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.     

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.     

Enriched Air or Pure Oxygen as Oxidant for Gas‐to‐Liquid Process with Microchannel Reactors

The syngas production step is one of the most costly steps in a gas‐to‐liquid plant. Commonly, oxygen is used as an oxidant in the reforming step. However, through the introduction of microchannel reactors, the use of enriched air may be justified. The merits of using enriched air versus pure oxygen are analyzed by utilizing an autothermal reformer, with microchannel reactors in the once‐through Fischer‐Tropsch (FT) step. Pure oxygen is provided by a cryogenic air separation unit (ASU) and enriched air by use of air separation membranes. Pure oxygen requires a smaller FT reactor volume, which means lower reactor costs at the expense of having a costly cryogenic ASU to produce pure oxygen. The operating cost of the ASU is lower than that of the air membrane, but the installed cost is higher.     

Mid‐Infrared Monitoring of Gas‐Liquid Reactions in Vitamin D Analogue Synthesis with a Novel Fiber Optical Diamond ATR Sensor

A novel mid‐infrared optical sensor enabling in situ ATR measurements was applied to investigate several steps of a vitamin D analogue synthesis. The probe based on silver halide fibers coupled to a diamond prism was connected to a conventional FTIR spectrometer with internal MCT detector. All steps of the reaction were monitored by real‐time in situ FTIR measurements. The steps carried out were the dissolution of SO₂ in a CH₂Cl₂/CH₃OH solvent mixture as well as the addition of SO₂ to a vitamin D analogue, the subsequent ozonation of the double bond in the SO₂ addition product, and the following reduction of the formed hydroperoxide with triphenylphosphine. The dissolving process of SO₂ and the addition of SO₂ to the vitamin D analogue were monitored by changing the characteristic ν_as(SO₂) and ν_s(SO₂) modes of dissolved and incorporated SO₂. It was found that during ozonation of the SO₂ addition product the formation of hydroperoxide is accompanied by the simultaneous formation of the corresponding aldehyde identified by the typical ν(C=O) band at 1720 cm^–1. Extended ozone exposure favors the formation of the corresponding acid detected by an additional carbonyl band at lower wavenumbers. During the reaction with triphenylphosphine the increasing intensity of the aldehyde band and the appearance of the ν(P=O) mode of the formed triphenylphosphine oxide indicate the progressive reduction of hydroperoxide. The hydroperoxide band disappears completely during the reaction whereas the ν_as(SO₂) band remains unaffected.     

Numerical Simulation of the Two‐Phase Fluid Field in a Gas‐Around‐Liquid Spray Nozzle

A new gas‐around‐liquid spray nozzle (GLSN) was designed, and the two‐phase flow fluid field in this nozzle was simulated numerically. Flow characteristics under different structural parameters were obtained by changing the L/D ratio of the premixing chamber, incident angle, and inlet pressures. Increasing the L/D ratio and incident angle improved flow characteristics such as atomization flow, outlet velocity, and turbulence intensity. The nozzle performed optimally at an L/D ratio of 0.5 and incident angle of 60°. The atomization flow decreased with higher gas pressure and increased with higher liquid pressure. The outlet velocity mainly depended on the inlet gas pressure, not on the inlet liquid pressure. These results provide an indication for optimum structures and parameters of the GLSN.     

Gas‐Liquid Mass Transfer in Fibrous Bed Reactor with Counter‐Current Liquid Recycle

In this work, the gas‐liquid mass transfer in a lab‐scale fibrous bed reactor with liquid recycle was studied. The volumetric gas‐liquid mass transfer coefficient, k_La, is determined over a range of the superficial liquid velocity (0.0042–0.0126 m.s^–1), gas velocity (0.006–0.021 m.s^–1), surface tension (35–72 mN/m), and viscosity (1–6 mPa.s). Increasing fluid velocities and viscosity, and decreasing interfacial tension, the volumetric oxygen transfer coefficient increased. In contrast to the case of co‐current flow, the effect of gas superficial velocity was found to be more significant than the liquid superficial velocity. This behavior is explained by variation of the coalescing gas fraction and the reduction in bubble size. A correlation for k_La is proposed. The predicted values deviate within ± 15 % from the experimental values, thus, implying that the equation can be used to predict gas‐liquid mass transfer rates in fibrous bed recycle bioreactors.     

Gas‐Liquid Mass Transfer Characteristics in a Rotating‐Drum Bioreactor

The oxygen volumetric mass transfer coefficient is a key parameter to characterize the performance of aerobic bioreactors. A novel rotating‐drum bioreactor (RDB) fitted with a sparger as proposed in a previous work has demonstrated its excellent gas‐liquid mass transfer performance. To provide primary information on the design and scale‐up of the novel RDB, effects of reactor configuration including the number and width of lifters and operation conditions such as rotational speed, aeration rate, and solid volume fraction on mass transfer performance were systematically investigated in a new medium‐sized RDB. Compared with the stirred bioreactor and traditional RDBs, this new RDB exhibits better mass transfer performance. Taking both operational and reactor configuration parameters into consideration, an empirical correlation to predict the volumetric mass transfer coefficient in this type of RDBs was proposed which is valuable for its design and scale‐up.     

Gas‐Liquid Mass Transfer in Pulp Retention Towers

The volumetric gas‐liquid mass transfer rate, k_La, was measured under batch conditions in a 0.28 m diameter laboratory‐scale retention column. Tests on water, and on unbleached kraft (UBK) pulp suspensions (mass fractions, C_m from 0.013 to 0.09) were made with air or nitrogen sparged through the column at superficial gas velocities between 0.0015 to 0.05 m/s. k_La varied with suspension mass concentration and superficial gas velocity, initially decreasing with increasing mass concentration, reaching a minimum between C_m = 0.03 and 0.06, and then increasing. The minimum in k_La coincided with a change in hydrodynamics within the column, from bubble column behaviour below C_m = 0.03 to porous solid behaviour above C_m = 0.06.     

Gas‐Liquid Mass Transfer Rates and Impeller Power Consumptions for Industrial Vessel Design

Volumetric mass transfer coefficients (k_La) and power input (P) are often the key parameters in the design of gas‐liquid contactors. However, due to the limitations of most measurement methods, there is a lack of reliable data for predicting k_La for non‐coalescent batches under high energy dissipation rates. Accurate k_La and P correlations are proposed. The reliability of the correlations is ensured by using experimental data from a wide range of process conditions conducted in multiple‐impeller vessels of both laboratory scale and pilot scale, and including both non‐coalescent and coalescent batches. Applying the proposed correlations, the scale‐up and optimization of industrial vessels can be performed more accurately.     

High‐Pressure High‐Temperature Transparent Fixed‐Bed Reactor for Operando Gas‐Liquid Reaction Follow‐up

A 3‐MPa, 350 °C fixed‐bed reactor was designed to follow‐up gas‐liquid‐solid reactions on a millimetric size heterogeneous catalyst with Raman spectroscopy. The transparent reactor is a quartz cylinder enclosed in a Joule effect heated stainless‐steel tube. A methodology to determine how to focus the microscope for liquid and solid phase characterization is presented. The setup was validated by performing diesel hydrodesulfurization on a CoMo/alumina extrudate catalyst with a conversion very close to expected values along with the acquisition of Raman spectra of the solid catalyst showing an evolution of the catalyst phase during sulfidation.     

Modeling of Slug Velocity and Pressure Drop in Gas‐Liquid‐Liquid Slug Flow

Gas‐liquid‐liquid slug flow in a capillary reactor is a promising new concept that allows one to incorporate gas‐liquid reaction, liquid‐liquid extraction, and facile catalyst separation in a single unit. In order to assess the performance of a gas‐liquid‐liquid slug flow reactor, it is necessary to predict the slug velocity and pressure drop to ascertain residence times and reaction rates. New empirical models for velocity and pressure drop were developed based on existing models for two‐phase gas‐liquid and liquid‐liquid slug flows, and these were validated experimentally.     

Efficient Gas‐Liquid Cyclone Device for Recycled Hydrogen in a Hydrogenation Unit

An efficient cyclone device for removing hydrocarbon fog droplets in recycled hydrogen was developed based on experimental studies and industrial application. Conditions for optimal separation efficiency of the gas‐liquid cyclone were determined. The device reduced raw material losses and desulfurizer consumption and improved desulfurization efficiency, thereby increasing the purity of the cycled hydrogen and decreasing the mean molecular weight of gas. Energy consumption of the cycled hydrogen compressor as well as the pollution discharge of the hydrogenation unit were also diminished.     

Liquid Flow Visualization in Packed‐Bed Multiphase Reactors: Wire‐Mesh Sensor Design and Data Analysis for Rotating Fixed Beds

Wire‐mesh sensors are increasingly used for flow imaging in packed beds. In this study, a capacitance wire‐mesh sensor is applied to measure the cross‐sectional liquid phase distribution in a rotating fixed‐bed reactor. The liquid filling level is derived as a crucial parameter defining the operational window of the reactor concept. Contrary to the standard sensor configuration, wireless data transfer and autonomous power supply is integrated. Furthermore, appropriate data processing is required to visualize the liquid flow of the three‐phase system (nitrogen, cumene and γ‐Al₂O₃ particles).     

Numerical Simulation of Gas‐Liquid Flow in a Stirred Tank with Swirl Modification

Although the standard k‐? model is most frequently used for turbulence modeling, it often leads to poor results for strongly swirling flows involved in stirred tanks and other processing devices. In this work, a swirling number, R_S, is introduced to modify the standard k‐? model. A Eulerian‐Eulerian model is employed to describe the gas‐liquid, two‐phase flow in a baffled stirred tank with a Rushton impeller. The momentum and the continuity equations are discretized using the finite difference method and solved by the SIMPLE algorithm. The inner‐outer iterative algorithm is used to account for the interaction between the rotating impeller and the static baffles. The predictions, both with and without R_S corrections, are compared with the literature data, which illustrates that the swirling modification could improve the numerical simulation of gas‐liquid turbulent flow in stirred tanks.     

A Multi‐Stream Microchip for Process Intensification of Liquid‐Liquid Extraction

Solvent extraction is a critical step in many industrial mineral‐processing circuits and is affected by chemical (e.g., metal ions, extractant, pH, reaction rate) and physical (e.g., interfacial phenomena, mass transport, temperature) factors. Here, a new type of microfluidic contactor is presented that enables higher volumetric throughputs and straightforward counter‐current operation compared with Y‐Y chips. A single chip design can handle a wide range of organic/aqueous phase ratios, thereby enabling stable operation for non‐ideal solutions and fluctuating flow. An expression defining this widened operational window has been derived based on the relative stream geometries and liquid viscosities. A two‐stage counter‐current circuit is demonstrated for the extraction of platinum(IV) chloride.     

Heat Transfer from Immersed Vertical Cylinders in Gas‐Liquid and Gas‐Liquid‐Solid Fluidized Beds

The heat transfer coefficient, h, was measured using a cylindrical heater vertically immersed in liquid‐solid and gas‐liquid‐solid fluidized beds. The gas used was air and the liquids used were water and 0.7 and 1.5 wt‐% carboxymethylcellulose (CMC) aqueous solutions. The fluidized particles were sieved glass beads with 0.25, 0.5, 1.1, 2.6, and 5.2 mm average diameters. We tried to obtain unified dimensionless correlations for the cylinder surface‐to‐liquid heat transfer coefficients in the liquid‐solid and gas‐liquid‐solid fluidized beds. In the first approach, the heat transfer coefficients were successfully correlated in a unified formula in terms of a modified j_H‐factor and the modified liquid Reynolds number considering the effect of spatial expansion for the fluidized bed within an error of 36.1 %. In the second approach, the heat transfer coefficients were also correlated in a unified formula in terms of the dimensionless quantities, Nu/Pr^1/3, and the specific power group including energy dissipation rate per unit mass of liquid, E^1/3D^4/3/ν_l, within a smaller error of 24.7 %. It is also confirmed that a good analogy exists between the surface‐to‐liquid heat transfer and mass transfer on the immersed cylinder in the liquid‐solid and gas‐liquid‐solid fluidization systems.     

Numerical Study on Bubble Formation of a Gas‐Liquid Flow in a T‐Junction Microchannel

Bubble emergence in a gas‐liquid flow in a T‐junction microchannel of 100 μm diameter, operated under a squeezing regime, was simulated with the computational fluid dynamics method. In general, bubble formation in channels includes three stages: expansion, collapse and pinching off. After analyzing and comparing quantitatively the three forces of pressure, surface tension and shear stress acting on the gas thread in the whole process, their effects in the different stages were identified. The collapse stage was the most important for bubble formation and was investigated in detail. It was found that the collapse process was mostly influenced by the liquid superficial velocity, and the rate and time of collapse can be correlated with empirical equations including the liquid superficial velocity, the capillary number and the Reynolds number.