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Olaf Deutschmann - One of the best experts on this subject based on the ideXlab platform.
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Numerical Simulation of Methane and Propane Reforming Over a Porous Rh/Al$_{2}$O$_{3}$ Catalyst in Stagnation-Flows: Impact of Internal and External Mass Transfer Limitations on Species Profiles
Catalysts, 2020Co-Authors: Hüseyin Karadeniz, Steffen Tischer, Canan Karakaya, Olaf DeutschmannAbstract:Hydrogen production by catalytic partial Oxidation and steam reforming of methane and propane towards synthesis gas are numerically investigated in stagnation-flow over a disc coated with a porous Rh/Al$_{2}$O$_{3}$ layer. A one-dimensional flow field is coupled with three models for internal diffusion and with a 62-step surface reaction mechanism. Numerical simulations are conducted with the recently developed computer code DETCHEM$^{STAG}$. Dusty-Gas model, a reaction-diffusion model and a simple effectiveness factor model, are alternatively used in simulations to study the internal mass transfer inside the 100 µm thick washcoat layer. Numerically predicted species profiles in the external boundary layer agree well with the recently published experimental data. All three models for internal diffusion exhibit strong species concentration gradients in the catalyst layer. In partial Oxidation conditions, a thin total Oxidation Zone occurs close to the gas-washcoat interface, followed by a Zone of steam and dry reforming of methane. Increasing the reactor pressure and decreasing the inlet flow velocity increases/decreases the external/internal mass transfer limitations. The comparison of reaction-diffusion and Dusty-Gas model results reveal the insignificance of convective flow on species transport inside the washcoat. Simulations, which additionally solve a heat transport equation, do not show any temperature gradients inside the washcoat.
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numerical simulation of methane and propane reforming over a porous rh al _ 2 o _ 3 catalyst in stagnation flows impact of internal and external mass transfer limitations on species profiles
Catalysts, 2020Co-Authors: Hüseyin Karadeniz, Steffen Tischer, Canan Karakaya, Olaf DeutschmannAbstract:Hydrogen production by catalytic partial Oxidation and steam reforming of methane and propane towards synthesis gas are numerically investigated in stagnation-flow over a disc coated with a porous Rh/Al$_{2}$O$_{3}$ layer. A one-dimensional flow field is coupled with three models for internal diffusion and with a 62-step surface reaction mechanism. Numerical simulations are conducted with the recently developed computer code DETCHEM$^{STAG}$. Dusty-Gas model, a reaction-diffusion model and a simple effectiveness factor model, are alternatively used in simulations to study the internal mass transfer inside the 100 µm thick washcoat layer. Numerically predicted species profiles in the external boundary layer agree well with the recently published experimental data. All three models for internal diffusion exhibit strong species concentration gradients in the catalyst layer. In partial Oxidation conditions, a thin total Oxidation Zone occurs close to the gas-washcoat interface, followed by a Zone of steam and dry reforming of methane. Increasing the reactor pressure and decreasing the inlet flow velocity increases/decreases the external/internal mass transfer limitations. The comparison of reaction-diffusion and Dusty-Gas model results reveal the insignificance of convective flow on species transport inside the washcoat. Simulations, which additionally solve a heat transport equation, do not show any temperature gradients inside the washcoat.
Sylvain Salvador - One of the best experts on this subject based on the ideXlab platform.
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Oxidative pyrolysis of pine wood, wheat straw and miscanthus pellets in a fixed bed
Fuel Processing Technology, 2018Co-Authors: Xuan-huynh Pham, Bruno Piriou, Sylvain Salvador, Jeremy Valette, Laurent Van De SteeneAbstract:Oxidative pyrolysis is a key step in the autothermal operation of many fixed-bed reactors for staged gasification and advanced carbonisation. In these reactors, biomass is converted into charcoal, condensates and permanent gases inside a moving Oxidation Zone (OZ) which also produces energy to self-sustain the process. Oxidative pyrolysis of three different biomass types: pine wood, miscanthus and wheat straw pellets, was performed in a batch 20 cm diameter fixed bed reactor. Results showed that the OZ consumed 11% to 14% of the stoichiometric air to self-sustain the process and reached a peak temperature around 720 °C whatever the biomass. The propagation velocity and thickness of the OZ were inversely proportional to the ash content and to the bulk density of the biomass. Ash was also shown to influence the yield and composition of the resulting products due to a catalytic effect on primary and secondary pyrolysis reactions.
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Oxidative Pyrolysis of Agricultural Residues in Gasification and Carbonization Processes
2018Co-Authors: Xuan-huynh Pham, Laurent Van De Steene, Bruno Piriou, Sylvain SalvadorAbstract:Oxidative pyrolysis, in which heat is provided by the partial Oxidation, occurs in many fixed bed reactors of air staged gasification and advanced carbonization processes. In these reactors, an Oxidation Zone (OZ) propagates and separates the virgin biomass from the produced char, and self-sustains the process. To investigate the energy transfer efficiency and to characterize the OZ features, oxidative pyrolysis was performed in a 20 cm diameter fixed bed reactor with Wheat straw pellets. Temperatures and biomass bed height were measured continuously during the experiment. The OZ propagated at 0.41 cm/min and consumed about 11 % of the biomass. The role of bed compaction on the effective propagation velocity was highlighted. Char yield was measured to 28.6 % and char accounted for 39.56 % of the total energy content of the Wheat straw. Maximum temperature in the bed reached 780°C. This paper proposes a new insight into the OZ features when it propagates in a biomass fixed bed.
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Oxidative pyrolysis of wood chips and of wood pellets in a downdraft continuous fixed bed reactor
Fuel, 2017Co-Authors: Elias Daouk, Jeremy Valette, Laurent Steene, Frederic Paviet, Éric Martin, Sylvain SalvadorAbstract:In air staged gasification and advanced carbonization processes, oxidative pyrolysis occurs in downdraft continuous fixed bed reactors. An Oxidation Zone separates the virgin fuel from the resulting char and propagates upward. Here, the Oxidation Zone was stabilized at a fixed elevation in a 20 cm I.D. fixed bed reactor using wood chips or wood pellets. In controlled continuous operating mode, we investigated the impact of air flux and bed bulk density on the behavior of the Oxidation Zone in terms of wood consumption, and yields of chit., gas and tars. An air:wood mass ratio of 0.7 was measured and in our operating conditions, and was not sensitive to air mass flux and bed density. With oxidative pyrolysis, yields of organic condensates were lower than with allothermal pyrolysis, whereas the production of pyrolysis water and permanent gases increased. Finally, the Oxidation Zone was shown to be flat and horizontal in a wood pellet bed but inclined in a wood chip bed.
V. G. Krivovichev - One of the best experts on this subject based on the ideXlab platform.
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thermodynamics of arsenates selenites and sulfates in the Oxidation Zone of sulfide ores xiv selenium minerals in the Oxidation Zone of the yubileynoe massive sulfide deposit the south urals
Geology of Ore Deposits, 2018Co-Authors: A V Vishnevsky, M. V. Charykova, V. G. Krivovichev, E. V. Belogub, Ivan A BlinovAbstract:Selenium is one of the most important minor elements in massive sulfide ores. This study focuses on selenium minerals present in the Oxidation Zone of the Yubeleinoe massive sulfide deposit, the South Urals, Russia: clausthalite (PbSe), tiemannite (HgSe), and naumannite (Ag2Se). These minerals are associated with goethite and siderite. Thermodynamic modeling was used to estimate the physicochemical parameters of selenide stability and the possible formation of Pb, Hg, and Ag selenites as a result of sulfide ore Oxidation. The Eh–pH diagrams for the Fe–S–CO2–H2O and Fe–Se–CO2–H2O systems were calculated to estimate the physicochemical formation conditions of the Yubileinoe Oxidation Zone, as well as for the M–Se–Н2О and M–S–H2O (M = Hg, Pb, Ag) systems. The physicochemical parameters of clausthalite, naumannite, and tiemannite stability are consistent with these conditions. Only the formation of PbSeO3 is theoretically possible among Pb, Ag, and Hg selenites.
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mineral systems and the thermodynamics of selenites and selenates in the Oxidation Zone of sulfide ores a review
Mineralogy and Petrology, 2017Co-Authors: M. V. Charykova, V. G. KrivovichevAbstract:Contemporary mineralogy and geochemistry are concerned with understanding and deciphering processes that occur near the surface of the Earth. These processes are especially important for resolving ecological challenges and developing principles of good environmental management. Selenium oxysalts, selenites and selenates, are relatively rare as minerals; there are presently only 34 known mineral species. Thirty-one “pure” selenites, which contain only selenite anionic groups, are known to occur naturally. The other three minerals each contain two anionic groups: selenate and selenite (schmiederite), selenate and sulphate (olsacherite), and selenate and iodate (carlosruizite).
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mineral systems and the thermodynamics of selenites and selenates in the Oxidation Zone of sulfide ores a review
Mineralogy and Petrology, 2017Co-Authors: M. V. Charykova, V. G. KrivovichevAbstract:Contemporary mineralogy and geochemistry are concerned with understanding and deciphering processes that occur near the surface of the Earth. These processes are especially important for resolving ecological challenges and developing principles of good environmental management. Selenium oxysalts, selenites and selenates, are relatively rare as minerals; there are presently only 34 known mineral species. Thirty-one “pure” selenites, which contain only selenite anionic groups, are known to occur naturally. The other three minerals each contain two anionic groups: selenate and selenite (schmiederite), selenate and sulphate (olsacherite), and selenate and iodate (carlosruizite). This work is intended to provide a classification of natural selenium oxysalts based on their chemical composition. Selenites belong to a particular mineral system, whose components are chemical elements required to construct the crystal structure of a mineral (species-defining constituents). The number of components represents the minimum number of independent elements necessary to define the composition of the system. All selenites and selenates are divided into two groups: anhydrous selenites (I) and hydrous selenites and selenates (II). The paper also presents systematized data published on the thermodynamics of selenites, which are formed in the weathering Zone of sulfide and selenide ores, and determines approaches to the quantitative physicochemical modeling of formation conditions. The Eh–pH diagrams of the Me–Se–H2O systems (Me = Cu, Co, Ni, Fe, Zn, Ca, Al) were calculated and plotted for the average contents of these elements in aqueous weathering solutions in sulfide deposit Oxidation Zones.
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thermodynamics of arsenates selenites and sulfates in the Oxidation Zone of sulfide ores xii mineral equilibria in the cd se h2o system at 25 c
Geology of Ore Deposits, 2016Co-Authors: M. V. Charykova, V. G. Krivovichev, A V Vishnevsky, N. M. Ivanova, E L Fokina, Natalia V Platonova, V. V. SemenovaAbstract:Understanding the mechanisms of cadmium and selenium behavior under near-surface conditions is very important for solving certain environmental problems. The principal aim of this study is physicochemical analysis of the formation conditions of synthetic cadmium selenite CdSeO3 · H2O and experimental investigation of its thermal stability and dehydration and dissociation mechanisms. The synthesis was performed by boiling-dry aqueous solutions of cadmium nitrate and sodium selenite. The obtained samples were identified with electron microprobe and powder X-ray diffraction. Complex thermal analysis (thermogravimetry and differential scanning calorimetry) have shown that CdSeO3 · H2O is dehydrated at 177–241°C in two stages, apparently corresponding to the formation of CdSeO3 · 2/3H2O. The Eh–pH diagrams were calculated using the Geochemist’s Workbench (GWB 9.0) software package. The Eh–pH diagrams have been calculated for the Cd–Se–Н2О and Cd–Se–CO2–H2O systems for the average content of these elements in underground waters. The formation of cadmium selenite, CdSeO3 · H2O in the Oxidation medium is quite possible. The existence of CdSeO3 is possible at high temperature.
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thermodynamics of arsenates selenites and sulfates in the Oxidation Zone of sulfide ores xii mineral equilibria in the cd se h 2 o system at 25 c
Geology of Ore Deposits, 2016Co-Authors: M. V. Charykova, V. G. Krivovichev, A V Vishnevsky, N. M. Ivanova, E L Fokina, Natalia V Platonova, V. V. SemenovaAbstract:Understanding the mechanisms of cadmium and selenium behavior under near-surface conditions is very important for solving certain environmental problems. The principal aim of this study is physicochemical analysis of the formation conditions of synthetic cadmium selenite CdSeO3 · H2O and experimental investigation of its thermal stability and dehydration and dissociation mechanisms. The synthesis was performed by boiling-dry aqueous solutions of cadmium nitrate and sodium selenite. The obtained samples were identified with electron microprobe and powder X-ray diffraction. Complex thermal analysis (thermogravimetry and differential scanning calorimetry) have shown that CdSeO3 · H2O is dehydrated at 177–241°C in two stages, apparently corresponding to the formation of CdSeO3 · 2/3H2O. The Eh–pH diagrams were calculated using the Geochemist’s Workbench (GWB 9.0) software package. The Eh–pH diagrams have been calculated for the Cd–Se–Н2О and Cd–Se–CO2–H2O systems for the average content of these elements in underground waters. The formation of cadmium selenite, CdSeO3 · H2O in the Oxidation medium is quite possible. The existence of CdSeO3 is possible at high temperature.
M. V. Charykova - One of the best experts on this subject based on the ideXlab platform.
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thermodynamics of arsenates selenites and sulfates in the Oxidation Zone of sulfide ores xiv selenium minerals in the Oxidation Zone of the yubileynoe massive sulfide deposit the south urals
Geology of Ore Deposits, 2018Co-Authors: A V Vishnevsky, M. V. Charykova, V. G. Krivovichev, E. V. Belogub, Ivan A BlinovAbstract:Selenium is one of the most important minor elements in massive sulfide ores. This study focuses on selenium minerals present in the Oxidation Zone of the Yubeleinoe massive sulfide deposit, the South Urals, Russia: clausthalite (PbSe), tiemannite (HgSe), and naumannite (Ag2Se). These minerals are associated with goethite and siderite. Thermodynamic modeling was used to estimate the physicochemical parameters of selenide stability and the possible formation of Pb, Hg, and Ag selenites as a result of sulfide ore Oxidation. The Eh–pH diagrams for the Fe–S–CO2–H2O and Fe–Se–CO2–H2O systems were calculated to estimate the physicochemical formation conditions of the Yubileinoe Oxidation Zone, as well as for the M–Se–Н2О and M–S–H2O (M = Hg, Pb, Ag) systems. The physicochemical parameters of clausthalite, naumannite, and tiemannite stability are consistent with these conditions. Only the formation of PbSeO3 is theoretically possible among Pb, Ag, and Hg selenites.
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mineral systems and the thermodynamics of selenites and selenates in the Oxidation Zone of sulfide ores a review
Mineralogy and Petrology, 2017Co-Authors: M. V. Charykova, V. G. KrivovichevAbstract:Contemporary mineralogy and geochemistry are concerned with understanding and deciphering processes that occur near the surface of the Earth. These processes are especially important for resolving ecological challenges and developing principles of good environmental management. Selenium oxysalts, selenites and selenates, are relatively rare as minerals; there are presently only 34 known mineral species. Thirty-one “pure” selenites, which contain only selenite anionic groups, are known to occur naturally. The other three minerals each contain two anionic groups: selenate and selenite (schmiederite), selenate and sulphate (olsacherite), and selenate and iodate (carlosruizite).
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mineral systems and the thermodynamics of selenites and selenates in the Oxidation Zone of sulfide ores a review
Mineralogy and Petrology, 2017Co-Authors: M. V. Charykova, V. G. KrivovichevAbstract:Contemporary mineralogy and geochemistry are concerned with understanding and deciphering processes that occur near the surface of the Earth. These processes are especially important for resolving ecological challenges and developing principles of good environmental management. Selenium oxysalts, selenites and selenates, are relatively rare as minerals; there are presently only 34 known mineral species. Thirty-one “pure” selenites, which contain only selenite anionic groups, are known to occur naturally. The other three minerals each contain two anionic groups: selenate and selenite (schmiederite), selenate and sulphate (olsacherite), and selenate and iodate (carlosruizite). This work is intended to provide a classification of natural selenium oxysalts based on their chemical composition. Selenites belong to a particular mineral system, whose components are chemical elements required to construct the crystal structure of a mineral (species-defining constituents). The number of components represents the minimum number of independent elements necessary to define the composition of the system. All selenites and selenates are divided into two groups: anhydrous selenites (I) and hydrous selenites and selenates (II). The paper also presents systematized data published on the thermodynamics of selenites, which are formed in the weathering Zone of sulfide and selenide ores, and determines approaches to the quantitative physicochemical modeling of formation conditions. The Eh–pH diagrams of the Me–Se–H2O systems (Me = Cu, Co, Ni, Fe, Zn, Ca, Al) were calculated and plotted for the average contents of these elements in aqueous weathering solutions in sulfide deposit Oxidation Zones.
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thermodynamics of arsenates selenites and sulfates in the Oxidation Zone of sulfide ores xii mineral equilibria in the cd se h2o system at 25 c
Geology of Ore Deposits, 2016Co-Authors: M. V. Charykova, V. G. Krivovichev, A V Vishnevsky, N. M. Ivanova, E L Fokina, Natalia V Platonova, V. V. SemenovaAbstract:Understanding the mechanisms of cadmium and selenium behavior under near-surface conditions is very important for solving certain environmental problems. The principal aim of this study is physicochemical analysis of the formation conditions of synthetic cadmium selenite CdSeO3 · H2O and experimental investigation of its thermal stability and dehydration and dissociation mechanisms. The synthesis was performed by boiling-dry aqueous solutions of cadmium nitrate and sodium selenite. The obtained samples were identified with electron microprobe and powder X-ray diffraction. Complex thermal analysis (thermogravimetry and differential scanning calorimetry) have shown that CdSeO3 · H2O is dehydrated at 177–241°C in two stages, apparently corresponding to the formation of CdSeO3 · 2/3H2O. The Eh–pH diagrams were calculated using the Geochemist’s Workbench (GWB 9.0) software package. The Eh–pH diagrams have been calculated for the Cd–Se–Н2О and Cd–Se–CO2–H2O systems for the average content of these elements in underground waters. The formation of cadmium selenite, CdSeO3 · H2O in the Oxidation medium is quite possible. The existence of CdSeO3 is possible at high temperature.
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thermodynamics of arsenates selenites and sulfates in the Oxidation Zone of sulfide ores xii mineral equilibria in the cd se h 2 o system at 25 c
Geology of Ore Deposits, 2016Co-Authors: M. V. Charykova, V. G. Krivovichev, A V Vishnevsky, N. M. Ivanova, E L Fokina, Natalia V Platonova, V. V. SemenovaAbstract:Understanding the mechanisms of cadmium and selenium behavior under near-surface conditions is very important for solving certain environmental problems. The principal aim of this study is physicochemical analysis of the formation conditions of synthetic cadmium selenite CdSeO3 · H2O and experimental investigation of its thermal stability and dehydration and dissociation mechanisms. The synthesis was performed by boiling-dry aqueous solutions of cadmium nitrate and sodium selenite. The obtained samples were identified with electron microprobe and powder X-ray diffraction. Complex thermal analysis (thermogravimetry and differential scanning calorimetry) have shown that CdSeO3 · H2O is dehydrated at 177–241°C in two stages, apparently corresponding to the formation of CdSeO3 · 2/3H2O. The Eh–pH diagrams were calculated using the Geochemist’s Workbench (GWB 9.0) software package. The Eh–pH diagrams have been calculated for the Cd–Se–Н2О and Cd–Se–CO2–H2O systems for the average content of these elements in underground waters. The formation of cadmium selenite, CdSeO3 · H2O in the Oxidation medium is quite possible. The existence of CdSeO3 is possible at high temperature.
Hüseyin Karadeniz - One of the best experts on this subject based on the ideXlab platform.
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Numerical Simulation of Methane and Propane Reforming Over a Porous Rh/Al$_{2}$O$_{3}$ Catalyst in Stagnation-Flows: Impact of Internal and External Mass Transfer Limitations on Species Profiles
Catalysts, 2020Co-Authors: Hüseyin Karadeniz, Steffen Tischer, Canan Karakaya, Olaf DeutschmannAbstract:Hydrogen production by catalytic partial Oxidation and steam reforming of methane and propane towards synthesis gas are numerically investigated in stagnation-flow over a disc coated with a porous Rh/Al$_{2}$O$_{3}$ layer. A one-dimensional flow field is coupled with three models for internal diffusion and with a 62-step surface reaction mechanism. Numerical simulations are conducted with the recently developed computer code DETCHEM$^{STAG}$. Dusty-Gas model, a reaction-diffusion model and a simple effectiveness factor model, are alternatively used in simulations to study the internal mass transfer inside the 100 µm thick washcoat layer. Numerically predicted species profiles in the external boundary layer agree well with the recently published experimental data. All three models for internal diffusion exhibit strong species concentration gradients in the catalyst layer. In partial Oxidation conditions, a thin total Oxidation Zone occurs close to the gas-washcoat interface, followed by a Zone of steam and dry reforming of methane. Increasing the reactor pressure and decreasing the inlet flow velocity increases/decreases the external/internal mass transfer limitations. The comparison of reaction-diffusion and Dusty-Gas model results reveal the insignificance of convective flow on species transport inside the washcoat. Simulations, which additionally solve a heat transport equation, do not show any temperature gradients inside the washcoat.
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numerical simulation of methane and propane reforming over a porous rh al _ 2 o _ 3 catalyst in stagnation flows impact of internal and external mass transfer limitations on species profiles
Catalysts, 2020Co-Authors: Hüseyin Karadeniz, Steffen Tischer, Canan Karakaya, Olaf DeutschmannAbstract:Hydrogen production by catalytic partial Oxidation and steam reforming of methane and propane towards synthesis gas are numerically investigated in stagnation-flow over a disc coated with a porous Rh/Al$_{2}$O$_{3}$ layer. A one-dimensional flow field is coupled with three models for internal diffusion and with a 62-step surface reaction mechanism. Numerical simulations are conducted with the recently developed computer code DETCHEM$^{STAG}$. Dusty-Gas model, a reaction-diffusion model and a simple effectiveness factor model, are alternatively used in simulations to study the internal mass transfer inside the 100 µm thick washcoat layer. Numerically predicted species profiles in the external boundary layer agree well with the recently published experimental data. All three models for internal diffusion exhibit strong species concentration gradients in the catalyst layer. In partial Oxidation conditions, a thin total Oxidation Zone occurs close to the gas-washcoat interface, followed by a Zone of steam and dry reforming of methane. Increasing the reactor pressure and decreasing the inlet flow velocity increases/decreases the external/internal mass transfer limitations. The comparison of reaction-diffusion and Dusty-Gas model results reveal the insignificance of convective flow on species transport inside the washcoat. Simulations, which additionally solve a heat transport equation, do not show any temperature gradients inside the washcoat.
