The Experts below are selected from a list of 11241 Experts worldwide ranked by ideXlab platform
F B Waanders - One of the best experts on this subject based on the ideXlab platform.
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physical property behaviour of north dakota lignite in an oxygen steam blown moving bed gasifier
Fuel Processing Technology, 2013Co-Authors: S J Mangena, John R Bunt, F B WaandersAbstract:Abstract In this study lignite originating from North Dakota (USA) was Thermally treated in an oxygen/steam blown commercial-scale moving bed gasifier operating on lump coal at the Dakota Gasification Company (DGC) in order to identify the physical property changes that occur during heating. After reaction, the solid particulate remnants were extracted from the reactor and characterised using standard techniques. Thermal Fragmentation was found to be severe with the coal tested, i.e. the lump coal was found to decrease in size to about 90%
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an understanding of lump coal physical property behaviour density and particle size effects impacting on a commercial scale sasol lurgi fbdb gasifier
Fuel, 2008Co-Authors: John R Bunt, F B WaandersAbstract:Abstract Thermal processes which utilize coarse coal, such as fixed-bed gasification and chain grate stoker boilers, are dependant on a stable particle size for stable operation. During coarse coal utilization, Thermal Fragmentation of lump coal (upon heating) produces hydrodynamic effects (pressure drop fluctuations) manifesting itself in a variety of ways, and include: channel-burning and solids elutriation. Primary Thermal Fragmentation occurring in the drying zone of a fixed-bed reactor is primarily a function of moisture content release with ensuing particle size reduction. Large particles tend to fragment more than finer particles, thus leading to hydrodynamic problems. From Fragmentation studies it was elucidated that a Thermal “stable size” is reached through the process of Thermal Fragmentation for optimum heat transfer and utilization during the drying and pyrolysis zone regions of the coarse coal utilization process. In this paper, the Sasol-Lurgi MK IV FBDB gasifier turn-out physical property profiles (bulk density and particle size distribution) results will be discussed. It was found that these profiles provided significant insight into the complex heterogeneous nature of the coal transformation processes occurring within the fixed-bed reactor. In the case of the bulk density profile, a shrinking core and flaking mechanism was proposed to explain the increase in density occurring in the bottom half of the gasifier. The +25 mm size fraction distribution profile was found to clearly show the Fragmentation effects occurring within the reactor. Primary Fragmentation was inferred as the mechanism responsible for causing breakage of this size fraction down to a remaining ca. 15% +25 mm fraction. The significant breakage of the coarse +25 mm fraction is expected to influence unstable gasifier conditions in the top part of the gasifier, due to pressure drop fluctuations caused by void packing. A good correlation was obtained for the relationship between bulk density versus the −25 mm + 6.3 mm size fraction content, indicating that the bed-packing density is highly dependent on the relative abundance of this intermediate size fraction. The −6.3 mm size fraction distribution profile was found to not be significantly different between the four reaction zones identified in the gasifier. Breakage of the coarser +6.3 mm sizes occurred continuously, and could possibly be related to breakage caused by the ash-grate when sampling. The Ergun Index was successfully used to profile the Fragmentation zones identified and to show areas within the gasifier where pressure drop and resultant instability occurs. This is the first-ever identification of this phenomenon occurring within a fixed-bed gasifier and is expected to lead to significant optimization challenges to ensure better stability.
John R Bunt - One of the best experts on this subject based on the ideXlab platform.
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physical property behaviour of north dakota lignite in an oxygen steam blown moving bed gasifier
Fuel Processing Technology, 2013Co-Authors: S J Mangena, John R Bunt, F B WaandersAbstract:Abstract In this study lignite originating from North Dakota (USA) was Thermally treated in an oxygen/steam blown commercial-scale moving bed gasifier operating on lump coal at the Dakota Gasification Company (DGC) in order to identify the physical property changes that occur during heating. After reaction, the solid particulate remnants were extracted from the reactor and characterised using standard techniques. Thermal Fragmentation was found to be severe with the coal tested, i.e. the lump coal was found to decrease in size to about 90%
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an understanding of lump coal physical property behaviour density and particle size effects impacting on a commercial scale sasol lurgi fbdb gasifier
Fuel, 2008Co-Authors: John R Bunt, F B WaandersAbstract:Abstract Thermal processes which utilize coarse coal, such as fixed-bed gasification and chain grate stoker boilers, are dependant on a stable particle size for stable operation. During coarse coal utilization, Thermal Fragmentation of lump coal (upon heating) produces hydrodynamic effects (pressure drop fluctuations) manifesting itself in a variety of ways, and include: channel-burning and solids elutriation. Primary Thermal Fragmentation occurring in the drying zone of a fixed-bed reactor is primarily a function of moisture content release with ensuing particle size reduction. Large particles tend to fragment more than finer particles, thus leading to hydrodynamic problems. From Fragmentation studies it was elucidated that a Thermal “stable size” is reached through the process of Thermal Fragmentation for optimum heat transfer and utilization during the drying and pyrolysis zone regions of the coarse coal utilization process. In this paper, the Sasol-Lurgi MK IV FBDB gasifier turn-out physical property profiles (bulk density and particle size distribution) results will be discussed. It was found that these profiles provided significant insight into the complex heterogeneous nature of the coal transformation processes occurring within the fixed-bed reactor. In the case of the bulk density profile, a shrinking core and flaking mechanism was proposed to explain the increase in density occurring in the bottom half of the gasifier. The +25 mm size fraction distribution profile was found to clearly show the Fragmentation effects occurring within the reactor. Primary Fragmentation was inferred as the mechanism responsible for causing breakage of this size fraction down to a remaining ca. 15% +25 mm fraction. The significant breakage of the coarse +25 mm fraction is expected to influence unstable gasifier conditions in the top part of the gasifier, due to pressure drop fluctuations caused by void packing. A good correlation was obtained for the relationship between bulk density versus the −25 mm + 6.3 mm size fraction content, indicating that the bed-packing density is highly dependent on the relative abundance of this intermediate size fraction. The −6.3 mm size fraction distribution profile was found to not be significantly different between the four reaction zones identified in the gasifier. Breakage of the coarser +6.3 mm sizes occurred continuously, and could possibly be related to breakage caused by the ash-grate when sampling. The Ergun Index was successfully used to profile the Fragmentation zones identified and to show areas within the gasifier where pressure drop and resultant instability occurs. This is the first-ever identification of this phenomenon occurring within a fixed-bed gasifier and is expected to lead to significant optimization challenges to ensure better stability.
Marc L Snapper - One of the best experts on this subject based on the ideXlab platform.
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intramolecular 2 2 photocycloaddition Thermal Fragmentation formally allowed and forbidden pathways toward 5 8 5 ring systems
Journal of the American Chemical Society, 2005Co-Authors: Scott J Bader, Marc L SnapperAbstract:The Thermal Fragmentation of highly functionalized, linear polycyclobutanes with a cis,syn,cis-relative stereochemistry is shown to offer a rapid entry into the dicyclopenta[a,d]cyclooctenyl (5−8−5) ring system. The thermolysis of polyfused cyclobutanes with a cis,syn,cis- or a cis,anti,cis-relationship proceeds in a formally “symmetry-allowed” manner through the intermediacy of a cis,trans-cyclooctadiene. When a bridging tether used to establish the cis,syn,cis-stereochemistry in the intramolecular [2 + 2] photocyclization is present in the thermolysis step, however, the result of a formally “symmetry-forbidden” Fragmentation is observed yielding cis,cis-cyclooctadiene-containing 5−8−5 products. In general, the stereochemical observations noted in these Fragmentations offer new opportunities for accessing a variety of stereochemical relationships in these 5−8−5 ring systems.
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intramolecular 2 2 photocycloaddition Thermal Fragmentation approach toward 5 8 5 ring systems
Organic Letters, 2001Co-Authors: Marc L SnapperAbstract:[reaction: see text]. An intramolecular [2 + 2]-photocycloaddition is used to provide a photoadduct, which upon Fragmentation, lactone cleavage, and subsequent Cope rearrangement provides a dicyclopenta[a,d]cyclooctene ring system with substituents in place (e.g., C3 and C11) to access several 5-8-5 diterpene and sesterterpene natural products.
Patrick J Walsh - One of the best experts on this subject based on the ideXlab platform.
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Palladium-Catalyzed Arylation of Alkyl Sulfenate Anions
Journal of the American Chemical Society, 2015Co-Authors: Mengnan Zhang, Carol Y. Wang, Hui Jiang, Patrick J WalshAbstract:A unique palladium-catalyzed arylation of alkyl sulfenate anions is introduced that affords aryl alkyl sulfoxides in high yields. Due to the base sensitivity of the starting sulfoxides, sulfenate anion intermediates, and alkyl aryl sulfoxide products, the use of a mild method to generate alkyl sulfenate anions was crucial to the success of this process. Thus, a fluoride triggered elimination strategy was employed with alkyl 2-(trimethylsilyl)ethyl sulfoxides to liberate the requisite alkyl sulfenate anion intermediates. In the presence of palladium catalysts with bulky monodentate phosphines (SPhos and Cy-CarPhos) and aryl bromides or chlorides, alkyl sulfenate anions were readily arylated. Moreover, the Thermal Fragmentation and the base promoted elimination of alkyl sulfoxides was overridden. The alkyl sulfenate anion arylation exhibited excellent chemoselectivity in the presence of functional groups, such as anilines and phenols, which are also known to undergo palladium catalyzed arylation reactions.
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Palladium-Catalyzed Arylation of Alkyl Sulfenate Anions
2015Co-Authors: Tiezheng Jia, Mengnan Zhang, Carol Y. Wang, Hui Jiang, Patrick J WalshAbstract:A unique palladium-catalyzed arylation of alkyl sulfenate anions is introduced that affords aryl alkyl sulfoxides in high yields. Due to the base sensitivity of the starting sulfoxides, sulfenate anion intermediates, and alkyl aryl sulfoxide products, the use of a mild method to generate alkyl sulfenate anions was crucial to the success of this process. Thus, a fluoride triggered elimination strategy was employed with alkyl 2-(trimethylsilyl)ethyl sulfoxides to liberate the requisite alkyl sulfenate anion intermediates. In the presence of palladium catalysts with bulky monodentate phosphines (SPhos and Cy-CarPhos) and aryl bromides or chlorides, alkyl sulfenate anions were readily arylated. Moreover, the Thermal Fragmentation and the base promoted elimination of alkyl sulfoxides was overridden. The alkyl sulfenate anion arylation exhibited excellent chemoselectivity in the presence of functional groups, such as anilines and phenols, which are also known to undergo palladium catalyzed arylation reactions
S J Mangena - One of the best experts on this subject based on the ideXlab platform.
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physical property behaviour of north dakota lignite in an oxygen steam blown moving bed gasifier
Fuel Processing Technology, 2013Co-Authors: S J Mangena, John R Bunt, F B WaandersAbstract:Abstract In this study lignite originating from North Dakota (USA) was Thermally treated in an oxygen/steam blown commercial-scale moving bed gasifier operating on lump coal at the Dakota Gasification Company (DGC) in order to identify the physical property changes that occur during heating. After reaction, the solid particulate remnants were extracted from the reactor and characterised using standard techniques. Thermal Fragmentation was found to be severe with the coal tested, i.e. the lump coal was found to decrease in size to about 90%
