The Experts below are selected from a list of 63 Experts worldwide ranked by ideXlab platform
Fariborz Rashidi - One of the best experts on this subject based on the ideXlab platform.
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Effect of dividing single Flare Tip into mulTiple Tips on soot reduction
Clean Technologies and Environmental Policy, 2020Co-Authors: Seyed Sepehr Mostafayi, Fariborz RashidiAbstract:Several methods are applied for soot reduction in industrial Flares. However, they usually involve other issues such as flame safety and other pollutant formations; therefore, they should be handled carefully. Splitting Flare Tip into mulTiple branches is an idea that is thought to reduce soot formation by increasing the contact surface and providing better mixing. In this study, changing a single Tip of an industrial Flare into mulTiple Tips was investigated by Computational Fluid Dynamic software Ansys Fluent 18. Reynolds Average Navier–Stokes approach was used to model the fluid flow, and its turbulence was modeled by realizable k – ε model. The steady laminar flamelet model was chosen as the combustion model. Soot formation was modeled using Moss–Brookes approach, and validated by comparing the simulation results with available experimental data. Effects of Tip diameter, number of branches, and distance between branches on soot and NO_x yields, and flame stability were studied. According to the results, increasing the number of branches having larger diameters by taking flame stability limitations into consideration, and choosing optimum distances between branches caused significant soot reduction without noticeable changes in the NO_x formation. Graphic abstract
P. J. Mullinger - One of the best experts on this subject based on the ideXlab platform.
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Investigation of a combustion driven oscillation in a refinery Flare - Part B: Visualisation of a periodic flow instability in a bifurcating duct following a contraction
Experimental Thermal and Fluid Science, 2007Co-Authors: M. Riese, Richard M. Kelso, Graham J. Nathan, P. J. MullingerAbstract:Abstract A flow visualisation study was performed to investigate a periodic flow instability in a bifurcating duct within the Tip of the Flares at the Shell refinery in Clyde, NSW, to verify the trigger of a combustion-driven oscillation proposed in Part A of this study, and to identify its features. The model study assessed only the flow instability, uncoupled from the acoustic resonance and the combustion that are also present in the actual Flare. Three strong, coupled flow oscillations were found to be present in three regions of the fuel line in the Flare Tip model. A periodic flow separation was found to occur within the contraction at the inlet to the Tip, a coupled, periodic flow oscillation was found in the two transverse “cross-over ducts” from the central pipe to the outer annulus and an oscillating flow recirculation was present in the “end-cap” region of the central pipe. The dimensionless frequency of these oscillations in the model was found to match that measured in the full-scale plant for high fuel flow rates. This, and the strength of these flow oscillations, gives confidence that they are integral to the full-scale combustion-driven oscillation and most likely the primary trigger. The evidence indicates that the periodic flow instability is initiated by the separation and roll-up of the annular boundary layer at the start of the contraction in the fuel section of the Flare Tip. The separation generates an annular vortex which interacts with the blind-ended pipe downstream, leading to a pressure wave which propagates back upstream, initiating the next separation event and repeating the cycle. The study also investigated flow control devices with a view to finding a practical approach to mitigate the oscillations. The shape of these devices was constrained to allow installation without removing the Tip of the Flare. This aspect of the study highlighted the strength and nature of the coupled oscillation, since it proved to be very difficult to mitigate the oscillation in this way. An effective configuration is presented, comprising of three individual components, all three of which were found to be necessary to eliminate the oscillation completely.
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Investigation of a combustion driven oscillation in a refinery Flare. Part A: Full scale assessment
Experimental Thermal and Fluid Science, 2006Co-Authors: Graham J. Nathan, P. J. Mullinger, D. Bridger, B. MartinAbstract:Abstract An assessment of the cause of an intermittent combustion-driven oscillation in a full-scale refinery Flare is reported. When present, ambient sound pressure levels in excess of 100 dBA are generated. The oscillations began after the replacement of an old Flare Tip with one of a different design which required the use of non-standard components. The assessment included measurements of time resolved and integrated sound pressure in the ambient environment, and pressure in the fuel pipe and the air duct. Images obtained from video recorded from two directions are presented along with relevant process data. A review is also presented of the conditions under which the oscillations are inhibited or enhanced, and a comparison is made with another Flare of similar design which does not exhibit an oscillation. The Strouhal numbers of the potential causes of flow oscillation and the wavelength of acoustic resonances in the supply pipes are calculated. The findings are then compared with related investigations found in the literature. The frequency of the oscillation was found to scale with the speed of sound in the fuel and also to match a resonant frequency within three consecutive segments of the fuel supply pipe. In contrast, the speed of sound in air was constant for all tests, while the frequency varied. This shows that the resonance occurs within the fuel system. The frequency also scales approximately with the fuel flow-rate, although more poorly than with the speed of sound, and matches a vortex shedding deduced to be present within the fuel side of the Flare Tip. In addition the frequency also matches the fundamental vortex shedding frequency of the air jet emerging from the Tip. At the same time the visual appearance of the base of the flame was consistent with the air jet being driven at its fundamental mode. This suggests that the oscillations are caused by the coincidence of several coupling mechanisms. The acoustic resonance in the fuel pipe is deduced to control the frequency of oscillation and to amplify the pressure fluctuations. However the root cause of the oscillation is deduced to be a vortex shedding within the fuel supply. This causes fluctuations in the fuel flow rate which are amplified by the heat release. This creates positive feedback in further amplifying the pressure fluctuations in the fuel jet and the acoustic resonance.
Seyed Sepehr Mostafayi - One of the best experts on this subject based on the ideXlab platform.
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Effect of dividing single Flare Tip into mulTiple Tips on soot reduction
Clean Technologies and Environmental Policy, 2020Co-Authors: Seyed Sepehr Mostafayi, Fariborz RashidiAbstract:Several methods are applied for soot reduction in industrial Flares. However, they usually involve other issues such as flame safety and other pollutant formations; therefore, they should be handled carefully. Splitting Flare Tip into mulTiple branches is an idea that is thought to reduce soot formation by increasing the contact surface and providing better mixing. In this study, changing a single Tip of an industrial Flare into mulTiple Tips was investigated by Computational Fluid Dynamic software Ansys Fluent 18. Reynolds Average Navier–Stokes approach was used to model the fluid flow, and its turbulence was modeled by realizable k – ε model. The steady laminar flamelet model was chosen as the combustion model. Soot formation was modeled using Moss–Brookes approach, and validated by comparing the simulation results with available experimental data. Effects of Tip diameter, number of branches, and distance between branches on soot and NO_x yields, and flame stability were studied. According to the results, increasing the number of branches having larger diameters by taking flame stability limitations into consideration, and choosing optimum distances between branches caused significant soot reduction without noticeable changes in the NO_x formation. Graphic abstract
Graham J. Nathan - One of the best experts on this subject based on the ideXlab platform.
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Investigation of a combustion driven oscillation in a refinery Flare - Part B: Visualisation of a periodic flow instability in a bifurcating duct following a contraction
Experimental Thermal and Fluid Science, 2007Co-Authors: M. Riese, Richard M. Kelso, Graham J. Nathan, P. J. MullingerAbstract:Abstract A flow visualisation study was performed to investigate a periodic flow instability in a bifurcating duct within the Tip of the Flares at the Shell refinery in Clyde, NSW, to verify the trigger of a combustion-driven oscillation proposed in Part A of this study, and to identify its features. The model study assessed only the flow instability, uncoupled from the acoustic resonance and the combustion that are also present in the actual Flare. Three strong, coupled flow oscillations were found to be present in three regions of the fuel line in the Flare Tip model. A periodic flow separation was found to occur within the contraction at the inlet to the Tip, a coupled, periodic flow oscillation was found in the two transverse “cross-over ducts” from the central pipe to the outer annulus and an oscillating flow recirculation was present in the “end-cap” region of the central pipe. The dimensionless frequency of these oscillations in the model was found to match that measured in the full-scale plant for high fuel flow rates. This, and the strength of these flow oscillations, gives confidence that they are integral to the full-scale combustion-driven oscillation and most likely the primary trigger. The evidence indicates that the periodic flow instability is initiated by the separation and roll-up of the annular boundary layer at the start of the contraction in the fuel section of the Flare Tip. The separation generates an annular vortex which interacts with the blind-ended pipe downstream, leading to a pressure wave which propagates back upstream, initiating the next separation event and repeating the cycle. The study also investigated flow control devices with a view to finding a practical approach to mitigate the oscillations. The shape of these devices was constrained to allow installation without removing the Tip of the Flare. This aspect of the study highlighted the strength and nature of the coupled oscillation, since it proved to be very difficult to mitigate the oscillation in this way. An effective configuration is presented, comprising of three individual components, all three of which were found to be necessary to eliminate the oscillation completely.
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Investigation of a combustion driven oscillation in a refinery Flare. Part A: Full scale assessment
Experimental Thermal and Fluid Science, 2006Co-Authors: Graham J. Nathan, P. J. Mullinger, D. Bridger, B. MartinAbstract:Abstract An assessment of the cause of an intermittent combustion-driven oscillation in a full-scale refinery Flare is reported. When present, ambient sound pressure levels in excess of 100 dBA are generated. The oscillations began after the replacement of an old Flare Tip with one of a different design which required the use of non-standard components. The assessment included measurements of time resolved and integrated sound pressure in the ambient environment, and pressure in the fuel pipe and the air duct. Images obtained from video recorded from two directions are presented along with relevant process data. A review is also presented of the conditions under which the oscillations are inhibited or enhanced, and a comparison is made with another Flare of similar design which does not exhibit an oscillation. The Strouhal numbers of the potential causes of flow oscillation and the wavelength of acoustic resonances in the supply pipes are calculated. The findings are then compared with related investigations found in the literature. The frequency of the oscillation was found to scale with the speed of sound in the fuel and also to match a resonant frequency within three consecutive segments of the fuel supply pipe. In contrast, the speed of sound in air was constant for all tests, while the frequency varied. This shows that the resonance occurs within the fuel system. The frequency also scales approximately with the fuel flow-rate, although more poorly than with the speed of sound, and matches a vortex shedding deduced to be present within the fuel side of the Flare Tip. In addition the frequency also matches the fundamental vortex shedding frequency of the air jet emerging from the Tip. At the same time the visual appearance of the base of the flame was consistent with the air jet being driven at its fundamental mode. This suggests that the oscillations are caused by the coincidence of several coupling mechanisms. The acoustic resonance in the fuel pipe is deduced to control the frequency of oscillation and to amplify the pressure fluctuations. However the root cause of the oscillation is deduced to be a vortex shedding within the fuel supply. This causes fluctuations in the fuel flow rate which are amplified by the heat release. This creates positive feedback in further amplifying the pressure fluctuations in the fuel jet and the acoustic resonance.
B. Martin - One of the best experts on this subject based on the ideXlab platform.
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Investigation of a combustion driven oscillation in a refinery Flare. Part A: Full scale assessment
Experimental Thermal and Fluid Science, 2006Co-Authors: Graham J. Nathan, P. J. Mullinger, D. Bridger, B. MartinAbstract:Abstract An assessment of the cause of an intermittent combustion-driven oscillation in a full-scale refinery Flare is reported. When present, ambient sound pressure levels in excess of 100 dBA are generated. The oscillations began after the replacement of an old Flare Tip with one of a different design which required the use of non-standard components. The assessment included measurements of time resolved and integrated sound pressure in the ambient environment, and pressure in the fuel pipe and the air duct. Images obtained from video recorded from two directions are presented along with relevant process data. A review is also presented of the conditions under which the oscillations are inhibited or enhanced, and a comparison is made with another Flare of similar design which does not exhibit an oscillation. The Strouhal numbers of the potential causes of flow oscillation and the wavelength of acoustic resonances in the supply pipes are calculated. The findings are then compared with related investigations found in the literature. The frequency of the oscillation was found to scale with the speed of sound in the fuel and also to match a resonant frequency within three consecutive segments of the fuel supply pipe. In contrast, the speed of sound in air was constant for all tests, while the frequency varied. This shows that the resonance occurs within the fuel system. The frequency also scales approximately with the fuel flow-rate, although more poorly than with the speed of sound, and matches a vortex shedding deduced to be present within the fuel side of the Flare Tip. In addition the frequency also matches the fundamental vortex shedding frequency of the air jet emerging from the Tip. At the same time the visual appearance of the base of the flame was consistent with the air jet being driven at its fundamental mode. This suggests that the oscillations are caused by the coincidence of several coupling mechanisms. The acoustic resonance in the fuel pipe is deduced to control the frequency of oscillation and to amplify the pressure fluctuations. However the root cause of the oscillation is deduced to be a vortex shedding within the fuel supply. This causes fluctuations in the fuel flow rate which are amplified by the heat release. This creates positive feedback in further amplifying the pressure fluctuations in the fuel jet and the acoustic resonance.