stage combustion)". IEA Clean Coal Centre. 20 January 2018. Retrieved 21 July 2020.
^"Fuel staging (burner out of service (boos), fuel biasing, reburning, or three-stage combustion)". IEA Clean Coal Centre. 20 January 2018. Retrieved 26 June 2020.
staged, combustion, this, article, multiple, issues, please, help, improve, discuss, these, issues, talk, page, learn, when, remove, these, template, messages, this, article, needs, additional, citations, verification, please, help, improve, this, article, add. This article has multiple issues Please help improve it or discuss these issues on the talk page Learn how and when to remove these template messages This article needs additional citations for verification Please help improve this article by adding citations to reliable sources Unsourced material may be challenged and removed Find sources Staged combustion news newspapers books scholar JSTOR July 2020 Learn how and when to remove this message This article may be too technical for most readers to understand Please help improve it to make it understandable to non experts without removing the technical details July 2020 Learn how and when to remove this message Learn how and when to remove this message Staged combustion is a method used to reduce the emission of nitrogen oxides NOx during combustion There are two methods for staged combustion air staged supply and fuel staged supply Applications of staged combustion include boilers 1 and rocket engines 2 Contents 1 Air staged supply 2 Fuel staged supply 3 History 4 See also 5 References 6 External linksAir staged supply editThis section needs expansion You can help by adding to it February 2012 This section needs additional citations for verification Please help improve this article by adding citations to reliable sources in this section Unsourced material may be challenged and removed July 2020 Learn how and when to remove this message Air staging or two stage combustion is generally described as the introduction of over fire air into a boiler or furnace Staging the air in the burner internal air staging is generally a design feature of low NOx burners Furnace over fire air OFA technology requires the introduction of combustion air to then be separated into primary and secondary flow sections This achieves complete burnout and encourages the formation of nitrogen gas N2 rather than NOx Primary air 70 90 is mixed with the fuel producing a relatively low temperature oxygen deficient fuel rich zone leading to only moderate amounts of NOx being formed The secondary 10 30 combustion air is injected above the combustion zone through a special wind box with air introducing ports and or nozzles which are mounted above the burners Combustion is completed at this increased flame volume Hence the relatively low temperature secondary stage limits the production of thermal NOx The location of the injection ports and the mixing of over fire air is critical to maintaining efficient combustion Retrofitting over fire air on an existing boiler involves water wall tube modifications to create the ports for the secondary air nozzles and the addition of ducts dampers and the wind box This technique is currently used in 116 pulverized coal fired units on a total capacity of 50 gigawatt electrical GWe as a standalone measure It is used in combination with other primary measures for NOx control in 175 coal fired units on a total capacity of 53 GWe 3 Via air staged supply a NOx reduction rate from 50 75 is possible Air staged supply also leverages a simple configuration and is applicable in small scale combustion Fuel staged supply editThis section needs expansion You can help by adding to it February 2012 This section needs additional citations for verification Please help improve this article by adding citations to reliable sources in this section Unsourced material may be challenged and removed July 2020 Learn how and when to remove this message One form of fuel staged combustion is the procedure known as burner out of service BOOS 4 The technique involves shutting off the fuel flow from one burner or more to create fuel rich and fuel lean zones achieving some NOx emission control 10 The technique is not widely used in pulverized coal fired plants 2 units 350 MWe Another method of fuel staged combustion is fuel biasing In fuel biasing combustion is staged by diverting fuel from the upper level burners to the lower ones or from the center to the side burners The aim is to create a fuel rich lower or central zone and a fuel lean upper or side zone in order to achieve complete burnout The technology lowers the flame temperature and improves the balance of the oxygen concentration in the furnace NOx emissions may be reduced by up to 30 using this technology This technique is used in 13 pulverized coal fired units on a total capacity of 2 7 GWe 5 Via fuel staged supply a NOx reduction rate from 50 75 is also possible though minor temperature instabilities at the reduction zone can occur and a lower temperature is necessary While applicable in large scale combustion fuel staged combustion uses a more complex constructive configuration History editThis section does not cite any sources Please help improve this section by adding citations to reliable sources Unsourced material may be challenged and removed July 2020 Learn how and when to remove this message Staged combustion dates back to the hot bulb engine of the 1890s The first stage of combustion occurred inside a hot bulb where the hot gases were forced out into the cylinder Then when mixed with additional air the second stage of combustion took place During those times staged combustion was used because it was a convenient method of ignition and likely there was not much concern about air pollution A modern application of the principle is the Stratified charge engine in which a spark ignites a rich mixture and the resulting flame front ignites the weaker mixture elsewhere in the cylinder See also editStaged combustion cycle rocket References edit Archived copy PDF Archived from the original PDF on 8 March 2012 Retrieved 3 February 2012 a href Template Cite web html title Template Cite web cite web a CS1 maint archived copy as title link ESA Launchers Home First hot firing of European staged combustion demonstration engine Esa int 26 February 2008 Retrieved 3 February 2012 Air staging for NOx control overfire air and two stage combustion IEA Clean Coal Centre 20 January 2018 Retrieved 26 June 2020 Fuel staging burner out of service boos fuel biasing reburning or three stage combustion IEA Clean Coal Centre 20 January 2018 Retrieved 21 July 2020 Fuel staging burner out of service boos fuel biasing reburning or three stage combustion IEA Clean Coal Centre 20 January 2018 Retrieved 26 June 2020 External links editRegenerative Thermal Oxidizer 1 Retrieved from https en wikipedia org w index php title Staged combustion amp oldid 1072454800, wikipedia, wiki, book, books, library,
