3D CFD modeling of acetone hydrogenation in fixed bed reactor with spherical particles

Acetone hydrogenation in a fixed bed reactor packed with spherical catalyst particles was simulated to study the effects of inlet gas velocity and particle diameter on hydrogenation reaction. Computational results show that the catalyst particles in the reactor are almost isothermal, and the high isopropanol concentration appears at the lee of the particles. With the increase of inlet velocity, the outlet isopropanol mole fraction decreases, and the total pressure drop increases drastically. Small diameter catalyst particles are favorable for acetone hydrogenation, but result in large pressure drop.     

Kinetics studies of <Emphasis Type="SmallCaps">d</Emphasis>-glucose hydrogenation over activated charcoal supported platinum catalyst

The kinetics of the catalytic hydrogenation of d-glucose to produce d-sorbitol was studied in a three-phase laboratory scale reactor. The hydrogenation reactions were performed on activated charcoal supported platinum catalyst in the temperature range 25–65°C and in a constant pressure of 1 atm. The kinetic data were modeled by zero, first and second-order reaction equations. In the operating regimes studied, the results show that the hydrogenation reaction was of a first order with respect to d-glucose concentration. Also the activation energy of the reaction was determined, and found to be 12.33 kJ mole⁻¹. A set of experiment was carried out to test the deactivation of the catalyst, and the results show that the deactivation is slow with the ability of using the catalyst for several times with a small decrease in product yield.     

L-S mass transfer in G-L-S countercurrent magnetically stabilized bed with amorphous alloy SRNA-4 catalyst

Liquid-solid （L-S） mass transfer coefficients （Ks） were characterized in a gas-liquid-solid （G-L-S） three-phase countercurrent magnetically stabilized bed （MSB） using amorphous alloy SRNA-4 as the solid phase. Effects of superficial liquid velocity, superficial gas velocity, magnetic field strength, liquid viscosity and surface tension were investigated. Experimental results indicated that the external magnetic field increased Ks in three-phase MSB, as compared to those in conventional G-L-S fluidized beds; that Ks increased with magnetic field strength, superficial gas and liquid velocities and decreased with liquid viscosity and surface tension; and that Ks showed uniform axial and radial distributions except for small increases close to the wall. Dimensionless correlations were established to estimate Ks of the G-L-S countercurrent MSB using SRNA-4 catalyst, with an average error of 3.6%.     

Hydrodynamic behavior of magnetized fluidized beds with admixtures of Geldart-B magnetizable and nonmagnetizable particles

This work focuses on the hydrodynamic behavior of admixtures of Geldart-B magnetizable and nonmagnetizable particles in a magnetized fluidized bed. The applied magnetic field was axial, uniform, and steady. In operating the beds, the magnetization-LAST mode was adopted under which four distinct flow regimes exist: fixed, magnetized-bubbling, partial segregation-bubbling, and total segregation-bubbling. The operational phase diagram was drawn to display the transitions between flow regimes in an intuitive manner. Only in the magnetized-bubbling regime could the magnetic field reduce the bubble size and improve fluidization quality. In the segregation-bubbling regimes, fluidization quality deteriorated as segregation developed. The segregation of the binary mixture was quantitatively studied by observing pressure drops in the local bed. Reasons for the improvement in fluidization quality as well as the occurrence of segregation were analyzed. Furthermore, the flow regime transition under magnetization-LAST operation mode was different from that under magnetization-FIRST mode. The magnetically stabilized bed (MSB) flow regime, which could be easily created under magnetization-FIRST mode, could no longer be achieved under magnetization-LAST mode. With the admixture, the MSB was proved to be a metastable equilibrium state. Under the magnetization-LAST mode, the admixture bed reached directly the stable equilibrium state—bubbling with segregation.     

Pore-structure-mediated hierarchical SAPO-34: Facile synthesis,tunable nanostructure,and catalysis applications for the conversion of dimethyl ether into olefins

Hierarchical cross-like SAPO-34 catalysts with different pore size distributions were obtained via hydrothermal synthesis with polyethylene glycol (PEG) as the mesopore-generating agent. The hierarchical SAPO-34 molecular sieves were characterized using X-ray diffraction, scanning electron microscopy, N₂ adsorption–desorption, thermogravimetric analysis, and temperature-programmed NH₃ desorption. The cross-like SAPO-34 catalysts exhibited enriched multi-porosity, and the sizes of their mesopores ranged from 10 to 50 nm. Both the mesoporous structures and morphologies of the hierarchical SAPO-34 could be further tuned through adjustments of the amount of PEG used. The as-obtained SAPO-34 showed dramatic catalytic performance in the conversion of dimethyl ether into olefins. A maximum selectivity of olefins of 96% was achieved, which was attributed to the rapid transport of the reactants and products in zeolitic micropores through mesopores.     

An overview of separation by magnetically stabilized beds： State-of-the-art and potential applications

This article deals with problems relevant to implementation of magnetically stabilized beds （MSB） as separation devices. The main issues discussed are： bed mechanics, bed structure, possibilities to create controllable filter media, etc. As examples several separation techniques are discussed： dust filtration-magnetic and non-magnetic, ion-exchange, copper cementation, yeast filtration from biological liquids, particle separation by density and magnetic properties, dangerous wastes removal. Only key publications will be quoted that provide a basis for further reading and study and relevant information.     

Mechanisms of nozzle type reactor operation with gas removal

A nozzle type reactor with provision for gas removal has been studied for the neutralisation of dodecylbenzene sulphonic acid with sodium carbonate solution. Gas was removed via a central air core so that the product was essentially foam-free. The rate of mixing and the chemical reaction between dodecylbenzene sulphonic acid and sodium carbonate solution, were observed to be much faster than the liquid residence time so complete conversion into the product was achieved within seconds. Some gas bubbles were entrained in the product: however these were negligible compared with the bulk of the gas bubbles expelled at the top of the reactor. The criteria for gas removal was that the time for bubbles to travel to the air core under the prevailing centripetal force was less than the liquid phase residence time in the reactor. Mathematical models were therefore proposed to predict the equilibrium bubble diameter and the time for bubble travel to the core. Predicted times were found to be very much less than the average residence time.     

A structured packed-bed reactor designed for exothermic hydrogenation of acetone

Fixed-bed reactors randomly packed with catalysts have many disadvantages that may adversely affect the desired chemical reaction. The increasingly used monolithic reactor, in contrast, has many operational advantages; however, for a kinetically-controlled reaction, it does not contain sufficient catalyst to sustain the reaction. To address the problems associated with both randomly packed-bed reactor and the monolithic reactor, a structured packed-bed reactor was proposed and mathematical models were built for randomly packed-bed reactor and structured packed-bed reactor. Their respective performances were compared when applied to the exothermic reaction of the isopropanol–acetone–hydrogen chemical heat pump system. The results showed that the structured packed-bed reactor performed better in terms of pressure drop and heat transfer capacity, and had a lower radial temperature gradient, indicating that this reactor had a higher effective heat conductivity. Isopropanol on the catalyst particle surfaces was more concentrated near the tube wall because a wall effect existed in the boundary layer around the particle-wall contact points.     

A structured packed-bed reactor designed for exothermic hydrogenation of acetone

Fixed-bed reactors randomly packed with catalysts have many disadvantages that may adversely affect the desired chemical reaction.The increasingly used monolithic reactor,in contrast,has many operational advantages;however,for a kinetically-controlled reaction,it does not contain sufficient catalyst to sustain the reaction.To address the problems associated with both randomly packed-bed reactor and the monolithic reactor,a structured packed-bed reactor was proposed and mathematical models were built for randomly packed-bed reactor and structured packed-bed reactor.Their respective performances were compared when applied to the exothermic reaction of the isopropanol-acetone-hydrogen chemical heat pump system.The results showed that the structured packed-bed reactor performed better in terms of pressure drop and heat transfer capacity,and had a lower radial temperature gradient,indicating that this reactor had a higher effective heat conductivity.Isopropanol on the catalyst particle surfaces was more concentrated near the tube wall because a wall effect existed in the boundary layer around the particle-wall contact points.     

CFD modeling using heterogeneous reaction kinetics for catalytic dehydrogenation syngas reactions in a fixed-bed reactor

A comprehensive 2D computational fluid dynamics （CFD） model was developed to simulate the flow behavior and catalytic dehydrogenation reaction of syngas in a heterogenous fixed-bed reactor （FBR）. The model combined the porous medium CFD model with a reaction kinetics model. To acquire an accu- rate reaction kinetics model, a comprehensive reaction mechanism was studied for the heterogeneous catalytic dehydrogenation reaction ofsyngas over a supported metal catalyst. Based on the reaction mech- anism and a statistical test, a reliable kinetics model was proposed. The CFD model combined with the above kinetics model was validated with one set of experimental data. The CFD model was also used to predict key reaction variable distributions such as the temperature and the component concentrations in the reactor.     

Operating conditions of an ideal-displacement reactor with recycle

The effect of recirculation on the operating conditions of a chemical reactor, a model of which was proposed earlier in [1], is discussed. The feasibility and efficiency of carrying out many chemical processes in systems with recirculation was demonstrated in [2]. An investigation has also been made of the stability of operating conditions for one simple model of a reactor with a recycle [3]. In [1], a mathematical model was proposed for an ideal-displacement chemical reactor, taking integral account of heat evolution, in which diffusional transfer is negligibly small in comparison with convective transfer, and the thermal conductivity is so great that the temperature inside the reactor can be assumed to be identical. An investigation was made of the question of steady-state conditions and their stability. Below, this question is discussed for the case where, in such a reactor, part of the stream passing through the reactor is again fed to its inlet. As in [1, 4], account is taken of the dependence of the viscosity of the mixture of reagents and the reaction products on the temperature.     

Numerical simulation of the flow field in a thermal plasma reactor

A numerical simulation is presented for a thermal plasma reactor with particle-trajectory model in this paper.Turbulance is considered by using simple SGS model.Thegoverning equations are solved by means of the algorithm of SIMPLER.The calculatedresults give the velocity and the temperature fields within plasma reactor,and thetrajectories of the injected particles.     

Thermal degradation of two liquid fuels and detonation tests for pulse detonation engine studies

The use of liquid fuels such as kerosene is of interest for the pulse detonation engine (PDE). Within this context, the aim of this work, which is a preliminary study, was to show the feasibility to initiate a detonation in air with liquid-fuel pyrolysis products, using energies and dimensions of test facility similars to those of PDEs. Therefore, two liquids fuels have been compared, JP10, which is a synthesis fuel generally used in the field of missile applications, and decane, which is one of the major components of standard kerosenes (F-34, Jet A1, ...). The thermal degradation of these fuels was studied with two pyrolysis processes, a batch reactor and a flow reactor. The temperatures varied from 600°C to 1,000°C and residence times for the batch reactor and the flow reactor were, respectively, between 10–30 s and 0.1–2 s. Subsequently, the detonability of synthetic gaseous mixtures, which was a schematisation of the decomposition state after the pyrolysis process, has been studied. The detonability study, regarding nitrogen dilution and equivalence ratio, was investigated in a 50 mm-diameter, 2.5 m-long detonation tube. These dimensions are compatible with applications in the aircraft industry and, more particularly, in PDEs. Therefore, JP10 and decane were compared to choose the best candidate for liquid-fuel PDE studies. This paper was based on work that was presented at the 20th International Colloquium on the Dynamics of Explosions and Reactive Systems, Montreal, Canada, July 31 – August 5, 2005.     

Thermomechanical instability in steady operating regime of continuous-flow chemical reactor with fixed catalyzer bed

A continuous-flow chemical reactor with fixed bed is a vessel filled with a porous catalyzer through which a liquid or gaseous reagent mixture is filtered. The motion of the mixture in this system is maintained by the pressure differential which compensates for the hydraulic resistance.The complete system of equations describing the mass-and heat-transfer processes in the continuous-flow chemical reactor includes the mass, momentum, and energy conservation equations [1], Usually, in the study of the existence and stability of steady reactor operating regimes, very simple reactor models are analyzed, in which only the mass-conservation equation in the form of the diffusion equation and the energy-conservation equation in the form of the heat-conduction equation are taken into account. The equation of motion drops out of consideration, since the velocity of the reagent mixture with the reaction products through the reactor is considered given and unvarying for disturbances of the steady operating regime.The purpose of the present study is to indicate the possibility of instability in the steady-process regime of a chemical reactor, which is associated with the fact that any temperature (and also concentration) variation within the reactor with disturbances of the steady regime will, generally speaking, lead to variation of the mixture viscosity and, consequently, to variation of the hydraulic resistance and the filtration velocity. This interconnection is an additional factor which may have a significant effect on the behavior of disturbances of the steady regime.In contrast with thermal, kinetic, and thermokinetic instability [2], it is natural to refer to the instability being investigated as thermomechanical instability. Let us consider an example.     

Microfluidic characteristics of a multi-holed baffle plate micro-reactor

As part of a larger project aiming at development of a miniaturized hydrogen generator for small mobile/onboard fuel cell applications, a series of experiments was conducted on a novel micro-reactor to examine the effectiveness of its design in promoting the mixing of reactant agents. The reactor is essentially a tubular vessel fitted with a multi-holed baffle plate mounted on a central tube. The mixing phenomenon within the micro-reactor was studied using the micro-PIV (micro-particle image velocimetry) flow visualization technique. Experiments were conducted on a 1:1 scale replica of the reactor. Results indicate that the application of the multi-holed baffle plate considerably improves the mixing performance of the reactor when compared with a simpler co-axial jet tubular reactor. However, the geometrical characteristics of the baffle plate and central tube are found to have dramatic impacts upon the flow structure and mixing patterns within the reactor. Hence, the optimization of the reactor geometry is required to achieve the desirable mixing performance. For the range of Reynolds numbers studied here, the optimum reactor geometry is achieved when the central tube and baffle holes are of similar diameters and baffle holes are located half way between the stream-wise axis and the reactor wall.     

Effects of vapor pressure on thermodynamic equilibrium in multiphase flow for thermochemical hydrogen production

This paper examines the effects of H₂O vapor pressure on the equilibrium conditions of a CuCl₂ hydrolysis reactor in the thermochemical Cu–Cl cycle of hydrogen production. A new predictive model is developed to determine the minimum steam requirement in the reactor based on the chemical equilibrium condition, reactor pressure and fraction of gaseous reactant. Experimental data, at three separate vapour pressures of steam, compared well with the new predictive formulation.     

秦山三期核电工程反应堆地段节理裂隙模拟

以秦山三期核电工程反应堆地段作为研究对象 ,针对节理裂隙在岩体中的分布具有随机性的特点 ,运用随机方法对其分布规律进行了研究。根据实测的节理裂隙产状、间距及迹线长度 ,推断节理裂隙概率分布特征。同时充分考虑到节理裂隙分布的不均匀性和方向性等特点 ,采用非平稳态随机过程模拟节理裂隙间距 ,通过 Monte- Carlo方法得到等效的节理裂隙网络。根据统计和拟合的结果 ,对反应堆地段岩体的节理裂隙进行了评价。     

Modeling and simulation of circulating fluidized bed reactors applied to a carbonation/calcination loop

A fluid dynamic model for a gas-solid circulating fluidized bed （CFB） designed using two coupled riser reactors is developed and implemented numerically with code programmed in Matlab. The fluid dynamic model contains heat and species mass balances to calculate temperatures and compositions for a carbonation/calcination loop process. Because of the high computational costs required to resolve the three-dimensional phenomena, a model representing a trade-offbetween computational time requirements and accuracy is developed. For dynamic processes with a solid flux between the two reactor units that depends on the fluid dynamics of both risers, a dynamic one-dimensional two-fluid model is sufficient. A two-fluid model using the constant particle viscosity closure for the stress term is used for the solid phase, and an algebraic turbulence model is applied to the gas phase. The numerical model implementa- tion is based on the finite volume method with a staggered grid scheme. The exchange of solids between the reactor units constituting the circulating fluidized bed （solid flux） is implemented through additional mass source/sink terms in the continuity equations of the two phases, For model validation, a relevant experimental analysis provided in the literature is reproduced by the numerical simulations, The numerical analysis indicates that sufficient heat integration between the two reactor units is important for the performance of the circulating fluidized bed system, The two-fluid model performs fairly well for this chemical process operated in a CFB designed as two coupled riser reactors. Further analysis and optimization of the solution algorithms and the reactor coupling strategy is warranted.     

Modeling of pyridine synthesis process in a coupled fluidized bed reactor

To obtain the optimal operating conditions of a coupled reactor for pyridine synthesis, reactor modeling process is carried out in this paper. During the modeling process, the flow hydrodynamics, heat transfer behavior, inter-phase mass transfer behavior and reaction kinetics were taken into consideration consequently. Further, a regression program based on least square method was proposed to regress the model parameters. The prediction results agreed well with the experimental results with an average deviation of 5.9%. Finally, by setting suitable aim function, the optimal operating conditions of the coupled reactor for pyridine synthesis were determined.     

Toughness and failure of heat resistant steel before and after hydrogenation

Fracture toughness of heat-resistant steel can be increased by a preliminary thermomechanical loading called warm pre-stressing (WPS). The procedure creates a plastic deformed area around the crack tip and hence allows larger service loads to be tolerated by the cracked specimen. It is shown that a hydrogenation in the preloading stage decreases the fracture toughness of material.Investigations are also presented of the applicability of physical and mechanical approaches for the prediction of cleavage stress of materials after preliminary plastic deformation (PPD) effects and hydrogenation. Different schemes of the plastic deformation and influence of hydrogenation are considered in the preloading stage to provide different levels cleavage stress of steel 15Kh2MFA.