Identification of Various Transition Velocities in a Bubble Column Based on Kolmogorov Entropy

The Kolmogorov entropy (KE) algorithm was applied successfully to gas holdup fluctuations measured in a 0.102 m I.D. stainless steel bubble column equipped with a perforated plate distributor (19 holes ?? 1 mm). Nitrogen was used as the gas, while both 1‐butanol and gasoline were used as liquids. 1‐Butanol was aerated at pressures, P = 0.1 and 0.5 MPa, whereas gasoline was aerated at P = 0.1 and 0.2 MPa. Based on the peaks in the KE values under the pressures examined in both liquids, the boundaries of the following five regimes were identified: bubbly flow, first transition, second transition, coalesced bubble (4‐region flow) and coalesced bubble (3‐region flow). As the pressure increases to P = 0.5 MPa in 1‐butanol, all four transition velocities shift to higher superficial gas velocity, u_G. In addition, in gasoline at P = 0.2 MPa and u_G ≤ 0.017 m s^–1, the existence of a chain bubbling regime was detected, whereas in 1‐butanol at P = 0.5 MPa and u_G ≤ 0.02 m s^–1, both laminar and turbulent chain bubbling subregimes were identified. It was found that in 1‐butanol under ambient pressure, the second and fourth transition velocities occur earlier than in gasoline.     

Simulation Analysis of a GTL Process Using Aspen Plus

Gas‐to‐liquid (GTL) processes are becoming attractive due to the increasing price of crude oil. Process simulation analysis on the integrated GTL process is essential as part of an extended process integration analysis of the research subjects. The two sub‐process models for the GTL process, i.e., the syngas generation process and the Fischer Tropsch synthesis (FTS) process, are analyzed in detail with ASPEN Plus. The autothermal reforming process (ATR) is analyzed using Aspen Plus based on the Gibbs reactor model, while FTS is simulated with ASPEN Plus based on detailed kinetic models for industrial iron and cobalt catalysts. Integrated GTL processes with iron and cobalt‐based catalysts were simulated using ASPEN Plus. The optimal flowsheet structures were selected for each catalyst based on the overall performance in terms of thermal and carbon efficiency and product distributions. For the cobalt‐based catalyst, the full conversion concept without CO₂ removal from the FT tail gas is optimal. On the other hand, the once‐through concept with two series reactors and CO₂ removal from raw syngas is considered optimal for the iron‐based catalyst. The thermal efficiency to crude products is likely to be ca. 60 % for the cobalt‐based catalyst, whereas it is in the range of 49–55 % for the iron‐based catalyst. The carbon efficiency using the water‐gas shift reaction is lower using the iron‐based catalyst (61–68 %) than the cobalt‐based catalyst (73–75 %). As expected, the cobalt‐based catalyst is more active and selective, which offers better selectivity towards C₅+ (75–79 %). The selectivity towards C₅+ for the iron‐based catalyst lies in the range 63–75 %.     

Regional Mean Bubble Diameters and Gas Holdup in Agitated Gas‐Liquid Contactors

Gas‐liquid contacting in mechanically agitated vessels is widely used in the process industry. Bubble size measurements at different flow regions in the vessel provide useful information for the mechanisms of gas dispersion and gas‐liquid flow. In this work, bubble size distributions and distributions of Sauter mean bubble diameters at four different regions in air‐water and air‐NaCl solution systems agitated by a six‐blade disk turbine are measured by using the photographic method. The effects of gassing rate, impeller speed and electrolyte presence in the system have been examined.     

Synthesis Gas Production Configurations for Gas‐to‐Liquid Applications

Different syngas configurations in a gas‐to‐liquid plant are studied including autothermal reformer (ATR), combined reformer, and series arrangement of gas‐heated reformer and ATR. The Fischer‐Tropsch (FT) reactor is based on a cobalt catalyst and the degrees of freedom are steam‐to‐carbon ratio, purge ratio of light ends, amount of tail gas recycled to synthesis gas (syngas) and FT synthesis units, and reactor volume. The production rate of liquid hydrocarbons is maximized for each syngas configuration. Installing a steam methane reformer in front of an ATR will reduce the total oxygen consumption per barrel of product by 40 % compared to the process with only an ATR. The production rate of liquid hydrocarbons is increased by 25.3 % since the flow rate of the purge stream for the ATR is the highest one compared to other configurations and contains mainly CO₂.     

Microwave‐Assisted Heterogeneous Gas‐Phase Catalysis

This article reviews microwave‐assisted heterogeneous gas‐phase catalysis. To date, this special means of non‐classical energy input by microwave radiation is still a fringe area of catalysis research, and alternative reaction engineering in chemistry and chemical engineering. However, microwave‐assisted heterogeneous gas‐phase catalysis is expected to gain significant popularity in academia and industry in the near future. Experimental set‐ups that have been described in literature are critically reviewed, and concepts for the design of improved experimental set‐ups are provided in this article. Historical developments, current tendencies, and a short introduction to the theory of dielectric heating are discussed.     

Simulating the Rise Characteristics of Gas Bubbles in Liquids Using CFD

With the advent of modern tools of computational fluid dynamics (CFD), it is now possible to obtain detailed information on the bubble shape, morphology and rise characteristics from knowledge of system properties and geometry. In this paper we try to give a flavor of the power of CFD tools and summarize recent advances.     

Further Studies of the Gas Penetration Process in Gas‐Assisted Injection Molding

Abstract

Gas‐assisted injection molding is one of the innovation injection‐molding processes recently developed. The solution of gas penetration thickness interface is the key problem in the simulation of gas‐assisted injection molding, but also the puzzle. By applying the matching asymptotic expansion method, an analytical solution of the gas penetration interface is deduced. First, the governing equations and boundary conditions are transformed to be dimensionless. And then matching asymptotic expansion method is applied to solve the dimensionless equations, where capillary number Ca and Ca ^2/3 are used as perturbation parameters. Compared with experimental results, the presented mathematical model and solving method are proved to be correct.     

Correlation and Prediction of Carbon Dioxide Solubility in n‐Paraffin Systems

This work discusses high‐pressure gas solubility. Reference state is the Henry's law and a two‐parameter corresponding states model is used for the liquid phase. Pure gas is used as the vapor phase for the high‐molecular paraffin's gas‐liquid equilibrium. The systems under study are mixtures of carbon dioxide and normal paraffin up to a chain length of 44 carbon atoms. Correlated liquid compositions are in the 1 % to 3 % average absolute relative deviation range, with a maximum error of about 7 %. Using a known system as reference, the model could be used to predict solubility. In this case average absolute relative deviations are below 6 % in most cases.     

Power Consumption in Dual Impeller Gas‐Liquid Contactors: Impeller Spacing,Gas Flow Rate,and Viscosity Effects

The dependence of power consumption on impeller spacing, and also in relation to gas flow rate and viscosity, in unaerated and aerated gas‐liquid contactors agitated by dual Rushton‐ and by dual pitched blade turbines was comparatively studied. In tap water the two Rushton impellers acted independently for spacings greater than ΔH = 1.65d, while in glycerol solutions the impellers acted independently on reaching an impeller spacing equal to 1.20d; the corresponding values for the two pitched blade impellers were 1.50d for tap water, 1.07d for relatively high viscosities, and 0.53d for very high viscosity values. The Newton number Ne decreases with increasing viscosity for the dual Rushton turbine systems, while an increase of Ne can be observed with increasing viscosity for the corresponding pitched blade systems. For the dual Rushton turbines, gas flow number Q has no effect on Ne, at very high values of viscosity, while at low and relatively high viscosity values a small effect of Q on Ne can be detected. As observed for the dual Rushton turbine systems, Ne is also not affected by Q for the corresponding pitched blade systems at very high viscosity values. Flow number Q does not significantly affect the Newton number for the water‐glycerol solutions with a relatively high viscosity agitated by dual pitched blade turbines, while for the aerated water systems a decrease of Ne can be observed at relatively small gas flow numbers; high values of Q do not affect the Newton number.     

Design and Numerical Simulation Analysis of an Integrative Gas‐Liquid‐Solid Separation Hydrocyclone

Normally, a gas‐liquid‐solid separation includes both degassing and desanding processes, which means a relatively higher facility investment and larger energy consumption. Based on an inner‐cone hydrocyclone developed before, an integrative degassing and desanding hydrocyclone was designed. Its design idea and process are described in detail. By means of a hollow inner cone (IC), the separated liquid enters into the cone through holes on it and then flows to the liquid‐phase outlet. Due to integrative separation and tangential solid outlet, the separator has a more compact size. Simulation analysis of the effect of IC diameter and IC height on separation performance was carried out. Results indicate that with a larger IC diameter the gas content in the solid outlet decreases, while as the IC height rises, the gas content in the liquid outlet increases.     

Optimal Design of a Gas‐to‐Liquids Process with a Staged Fischer‐Tropsch Reactor

The optimal design of a natural gas‐to‐liquid hydrocarbons (GTL) process with a multistage cobalt‐based Fischer‐Tropsch reactor and interstage product separation is considered. The objective function is to maximize the wax (C₂₁₊) production rate at the end of the reactor path. Sectioning of the Fischer‐Tropsch reactor increases the chain growth probability inside the reactor which results in a higher production of wax. The carbon efficiency of the two‐stage reactor is distinctly higher than that of the single‐stage reactor.     

Drying Kinetics in a Vertical Gas‐Solid System

A one‐dimensional steady‐state two‐fluid model has been developed to demonstrate the drying kinetics in the vertical up‐flow gas‐solid system. The model takes into account mass, momentum, and heat transfer between the continuous and dispersed phases. A set of non‐linear differential equations have been solved numerically for the velocity, moisture content, and temperature of both the continuous and dispersed phases along the dryer length. The effect of operating parameters on drying kinetics has been critically examined and the model simulations are compared with the data reported in the literature.     

Effect of Plate Oscillation on Bubble Residence Time in an Aerated Stagnant Liquid

Gas transfer efficiency during absorption is an important factor in various technological processes involving the interaction between liquid and gaseous systems. It is known that gas bubble motion characteristics strongly affect the efficiency of mass transfer during gas absorption. A device for mechanical vibration of an aerated liquid was designed, based on a cylindrical column filled up with tab water and a plate oscillating in the vertical direction. The goal of the present study is to investigate the effect of vibration parameters such as amplitude, frequency and form of the applied signal on the efficiency of the oxygenation process. Bubble residence time in the liquid and bubble depth of submergence related to the oscillating plate surface were chosen as main parameters for measurements. Furthermore, experiments were conducted to study the effect of the design parameters of the vibrating plate on bubble motion characteristics. The resultant data show that bubble residence time and depth of submergence can be controlled by changing the amplitude, the frequency and the form of the vibration field applied.     

Liquid Oxygenation Improvement by Interaction of Bubbles and Vibration Fields

Gas bubble motion characteristics and bubble size are important factors in various technological processes involving the interaction between liquid and gaseous systems. The present work studies the effect of vibration fields on the characteristics of bubble motion and bubble size. Bubble retention time in the liquid (rise velocity) and bubble mean diameter were chosen as main parameters effecting the oxygen mass transfer rate. A device for mechanical vibration of the aerated liquid was used. The influence of the device design parameters on the chosen bubble parameters is studied experimentally and discussed in this work. The results obtained show the possibility of controlling bubble retention time and bubble size by employing vibration fields. Thus, by applying rather simple techniques, one can considerably improve the process of liquid oxygenation.     

Optical Probes for Multiphase Flow Characterization: Some Recent Improvements

Concentration, velocity, size and interfacial area density are key parameters in the design of multiphase processes involving bubbles or droplets. Optical probes provide a relatively simple and cheap mean to measure these quantities. In this paper, recent advances in probe design and signal processing are summarized, and the performances of these systems are discussed. Finally, various applications are presented and known limitations of the technique are underlined.     

Chemische Speicherung regenerativer elektrischer Energie durch Methanisierung von Prozessgasen aus der Stahlindustrie

The increasing importance of renewable energy necessitates the adjustment of demand and supply, which can be achieved by chemical energy storage based on methane. Besides hydrogen this option also requires a carbon source. In the present contribution we suggest process gases from the steel industry for that purpose, since they occur in reasonable amounts. We critically discuss the suitability based on the degree of efficiency and quality of the product gases. It will be shown that process gases from the steel industry are an interesting feedstock for chemical storage of renewable energy.     

Reactor Modeling of Gas‐Phase Polymerization of Ethylene

A model is developed for evaluating the performance of industrial‐scale gas‐phase polyethylene production reactors. This model is able to predict the properties of the produced polymer for both linear low‐density and high‐density polyethylene grades. A pseudo‐homogeneous state was assumed in the fluidized bed reactor based on negligible heat and mass transfer resistances between the bubble and emulsion phases. The nonideal flow pattern in the fluidized bed reactor was described by the tanks‐in‐series model based on the information obtained in the literature. The kinetic model used in this work allows to predict the properties of the produced polymer. The presented model was compared with the actual data in terms of melt index and density and it was shown that there is a good agreement between the actual and calculated properties of the polymer. New correlations were developed to predict the melt index and density of polyethylene based on the operating conditions of the reactor and composition of the reactants in feed.