Reactant Stream Research Articles

Development of Innovative Methanol Synthesis Process Based on Self-Heat Recuperation

In recent years, the demand for methanol will continue increasing. As well as other chemical processes, many methanol synthesis processes have reactant recycle system with product separation due to the low conversion ratio of the reactor. For this product separation from reactant recycle stream, a gas-liquid separator or distillation process has often been used. However, this gas-liquid separator and distillation processes are well known as an energy intensive process. Thus, many chemical engineers and investigators have been managing to produce a catalyst which achieves high conversion from reactant to production in the reactor for whole process optimization. In contrast, authors have developed self-heat recuperation technology based on exergy recuperation, in which whole process heat is utilized without any additional heat, leading to the reduction of energy requirement in several chemical processes. In this research, we developed an innovative integrated process design method based on self-heat recuperation for methanol synthesis process from energy saving point of view.

A MEMS-Based Catalytic Microreactor for a H$_{\bf 2}$O$_{\bf 2}$ Monopropellant Micropropulsion System

The next generation of miniaturized satellites (`nanosats') feature dramatically reduced thrust and impulse requirements for purposes of spacecraft attitude control and maneuvering. The present study is a joint computational and experimental design effort at developing a new MEMS-based microreactor configuration for incorporation into a monopropellant micropropulsion system. Numerical models of the gas phase catalytic decomposition in microchannel configurations are used to obtain critical sizing requirements for the reactor design. The computational results show that the length scales necessary for complete decomposition are compatible with MEMS-based designs; however, it is also found that the catalytic process is dominated by mass diffusion characteristics within the flow at this scale. Experimentally, a microscale catalytic reactor prototype has been designed and microfabricated using MEMS techniques. The reactor uses self-assembled ruthenium oxide nanorods grown on the wall surfaces as a catalyst. Experimental testing indicates that only partial decomposition of the hydrogen peroxide is achieved. Among the potential sources of the incomplete decomposition, a likely cause appears to be the inability of the H2O2 reactant stream to adequately wet the surface of the catalyst film composed of a high surface density of RuO2 nanorods.

Combustion performance of eccentrically rotated flames

Experimental/computational work highlighted the combustion performance with eccentric blockage rotation in the reactive flow passage to augment the turbulence production rates in the flame for acquiring high power to weight ratios and effective heat transfer in industrial applications. The temporal/spatial velocity gradients stimulated around the reactive stream boundaries enhanced the turbulence development in both premixed and non-premixed flames. The eccentric shapes included circular, elliptical, squared and triangular shafts as well as a triple/straight blade rotor. The design was further developed to incorporate simultaneous rotation of the eccentric blockage around its axis via a planetary gear assembly to duplicate the vortical structure. While the premixed flames responded to such cyclic action by having a mixture velocity of 16.8 m/s, the non-premixed flames acquired an increase of 341% in the largest eddy size and a flame length reduction by 42%. Increasing the Strouhal number to 0.94 and the swirl ratio to 0.78 increased the turbulent kinetic energy to 9.1 m2/s2. By controlling the drag coefficient and wake vorticity for the solid shapes, the triangular rotor enhanced the combustor outward heat flux to exhibit a heater efficiency of 36.8% in the premixed flame mode and reduced the HC and CO emissions, respectively, to 0.1% and 513 ppm for non-premixed flames. Decreasing the reactive stream cross-section favorably increased the flow shearing effects, while the elliptical shape showed the highest sensitivity to axes’ orientation with respect to the direction of rotation. Due to the reduction in peak temperatures via increasing the turbulence intensity and heat transfer rate from the flame, the NO x exhaust concentrations decreased to a minimum value around 10 ppm. The combustion efficiency of diffusion flames was optimized with the fuel port central positioning in the burner, where the planetary gear design provided a turbulence intensity of 13.7% by the triple blade rotor.

Modeling and inverting reactive stream tracers undergoing two-site sorption and decay in the hyporheic zone

[1] Performing stream-tracer experiments is an accepted technique to assess transport characteristics of streams undergoing hyporheic exchange. Recently, combining conservative and reactive tracers, in which the latter presumably undergoes degradation exclusively within the hyporheic zone, has been suggested to study in-stream transport, hyporheic exchange, and the metabolic activity of the hyporheic zone. The combined quantitative analysis to adequately describe such tests, however, has been missing. In this paper, we present mathematical methods to jointly analyze breakthrough curves of a conservative tracer (fluorescein), a linearly degrading tracer (resazurin), and its daughter compound (resorufin), which are synchronously introduced into the stream as pulses. In-stream transport is described by the one-dimensional advection-dispersion equation, amended with a convolution term to account for transient storage within the hyporheic zone over a distribution of travel times, transformation of the reactive tracer in the hyporheic zone, and two-site sorption of the parent and daughter compounds therein. We use a shape-free approach of describing the hyporheic travel-time distribution, overcoming the difficulty of identifying the best functional parameterization for transient storage. We discuss how this model can be fitted to the breakthrough curves of all three compounds and demonstrate the method by an application to a tracer test in the third-order stream Goldersbach in Southern Germany. The entire river water passes once through the hyporheic zone over a travel distance of about 200 m with mean hyporheic residence times ranging between 16 and 23 min. We also observed a secondary peak in the transfer functions at about 1 h indicating a second hyporheic flow path. We could jointly fit the breakthrough curves of all compounds in three monitoring stations and evaluated the parameter uncertainty of the individual and joint fits by a method based on conditional realizations of the hyporheic travel-time distribution. The approach gives insight into in-stream transport, hyporheic exchange, metabolic activity, and river-bed sorption of the stream under investigation.

PEMFC GDE Oxygen Mass Transport Coefficient Separation with Different Gas Diluents

A parametric current distribution model is proposed for the overall PEMFC reactant mass transfer coefficient determination. The model was derived for a dilute reactant stream and a low cell voltage (limiting current). Separation of the mass transfer coefficient into gas and ionomer phase components is achieved with similar current distribution measurements completed with different molecular mass diluents. An extrapolation to a diluent with zero molecular mass leads to the ionomer phase mass transfer coefficient. The gas phase mass transfer coefficient is subsequently calculated using an additive relationship between the overall mass transfer coefficient and its components (gas and ionomer phase coefficients). Experimental measurements demonstrate the validity of the current distribution model and emphasize the need to use dilute reactant streams to facilitate data treatment.

On-line fluorometry of multiple reactive and conservative tracers in streams

Performing tracer tests using artificial tracer compounds is a common practice to characterize natural streams regarding their (reactive) transport properties. Recently, the fluorescent compound resazurin was introduced as a reactive stream tracer to quantify hyporheic exchange and metabolic activity of streams. This tracer, together with its reaction product resorufin and a conservative tracer (in our case fluorescein), provides additional information about transport properties of the stream and its hyporheic zone and can therefore overcome restrictions that are commonly affiliated with the use of conservative tracers alone. However, all previously published studies using this tracer system were based on manual sampling of the water. This usually limits the number of measurements and thus the achievable temporal resolution, and potentially endangers data quality due to inadequate handling of samples. In this paper, a modified version of the GGUN-FL30 on-line fluorometer is presented in which the optics have been modified to allow measuring the concentrations of all three tracers simultaneously at intervals of 10 s. Experiments under controlled and natural conditions showed that the performance of the on-line fluorometer regarding tracer separation efficiency and practical detection limits is comparable to a high-performance laboratory spectrofluorometer. Furthermore, suggestions are given on how to correct tracer signal fluctuations caused by temporal changes in temperature and pH that might occur during a field tracer test.

The behaviour of laminar stratified methane/air flames in counterflow

Flames propagating through a mixture with a gradient of equivalence ratio have been previously demonstrated to travel faster or slower than their equivalent premixed flames. The present study aims to numerically investigate the response of strained laminar methane–air flames to such gradients. The flames are simulated in a counterflow configuration where a premixed reactant stream at equivalence ratio ϕR opposes a hot equilibrium stream at equivalence ratio ϕP. Premixed and stratified flames are compared with respect to the equivalence ratio ϕ* and the corresponding gradient ∇ϕ* at the point of peak heat release rate, for three strain rates, a=50, 300 and 500s−1 and a range of ϕ*. The effect of different stratification levels is also investigated by varying the ratio of ϕP to ϕR, Θ. Results indicate that, as long as flames stabilize within the diffusion layer and Θ>1, increased heat release rate Q is seen throughout the progress variable space in comparison to the premixed state. In contrast, an attenuation of heat release rate is seen for Θ<1. The enhancement (or attenuation) of heat release varies monotonically with Θ. The effect of stratification on flame behavior becomes more pronounced as the strain rate increases. The present study reveals the mechanisms for the propagation of quasi-steady stratified flames under lean and rich conditions: stratified flames are primarily dominated by the diffusion of heat under lean conditions, and diffusion of H2 under rich conditions. Thanks to species and thermal support, stratified flames continue to burn beyond the premixed lean and rich flammability limits. Further investigation on the unsteady response of flames to the fluctuating equivalence ratio implies that the steady results represent the unsteady response well, as long as ϕ* and ∇ϕ* are similar in both steady and unsteady cases.

Swirl and Cross-Flow Effects on Vitiated Jet Flames

A burner was developed to accommodate extensive limits of firing for lean and rich fuel/air mixtures via efficient vitiation of the reactive streams by a pilot premixed flame jet under swirl and cross-flow effects. The stability and combustion characteristics of the corresponding normal and inverse triple flames were addressed for vitiating a double-swirled flow through a concentric vane swirler by a pilot stream swirled due to a tangential entry. Increasing the vitiating stream heat input ratio to 0.5 increased the stability limit to eight times the laminar flame speed as the inner swirl number increased to 2.0. Increasing the cross-flow air momentum flux ratio from 1.0 to 3.0 further increased the normalized stability limit to 8.5, while employing double coswirl and triple coswirl increased such limit to respective values of 10.2 and 11.9. Vitiating a double-swirled rich fuel/air mixture stream by a tangential entry-swirled lean fuel/air mixture stream enlarged the stoichiometric zone to pronounce a peak turbulent kinetic energy of 3.5 m2/s2. Increasing the fuel mass fraction gradient increased the stability limit only with a vitiating lean mixture, while increasing the swirled portion of the vitiating stream increased the normalized stability limit to 19.6. Allocating the counterswirl across the vitiated stream was more efficient to increase the normalized stability limit to 26.7 as the relative swirl angle reached 120°. Increasing the cross-flow opposing jet strain rate enhanced the H and H2 preferential diffusion, increased the temperature homogeneity, and reduced the flame length. There was a corresponding reduction in NOx emissions to a minimum of 38 ppm as the strain rate increased to 13000 s−1, while the normalized stability limit increased to 27.3. Decreasing the longitudinal spacing between the cross-flow stages from 12.0 to 4.0 cm decreased the NOx emissions further to 18 ppm and increased the normalized stability limit to 30.5.

Characterization of Dispersion Effects on Reaction Optimization and Scale-Up for a Packed Bed Flow Hydrogenation Reactor

A well known advantage of flow chemistry reactors in chemical synthesis is the ability to screen multiple catalysts and reaction parameters with optimal conditions scaled accordingly. This approach, however, consumes significant quantities of material as the reactor must be equilibrated with the reactants in a continuous, steady-state mode before the start of the reaction. In this work we explore a screening and reaction approach using bolus injections, which is more conducive to the lower material consumption that may be required in a drug discovery setting. A commercially available ThalesNano H-Cube® was evaluated to determine the practicality of this approach for heterogeneous hydrogenations. When working with boluses in flow systems, one of the biggest limitations can be the inherent dispersion of the reactant stream caused by the reactor. The dispersion on the H-Cube® was characterized to determine the minimum volume for the reactor to reach a steady-state. The H-Cube® fluidics and heating coil were found to generate significantly more dispersion than the reaction cartridge (CatCart®) itself, increasing the minimum volume of injection required to achieve steady-state. A 2 mL injection was found as a good compromise between maximizing material conservation and sufficient volume of reaction at steady-state condition. Conditions optimized at 2 mL screening scale were successfully scaled five-fold, while lower volume bolus injections were shown to be less predictable. A stacked injection protocol using lower volume boluses was found to be a reliable alternative to scale reactions while efficiently conserving material. This application of small bolus injections to flow reaction screening and scale-up provides a desirable alternative to traditional continuous flow approaches in the material-limited discovery setting.

Scaling the flame transfer function of confined premixed conical flames

The influence of confinement side walls on the response of premixed conical flames submitted to velocity disturbances is investigated experimentally and theoretically. When the flame is sufficiently confined, the burnt gases cannot fully expand at the nozzle outlet. In that case, the confinement ratio Cr=R0/R1 between the burner and flame tube radii and the burnt to unburnt gas volume expansion ratio E=ρu/ρb need to be taken into account in the description of the flame transfer function (FTF). The main effect of confinement is an acceleration of the fresh stream of reactants induced by the over-pressure of the confined burnt gases. Experiments on steady flames reveal that the flame height increases for increasing confinement ratios Cr, leading to a gain shift and a phase drop for the FTF. A theoretical analysis is conducted to model this acceleration and examine its impact on the steady flame shape and flame response to flow disturbances. The change in the FTF phase is shown to be related to a reduction of the mean time lag between heat release rate perturbations and velocity modulations induced by both the velocity acceleration in the fresh reactants and a change in the location of the steady flame front. An expression to scale the FTF of confined flames is derived based on a modification of the classical reduced frequency ω∗ used to scale the response of unconfined flames. This expression includes explicitly the confinement ratio Cr and the volume expansion ratio E. This new dimensionless number enables to plot FTF measured for different confinements with reasonable collapse. It may also be used to transpose FTF gathered on single burners to multiple injection configurations when the burnt gases cannot fully expand due to the presence of neighboring flames.

Design of a Numerical Microcombustor for Diffusion Flames

This article focuses on the development of a numerical microcombustor capable of stabilizing a diffusion flame of methane. Different designs are tested with the objective of optimizing mixing of the methane and air streams. Stability of the flame is then ensured by increasing the temperature of the incoming streams of reactants and changing the internal conductivity of the combustor material with and without allowing heat transfer to the surrounding. Two-dimensional (2D) as well as three-dimensional (3D) computations of the microreactor are presented using detailed chemical kinetics. It was found that the optimal design that ensures adequate mixing requires the presence of a restriction at the inlet of the combustion chamber forcing the incoming streams to converge while introducing minor pressure drop. A flame could not be sustained in an adiabatic microreactor for mixtures entering at ambient temperature (27°C), but stability was achieved at inlet temperatures of 100°C and 300°C. When heat is allowed to transfer from the products to the reactants, while keeping the microburner externally adiabatic, stronger and more stable flames were observed within the domain and the strength of the flame increases with decreasing the thermal conductivity of the walls. Calculations in 3D were carried out on a scaled-up version of the domain to demonstrate the effects of thermal conductivity and gap size (distance between the two plates that constrain the burner). Such calculations provide useful information that assist in the construction of a physical microreactor.

Play2: A New Era of Web Application Development

Today's Web evolutions and the emergence of software as a service and Web services have led to new challenges in programming: distribution, scalability, management of various data formats, stream management, and so on. A Web framework that considers these issues can significantly aid developers in capitalizing on the opportunities the Web offers while minimizing potential risks. The open source Play2 framework does just that by leveraging the strengths of functional programming. This article outlines functional programming's power in this context at several levels: data and data format manipulation using higher-order functions; reactive composition with nonblocking IO for scalability; and reactive stream processing and manipulation using Iteratees with WebSockets and Server-Sent Events.

A comprehensive study on wastewater treatment using photo-impinging streams reactor: Continuous treatment

The degradation of phenol was investigated in a continuous flow impinging streams system. In the first step, statistical experimental designs were used to optimize the process of phenol degradation in a photo-impinging streams reactor. The more important factors affecting phenol degradation (p<0.05) were screened by a two-level Plackett-Burman design. Four of the latter parameters, namely phenol concentration, catalyst loading, pH and slurry flow rate, were selected for final process optimization, applying central composite design (CCD). The predicted data showed that the maximum removal efficiency of phenol (99%) could be obtained under the optimum operating conditions (phenol concentration=50 mg l−1, catalyst loading=2.1 g l−1, pH 6.2 and slurry flow rate=550ml min−1). These predicted values were then verified by certain validating experiments. A good correlation was observed between the predicted data and those determined by the experimental study. This may confirm the validity of the statistical optimum strategy. Finally, continuous degradation of phenol was performed, and the results indicated a higher efficiency and an increased performance capability of the present reactor in comparison with the conventional processes.

Characteristics of Coal Liquefaction in an Impinging Stream Reactor

Liquefaction of coal is studied in a laboratory-scale impinging stream reactor. The effects of the temperature (430–520 °C), solvent/coal ratio (1–5), slurry/gas flow ratio (0.5–0.9), and nozzle distance (12–4 cm) on coal total conversion and product distribution are investigated. To determine the role of hydrogen gas, reactions are also carried out under a nitrogen gas atmosphere at the same reaction conditions. On the basis of the above studies, the determining step of coal liquefaction is the gas/liquid mass-transfer step. The use of this reactor system reduces the impact of slow diffusion of gas into the reaction medium. Hence, rather high conversion (80.21 wt %) is achieved.

Large-Eddy Simulation of a Jet-in-Hot-Coflow Burner Operating in the Oxygen-Diluted Combustion Regime

Large-eddy simulations of moderate and intense low-oxygen dilution (MILD) combustion of a jet-in-hot-coflow (JHC) burner are performed. This burner configuration consists of three streams, providing fuel, oxygen-diluted coflow, and air to the burner. To account for the mixing between the three reactant streams, a three-stream flamelet/progress variable (FPV) formulation is utilized. This model was previously applied to a condition corresponding to the upper range of MILD-combustion, and the objective of this contribution is to further investigate this model in application to highly diluted operating conditions. Comparisons of mean and conditional results show that the model accurately captures effects of increasing oxygen-depletion on the flame-structure and heat-release, and predictions for temperature and species mass fractions are in overall good agreement with experiments.

Modeling and Simulation of Hydrocracking of Fischer–Tropsch Hydrocarbons in a Catalytic Microchannel Reactor

Product quality of Fischer–Tropsch synthesis is improved by catalytic hydrocracking which converts heavy hydrocarbon fractions (wax) to commercially valuable fuels. The process is highly exothermic and requires strict temperature control; high temperatures cause overcracking to lower, commercially undesired hydrocarbons, whereas low temperatures reduce the conversions. Running hydrocracking in microchannel reactors is promising, since submillimeter dimensions lead to significant compaction that favors robust temperature control. This work investigates modeling and simulation of hydrocracking in a heat-exchange-integrated microchannel reactor involving parallel groups of square-shaped cooling and catalyst-coated reaction channels. Effects of material type and thickness of the wall separating the channels, and operating parameters (reactant and coolant feed temperatures and space velocity of the reactant stream) on reaction temperature and product distribution are investigated. Mole fractions of the product...

Kinetics of thermal decomposition of lanthanum oxalate hydrate

Lanthanum oxalate hydrate La2(C2O4)3·10H2O, the precursor of La2O3 ultrafine powders, was prepared by impinging stream reactor method with PEG 20000 as surfactant. Thermal decomposition of La2(C2O4)3·10H2O from room temperature to 900 °C was investigated and intermediates and final solid products were characterized by FTIR and DSC-TG. Results show that the thermal decomposition process consists of five consecutive stage reactions. Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) methods were implemented for the calculation of energy of activation (E), and the results show that E depends on α, demonstrating that the decomposition reaction process of the lanthanum oxalate is of a complex kinetic mechanism. The most probable mechanistic function, G(α)=[1−(1+α)1/3]2, and the kinetic parameters were obtained by multivariate non-linear regression analysis method. The average E-value that is compatible with the kinetic model is close to value which was obtained by FWO and KAS methods. The fitting curve matches the original TG curve very well.

Systematic studies of the gas humidification effects on spatial PEMFC performance distributions

a b s t r a c t The overall current density that is measured in a proton exchange membrane fuel cell (PEMFC) represents the average of the local reaction rates. The overall and local PEMFC performances are determined by several primary loss mechanisms, namely activation, ohmic, and mass transfer. Spatial performance and loss variabilities are significant and depend on the cell design and operating conditions. A segmented cell system was used to quantify different loss distributions along the gas channel to understand the effects of gas humidification. A reduction in the reactant stream humidification decreased cell performance and resulted in non-uniform distributions of overpotentials and performance along the flow field. Activation and ohmic overpotentials increased with a relative humidity decrease due to insufficient membrane and catalyst layer hydration. The relative humidity of the cathode had a strong impact on the mass transfer overpotential due to a lower oxygen permeability through the dry Nafion film covering the catalyst surface. The mass transfer loss distribution was non-uniform, and the mass transfer overpotential increased for the outlet segments due to the oxygen consumption at the inlet segments, which reduced the oxygen concentration downstream, and a progressive water accumulation from upstream segments. Electrochemical impedance spectroscopy (EIS) and an equivalent electric circuit (EEC) facilitated the analysis and interpretation of the segmented cell data.

Comprehensive Study on Wastewater Treatment Using Photo-Impinging Streams Reactor: Residence Time Distribution and Reactor Modeling

A photo impinging streams reactor was employed to study the degradation of phenol in aqueous solutions applying titanium dioxide nanoparticles as the reaction catalyst. The central composite experimental design method was applied to determine the pertinent operating parameters of such a process. These were phenol concentration, catalyst loading, pH of the slurry, and the feed flow rate. Residence time distribution (RTD) of the slurry phase within the reactor was measured using the impulse tracer method. A compartment model consisting of a number of mixed and plug flow regions was assigned to describe the flow pattern in the reactor. On the basis of such an arrangement and applying the Markov chains discrete time formulation, a three parameters model was derived for the RTD. The parameters of the theoretical RTD model were evaluated by comparing the latter with those determined experimentally. The RTD expression was applied in conjunction with the phenol degradation kinetic model to predict the apparent ra...

천연가스의 수증기-이산화탄소 복합개질을 위한 충진층 관형반응기의 전산모사

Abstract >> A 2-dimensional heterogeneous reactor model was developed and simulated for a tube reactorof packed bed where the steam-CO 2 combined reforming reaction of natural gas proceeded to produce synthesis gas. Under the reactor feeding rate, 45 Nm 3 /h, of the reactant gas stream, the 2-dimensional heterogeneous reactor model showed the similar results to those from the ASPEN simulator although there were some discrepancies between the two in the temperature and the H 2 /CO ratio of the reformed gas atthe reactor exit. The calculated enthalpy difference between the reformed gas at the reactor exit and the reactant gas fed to the reactor was closely correspondent to the total amount of heat transferred to the reactorinterior from the furnace. This supports that the 2-dimensional heterogeneous reactor model was reasonablyestablished and the numerical solution was properly obtained. Key words : Simulation(모사), Methane(메탄), Steam-CO 2 reforming(수증기-이산화탄소 개질), Synthesis gas(합성가스), 2-dimensional heterogeneous reactor model(2-차원 비균일 반응기 모델)