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Photocatalytic nanomaterials, using only light as the source of excitation, have been developed for the breakdown of volatile organic compounds (VOCs) in air for a long time. It is a tough challenge to immobilize these powder photocatalysts and prevent their entrainment with the gas stream. Conventional methods for making stable films typically require expensive deposition equipment and only allow the deposition of very thin layers with limited photocatalytic performance. The present work presents an alternative approach, using the combination of commercially available photocatalytic nanopowders and a polymer or inorganic sol–gel-based matrix. Analysis of the photocatalytic degradation of ethanol was studied for these layers on metallic substrates, proving a difference in photocatalytic activity for different types of stable layers. The sol–gel-based TiO2 layers showed an improved photocatalytic activity of the nanomaterials compared with the polymer TiO2 layers. In addition, the used preparation methods require only a limited amount of photocatalyst, little equipment, and allow easy upscaling.

A gas–liquid vortex reactor (GLVR) is considered one of the promising Process-Intensified Equipment for applications that require high mixing and mass transfer efficiency. To gain understanding of the fundamentals of GLVR operation, the gas–liquid hydrodynamics in the GLVR has been investigated by high-speed imaging, digital images analysis and cross correlation. Gas bubbles and liquid ligaments are observed in the GLVR over a wide operating window. The dynamic liquid layer thickness in the GLVR chamber varies in the range of 26–36 mm. The instantaneous and time-average velocity fields of the liquid phase are obtained with a guaranteed high signal-to-noise ratio (cross correlation peak ratio higher than 10), allowing the analysis of liquid turbulent properties including the turbulent kinetic energy and its dissipation rate. Results show that the high turbulent kinetic energy dissipation rate ranging from 23 to 114 m2/s3 contributes to a high mixing and mass transfer efficiency in the GLVR.

The hydrodynamics of secondary flow phenomena in a disc-shaped gas vortex unit (GVU) is investigated using experimentally validated numerical simulations. The simulation using ANSYS FLUENT® v.14a reveals the development of a backflow region along the core of the central gas exhaust, and of a counterflow multivortex region in the bulk of the disc part of the unit. Under the tested conditions, the GVU flow is found to be highly spiraling in nature. Secondary flow phenomena develop as swirl becomes stronger. The backflow region develops first via the swirl-decay mechanism in the exhaust line. Near-wall jet formation in the boundary layers near the GVU end-walls eventually results in flow reversal in the bulk of the unit. When the jets grow stronger the counterflow becomes multivortex. The simulation results are validated with experimental data obtained from Stereoscopic Particle Image Velocimetry and surface oil visualization measurements.

Innovative gas-solid fluidized beds with process intensification capabilities are among the most promising alternatives for the current state of the art in the chemical industry. In the present work the advantages of such a reactor that sustains a rotating fluidized bed with gas-solid slip velocities much higher than those in conventional fluidized beds are illustrated computationally and experimentally. A Gas-Solid Vortex Reactor (GSVR) demonstration unit is designed to operate at typical biomass fast pyrolysis conditions targeting the production of chemicals and fuels from renewable feedstocks. For the demonstration unit preheated N 2 supplies the thermal energy required by the fast pyrolysis process but alternative sources can also be evaluated. A broad range of operation conditions in the 80 mm diameter and 15 mm height GSVR can be evaluated: N 2 mass flow rates of 5–10 g s −1 and biomass feed mass flow rates of 0.14–1.4 g s −1 . Particle-free and particulate flow experiments confirmed that the carrier gas is evenly distributed around the GSVR cylindrical chamber as anticipated by computational fluid dynamic simulations. The latter also supported the inclusion of a profiled bottom end wall and a diverging exhaust. Cold flow experiments with biomass confirmed that the GSVR sustains a rotating fluidized bed with average bed height of 10 mm and solids azimuthal velocities of 6–7 m s −1 .

To study fouling in steam cracker convection section tubes, accurate tube wall temperature profiles are needed. In this work, tube wall temperature profiles are calculated using a hybrid model, combining a one-dimensional (1D) process gas side model and a computational fluid dynamics (CFD) flue gas side model. The CFD flue gas side model assures the flue gas side accuracy, accounting for local temperatures, while the 1D process gas side model limits the computational cost. Flow separation in the flue gas side at the upper circumference of each tube suggests the need for a compartmentalized 1D approach. A considerable effect is observed. The hybrid CFD-1D model provides accurate tube wall temperature profiles in a reasonable simulation time, a first step towards simulation-based design of more efficient steam cracker convection sections.

Biomass fast pyrolysis has been considered one of the best alternatives for the thermal conversion of biomass into bio-oil. This work introduces a new reactor technology for biomass fast pyrolysis, the Gas-Solid Vortex Reactor (GSVR), to obtain high bio-oil yields. The GSVR was designed to decrease the residence time of the pyrolysis vapors; thus, the secondary cracking reactions are reduced, to enhance the segregation of the char and the unreacted biomass and to improve the heat transfer rate. Biomass fast pyrolysis experiments have been carried out for the first time in a Gas-Solid Vortex Reactor (GSVR) at 773 K, using softwood (pine) and hardwood (poplar) as feedstock. Char yields as low as 10 wt. % in the GSVR were comparable to those reported for the same feedstocks processed in conventional fluidized bed reactors. The yields of non-condensable gases in the range of 15–17 wt. % were significantly lower than those reported for other commonly used biomass fast pyrolysis reactors. Two-dimensional gas chromatography (GC × GC) revealed noticeable differences at the molecular level between the bio-oils from the GSVR and bio-oils from other reactors. The aromatics in the pine bio-oil consist almost entirely (85 wt. %) of guaiacols. For poplar bio-oils no predominant group of aromatics was found, but phenolics, syringols, and catechols were the most pronounced. The experimental results highlight the advantages of the GSVR for biomass pyrolysis, reaching stable operation in around 60 s, removing the formed char selectively during operation, and enabling fast entrainment of pyrolysis vapors. Results indicate a great potential for increasing yield and selectivity towards guaiacols in softwood (e.g., pine) bio-oil. Likewise, decreasing pyrolysis temperature could increase the yield of guaiacols and syringols in hardwood (e.g., poplar) bio-oil.

A three-dimensional numerical analysis of the flow in a Gas-Solid Vortex Unit (GSVU) is carried out. The numerical model is first validated by comparing the bed pressure drop and solids velocity with experimental data. Next, the influence of gas flow rate, solids density, and particle diameter on the pressure drop, solids velocity, bed void fraction and slip velocity between the two phases is studied. A stable, solids bed is achieved for the entire range of gas flow rates tested (0.1–0.6 Nm3/s). No particle entrainment is observed when varying the solid density (1800–450 kg/m3) or the particle diameter (2–0.5 mm). A shift to bubbling fluidization regime is observed for small particle diameters (0.5 mm). The observed changes in the GSVU flow patterns are discussed by analyzing the changes in the cumulative centrifugal to drag force ratio over the bed.

To clarify the three-dimensional structure of near-wall jets observed in disc-like gas vortex units, experimental and numerical studies are performed. The experimental results are obtained using Particle Image Velocimetry (PIV), Laser Doppler Anemometry (LDA), pressure probes and surface oil flow visualization techniques. The first three techniques have been used to investigate the bulk flow hydrodynamics of the vortex unit. Surface oil flow visualization is adopted to visualize streamlines near the end-walls of the vortex unit. The surface streamlines help determine the azimuthal and radial velocity components of the radial near-wall jets. Simulations of the vortex unit using FLUENT® v.14a are simultaneously performed, computationally resolving the near-wall jet regions in the axial direction. The simulation results together with the surface oil flow visualization establish the three-dimensional structure of the near-wall jets in gas vortex units for the first time in literature. It is also conjectured that the near-wall jets develop due to combined effects of bulk flow acceleration and swirl. The centrifugal force diminishes in the vicinity of the end-walls. The radially inward pressure gradient in these regions, no longer balanced by the centrifugal force, pushes gas radially inward thus developing the near-wall jets. This article is protected by copyright. All rights reserved.

Coincident (simultaneous) three‐component particle velocity measurements performed using two laser Doppler anemometry probes at the outlet section of a 9 m high cylindrical riser are for the first time presented for dilute flow conditions. Near the blinded extension of the T‐outlet a solids vortex is formed. Particle downflow along the riser wall opposite the outlet tube is observed, which is restricted to higher riser heights at higher gas flow rates. Increased velocity fluctuations are observed in the solids vortex and downflow region as well as at heights corresponding to the outlet tube. Contrary to the rest of the riser, in the downflow region time and ensemble velocity averages are not equal. Given the local bending of the streamlines, axial momentum transforms to radial and azimuthal momentum giving rise to the corresponding shear stresses. Turbulence intensity values indicate the edges of the downflow region. © 2016 The Authors AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers AIChE J, 62: 3575–3584, 2016

Účinek vysoceemisivních povlaků na radiační přenos tepla v parních krakovacích pecích není zdaleka znám. Chybí experimentální data popisující emisivní vlastnosti materiálů, které se používají v parních krakovacích pecích. Z tohoto důvodu se provádí měření spektrální normálové emisivity na zvýšených teplotách, přičemž se hodnotí emisivní vlastnosti žáruvzdorných šamotových cihel před a po depozici vysoceemisivního povlaku. Po nanesení povlaku s vysokou emisivitou na základní šamotový materiál se výrazně zvýší jeho emisivita. Provedené experimenty s parní krakovací jednotkou ukazují 5% snížení rychlosti spalování topného plynu po nanesení vysoceemisivního povlaku na žáruvzdorný materiál krakovací komory. Parametrické studie zabývající se účinkem emisivních vlastností reaktorové cívky a stěny pece na radiační přenos tepla ve spalovací komoře potvrzují, že pro přesné modelování chování povlaků s vysokou emisivitou je vyžadován jiný model než model šedého plynu. Přestože model šedého plynu postačuje k zachycení chování chladiče reaktorové cívky, je nezbytný jiný, nešedý model, který zobecňuje absorpci a opětovné vyzařování plynu ve spcifických spektrálních pásmech, aby mohl přesně zachytit výhody využití vysoceemisivního povlaku na stěně pece. The effect of high emissivity coatings on the radiative heat transfer in steam cracking furnaces is far from understood. To start, there is a lack of experimental data describing the emissive properties of the materials encountered in steam cracking furnaces. Therefore, spectral normal emissivity measurements are carried out, evaluating the emissive properties of refractory firebricks before and after applying a high emissivity coating at elevated temperatures. The emissive properties are enhanced significantly after applying a high emissivity coating. Pilot unit steam cracking experiments show a 5 % reduction in fuel gas firing rate after applying a high emissivity coating on the refractory of the cracking cells. A parametric study, showing the effect of reactor coil and furnace wall emissive properties on the radiative heat transfer inside a tube-in-box geometry, confirms that a non-gray gas model is required to accurately model the behavior of high emissivity coatings. Even though a gray gas model suffices to capture the heat sink behavior of a reactor coil, a non-gray gas model that is able to account for the absorption and re-emission in specific bands is necessary to accurately model the benefits of applying a high emissivity coating on the furnace wall.

A unique normalized radial pressure profile characterizes the bed of a gas‐solid vortex reactor over a range of particle densities and sizes, solid capacities, and gas flow rates: 950–1240 kg/m3, 1–2 mm, 2 kg to maximum solids capacity, and 0.4–0.8 Nm3/s (corresponding to gas injection velocities of 55–110 m/s), respectively. The combined momentum conservation equations of both gas and solid phases predict this pressure profile when accounting for the corresponding measured particle velocities. The pressure profiles for a given type of particles and a given solids loading but for different gas injection velocities merge into a single curve when normalizing the pressures with the pressure value downstream of the bed. The normalized—with respect to the overall pressure drop—pressure profiles for different gas injection velocities in particle‐free flow merge in a unique profile. © 2015 The Authors AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers AIChE J, 61: 4114–4125, 2015

Regime maps that predict the heavy hydrocarbon droplet impingement behavior on a heated wall (Weber number of the impinging droplet v/s wall temperature) are constructed based on CFD simulations using the Volume of Fluid model with the geo-reconstruct scheme. Based on the simulation results, maps are constructed for single-component droplets with a diameter of 50 and of 100 µm. The applied CFD model is validated by comparing these with regime maps available in literature, constructed based on experimental data for model liquids and liquid mixtures. The impingement regimes of Splash, Stick, Rebound and Breakup are well-predicted. Two distinct types of Splash (Splash with ligament formation and Splash with ring detachment) are reported for the first time. Using the validated CFD model, regime maps are constructed for multi-component heavy hydrocarbon droplets with a diameter of 50 and of 100 µm. Significant differences between the single-component and the multi-component droplet impact behavior are observed. Improved and new correlations for regime transitions, droplet stretching on the wall, droplet rebounding velocity and number of splashed droplets are derived based on energy balances. They are found to correlate well with CFD predictions.

Coincident three-component particle velocity measurements are performed in an almost 9 m high cylindrical riser (internal diameter 0.10 m) of a pilot-scale cold-flow Circulating Fluidized Bed set-up, using two Laser Doppler Anemometry (LDA) probes. Experiments are performed with superficial gas velocities of 3.5 m/s and 5.3 m/s near the solids inlet line and with an average solids volume fraction of 0.0002. The particle flow is observed to be highly disturbed due to the asymmetrical position of both the gas and the Y-shaped solids inlet line. A jet-like particle flow and a by-passing streaming gas jet around the particles are formed. Just below the solids inlet line a downward oriented particle velocity is measured. Particles are immediately lifted by the ascending gas and spread over the entire cross-sectional tube area. Near the solids inlet line the axial and radial particle velocity fluctuations are of the same order of magnitude as the corresponding mean particle velocity components, showing that the flow is anisotropic. The radial particle velocity fluctuations decrease fast as the radial inflow of particles is transformed into axial particles flow. The turbulence intensity in the inlet section of the dilute riser flow is found to be extremely high, indicating that the flow is far from being fully developed. The total particle shear stress profiles near the solids inlet line indicate a high momentum transfer from radial to axial particle transport. The particle fluctuation energy values calculated based on experimental data are nearly double than the values corresponding in fully developed flow studied previously.

The process intensification possibilities of a gas–solid vortex reactor have been studied for biomass fast pyrolysis using a combination of experiments (particle image velocimetry) and non-reactive and reactive three-dimensional computational fluid dynamics simulations. High centrifugal forces (greater than 30g) are obtainable, which allows for much higher slip velocities (>5 m s–1) and more intense heat and mass transfer between phases, which could result in higher selectivities of, for example, bio-oil production. Additionally, the dense yet fluid nature of the bed allows for a relatively small pressure drop across the bed (∼104 Pa). For the reactive simulations, bio-oil yields of up to 70 wt % are achieved, which is higher than reported in conventional fluidized beds across the literature. Convective heat transfer coefficients between gas and solid in the range of 600–700 W m–2 K–1 are observed, significantly higher than those obtained in competitive reactor technologies. This is partly explained by reducing undesirable gas–char contact times as a result of preferred segregation of unwanted char particles toward the exhaust. Experimentally, systematic char entrainment under simultaneous biomass–char operation suggested possible process intensification and a so-called “self-cleaning” tendency of vortex reactors.

IMPROOF will develop and demonstrate the steam cracking furnace of the 21st century by drastically improving the energy efficiency of the current state-of-the-art, in a cost effective way, while simultaneously reducing emissions of greenhouse gases and NOX per ton of ethylene produced by at least 25%. Therefore, the latest technological innovations in the field of energy efficiency and fouling minimization are implemented and combined, proving that these technologies work properly at TRL 5 and 6 levels. The first steps to reach the ultimate objective, i.e. to deploy the furnace at the demonstrator at commercial scale with the most effective technologies, will be discussed based on novel pilot scale data and modeling results.

In a Gas–Solid Vortex Reactor (GSVR), also referred to as a Rotating Fluidized Bed in Static Geometry, a fluidized bed is generated in a centrifugal field by introducing the gas via tangential inlet slots to the reactor chamber. Better heat and mass transfer are observed, making this a promising reactor type for Process Intensification. Developing GSVRs on industrial scale requires, amongst other, a good insight and understanding of the hydrodynamics of the granular flow. In the present work experiments are performed over a wide range of operating conditions in a cold flow pilot-scale set-up. The set-up has a diameter of 0.54 m, a length of 0.1 m and 36 tangential inlet slots of 2 mm. Different materials with solids density between 950–1800 kg/m3 and particle diameters of 1–2 mm, at varying gas injection velocities from 55 to 110 m/s are tested between minimum and maximum solids capacities. All these operating conditions are used to follow the change of granular flow by performing PIV. The rotating fluidized bed can change from a smoothly rotating, densely fluidized bed to a highly bubbling rotating fluidized bed depending on the operating conditions. Bubbling diminishes with increasing solids density and particle diameter. Experimental measurements of azimuthal particle velocity fields in a GSVR are for the first time reported. Azimuthal solids velocity is found to decrease with higher solids density and larger particle diameter. The critical minimum fluidization velocity, that is the minimum velocity at which the complete bed is fluidized, is calculated and the centrifugal bed behavior is mapped in terms of a dimensionless radial gas velocity and a dimensionless particle diameter, as conventionally done for gravitational beds.

Coke formation in the convection section of a steam cracker occurs when heavy feeds are cracked. This work presents CFD simulations of coke formation in the mixture superheater tubes in the convection section of a steam cracker. The hydrocarbon feed used for the simulations is a gas condensate. Eleven representative chemical species are selected, based on their boiling points, to mimic the entire range of feed components. The liquid–vapor spray flow in the mixture superheater tube is simulated based on an Eulerian–Lagrangian approach using ANSYS FLUENT 13.0. Evaporation of multicomponent droplets suspended in the vapor phase or deposited on a tube wall is considered. The mixture superheater tubes make three horizontal passes (11.3 m long and 0.077 m diameter) through the convection section. The droplet–wall interaction model considers ‘Splash’, ‘Rebound induced breakup’, ‘Rebound’ and ‘Stick’. The amount of liquid deposited on the mixture superheater tube wall is obtained by simulating the spray flow. The amount of coke formed from the liquid deposited on a wall is based on the phase separation model of (Wiehe, 1993). Industrial & Engineering Chemistry Research 32, 2447–2454. Spatial variations of the coke layer formed in the mixture superheater tubes as a function of outer tube wall temperatures and initial droplet diameter are presented. For outer tube wall temperatures lower than the boiling point of the highest-boiling species in the feed a 1 mm thick coke layer is formed over a period of 1 month. For outer tube wall temperatures higher than the boiling point of the highest boiling component in the feed no coke is formed in the mixture superheater tubes. This work provides guidelines to minimize the extent of coke formation in the steam cracker convection section when a heavy feed is cracked. It also provides possible remedies to completely eliminate the coking problem when cracking heavy feeds.

An industrial project was developed to optimize the biodiesel production from crude palm oil. This process was developed for a one ton scale application on the palm oil production facility in equatorial Africa, to be used on the plantation to provide fuel for the fleet of the company. Because of the specific conditions (crude palm oil as starting material, application in technologically difficult conditions), it was essential for the developed procedure to be robust and simple, and to use minimum amounts of chemicals. The process was optimised on lab-scale in 2005 and 2006, scaled up in the following year, and is since then successfully applied as intended on the palm oil plantation. The produced biodiesel is used pure, without mixing with diesel fuel and without additives. After several years of continuous use, no negative effects were noticed on the engines. The process efficiency and durability are therefore confirmed.

Coincident three-component solids velocity measurements are performed in a 8.7-m-high cylindrical riser (internal diameter 0.10 m) of a pilot-scale cold-flow Circulating Fluidized Bed set-up, using two Laser Doppler Anemometry (LDA) probes. Experiments are performed with superficial gas velocities of 3.5 and 5.3 m/s at riser heights from 0.9 to 5.5 m and with an average solids volume fraction of 0.0002. At the lower riser heights, the solids flow is observed to be highly disturbed due to the asymmetrical position of both the air and solids inlet. A fully developed parabolic axial solids velocity field is observed about 2 m above the solids inlet line. The measured radial and azimuthal particle velocity components are significantly smaller than the axial one. The particle velocity fluctuations in the axial flow direction are larger than in the radial and azimuthal directions, showing that the solids flow is anisotropic. However, both the radial and azimuthal velocity fluctuations are higher than the corresponding mean velocities, as observed when studying the turbulence intensity in the three directions. All fluctuating velocities are decreasing significantly with increasing riser height, i.e. as the flow becomes more developed. No average down-flow of solids is recorded, not even close to the wall, due to the highly diluted flow. The total particle shear stress profiles designate a mean transport of fluctuating momentum along the riser radius due to velocity fluctuations. The particle fluctuation energy calculated based on experimental data indicates that the solids flow is dominated by wall-particle rather than intra-particle collisions.

A drag model for the Gas-Solid Vortex Unit is presented. A large set of experimental data, obtained using static gauge pressure measurements, Particle Image Velocimetry and Digital Image Analysis in different GSVU geometries is used to estimate the model parameters with regression analysis. A large range of radial particle Reynolds numbers, particle densities and particle diameters is investigated. The newly proposed drag coefficient correlation, including 95% confidence intervals, reads: C D , GSVU = 15.00 ± 4.65 e 2 R e p , R − 0.28 ± 0.05 S 0.76 ± 0.03 The drag coefficient correlation is found to depend on the swirl ratio S, a variable determined by the GSVU geometry. The model suggests that, for the operating conditions in the GSVU, the particles mostly behave independently of one another. The performance of the model to predict the pressure drop over fluidized beds in a centrifugal field is high as compared to the standard drag models for fluidized beds in the gravitational field. Additionally, the drag model eventually allows to calculate the azimuthal solids velocity in a GSVU under varying operating conditions using an Archimedes/Reynolds number correlation derived from the radial momentum balances for both phases.

Liquid lead-bismuth eutectic (LBE) is an important candidate to become the primary coolant of future, generation IV, nuclear fast reactors and Accelerator Driven System (ADS) concepts. One of the main challenges with the use of LBE as a coolant is to avoid its oxidation which results in solid lead oxide (PbO) precipitation. The chemical equilibria governing PbO formation are well understood. However, insufficient kinetic information is currently available for the development of LBE-based nuclear technology. Here, we report the results of experiments in which the nucleation, growth and dissolution of PbO in LBE during temperature cycling are measured by monitoring dissolved oxygen using potentiometric oxygen sensors. The metastable region, above which PbO nucleation can occur, has been determined under conditions relevant for the operation of LBE cooled nuclear systems and was found to be independent of setup geometry and thus thought to be widely applicable. A kinetic model to describe formation and dissolution of PbO particles in LBE is proposed, based on Classical Nucleation Theory (CNT) combined with mass transfer limited growth and dissolution. This model can accurately predict the experimentally observed changes in oxygen concentration due to nucleation, growth and dissolution of PbO, using the effective interfacial energy of a PbO nucleus in LBE as a fitting parameter. The results are invaluable to evaluate the consequences of oxygen ingress in LBE cooled nuclear systems under normal operating and accidental conditions and form the basis for the development of cold trap technology to avoid PbO formation in the primary reactor circuit.

The feasibility of performing the SO2/NOx adsorption process in a gas-solid vortex reactor (GSVR) is examined and compared with the more traditional riser technology. The multiphase reacting flow is modeled using the Eulerian-Eulerian two-fluid model. Models of nonreacting flows were validated using data from a bench-scale experimental setup. The GSVR has the potential to significantly improved heat/mass transfer between phases, as compared to more conventional fluidization technologies. Process intensification opportunities are investigated. The model predicts continuous removal efficiencies greater than 99% for SO2 and approximately 80% for NOx. The gas-solid slip velocity and convective mass transfer coefficient for the riser were 0.2-0.5 and 0.06-0.12 m/s, respectively, whereas the values for the GSVR were 6-7 and 1.0-1.1 m/s, respectively. This order of magnitude increase in the external mass transfer coefficient highlights the potential intensification opportunities provided by the GSVR.

The hydrodynamic behavior of dispersed gas–solid flow is simulated for an industrial-scale Fluid Catalytic Cracking (FCC) riser using the multi-fluid approach, with complementary information from the Kinetic Theory of Granular Flow (KTGF) for the transport coefficients of the solid phase. A continuous Particle Diameter Distribution (PDD) is considered for the solid phase catalyst. The three-dimensional gas–solid flow is considered to be non-isothermal and turbulent. The hydrodynamics of the riser reactor is coupled to a 12-lump FCC kinetic model to predict the influence of a polydisperse distribution on gas–solid reactive flow. The kinetic model involves lumped species consisting of paraffins, naphthenes, aromatic rings, and aromatic substituent groups in medium and heavy fuel oil fractions and includes the effect of aromatic ring adsorption and catalyst deactivation due to coke formation. In this study, a Computational Fluid Dynamics (CFD) model using the Eulerian–Eulerian multi-fluid approach and a Population Balance Model (PBM) are coupled. The hydrodynamic equations are solved by means of a finite volume method, while the population balance equations are solved using the Direct Quadrature Method of Moments (DQMOM). The moments of the solids phase velocity are modeled using classical kinetic theory, while the moments of the PDD are described using quadrature weights and abscissas. To account for the catalyst PDD, three different approaches namely simple, surface-averaged and volume-averaged coupling have been attempted. The latter two approaches, assuming surface and volumetric reaction kinetics respectively, predict with a good precision the yields of the different product families obtained in an industrial FCC unit showing a slight improvement from a conventional heterogeneous reactor model with a monodispersed distribution.

The Kiliani reaction, i.e. the elongation of the carbon chain by means of cyanide addition to the carbonyl group of carbohydrate derivatives, is studied on lower C3-, C4- and C6-ketoses under continuous flow conditions. Depending on the process parameters, the corresponding cyanohydrins or alpha-hydroxycarboxylic acids are obtained. A simple on-line purification of the effluent is studied using cation exchange resins. Reactions provide high yields and selectivity within short residence times, emphasizing the assets of the continuous flow process versus the batch process.

Riser outlet effects induced by an L-outlet and by abrupt T-outlets with different extension heights and outlet surface areas are studied experimentally and computationally. Experiments are carried out in a cold flow riser. The cold flow riser has a diameter of 0.1 m and a height of 8.765 m and is operated in the dilute flow regime with a superficial gas velocity of 2.48-7.43 m/s and a solids flux of 3.0 kg/m²/s. Particle velocities are measured using Laser Doppler Anemometry (LDA). Vortex formation in the extension part of the riser is observed. The vortex circulates the solids along the wall opposite to the outlet, thus inducing a solids reflux. The flow pattern upstream the outlet is, however, hardly affected in the small diameter riser. The vortex position and length are affected by the extension height, but hardly by the outlet surface area and the superficial gas velocity. The use of an L-outlet significantly reduces the vortex formation. The experimental measurements are used to validate a 3D Eulerian–Eulerian and Kinetic Theory of Granular Flow (KTGF) based gas–solid flow model. In general, the calculated trends are qualitatively in agreement with the experimentally observed phenomena. The exact shape of the vortex is not always accurately predicted.

A Eulerian–Lagrangian method is implemented to simulate turbulent two-phase gas–solid riser flow, using a mean-field/probability density function (PDF) method. The mean-field method is applied to the gas phase while the PDF method is applied to the solid phase. Using the PDF method for the solid phase is advantageous as there is no need for closure models for the convection term in the momentum equation contrary to the situation where the mean-field method is used. The present method is implemented to investigate the influence of a side inlet on the flow pattern in a dilute gas–solid riser configuration. When applying the Eulerian–Lagrangian method, a perfect correspondence with the experimental observations is obtained. On the contrary, when using the Eulerian–Eulerian method significant differences with the experimental data are observed.

A coupled and a decoupled solution method are applied to the steady-state simulation of one-dimensional, reactive gas flow. The accuracy of the numerical steady-state solution depends to a significant extent on the molar expansion of the gas. The convergence rate of the coupled solution method is almost independent of molar expansion. The convergence rate of the decoupled solution method is at least 50% lower for strong molar expansion than for nonexistent molar expansion. By adding a transport equation for molar mass, the convergence rate of the decoupled solution method becomes almost independent of molar expansion. The results for the decoupled solution method apply to other methods in which composition is determined on a fixed flow field. A tool is presented to quantify the perturbation of the flow field by the chemical reactions.

s Hydrodynamics of a gas–solid rotating bed reactor (RBR) in static geometry are investigated. Tangential injection of a gas at mass flow rate of 0.4–1 kg/s in a cylindrical vessel with a diameter of 0.54 m generates a rotating gas phase flow field. Introduction of solid particles in this field results into an annular dense gas–solid rotating bed. A stable annular gas–solid rotating bed without solids particles loss is achieved over a wide range of operating conditions. Goal of the presented work is to investigate, by means of experiments, the window for a stable operation of the gas–solid RBR, as a function of the solid particle diameter and density, the geometry of the RBR and the gas flow rate. If the solid particle diameter is comparable to tangential gas injection slot width, the establishment of a stable flow is delayed due to an increased slugging tendency. The upper limit of the solids content is found to decrease with decreasing solid particle diameter. Obtained experimental cold flow results are the initial steps in assessing the potentials of a RBR as an efficient gas–solid processing reactor from a process intensification point of view.

Computational fluid dynamics (CFD) simulations of the hydrodynamic behavior of rotating fluidized beds in static geometry (RFB-SG) are carried out for gas–solid flows. The rotating motion of the reactor bed is induced by the tangential injection of the gas along the circumference of the fluidization chamber. Steep gradients in the gas velocity fields both in radial and tangential direction generate turbulence. The radial and tangential drag forces fluidize the particle bed in both radial and tangential direction. An Eulerian two-fluid model is used. Gas phase turbulence is accounted for by a k–e model adapted for rotational flows. The RFB-SG simulations provide guidelines for a design and operation with a high efficiency in gas–solid momentum transfer, excellent gas–solid separation and limited solids losses. Hydrodynamic variables like the centrifugal force, the injection pressure, the radial and tangential slip velocities, solids hold-up are calculated for both polymer particles (300 μm, 950 kg/m3, Geldart Group B) and glass beads (70 μm, 2500 kg/m3, Geldart Group A) to allow for a comparison among different fluidization chamber designs. Unstable bed behavior, like slugging and channeling, is also numerically predicted.

A model has been developed allowing to simulate the flow boiling process of a hydrocarbon feedstock. For the calculation of the different horizontal two-phase flow regimes that evolve during flow boiling, use is made of the Volume Of Fluid (VOF) model that uses a Piecewise Linear Interface Calculation (PLIC) method to reconstruct the interface between both phases in each computational cell. In-house developed codes calculate the mass and energy transfer phenomena occurring during this flow boiling process. As such, an existing CFD code is completed with a newly developed complete evaporation model. The developed model is used to simulate the flow boiling process of a hydrocarbon feedstock in the tubes of a convection section heat exchanger of a steam cracker. The simulation results show a succession of horizontal two-phase flow regimes in agreement with the literature.

The efficiency of the application of high-emissivity coatings on the furnace walls in steam cracking technology can only be evaluated on the basis of a description of radiative heat transfer distinguishing between the frequency bands. To this end, a non-grey gas radiation model based on the exponential wide band model (EWBM) has been developed and applied in the context of three-dimensional CFD simulations of an industrial naphtha cracking furnace with side-wall radiation burners. Applying a high-emissivity coating on the furnace wall decreases the net outgoing radiation from the furnace wall in the absorption bands and increases the net outgoing radiation from the furnace wall in the clear windows. Since radiation that is emitted by the furnace wall and travels through the flue gas in the clear windows can reach the reactor tubes without partially being absorbed by the flue gas, contrary to radiation that is emitted by the furnace wall and travels through the flue gas in the absorption bands, the thermal efficiency of the furnace increases. It was found that application of a high-emissivity coating on the furnace walls improves the thermal efficiency of the furnace (∼1%), the naphtha conversion (∼1%) and the ethylene yield (∼0.5%). These differences are small but, considering the industrial importance and scale of the steam cracking process, significant.

The endothermic thermal cracking process of hydrocarbons takes place in tubular reactor coils suspended in large gas-fired pyrolysis furnaces. Heat transfer to the reactor tubes is mostly due to radiation from the furnace refractory walls and the flue gas. A three-dimensional (3-D) simulation of the flow in an industrial scale steam cracking furnace is performed. The renormalization group (RNG) k − ɛ turbulence model is used. The combustion kinetics is modeled by a three-step reaction mechanism, while turbulence–chemistry interaction is taken into account through the Finite Rate/Eddy-Dissipation model. The Discrete Ordinates model (DOM), the P-1 and the Rosseland Radiation model are used for modeling of the radiative heat transfer. The results of using the different radiation models are compared mutually with adiabatic simulation results. The absorption coefficient of the gas mixture is calculated by means of a Weighted-Sum-of-Gray-Gas model (WSGGM). The effect is discussed of the use of different radiation models on the predicted wall, tube skin and flue gas temperature profiles and heat fluxes towards the reactor tubes, as well as on the predicted species concentration profiles and structure of the furnace flames under normal firing conditions.

To account for meso-scale phenomena in coarse grid simulations, correlation terms appearing in the filtered gas-solid flow equations have to be modeled. Possible approaches to describe filtered gas-solid momentum transfer are evaluated via a mixture speed of sound test. In contrast to the effective drag coefficient closure model for the filtered drag force, the generalized added mass closure model for the correlation between the solid volume fraction and the gas phase pressure gradient shows an acceptable behavior. Furthermore, the generalized added mass may become determining in describing filtered gas-solid momentum transfer when sufficiently coarse grids are used. 3D steady-state riser simulations demonstrate the impact of the generalized added mass based description of filtered gas-solid momentum transfer on the calculated gas-solid flow behavior, in particular on the gas-solid slip velocity profile. (c) 2007 Elsevier Ltd. All rights reserved.

The propagation speeds of linear waves in gas-solid suspensions depend strongly on the solids volume fraction and the wave frequency. The latter is due to gas-solid momentum transfer and allows a simple test on filtered gas-solid momentum transfer models. Such models may predict linear wave propagation speeds different from those obtained with the nonfiltered model at wave frequencies higher than the filter frequency, but not at wave frequencies lower than the filter frequency. For the filtered drag, an effective drag coefficient approach is shown to alter the linear wave propagation speeds in the entire wave frequency range, independent of the applied effective drag coefficient. Furthermore, as the effective drag coefficient decreases, the high frequency linear wave propagation speeds are gradually introduced at lower wave frequencies. For the filtered momentum transfer due to the correlation between the solids volume fraction and the gas phase pressure gradient, the behavior of an apparent added mass closure model and an apparent history force closure model are investigated. An apparent added mass introduces the filter frequency linear wave propagation speeds to frequencies higher than the filter frequency. The linear wave propagation speeds for wave frequencies lower than the filter frequency are, however, not altered. Furthermore, an apparent added mass introduces no intrinsic wave frequency dependence in the linear wave propagation speeds, in agreement with its source term in the non-filtered model. Hence, the frequency dependence of the linear wave propagation speeds at frequencies lower than the filter frequency is still to be provided by a drag type term. As such, the behavior introduced by an apparent added mass is acceptable for filtered models. Also, to a certain extent, an apparent added mass can restore the linear wave propagation speed behavior at wave frequencies lower than the filter frequency altered by an effective drag coefficient approach. The reformulation of the apparent added mass in terms of an apparent distribution of the filtered gas phase pressure gradient over the phases and an apparent (effective) drag force is investigated. An apparent history force introduces intrinsic wave frequency dependence in the linear wave propagation speeds and alters the latter from the low wave frequencies on. As such, the behavior introduced by an apparent history force is unacceptable for filtered models, (C) 2006 Elsevier Ltd. All rights reserved.

Inlet phenomena in a 0.1 m diameter cold-flow riser with a 35 ∘ inclined side inlet are studied experimentally using 3D-Laser Doppler Anemometry for solids fluxes of 0.5– 4.5 kg / m 2 / s and gas velocities of 5.3–7.4 m/s. In the vicinity of the solids inlet, radial gas-solids mixing is hindered and bypassing of the solids jet occurs, resulting in steep velocity gradients and off-centre maxima in the velocity field. The feeding conditions and the type of the solids affect the bottom operation and gas–solids mixing to a large extent: compared to FCC particles, silica particles extend the acceleration zone in the riser. Low gas flow rates and/or high solids feeding rates result in an increased penetration depth of the solids jet and in explicit bypass zones in the plane facing the inlet. High root mean square fluctuating particle velocities are observed at the solids jet boundaries. A non-aerated Y-inlet configuration causes vortex formation, inducing a small reflux into the upper dilute part of the standpipe. The influence of dilution of the inlet solids jet is also investigated using an “aerated” inlet configuration. Aerated inlets lead to better entrainment, improved radial mixing, less pronounced broader bypass zones and a firm reduction of the penetration depth. In the 0.1 m diameter riser, radial mixing quickly dissipates the non-uniformities introduced by the solids inlet. Reflection phenomena can, however, occur in the case of a non-aerated solids inlet.

A combined furnace and reactor calculation is performed for the simulation of the decoking of an ethane cracker with a steam/air mixture. Different gas–solid reaction/diffusion models with a corresponding texture model describing the solid phase changes during the decoking operation are combined with kinetics for the decoking by combustion and gasification, determined based on experimental data [Heynderickx, G.J., Schools, E.M., Marin, G.B., 2005. Coke combustion and gasification kinetics in ethane steam crackers. A.I.Ch.E. Journal 51 (5), 1414–1428]. By comparing the calculated coil outlet temperatures and the calculated partial pressures of carbon dioxide at the coil outlet with the measured values in an industrial unit, the need for a general gas–solid reaction/diffusion model and the corresponding decoking kinetics is confirmed. The decoking time for an industrial unit is simulated adequately.

A three-dimensional mathematical model has been developed for the simulation of flow, temperature and concentration fields in the radiation section of industrial scale steam cracking units. The model takes into account turbulence–chemistry interactions through the Eddy Dissipation Concept (EDC) model and makes use of Detailed Reaction Kinetics (DRK), which allows the detailed investigation of the flame structure. Furthermore, simulation results obtained with the EDC-DRK model are compared with simulation results obtained with a simplified model combining the Eddy Break Up (EBU)/finite rate formulation with Simplified Reaction Kinetics (SRK). When the EBU-SRK model is used, much faster fuel oxidation and products formation is predicted. The location of the peak temperature is shifted towards the burner, resulting in a smaller flame and the confinement of the combustion process into a smaller area. This is most likely because of the inherent deficiency of the simplified model to correctly predict the overall (effective) burning rate when the turbulent mixing rate and the reaction rate are comparable. It is shown that when neither the “fast-chemistry” nor the “slow-chemistry” approximation is satisfied, the overall burning rate is overpredicted. The smaller flame volumes obtained with the EBU-SRK model have important effects on the predicted temperature distribution in the furnace as well as on other significant design parameters like the refractory wall and tube skin temperatures. It is suggested that more sophisticated turbulence–chemistry interaction models like the EDC model and more Detailed Reaction Kinetics should be used for combustion modeling in steam cracking furnaces under normal firing conditions.

The efficiency of the application of high-emissivity coatings on reactor tubes and furnace walls in steam cracking technology can only be evaluated based on a correct description of the radiative heat transfer in the furnace. For the flue gases, a banded gas radiation model is introduced; for the surfaces a non-grey surface approach is applied. For the same total heat input, a thermal efficiency rise of over 5% is calculated for a naphtha cracking furnace under normal operating conditions.

Radial temperature profiles during steam cracking result in radial nonuniformities in the product yields due to radial variations in the concentration of the radicals. The effect of using a 1-D or a 2-D reactor model on the calculated product yields is evaluated for the cracking of ethane. With a 2-D reactor model the simulated ethylene yield decreases. Ethylene formed at the high-temperature zone near the hot wall diffuses to the center where secondary reactions are favored, generating C3 and C4 olefins. This effect is confirmed by the calculation of a reactor of a Kellogg Millisecond Furnace. In this small-diameter reactor the 1-D behavior is more pronounced, resulting in higher ethylene yields at comparable conversions. The effect of the radial gradients on the coking rate calculated with a fundamental kinetic coking model based on elementary reaction steps is even more pronounced. Only when the coke model is coupled to a 2-D reactor model, a good agreement with the reference data is observed. In order to obtain accurate simulation results the more detailed 2-D reactor model is required, even if this increases the computational effort. © 2004 American Institute of Chemical Engineers AIChE J, 50: 173–183, 2004

Simultaneous adsorption of SO 2 –NO x in a riser configuration is a novel route for flue gas cleaning. The riser operates at a low flux (2 kg m −2 s −1 ) of small diameter (d p =60 μm ) Na- γ -Al 2 O 3 sorbent particles. The reaction scheme is adopted from previous work (Ind. Eng. Chem. Res. 40 (2001) 119), without adjusting any of the kinetic parameters. The significant concentration gradient between the gas and solid phase mainly arises from the low solid fraction (typically 5×10 −4 ) in the riser. Enhancing the fluctuating kinetic motion of gas and solid phase increases the SO 2 adsorption, whereas the NO adsorption is decreased marginally. The solid recirculation in the top section of the riser, induced by the abrupt T outlets, significantly decreases the NO and NO 2 removal, while the SO 2 removal remains mostly unaffected. Therefore, it is desirable to avoid recirculation for a maximum NO x removal. A comparison of the 3D and a 1D model shows that higher SO 2 and NO removal efficiencies are predicted by the 3D model in the major part of the riser. However, these positive effects are largely neutralized by the negative effects of the outlet-induced recirculation, resulting in similar overall removal efficiencies calculated by the two models. Unlike the 1D model, the 3D simulation shows a considerable axial variation in the solid fraction and slip velocity. The 3D simulation also allows to calculate the effects of outlet geometry on the flow and reaction fields. The reactor efficiency can be improved by modifying the outlet configuration to minimize the recirculation.

A three-dimensional simulation of a dilute phase riser reactor (solid mass flux: 2 kg m −2 s −1 ) is performed using a novel density based solution algorithm. The model equations consisting of continuity, momentum, energy and species balances for both phases, are formulated following the Eulerian–Eulerian approach. The kinetic theory of granular flow is applied. The gas phase turbulence is accounted for via a k – e model. An extra transport equation describes the correlation between the gas and solid phase fluctuating motion. The solution algorithm allows a simultaneous integration of all the model equations in contrast to the sequential multi-loop solution in the conventional pressure based algorithms, used so far in riser simulations. The simulations show an unsteady behaviour of the flow, but a core-annulus flow pattern emerges on a time-averaged basis. The abrupt nature of the T type outlets causes a significant recirculation of gas and solid from the top of the riser. The flow near the outlets is highly non-symmetric and has a three-dimensional character. A significant decrease of the gas phase turbulence and particle granular temperature across the riser length is attributed to the presence of small particles, which is qualitatively consistent with the experimental data from literature.

The simulation of correct flow and pressure fields in the radiation section of industrial thermal cracking furnaces is of practical interest since the amount of combustion air taken in by the burners in general is partly determined by the pressure field. For such engineering purposes often a (practical) simplified numerical treatment of the viscous terms in the flow equations is used to reduce the computational cost. It is shown that the interaction between such a simplified numerical treatment of the viscous terms and the alignment of the cell interfaces with the coordinate system can result in an erroneous (non-physical) calculation of the pressure field. This alignment problem is predominantly present when using a semi non-structured prismatic grid to solve the flow equations. Using a fully non-structured tetrahedral grid avoids this problem because of the random orientation of the cell interfaces for this type of grid. This is confirmed by assuring that the calculation results are independent with respect to grid refinement. At the same time the influence of the presence of the reactor tubes on the velocity field inside the furnace is examined.

Gas–solid flow in circulating fluidized beds is calculated using the Eulerian–Eulerian approach with the kinetic theory of granular flow. The usefulness of this approach and the necessity of performing 3D calculations are illustrated by calculating the exit effects of single abrupt outlet configurations of different outlet surface area.

Bubbles in confined geometries serve an important role for industrial operations involving bubble-liquid interactions. However, high Reynolds number bubble dynamics in confined flows are still not well understood due to experimental challenges. In the present paper, combined experimental and numerical methods are used to provide a comprehensive insight into these dynamics. The bubble behaviour in a vertical Hele-Shaw cell is investigated experimentally with a fully wetting liquid for a variety of gap thicknesses. A numerical model is developed using the volume of fluid method coupled with a continuum surface force model and a wall friction model. The developed model successfully simulates the dynamics of a bubble under the present experimental conditions and shows good agreement between experimental and simulation results. It is found that with an increased spacing between the cell walls, the bubble shape changes from oblate ellipsoid and spherical-cap to more complicated shapes, while the bubble path changes from only rectilinear to a combination of oscillating and rectilinear; the bubble drag coefficient decreases and this results in a higher bubble velocity caused by a lower pressure exerted on the bubble; the wake boundary and wake length evolve gradually accompanied by vortex formation and shedding.

Conversion of biomass via fast pyrolysis and other methods is positioned to be an important part of the energy landscape in the future. Pyrolysis of lignocellulosic biomass in a gas/solid vortex reactor (GSVR) is modeled to assess the potential of this centrifugal fluidization reactor technology and to explore its process intensification abilities. The production of pyrolysis gases, tar/liquids, and char/ash are examined for various operational scenarios using a simple reaction network. A brief comparison with traditional fluidization technologies is performed. The applied CFD model has been previously validated for non-reacting flows using experimental data from an in-house cold-flow apparatus. The product distribution from biomass pyrolysis between 450 and 500 °C was determined to be 14–17 wt.% char, 73–76 wt.% tar, and 8.5–9.5 wt.% pyrolysis gas, depending on the specific conditions of the process simulation, with all conditions yielding complete biomass conversion. The calculated convective gas/solid heat transfer coefficients in the GSVR were determined to be ∼650 W/(m 2 K), which is significantly larger than in non-rotating fluidization reactors. The GSVR exhibited the ability to intensify the biomass pyrolysis process with respect to both production per reactor volume and selectivity toward the desired products, indicating that further investigations with more detailed kinetics and/or experimental reactors is warranted.

Segregation and mixing effects of particle diameter distributions are numerically investigated in the riser section of a circulating fluidized bed. A granular kinetic theory based approach, which implements the Eulerian quadrature-based moment method to describe the particle phase, is coupled to an Eulerian multi-fluid solver through a population balance model. The gas-solid multiphase flow is two-dimensional, transient and isothermal. The particle distributions fed from each side inlet of the riser have different variances, but the same mean diameter. The core-annular regime used as a numerical benchmark for riser flows is well predicted. A comparison in the homogeneity of particle mixing is made from the lower-order moments of the particle distribution obtained at various positions and at different axial lengths along the riser. It is seen that the relative standard deviation of the particle distribution varies spatially, indicating dynamic mixing inside the riser.

Turbulent reactive flow simulation often requires accounting for turbulence-chemistry interactions and the sub-grid phenomena. Their complexity leads to a trade-off between computational efficiency on one hand and computational accuracy on the other. We attempt to bridge this gap by coupling the power of machine learning with the turbulent reactive flow simulation, specifically in the form of a deep artificial neural network. The Lagrangian Monte Carlo method is chosen as a demonstration case as it is one of the most accurate models for turbulent reactive flow simulation, but also one of the most time-consuming. The workflow consists of training data generation, deep neural network construction, and implementation in ANSYS-Fluent, followed by an evaluation of model accuracy and efficiency, which results in an order of magnitude faster simulation without loss of accuracy thanks to our data-driven deep neural network. This approach can be of universal relevance in speeding up time-consuming models in the field of reactive flow simulation.