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Marinization of Multiphase Reactors through the Prism of Chemical Engineers Amir Motamed Dashliborun, Jian Zhang, Seyed Mohammad Taghavi, and Faïçal Larachi Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b05695 • Publication Date (Web): 30 Jan 2019 Downloaded from http://pubs.acs.org on January 31, 2019

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Industrial & Engineering Chemistry Research

110th Anniversary: Marinization of Multiphase Reactors through the Prism of Chemical Engineers Amir Motamed Dashliborun, Jian Zhang, Seyed Mohammad Taghavi, Faïçal Larachi* Department of Chemical Engineering, Laval University, Québec, QC, Canada G1V 0A6 *Corresponding author. Tel.: +1 (418) 656-3566, Fax: +1 (418) 656-5993 E-mail address: [email protected] (F. Larachi) Abstract Offshore oil/gas industries have been employing multiphase scrubbers and reactors to treat hydrocarbons extracted from undersea reservoirs. Operation of floating scrubbers and reactors on non-stationary platforms undergoes remarkable technical and operational challenges stemming from the complex sea states. Indeed, ship tilts and motions affect the reactor hydrodynamics and consequently its chemical performance. Therefore, imperatives for predicting and controlling the performance of offshore reactors by accounting for the contribution of marine swells have opened up considerable opportunities for research. This contribution presents an extensive chemical engineering overview on experimental and theoretical studies related to the effect of floating vessel motions on the performance of multiphase reactors and scrubbers. Cocurrent downflow, cocurrent upflow and countercurrent gas-liquid packed beds, spinning gas-liquid packed beds, gas-solid fluidized bed, and bubble columns are reviewed with an emphasis on their hydrodynamic, mass and heat transfer, mixing behaviors and their impact on catalytic and non-catalytic reactions for the marine applications. Keywords Floating platform/offshore conditions; hydrodynamics; maldistribution; experiment; modeling and simulation; performance

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1. Introduction With an ever growing appetite for energy, the world offshore oil and gas field exploitations have been significantly extending towards deeper water transforming remoter high-sea resource areas into economically viable reserves thanks to auspicious conjunction of matured technologies and market prices.1,2 For instance, among proven reserves of natural gas in the world, almost one half of the gas reserves are found as stranded gas in offshore fields for which developments have remained uneconomical owing to their remoteness from potential markets either because of absence of economic transportation and infrastructure, or lack of conversion technologies.3 Moreover, the decreasing rates of discovery of new giant conventional fields antagonized by growing demands for natural resources is an established reality. Thus, the development of smaller oil and gas fields is virtually indispensable.4 Accordingly, there is growing interest in developing and monetizing oil and gas fields in far offshore where costly pipeline infrastructures to onshore facilities is impractical; especially, for marginal oil and gas fields with limited recoverable reserves and a small number of wells.1,4 The land-based technologies for tapping oil/gas fields, due to their anteriority, had to be adapted to the context of offshore activities in deep seas or areas far off continental shores. The main players in oil and gas exploration have been employing technologies such as deep draft semisubmersible, semi-submersible rigs, extendable draft or tensioned leg platform, single-point anchor reservoir, floating production storage and offloading (FPSO), and floating liquefied natural gas (FLNG).5-7 The learning curve shown in Figure S1 in Supporting Information illustrates the evolutionary path of technologies implemented for the exploitation of oil and gas fields afar from the continental coasts. As readily mobile complexes, FPSO and FLNG are technological breakthroughs which integrate extraction, production, and storage operations on 2. ACS Paragon Plus Environment

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the same floating system (Figure S2). Hence, they qualify for reducing the minimum economic field size as well as making possible the development of small stranded or remote hydrocarbon fields while eliminating installation of costly pipeline infrastructures to onshore refineries.1 In addition to the easily movable and re-locatable features of FPSOs, they can be time- and costeffectively constructed by retrofitting a range of existing oil carriers and tankers.7 From the first transformation of LNG carrier into FLNG unit in 2007, the number of construction projects of oil and natural gas FPSO units planned for the 2010-2015 period was increased to ca. one hundred vessels.5,7 To make sense of FPSO size and capacity, the Agbami FPSO with 320 m in length and 59 m in breadth produces 250 Mbpd of crude oil and 450 MMscfpd of gas while it can store ca. 2.3 MMb of products.3 The units of FPSOs can be potentially in service for the development of deep water production in a water depth range of 150-1500m.9 FPSO vessels bring together a large number of processing units on the topside and hull, depending on functionalities, including the hydrocarbons treatment and stabilization, the power plant, and the desalination unit.10 These operations effectively take advantage of seaborne transport of crude oil to produce en route a range of fuels and petrochemicals using onboard scrubbers and reactors similar to those in operation in onshore aboveground facilities.11 The economic model of FPSO and FLNG appears to facilitate the distribution of products directly to different markets and thus selling them with attractive profit margins. By virtue of these particular considerations, FPSO and FLNG platforms are being progressively adopted by the oil/natural gas sectors (Figure S3). Nevertheless, the floating production units or so-called mini-refineries encounter remarkable technical challenges stemming from the wind and wave actions on sea. A free-floating vessel has six degrees of freedom of motion including translational (surge, sway, and heave) and rotational (roll, pitch, and yaw) motions (Figure S4). Not all these degrees of freedom are active and 3. ACS Paragon Plus Environment


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sometimes some of them can be neglected such as in some mooring arrangements. For example, FPSOs with turret at the bow solely have, roll, and pitch motions.12 Harnessing the operation of separation vessels and reactors onboard floating systems requires implementation of efficient corrective measures to counter or to anticipate any performance deviation with respect to the well-trodden land-based treatment units. Offshore oil and gas industries have been widely using packed beds (i.e., fixed beds) as either two-phase reactors or scrubbers for onboard conversion or treatment due to their simplicity in construction and more importantly for the “assumed” attenuation of the rocking effect caused by the wave disruptive action.13,14 However, ship motions in general may subjugate reactor/contactor operations inflicting drastic reductions on unit-operation capacity and deviations from targeted product specifications. Therefore, controlling and predicting the efficiency and performance of offshore facilities by accounting for the contribution of marine swells opens up formidable opportunities for both fundamental and applied research. More specifically, experimental and theoretical studies regarding the effect of floating vessel motions on the performance of reactors and scrubbers onboard are mandatory. By summarizing the current state-of-art and by analyzing some of the bottlenecks stemming from sea swell/wind motions through the lens of experimental and numerical results available in literature, the present review aims at exposing the community of chemical reaction engineers to a non-traditional application area of multiphase reactors. Three main types of multiphase reactors and scrubbers, namely, gas-liquid packed beds, gas–solid fluidized beds and gas-liquid bubble columns, have been targeted by researchers for offshore applications. It should be indicated that as far as the open literature is concerned, a large portion of contributions in the field of offshore multiphase reactors has been devoted to packed-bed columns, whereas a few researchers worked 4. ACS Paragon Plus Environment

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on other types of multiphase reactors. Accordingly, packed beds made up the most parts of this literature review work. To stick to a vocabulary already in usage in marine engineering, we have chosen the coining “marinization of multiphase reactors” for this chemical engineering endeavor in which marinization is intended for the reliable multiphase reactor/separator design specifically for long-term use in marine environments in terms of hydrodynamics, mass transfer, dispersion, contacting area, and chemical conversion. 2. Gas-Liquid Packed Bed Multiphase packed beds consist of columns randomly filled with solid particles or packed with structured elements throughout which gas and liquid phases flow in cocurrent downward (trickle beds), cocurrent upward (packed bubble columns), or in countercurrent (packed towers) modes. Countercurrent packed columns using structured packings are the most frequent apparatuses operated on FPSO units.15 However, with contemplation of on-board Fischer-Tropsch fixed-bed reactors, concurrently downward syngas-liquid hydrocarbon products are also possible candidates to find interest in the realm of marine chemical reactor applications.2,3,16 Co-current upflow fixed beds are being the subject of a few academic studies, though no potential industrial applications have hitherto been identified. We shall restrict ourselves here to emphasize the emerging challenges related to the marinization of these reactor/separator units. 2.1. Design of adapted distributor/packings Contrarily to the motionless land-based processing units, fluid distribution onboard packed beds is likely to be altered by the oscillations from the hosting ships which only partly filter out the dynamics from the assaulting swells and wind.17,18 Therefore, mimicking offshore conditions compulsorily requires consideration in the design stage of careful archetypal piloting tests to 5. ACS Paragon Plus Environment


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ensure implementation of ad hoc packed bed systems for hydrocarbon treatment in deep waters. Solutions to offshore floating packed beds draw from two schools of thought. The first, driven by the patent literature, has been to ensure that fluid initial distribution remains as much as possible unaltered during column tilts and roll motions and for which various parries have been proposed. In this approach mainly privileged by applied and industrial research laboratories, developments and innovation focus on the design of adapted distributors. Armstrong et al.17 developed a liquid distribution plate for a packed liquid-vapor contact column with uniform crisscross structure enabling alternate vapor riser passages and reservoir cells the purpose of which is to compensate for sway or tilt when the column is mounted on a ship. To ensure fluid distribution to remain unaffected by horizontal flows as a result of reactor motion, dispensers were designed.18 Such devices consist of tandem collector/distributor connected via one or several relatively long vertical pipes to ensure hydraulic charge regardless of wave conditions.17,18 Recently, the Institut Francais du Petrole - Énergies Nouvelles (IFPEN) developed a distributor tray for contacting efficiently gas and liquid in offshore countercurrent gas treatment units for CO2 capture, dehydration or distillation.19,20 The distributor was partitioned into compartments each comprising functionalities for passing gas via chimneys and liquid via perforations thus allowing an inter-compartment circulation of a portion of the liquid (Figure 1). Such arrangement enhanced liquid repartition even under rolling conditions (angle ± 5°, period 10-20 s). On account of the downward liquid flow in both cocurrent trickle beds and counter-current packed beds, optimal designs of liquid distributors17-20 for the latter are expected to be equally applicable for trickle beds in marine applications.


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The Sulzer company engineers recently addressed maldistribution sensitivity and susceptibility in columns subject to accelerations and tilt in terms of flow correction or aggravation depending on the type of internals employed, i.e., random packing, structured packing and trays.21 Besides, Air Liquide developed cross-corrugated packing consisting of a stack of vertical corrugated strips with their corrugations alternately tilted in opposite directions to tackle fluid maldistribution inside the distillation columns embarked on offshore oil platform.22 2.2. Hydrodynamics A second group of researchers identified flaws in the former-approach assumptions whereby deterioration of fluid distribution along the column itself is haphazardly ignored. Although installation of distributors adapted to sea conditions would be efficient to curb fluid maldistributions at the top of the bed, slow and fast perturbations, echoed by the dynamic inclination of the columns which arises from the marine conditions, inexorably initiate other “delocalized” maldistribution areas within the main part of the column.23 No matter how meticulous are the efforts invested in designing marine-robust distributors, column oscillations and tilts degrade fluid distribution from column top to bottom on account of the lowered downhill slope and transverse inertial forces. A process coming across the multiphase/multiscale dynamics in such devices to cope with sea perturbations is yet to be invented, and thus basic research to develop new scrubber/reactor strategies is more than ever needed. Thus a path parallel to the design of ad hoc distributors was pursued by other research groups whose interest focused on describing the hydrodynamics prevailing inside stationary inclined packed beds – conjectured to be limiting column postures on ships under trim or heel ‒ or when packed columns are subjected to vessel oscillations. Table S1 (Supporting Information) summarizes the most recent experimental hydrodynamic/mass transfer studies of the characteristics of floating 7. ACS Paragon Plus Environment


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packed bed for the three gas-liquid contacting modes. In subsequent sections, investigation methods in those studies and analysis of findings are discussed in detail. Over the past recent past years, new multiphase flow measurement techniques have emerged to monitor flow patterns and to measure local phasic saturations in various multiphase reactors. Especially remarkable are the non-ionizing radiation-based techniques such as electrical capacitance imaging in its invasive (wire-mesh sensors, WMS) and non-invasive (tomography, ECT) variants. Capacitance wire-mesh sensors are able to register highly time- and spaceresolved phase saturation distribution images without recourse to sophisticated reconstruction algorithms.24 If superiority of non-invasive electrical capacitance tomography resides in its ability to avoid disturbing the fluid field texture, the associated low spatial resolution and more elaborate reconstruction algorithms are their main counterbalancing limitations.25 Matusiak et al.25 carried out detailed comparative liquid distribution measurements by means of electrical capacitance tomography and wire-mesh sensors in gas-liquid packed beds both under uniform distribution and severe maldistribution. The absolute differences in liquid holdups as measured by the two techniques, both for uniform and non-uniform liquid feeds, were noticeably small and did not exceed ca. 0.02. Similar comparisons confronting wire-mesh sensors, non-ionizing capacitance and ionizing-radiation transmission imaging techniques are also covered by the Dresden group of Prof. Hampel.26,27 2.2.1. Cocurrent downflow The hydrodynamics of inclined gas-liquid cocurrent downflow packed beds and its dependency to tilt angle was experimentally investigated by Schubert et al.28 A twin-plane electrical capacitance tomography (ECT) sensor was employed to measure liquid saturation and to 8. ACS Paragon Plus Environment

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characterize pulse flow regime in the tilted bed. The results showed that column deviation from verticality prompted remarkable gas-liquid segregation accompanied with a decrease in both liquid saturation and pressure drop (Figure 2). The reduction in liquid saturation was observed at different heights along the bed (results not shown here). Moreover, the trickle-to-pulse flow regime transition point was shifted towards higher liquid velocity by more inclination of the bed due to reduction of the interaction between phases. Increased inclinations also resulted in fading out of the pulsing flow whereby characteristics such as pulse frequency and pulse propagation velocity tended to decrease as compared to the standard vertical trickle bed (Figure 3). The effect of column tilt angle on the dynamics of liquid drainage in liquid-full packed columns was also studied using ECT sensors and a steel pendulum-like frame which allowed inclinations in the full angular range from horizontal to vertical position.28,29 Liquid saturation profiles and the evolution of flow regimes were monitored at various bed axial heights and tilt angles under gravity-driven drainage and absence of pressure gradients. Figure 4 shows an acceleration of the liquid draining rate upon tilting the column. In addition, spatiotemporal imaging of ECT demonstrated that 80% of the poral dynamic liquid was discharged rapidly at constant flow rate, whereas the remaining 20% liquid within partially saturated pores was drained slowly. This twostep drainage mechanism was ascribed to actions on the liquid motion, respectively, in the streamwise and transverse directions by the corresponding projections of the gravitational force due to bed tilt. Recently, Assima et al.30 and Motamed-Dashliborun and Larachi31 experimentally investigated the effect of column motions on the hydrodynamics of descending gas-liquid cocurrent flows in porous media via a laboratory-scale packed bed embarked on a hexapod ship motion simulator and submitted to a variety of motion regimes. They applied a capacitance Wire-Mesh Sensor 9. ACS Paragon Plus Environment


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(WMS) to measure the local instantaneous liquid saturation variations in the bed cross-section. The results revealed that tilting motions (roll, pitch, roll + pitch) induced significant perioddependent fluctuations in the time-series of maldistribution factor and pressure drop (Figure 5). Such variations were ascribed to the fact that at the approach of the extremum angular positions the intensity of gas-liquid interactions significantly decreases due to the emergence of an easy path for the gas phase close to the upper wall (maldistribution maxima), thereby leading to pressure drop minima. Conversely, when the bed turns vertical, the gas-liquid segregation gradually disappears and the pressure drop evolves from minimum towards maximum. The authors highlighted spatial non-homogeneities in the crosswise liquid distribution and liquid transversal migration during column angular oscillation by selecting orthogonal zones from the 2-D WMS slice to monitor the evolution of liquid saturation. As an illustration (Figure 6), while the liquid saturation of zone RI oscillates with a periodicity equal to the roll motion period due to being subjected frequently to the lowermost and uppermost positions, zone RII exhibited more or less a steady-state liquid saturation profile. This observation underlines severe spatial discrepancies in the cross-sectional liquid distribution. Secondary transverse displacements of the fluids across the bed are reflected in oscillations of the liquid saturation provoked by timedependent gravitational and inertial force components in the course of column angular motion. Besides, liquid residence time distribution (RTD) experiments were performed to determine the liquid mean residence time and Péclet number by implementing a stimulus-response tracer pulse technique and using a macro-mixing model.30 All ship translational (surge, sway, heave) and rotational oscillations (roll, pitch, yaw, roll + pitch) were found to exacerbate liquid back-mixing in comparison with the conventional stationary vertical bed (Figure 7). Motamed-Dashliborun and Larachi31 also detected a pronounced shift in the regime transition point from tickle flow or


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segregated/trickle flow to pulse flow towards higher fluid velocities by tilting the column as well as increasing the motion period of roll and roll + pitch. Open-cell solid foams as a new generation of structured packings providing higher open porosities and higher specific surface areas have been recently contemplated for replacement of conventional randomly packings.33,34 Hence, Motamed-Dashliborun et al.35 conducted an investigation focusing on the potential of solid foams as alternative packing internals for reactor and contactor applications in offshore floating platforms. The influence of column motions on the hydrodynamic behavior of SiSiC foam packed beds operated with concurrent descending gas-liquid flow was thoroughly studied using a similar WMS/hexapod ship motion simulator. Similar to random packings, fluid maldistribution was found to prevail in solid-foam beds with deviations from uniformity greater for rotational than for translational perturbations. Column tilts and oscillations adversely affect open-cell foam bed hydrodynamic performance yielding transient gas-liquid segregated flow regimes and oscillations of maldistribution factor as demonstrated in Figure 8. Furthermore, a notable deviation from liquid plug flow was found in the course of bed tilts and excitations. 2.2.2. Cocurrent upflow Bouteldja et al.36 studied the hydrodynamics of stationary tilted packed beds operated with cocurrent ascending gas-liquid flows where an ECT sensor was used for imaging the flow distribution. Segregation between gas and liquid was observed as in slanted downflow packed beds. Moreover, the regime transition from bubbly flow to segregated flow, whereby short circuits were created for the gas phase along the upper wall, was monitored as a function of bed tilt angle. The main reason for reduction of the pressure drop at higher inclinations was due to 11. ACS Paragon Plus Environment


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gas-liquid disengagement which in turn diminishes phase interactions. It was also reported that augmentation of bed tilt angle increases the cross-sectional averaged liquid saturation as a result of bubbles disengagement and replacement with liquid in the bottommost region of the column. Furthermore, Motamed-Dashliborun et al.37 experimentally investigated the effect of column translations and rotations on the gas-liquid dynamics in upflow packed beds using a hexapod ship motion simulator. Two WMSs were embedded in the packed bed to register the local instantaneous liquid saturation variations across the bed in order to characterize their flow patterns in the course of bed movements. The results indicated that column tilting motions significantly alter the hydrodynamics prevailing in the packed bed prompting development of gas-liquid segregated zones, fluctuations in the maldistribution factor and pressure drop time series, and delay in the inception of pulsing flow regime (Figure 9). It is seen that the transverse zigzag (roll) motions of liquid flow resulted in more axial dispersion as well. Interestingly, a rolling bed with 20 s motion period exhibited an intermittent pulsing flow regime, the emergence of which coincided with straightening of the column posture during oscillations. From above findings, one can conclude that the hydrodynamic parameters of upflow packed beds exhibit similar behavior to those of downflow packed beds in response to column tilts and motions. 2.2.3. Countercurrent flow Similar to cocurrent downflow and upflow packed beds, examination of the hydrodynamics of gas-liquid countercurrent packed beds under stationary tilts revealed a noticeable reduction of the overall pressure drop and liquid saturation at the expense of gravity-driven segregated flow patterns inside the bed. Using ECT sensors and a steel pendulum-like frame, Wongkia et al.38 showed that liquid accumulation in the column lowermost area led to an aggravation of phase 12. ACS Paragon Plus Environment

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maldistribution and a shift of the flooding limit towards higher throughputs as a result of tilting the column (Figure 10). For the sake of developing models for predicting liquid distribution, mass transfer and flooding under offshore conditions, Weiss et al.39 in a collaboration between TOTAL, IFPEN, Prosernat and Heriot-Watt University performed a scaled-up experiment for data gathering with two structured packed towers, 0.6 m diameter with 2.5 m height and 1 m diameter with 5 m height, respectively. Both columns were placed on a pivot-point frame and tilted/oscillated around the pivot point on the base of the column with angles up to 8° and periods from 15 to 40 s. The cross-sectional liquid load distribution was obtained via a liquid collection method in the lower end of the structured packing. In stationary tilt positions (3° and 5°), experiments showed the liquid accumulation in the bottommost part and gas migration to the upmost part. The liquid maldistribution severity was highly sensitive to the increase of height and tilt angle of packed tower. For the rolling column, less distortion of liquid distribution was observed compared with the stationary tilted one. However, slowly rolling motions provoked periodic transverse movement of the liquid across the packing. When the column tilted back through the vertical position, the general gross movement of liquid across the packing, to some extent, diminished the liquid maldistribution as a method of correction but depended on many factors (e.g., motion frequency and amplitude, type of packing, gas/liquid flow rate, column diameter and height, liquid properties). The above results confirmed the observations made formerly for the liquid distribution under column tilts and roll motions in pilot-scale testing.40-43 Using Electrical Resistance Tomography (ERT) and a sloshing device, Son et al.44,45 also experimentally investigated the effect of permanent tilts and roll motions on liquid distribution in a structured packed tower with gas-liquid countercurrent flows. In line with previous findings, 13. ACS Paragon Plus Environment


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the results showed that increasing the column tilt angle under stationary conditions as well as incrementing both amplitude and period of the roll motion aggravated the uniformity of crosssectional liquid distribution as illustrated in Figure 11. This maldistribution continued to worsen as the liquid flows downward. Besides, a strong impact of column tilting on the liquid maldistribution was observed at low liquid load and high gas factor. While an increase of liquid viscosity from 1 cP to 5 cP appeared to be effectless on liquid distribution, use of 10 cP liquid reduced notably liquid maldistribution. No attempt by this study’s authors was provided to highlight the reasons for such behavior. The observations made earlier underline the fact that regardless of gas-liquid contacting mode in packed beds, being cocurrent flow or countercurrent flow, column tilts and motions cause gasliquid disengagement zones and secondary transverse displacements of the fluids across the bed which in turn translates in fluctuations in the time series of the maldistribution factor, liquid saturation, and pressure drop. 2.3. Flow modulation and spinning packed bed As observed earlier, gas-liquid packed beds encounter severe fluid maldistribution under column tilts and angular oscillations, which in turn can cause considerable liquid back-mixing and mass transfer limitations as well as hot spot formation in exothermic catalytic reactions. The nonuniform liquid distribution would not wet efficiently all catalyst particles and then a large part of catalysts remains dry and unused. Accordingly, the performance of packed-bed reactors ought to be intensified either by operational methods or by the design of efficient reactors in order to ensure economic viability and environmental imperatives. As recommendations for process


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intensification, two operational concepts are discussed to increase packing utilization and enhance process performance for potential offshore floating packed-bed reactor applications. Flow rate modulation was recently employed to reduce liquid maldistribution in floating packed beds.46 In such periodic operation, a continuous flow of one phase meets the other phase at the bed inlet which is periodically cycled between a low and a high flow rate (base/peak mode) or intermittently interrupted (on/off mode).47 Using WMS and ECT imaging techniques and a hexapod robot with six-degree-of-freedom motions, Motamed-Dashliborun at al.46 evaluated the applicability of cyclic operation method to curb phase maldistribution in response to offshore perturbation conditions. The results demonstrated that the shock waves arising from the sudden flow rate perturbations were able to convey the accumulated liquid in the lower-wall column area and to disperse it across and along the bed, thereby diminishing the gas-liquid segregation. This observation underlined an appreciable influence of generated liquid waves on the hydrodynamics of offshore floating packed beds. They conclude that although bed tilts and motions tend to attenuate the travelling liquid wave by virtue of the gravity-driven segregation, wave identity can still be preserved to a certain extent provided appropriate tuning of the cycle time intervals and split ratio are imposed.46 Inclined spinning reactor48-50 and low-shear spinning vertical reactor51 have been recently introduced for process intensification of cocurrent gas-liquid flow packed beds. In the former concept, rotation of already-inclined packed beds around the column axis of revolution symmetry leads to periodic immersion of particles into the liquid accumulated in the lower wall region. This approach enables correcting for liquid maldistribution by periodically replacing, upon vessel spinning, the dewetted zones by wetted zones (Figure 12). In virtue of this concept, the catalyst surface is frequently refreshed and thus formation of hotspots is prevented, while 15. ACS Paragon Plus Environment


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access of the gas phase to the active sites is facilitated in the drained upper-wall region. Although the inclined spinning reactor concept is an efficient parry to cope with exothermic gas-limited heterogeneous catalytic reactions, it can also be considered as a potent tool to ensure nearly steady-state operation of reactor exposed to roll motions, whereby the column periodically comes across inclined positions and prompts gas-liquid segregation (Figure 12). Nevertheless, Motamed-Dashliborun et al.51 submitted low-shear spinning up to 90 rpm to upright packed beds in order to generate sufficient transverse forces to redistribute distinct flow paths of liquid streams and to achieve a uniform fluid distribution at the expense of a dispersed flow pattern. It is noteworthy to mention that more flexibility in adjusting liquid residence time and back-mixing was found for both spinning reactor concepts via control of column spinning frequency. They concluded that depending on the type of motion experienced by the bed during sea swells, either tilting or non-tilting oscillations, the packing could be effectively utilized via tuning an appropriate column rotational velocity similar to the aforementioned rotating reactor concepts. However, a comprehensive experimental study is required to implement these prospective parries into practice for process intensification in offshore packed-bed reactors. 2.4. Mass transfer In order to realize challenges in design and scale-up of offshore packed-bed reactors and scrubbers as well as to develop appropriate models for predicting their performance, mass transfer ought to be investigated along with hydrodynamics. Despite exhaustive investigations on hydrodynamic characteristics of packed beds in the context of offshore floating applications, there are a few experimental researches addressing the mass transfer performance of floating packed beds. Those works were limited to study gas-liquid mass transfer deviations of packedbed scrubbers under column tilts and motions with respect to stationary vertical units. 16. ACS Paragon Plus Environment

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Motamed-Dashliborun et al.52 recently addressed the potential bottlenecks stemming from ship tilts and oscillations on the mass transfer performance of the packed-bed scrubber in terms of effective gas-liquid interfacial area and CO2 removal efficiency. They conducted a systematic experimental study using a hexapod robot with six-degree-of-freedom motions and an embarked column packed with Mellapak 500X structured elements (M500X) and Raschig rings. Gas-liquid mass transfer tests were carried out based on the chemical absorption of CO2 into 30 wt% monoethanolamine (MEA) aqueous solutions and adjusting the operating conditions to correspond to the fast chemical absorption regime in the liquid film, thereby giving access to the gas-liquid interfacial areas. The results revealed a loss of mass-transfer efficiency rationalized in terms of a decrease of the effective gas-liquid interfacial area as the column deviated from the vertical position (Figure 13a). Under column roll motion, the interfacial area was also found to decrease monotonically with the oscillation period. Moreover, the M500X structured packing was shown to outperform the random Raschig ring packing in all bed configurations (Figure 13b,c). The CO2 removal efficiency was found to be sensitive to bed height, decreasing at increasing tilt angle/motion period of short-height beds packed with random packings. The structured packing showed lesser dependence with respect to column tilts and motions than Raschig rings; hence, future studies in the field of offshore floating packed beds can further exploit this type of packings. Gauthier et al.53 in collaboration between TOTAL, IFPEN, Prosernat and Heriot-Watt University performed pilot tests in columns of two different diameters (0.6 m and 1.0 m) with structured packings under a range of tilt and motion conditions in order to collect large experimental data set for developing a model to be embedded in a rate-based mass transfer proprietary simulator. The absorption of CO2 by a dilute caustic soda solution was considered to satisfy fast reaction 17. ACS Paragon Plus Environment


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regime and thus determining effective interfacial areas at a given gas-liquid flow rate. The experiments demonstrated an adverse impact of maldistribution on the performance of CO2 absorption. A decrease of mass transfer efficiency about ca. 10% was found in column tilting conditions. The findings of this study recommended taking precautions against any type of motion and its parameter (angle, period) to diminish the loss of tower performance. Likewise, Di et al.54,55 investigated the influence of tilt and roll motion on the mass transfer performance in structured packed columns using an air-NaOH system. They showed that the reduction of mass transfer area occurred in low-frequency roll motions and stationary tilting caused more deteriorative effect than the roll motion in agreement with previous findings. Moreover, M500X and M700Y structured packings showed a better performance than M250X structured packing under offshore conditions due to their relatively higher surface area (Figure 14). Ultimately, they suggested moving to amine-based CO2 capture systems for mass transfer studies under offshore floating conditions on account of their proven efficiency for gas-treating industrial units. 2.5. Modeling and simulation There is certainly no escape from conducting reliable experimental studies to investigate the hydrodynamic and mass transfer behaviors of packed-bed reactors. However, the associated restrictions and difficulties have limited application of experimental methods to small laboratoryscale setups, narrow operating range, and generally cold-flow conditions. Therefore, procurement of validated first-principle-based models can greatly enhance understanding and trust in the scale-up and optimization of the multiphase flow characteristics in packed beds. Furthermore, virtually cost-free and detailed sensitivity analyses can be performed with the aid of simulations saving redhibitory costs and time consuming experiments. Accordingly, some researchers carried out modeling and simulation studies of offshore floating packed beds to 18. ACS Paragon Plus Environment

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provide further insights into the influence of ship tilts and motions on the performance of packed-bed reactors onboard floating vessels/platforms. Table S2 (Supporting Information) summarizes the modeling and simulation efforts reported recently in the literature concerning offshore floating packed beds. Computational fluid dynamics (CFD) along with multiphase Eulerian approach are being used extensively in the field of multiphase flow reactors for describing the local fluid distributions and velocity fields.58 An exhaustive review on theoretical models available for packed beds along with their characteristics and limitations as well as comparison between different modeling approaches can be found in Wang et al.58 Atta et al.59 applied a two-fluid Eulerian CFD framework to identify the main causes for stratification in stationary tilted packed beds. Among the plethora of drag force closures available in the literature for gas-liquid cocurrent downflow packed beds, use was made of the relative permeability model to capture the physics of local flow and liquid saturation distribution inside the tilted porous media. In spite of satisfactorily predicting the trends, the numerical results revealed remarkable deviations with respect to the experimental data. These deviations were ascribed to phase maldistribution in tilted beds due to the segregated flow regime which were concluded to require formulation of more appropriate closure laws to be incorporated in the CFD models of tilted packed beds. Extensive CFD simulations have been attempted to predict the transient hydrodynamic behaviors of stationary tilted packed-bed reactors under gas, liquid, and gas/liquid alternating cyclic operations using a three-dimensional (3D) unsteady multi-fluid Euler approach consisting of closure laws for drag forces (i.e., fluid-solid and fluid-fluid interactions) as well as capillary and mechanical dispersion forces.60 The simulation results were validated against experimental data provided by ECT imaging and differential pressure transmitter. The applied model predicted 19. ACS Paragon Plus Environment


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satisfactorily the morphological characteristics of a liquid wave triggered by different cyclic strategies as well as the values and variations of bed overall pressure drop (Figure 15). With regard to Atta et al.59 diagnosis, the main reason behind failure of the traditional Eulerian model is attributed to the transient dynamics of flowing fluids being described only via fluid-solid and fluid-fluid interactions. Gas-liquid disengagements in tilted packed beds in preventing attainment of fully developed unidirectional flows require more physics to enrich the model descriptions. From Figure 16, it can be seen that increasing the bed deviations from the vertical position (0°) considerably influenced the liquid holdup gradient in the direction of column tilt. Since there is a direct relationship between the dispersion forces and the gradient of fluid volume fraction, both capillary and mechanical dispersion forces became significant with incrementing the column tilt. The main conclusion stemming from this study60 was that incorporation of capillary pressure and mechanical dispersion force terms in the Eulerian multi-fluid CFD model is essential to accurately capture the transient stratifications arising in tilted packed beds. Numerical simulations were recently conducted to elucidate the hydrodynamic behavior of gasliquid cocurrent downflow packed beds under ship tilts and roll motions using a transient 3D two-fluid Eulerian CFD model within porous media approach.61 Attou et al.62 drag force closures were used to account for the porous resistances (i.e., fluid-solid interactions) and gas-liquid interaction. In addition, the capillary pressure and the mechanical dispersion have been described as two distinct mechanisms contributing to momentum dispersion in the porous medium.62 Moving reference frame and sliding mesh as two different methods to simulate the roll motion in multiphase packed beds were implemented. Moreover, capacitance wire-mesh sensors and differential pressure transmitter were employed to obtain experimental data for validation of the simulation results in terms of local and cross-sectionally averaged liquid saturations and bed 20. ACS Paragon Plus Environment

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overall pressure drop, respectively. The numerical results indicated that omitting to incorporate the capillary and mechanical dispersion terms in the CFD model causes severe loss of temporal stability and an erratic behavior in the computed liquid saturation for the rolling and stationary tilted packed beds (Figure 17). Hence, these dispersion terms need to be implemented to accurately capture the transient hydrodynamics of cocurrent downflow packed beds under offshore conditions. The validated CFD model confirmed the experimental observations that column angular motions induce secondary transverse displacements of the gas and liquid phase in the radial and circumferential directions (Figure 18). In addition, an increase of rolling angle and period result in a decrease of liquid saturation, bed pressure drop, and uniformity degree of the liquid distribution (Figure 19). From sensitivity analysis, it was found that liquid saturation, pressure drop, and uniformity index were enhanced at higher liquid viscosity (2 cP to 4 cP) and smaller packing particle size, whereas the value of these parameters diminished at higher liquid density. Moreover, higher gas density augmented the pressure drop and uniformity index at the expense of lower liquid saturation. Steady-state and transient hydrodynamics of two-phase downward flow in packed beds with uniform and non-uniform radical porosity distributions were also simulated for stationary vertical and inclined positions as well as rolling conditions using two-fluid approaches.63 To emulate tilting and rolling conditions, an artificial gravity vector according to the desired configuration was imposed on the vertical cylindrical geometry. The results revealed that in vertical and slightly inclined packed beds, the porosity distribution of packing had limited effects on the fraction of liquid flowing through the bed cross section, which was considerably different from the highly inclined case with noticeable axially asymmetric two-phase flow. In the latter case, the liquid flow in the lowermost cross section appeared to be dominant. Figure 20a,b shows 21. ACS Paragon Plus Environment


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the oscillatory cross-sectionally averaged liquid holdup and two-phase pressure drop due to the reverse secondary flows in the radial and circumferential directions in oscillating condition. The oscillatory liquid holdup and two-phase pressure drop deviated around the middle inclination angle when the reactor moved between vertical and an inclined angle. However, when the reactor moved between two-angled symmetrical positions, higher liquid holdup and pressure drop fluctuated around the vertical one (Figure 20c,d). Both of the amplitude and frequency were affected by the inclined angle and travel time between positions. Liquid drainage dynamics in vertical, inclined and rolling packed beds was also simulated under the same modelling framework.64 The simulation results demonstrated that for a sufficiently large column-to-particle diameter ratio an elaborated radial porosity model was inessential to describe the liquid drainage dynamics and a constant porosity assumption can be applied in the model. In all configurations, gravity dominated the initial liquid flow drainage. Drainage in the vertical position was controlled by the core-region liquid flow and independent to bed porosity distribution. By contrast, drainage of inclined posture was subjected to liquid flow in the bed lowermost region where liquid withdrawal was accelerated. In addition, a delay in liquid drainage was found under column angular oscillations in comparison with the stationary inclined bed (Figure 21). Such delay was ascribed to reverse secondary flows induced by the column motion, thereby providing almost cross-sectionally uniform liquid drainage distribution. Simulations of the coupling between hydrodynamics and chemical reactions were also conducted in the context of offshore floating packed-bed reactors. Iliuta and Larachi65-68 coupled volume averaged mass, momentum, energy and species balance equations with simultaneous diffusion and chemical reaction to investigate the two-phase flow dynamics, high-pressure hydrodesulfurization (HDS),65 CO2-H2S-MEA absorption,66,67 and carbonic anhydrase enzyme22. ACS Paragon Plus Environment

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CO2 absorption68 performance in the case of column oscillatory motion between two angled symmetrical/vertical-inclined position. Oscillating cocurrent downflow and countercurrent packed beds generated an oscillatory HDS and CO2 abatement performance (Figure 22). The liquid downflow in packed bed at higher inclinations significantly deviated from axial symmetry with considerable liquid accumulation in the lower bottom part of the column cross section. For the case of periodic asymmetric oscillation, averaged liquid holdup and two-phase pressure drop over cross-section fluctuated around the steady-state solutions of the middle inclination position (not shown). Under symmetric oscillation, however, these parameters evolved near the steadystate solution of the vertical position. It is interesting to note that while in CO2 scrubbers (Figures 22a and c) the time-series of exit CO2 mole fraction oscillated around the mean solution of the vertical configuration, such symmetric oscillation cannot be observed for the exit dibenzothiophene concentration in hydrocarbon hydrodesulfurization reactor (Figure 22b). This behavior can be ascribed to the HDS kinetics and the influence of wetting efficiency variations on effectiveness factors for the hydrogenolysis and hydrogenation reactions.65 The intensified reverse secondary flow developed in the radial and circumferential directions substantially decreased the effectiveness factors followed by the inhibiting effect of H2S on the hydrogenolysis reaction due to reduction of the gas-liquid mass transfer.65 For a detailed review on the aforementioned modeling and simulation approaches, Iliuta and Larachi can be consulted.69 In the above works,63-69 the model validation was performed only with experimental results of the stationary vertical and/ tilted packed beds available in literature and there was no comparison between the simulation results and experimental data for oscillating packed beds. For gas-liquid countercurrent packed beds with structure packings, Pham et al.70 developed an Eulerian porous media CFD model in order to investigate the effect of tilting and roll motion on 23. ACS Paragon Plus Environment


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CO2 removal from natural gas by MEA solution. The 3D CFD model involved the sliding mesh method to perform the column roll motion and coupling the momentum equation with mass transfer and chemical reaction equations. Under very low tilt angles (0 to 4.5°), the CFD outputs indicated that increases of the tilt angle and motion period barely affected the effective interfacial area between gas and liquid as well as the CO2 removal efficiency (Figure 23a,b). Under the same CFD framework, Kim et al.71 also conducted further simulations to discover the impact of the center of gravity position (CoG) on CO2 removal efficiency. They examined three CoG positions (i.e., bottom of the column (Case 1), vertically under the column (Case 2) and diagonally under the column (Case 3)) for two different diameters of the CO2 absorber. The results revealed that column rotation over the diagonally-bottom CoG position worsened the liquid maldistribution due to a long distance between the CoG position and the column. Yet, such maldistribution was marginal under very low tilt angle (1.5°) to have an appreciable influence on effective interfacial area and CO2 removal efficiency (Figure 23c,d). It should be noticed that in these two works the model validation was performed only with experimental results of the stationary vertical packed bed available in literature. In a different approach from the above efforts, Son et al.72,73 implemented an intersection network model and a volume-cell network model with liquid split algorithm for predicting the liquid distribution in a packed column under representative offshore conditions, i.e., permanent tilt and roll motion. The originally developed liquid distribution model74,75 was modified in terms of liquid split algorithm to involve the vertical and wall rivulets. In addition, negligible acceleration was assumed for the liquid phase during column roll motion whereby the transient variation in the liquid distribution was represented as a concatenation of the stationary liquid distributions at different tilt angles. The model results showed that the packed height and 24. ACS Paragon Plus Environment

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diameter remarkably affected the liquid distribution in tilt condition (Figure 24). This study concluded that it was reasonable to reduce packed height and increase column diameter to attain uniform liquid distribution in offshore conditions. However, the limitation of current proposed model is that the flow splitting parameter may vary with column diameter because of wall effect, and thus resulting in a less generic model. The main outcome from above studies was to expose the fact that packed bed tilts and angular motions caused by marine conditions could adversely affect the gas-liquid dynamics inside packings directly translating in reductions of unit operation efficiency. Hence, consideration of the uncontrollable wind/swell incidence on the column tilt or motion in the context of industrial sea applications is compulsory to ensure reliable designs of onboard packed-bed reactors/scrubbers. 3. Gas-Solid Fluidized Bed Besides gas-liquid packed bed configurations, the effect of stationary inclination on flow regimes and circulation patterns in gas-solid and liquid-solid inclined fluidized beds was also addressed in a few studies.76-79 In this type of multiphase systems, a mass of solid particles in a vessel is subjected to operating conditions from which particle/fluid mixture behaves as a fluid. Literature findings indicated that fluidization of cohesive powders in inclined beds led to heterogeneities in the form of localized transition to bubbling regime in the vessel upper wall region.79 Even small inclination angles in inclined liquid-solid fluidized beds were found to be enough to yield measurable effects on the recirculation pattern of the granular phase.77 As a potential application for sulfur removal and waste heat recovery from the exhaust gas onboard ship, the influence of roll motion on the hydrodynamics and heat transfer of marine 25. ACS Paragon Plus Environment


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circulating fluidized beds (CFB) was also studied.80-88 From the experimental investigations, roll motions provoked gravity-driven breach in flow field axisymmetry like in the stationary inclined configuration, while augmenting complexity of the flow pattern in virtue of the riser periodic oscillating. Pressure drop increase with increased solids holdup at riser’s bottom, heat transfer increase along the walls84 and its decrease inside the bed,83 and the decline of the descending velocity of particles by augmenting swing amplitude82 were observed as a result of column rocking. Table S3 (Supporting Information) summarizes recent works in the area of rolling fluidized beds. Zhao et al.85 applied the moving reference frame in a 3-D CFD-discrete element method model to simulate marine circulating fluidized beds under roll motion. This numerical approach transformed the roll motion into simple time-dependent acceleration terms whereby body force terms were introduced in the corresponding phase momentum conservation equations. The Coriolis acceleration, centrifugal acceleration, and unsteady variation of the angular and translational velocity appear in the momentum balance equation due to translational and rotational movements of the non-inertial reference frame relative to the stationary reference frame. From Figure 25, both the experimental and simulation results illustrate that the roll motion prompted an appreciable non-uniformity on the particle distribution over the bed cross section. Besides, Zhao et al.86 quantitatively evaluated the particle motion near the riser wall by PIV measurement. The experimental findings revealed periodic variations of the descending velocity due to a swing motion Figure 26a. Furthermore, it was found that with increasing the swing amplitude under the same motion period, the particle descending velocity decreased significantly (Figure 26b).


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To evaluate the heat transfer performance in a rolling CFB, Zhao et al.87 developed an improved cluster-based model which was confronted to experimental data. Disappearance of the gas layer and increase of the particle volume fraction in clusters, as the dominant factors for heat transfer augmentation, had considerable impact on the heat transfer performance in the rolling CFB. Furthermore, a capacitance tomography technique (ECT) for visualizing the particles was employed to investigate how rolling amplitude and period affect the particle distribution behaviors in rolling CFBs.88 From ECT images (Figure 27), it was observed that the particle distribution in the rolling CFB was dominated by the shear effect. The rolling amplitude caused an augmentation of the particle volume fraction whilst deteriorated the stability and uniformity of particle distribution. The rolling period, nevertheless, had little effect on the particle distribution due to its minimal influence on the shear effect. 4. Gas-Liquid Bubble Column Bubble columns as multiphase reactors are also employed significantly in the chemical industry due to a number of their advantages both in design and operation.89 They provide high heat and mass transfer coefficients as well as low operation costs due to lack of moving parts and compactness. Bubble columns have wide applications either, in the simplest forms, to purely mix the liquid phases and, in further complicated forms, to transfer chemical species from one phase to another phase. They are widely exploited especially in chemical processes such as petroleum residues conversion, hydrotreating, Fischer–Tropsch synthesis, coal liquefaction, hydrogenation, wastewater treatment etc.90,91 Hence, bubble column reactors are also envisaged in offshore fuel processing and gas treatment applications.92 Since good gas-liquid contacting is essential for implementation of efficient bubble columns, Assima et al.92 conducted an experimental study to investigate the influence of ship motions on bubbly flow using a hexapod swell simulator and a 27. ACS Paragon Plus Environment


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dual capacitance wire-mesh sensor. From gas-liquid visualizations (Figure 28), roll, roll + pitch, and high-frequency sway motions were found as the most influential in terms of bubble zigzag and swirl, and bubble-clustering as well as segregation during column dynamic tilts. Consequently, transverse movement of bubbles and their clustering augmented liquid recirculation and local gas velocity. They concluded that column oscillation will affect the performances of offshore bubble column treatment units.

5. Summary and Outlook As far as unconventional reactor configurations are concerned, the features under scrutiny cannot be transposed on a one-to-one basis for their design, scale-up and performance prediction and thus insights are required on the new reactor configuration. In particular, it must account for moving reactor approaches such as offshore floating reactors and scrubbers whose characteristics are very different from conventional stationary upright reactors. In this work, studies on offshore floating multiphase reactors were reviewed pointing out major contributions with their key findings. The literature findings prefigured that column tilt and oscillations stemming from marine swells in deep water could adversely influence the phase distribution inside multiphase reactors, which would ultimately result in reductions of unit operation efficiency. Therefore, offshore floating production units ought to take into account the influence of marine swells and their detrimental impacts on the reactor design to ensure onboard operation capable of achieving the specified capacities. It is worthy of mention that the hydrodynamic parameters (e.g., liquid saturation, pressure drop) of packed beds under offshore conditions are confirmed to exhibit transient behaviors with dramatic variations in the bed cross section. To achieve robust transition towards reliable design 28. ACS Paragon Plus Environment

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tools for packed-bed reactors and scrubbers in sea contexts, much more measurements would be necessary with different bed heights and diameters, packing size and type, and more diverse operating modes accounting for various transient sea conditions. Hence, more research works need to be conducted to fully address other crucial aspects of the offshore floating multiphase reactors. For example, the extent of wetting of the particles, or so-called wetting efficiency, is another important parameter required for designing packed-bed reactors in trickle flow regime. Non-uniform flow of the liquid phase over the particles is indeed foreseen to yield different degrees of wetting as a function of tilts and types of motions of the column which induce gross liquid movement across the packing. Furthermore, development of correlations based on dimensionless numbers with physical significance and on comprehensive experimental databanks has proven useful to the design of packed-bed reactors and scrubbers as well. Thus, detailed experimental studies should be carried out for different column diameters/heights and considering both pilot and commercial operating ranges to acquire the mass of experimental data necessary for establishing reliable design correlations which allow sizing and rating packed beds onboard floating platforms. In addition to the macro-scale Eulerian CFD modeling, particle-scale CFD modelling will contribute to enhance our fundamental understanding on very local resolution of the multiphase flow in packed beds and diffusion of species inside the catalyst particle. In this approach, the volume of fluid (VOF) model characterizes the gas–liquid interface and allows studying liquid– solid particle interactions and predicting the wetting efficiency. Hence, a VOF particle-scale CFD model should be developed in the context of offshore floating conditions to describe the local phenomena and to determine the effect of each impacting parameter which otherwise would be hard to capture experimentally.



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Transverse migration of liquid across the packing during column angular oscillations would change dramatically liquid film thickness which in turn can lead to additional time and space fluctuations of the interfacial gas-liquid and liquid-solid (and thus complementarily, the gassolid) mass transfer resistances. Therefore, applying spatiotemporal measurement techniques in chemical reaction and mass transfer experiments to determine corresponding parameters will provide highly useful information and understandings. Thus, since mass transfer is one complicated phenomenon that takes place between phases in packed-bed reactors, systematic mass transfer studies are required to investigate the influence of bed tilts and oscillations on the liquid-solid, gas-solid, and gas-liquid mass transfers. Based on extensive experimental data, mass transfer correlations should be developed which eventually can be combined with kinetic and thermodynamic models to calculate the required column height for reaching product specifications. Since mass transfer and heat transfer studies, unlike hydrodynamics, received less attention, it is worthwhile to spend more efforts on investigating the mass transport and heat transport phenomena in offshore floating reactors. Moreover, implementation of new reactor concepts and/or operational techniques for process intensification of multiphase reactors in the context of floating industrial applications is worth addressing in future studies. ASSOCIATED CONTENT Supporting Information (Figure S1) Technologies adoption to fit with deeper sea; (Figure S2) Typical FPSO modules layout; (Figure S3) Growth of FPSO; (Figure S4) Ship motion degrees of freedom; (Table S1)


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Recent experimental studies on floating packed beds; (Table S2) Modeling and simulation studies of floating packed beds; (Table S3) Recent studies on rolling fluidized beds. AUTHOR INFORMATION Corresponding Author Email: [email protected] ORCID A. Motamed Dashliborun: 0000-0002-8785-5049 J. Zhang: 0000-0003-4913-2584 S.M. Taghavi: 0000-0003-2263-0460 F. Larachi: 0000-0002-0127-4738 Present Address Department of Chemical Engineering, Université Laval, 1065 Avenue de la Médecine, Québec, Québec G1V 0A6 Canada Notes The authors declare no competing financial interest.

Acknowledgments The authors gratefully acknowledge the Natural Sciences and Engineering Research Council of Canada and the Canada Research Chair on Sustainable Energy Processes and Materials for their financial support. 31. ACS Paragon Plus Environment


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Nomenclature ae

=

gas-liquid interfacial area (m2/m3)

A

=

area of facet (m2)

dp

=

particle diameter

D

=

column diameter (m)

Dax

=

axial dispersion coefficient (m2/s)

hL

=

liquid holdup

g

=

Gravitational acceleration (m/s2)

G

=

gas mass flux density(kg/m2/s)

H

=

axial distance from the top of bed

L

=

liquid mass flux density(kg/m2/s)

N

=

number of pixels in bed cross-section (-)

Pe

=

Péclet number (UlZ/ɛLDax)

P

=

pressure (kPa)

R

=

column radius (m)

SB

=

bed specific surface area (m2/m3)

t

=

time (s)

T

=

period (s)/ temperature (K)

U

=

superficial velocity (m/s)

Ud

=

particle descending velocity (m/s)

UF or Mf

=

uniformity/maldistribution factor (

UI

=

uniformity index (

)

) 32.

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Z

=

axial distance between two sensors (m)

zʹ

=

axial distance from the bottom of bed

α

=

gas/ particle volume fraction

β

=

spatial-averaged liquid saturation

βi

=

ith pixel liquid saturation

ε

=

void fraction

εl

=

spatial-averaged liquid holdup

εli

=

ith pixel liquid holdup

μ

=

dynamic viscosity (Pa s)

θ

=

tilt angle/angular position during tilting motion (°)

ρ

=

density (kg/m3)

τ

=

time (s)

g (or G)

=

Gas

I

=

facet index

l (or L)

=

Liquid

P

=

peak

w

=

water

CFB

=

circulating fluidized bed

CFD

=

computational fluid dynamics

CoG

=

center of gravity

Greek Letters

Subscripts

Abbreviations



DOF

=

degree of freedom

ECT

=

electrical capacitance tomography

ERT

=

electrical resistance tomography

FLNG

=

floating liquefied natural gas

FPSO

=

floating production storage and offloading

HDS

=

hydrodesulfurization

MEA

=

monoethanolamine

PIV

=

particle image velocimetry

RTD

=

residence time distribution

Semi

=

semi-submersible

SPAR

=

single point anchor reservoir

TBR

=

trickle bed reactor

TLP

=

tensioned leg platform

WMS

=

wire-mesh sensor

3-D

=

three-dimensional

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Figure Captions Figure 1

Illustration of the liquid guard level at the maximum oscillating angle with the standard orifice pan distributor (a, b) and partitioned distributor tray (c, d). Adapted with permission from ref 20. Copyright (2016) Revue d’IFP Energies Nouvelles.

Figure 2

Effect of inclination angle (a) on cross-sectional average liquid saturation (H = 70 cm) and (b) on pressure drop for a trickle bed reactor. Adapted with permission from ref 28. Copyright (2010) John Wiley and Sons.

Figure 3

(a) ECT Eulerian slices as function of inclination angle, fade out of pulsation (Ul = 0.005 m/s, Ug = 0.062 m/s, 30 cm above column bottom); global pulse flow characteristics at different inclination angles (b) pulse velocity and (c) pulse frequency for a trickle bed reactor. Adapted with permission from ref 28. Copyright (2010) John Wiley and Sons.

Figure 4

(a) Effect of tilt angle on the transient cross-sectional liquid saturation drainage dynamics in which S1 and S2 are points corresponding to three drainage steps: fast (0-S1), slow (S1-S2), and steady-state (S2-∞), (b) contour plot snapshots showing the effect of tilt angle on the crosssectional distribution of liquid during drainage at H = 65 cm axial position for an initially liquid-full packed bed (Uw = upper wall, Lw = lower wall). Adapted with permission from ref 29. Copyright (2015) Elsevier.

Figure 5

Effect of bed roll and roll + pitch motions (a,b) on the degree of uniformity factor (air-kerosene, Ug = 0. 032 m/s, Ul = 0.002 m/s) and (c,d) on the bed overall pressure drop (air-water, Ug = 0.190 m/s, Ul = 0.005 m/s) for a trickle bed reactor. Adapted with permission from refs 30 & 31. Copyrights (2015) John Wiley and Sons & Elsevier.

Figure 6

(a) Liquid saturation time series in the wall regions RI and RII of the same bed cross section for 20 s period rolling bed and 15°‐tilted static column along with 15°‐amplitude sine wave for the hexapod roll motion, (b) 2D WMS images of the bed cross‐sectional area in different angular positions (Ug = 0.190 m/s and Ul = 0.005 m/s) for a trickle bed reactor. Adapted with permission from ref 32. Copyright (2017) John Wiley and Sons. 45.



Figure 7

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(a) Tracer responses sensed by WMS2 and WMS3 under roll motion as a function of motion frequency (b) liquid effective axial Péclet number for a trickle bed reactor. Adapted with permission from ref 30. Copyright (2015) John Wiley and Sons.

Figure 8

Effect of column (a) roll motion and (b) roll + pitch motion on the uniformity factor (a1, b1) and 2-D (Eulerian slice) visualization of liquid saturation (a2, b2) at H = 80 cm (Ug = 0.062 m/s and Ul = 0.003 m/s) for a solid foam. Adapted with permission from ref 35. Copyright (2018) Elsevier.

Figure 9

Effect of column roll motion (a) on 3-D iso-surface visualization of gasrich and liquid-rich presence (b) on the uniformity factor, (c) on the overall bed pressure drop, (d) on tracer responses sensed by WMSs, and (e) on pulsing flow regime emergence for a cocurrent upflow packed bed. Adapted with permission from ref 37. Copyright (2017) Elsevier.

Figure 10

(a) Effect of inclination angle on the liquid uniformity factor (Ug = 0.157m/s), (b) Sherwood–Zenz–Lobo flooding diagram and shift of the flooding limits as a function of column inclination for a counter-current randomly-packed bed. Adapted with permission from ref 38. Copyright (2015) Elsevier.

Figure 11

Average maldistribution factor along the packed height under four different roll motions and three permanent tilt conditions. Liquid load = 50 m3/m2h, water, and no gas flow for a counter-current structured-packing bed. Adapted with permission from ref 44. Copyright (2017) Elsevier.

Figure 12

Prospective operational technique for preventing liquid maldistribution through superimposed low-shear spinning and rolling motion of embarked packed bed reactors: (a) stratified flow or (b) dispersed flow patterns in (c) oscillating column. Adapted with permission from ref 32. Copyright (2017) John Wiley and Sons.

Figure 13

(a) Examination of the effect of static tilt and roll motion on effective interfacial area (ae, m2/m3) in M500X packing (Ug = 0.231 m/s, Ul = 0.0023 m/s, H = 90 cm), CO2 absorption performance of M500X and Raschig ring 46.


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packings for two bed heights under (b) static tilt and (c) roll motion (Ug = 0.0666 m/s, Ul = 0.00066 m/s). Adapted with permission from ref 52. Copyright (2018) Elsevier. Figure 14

Comparison between roll motion and static tilt with (a) M250X, (b) M500X, and (c) M700Y structured packings; amplitude = tilt angle (°), fe = mass-transfer area (m2/m3), ∆fe = relative change in mass-transfer area ((femoving-fevertical)/fevertical×100), Q = liquid load (m3/m2/h), V = gas flow rate (m/s). Adapted with permission from ref 54. Copyright (2018) Elsevier.

Figure 15

Comparison of CFD results with experimental data 10° inclined packed beds, (a) liquid holdup, (b) normalized liquid holdup, (c) overall pressure drop. Liquid cyclic operation: 5 s OFF-5 s ON, Ug = 15.3 cm/s, Ul = 0-2 mm/s; H = 15 cm. Adapted with permission from ref 60. Copyright (2017) John Wiley and Sons.

Figure 16

Evolution of radial component of (a) liquid holdup gradient, (b) capillary dispersion force and (c) mechanical dispersion force at H = 70 cm for 0°, 5°, and 15° trickle bed inclinations under isoflow operation (Ug = 15.3 cm/s, Ul = 1 mm/s). Adapted with permission from ref 60. Copyright (2017) John Wiley and Sons.

Figure 17

Simulation results of (a) inclusion of dispersion terms in the CFD model and (b) the traditional model without dispersion terms for stationary-rolling packed beds. Ug = 9.2 cm/s, Ul = 1.2 mm/s; H = 50 cm. Adapted with permission from ref 61. Copyright (2018) John Wiley and Sons.

Figure 18

Contour plots of (a) liquid saturation, (b) gas velocity and (c) liquid velocity at H = 85 cm under 20 s-period roll motion with oscillation amplitudes of 15° in a trickle bed reactor. Corresponding contours for static tilted beds in same conditions are drawn for comparison (Ug = 9.2 cm/s, Ul = 1.2 mm/s). Adapted with permission from ref 61. Copyright (2018) John Wiley and Sons.

Figure 19

Effect of oscillation amplitude and period on (a) liquid saturation, (b) pressure drop, (c) uniformity index (Ug = 9.2 cm/s, Ul = 1.2 mm/s, H = 50 47.



Page 48 of 78

cm) for a trickle bed reactor. Adapted with permission from ref 61. Copyright (2018) John Wiley and Sons. Figure 20

(a) Time-dependent cross-sectionally averaged liquid holdup and (b) twophase pressure drop for the continuing moving of the trickle bed reactor between the vertical and an angled position with 10-s travel time between the vertical/angled and angled/vertical positions; (c) time‐dependent cross‐sectionally averaged liquid holdup and (d) two‐phase pressure drop for the continuing moving of the reactor between two angled positions. Air‐water system, Ug = 0.2 m/s, Ul = 0.0025 m/s, H = 1.30 m. Adapted with permission from ref 63. Copyright (2016) John Wiley and Sons.

Figure 21

Liquid drainage dynamics in terms of cross-sectionally averaged liquid holdup profiles in an initially liquid-full packed bed: Profiles captured at H = 1.3 m for the vertical, inclined and oscillating bed between two angled (a – 15°; b –5°) positions (period = 10 s). Adapted with permission from ref 64. Copyright (2016) Elsevier.

Figure 22

Time-dependent exit (a) CO2 mole fraction in CO2-MEA system scrubber, (b) dibenzothiophene concentration in hydrocarbon hydrodesulfurization, and (c) CO2 mole fraction in enzyme-mediated CO2 capture for symmetrically oscillating cocurrent and countercurrent packed beds. Adapted with permission from refs 65, 66, 68. Copyrights (2016, 2017, 2018) Elsevier & John Wiley and Sons.

Figure 23

Effect of ship tilting and motion on (a) effective interfacial area (ae, m2/m3) and (b) CO2 mole fraction in the gas phase (yCO2, %), effect of CoG position on (c) effective interfacial area (ae, m2/m3) and (d) CO2 mole fraction in the gas phase (yCO2, %) in counter-current structured packed bed scrubber. Adapted with permission from refs 70 and 71. Copyrights (2015) John Wiley and Sons and (2017) Elsevier.

Figure 24

Maldistribution factor along packed height (a) under various tilt angles and (b) under 4° tilt condition as a function of the diameter. Adapted with permission from ref 72. Copyrights (2016) Elsevier. 48.


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Figure 25

Particle distribution images from the ECT sensor and simulation of a gassolid circulating fluidized bed, z′‒axial distance from the bottom of column. Adapted with permission from ref 85. Copyrights (2014) Elsevier.

Figure 26

Time variation of descending velocity at θ = 15° and period = 5 s, (b) averaged descending velocity at different θ and period = 5 s of a gas-solid circulating fluidized bed. Adapted with permission from ref 86. Copyrights (2014) AIP Publishing.

Figure 27

Eulerian slices of the particle distribution image for a circulating gas-solid fluidized bed, Ug = 3.0 m/s, z′‒axial distance from the bottom of column = 0.3 m. Adapted with permission from ref 88. Copyrights (2016) Elsevier.

Figure 28

3-D and 2-D Euler representations of gas-rich and liquid-rich presence and gas holdup (α) space-time distribution, respectively, as a function of bubble column (a) roll frequency, (b) roll + pitch frequency, and (c) sway frequency. Adapted with permission from ref 92. Copyrights (2015) Elsevier.



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Figure 1


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Figure 2



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Figure 3

a)

θ = 0°

θ = 10°

θ = 30°

b)

θ = 50°

c )


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Figure 4

a)

H = 65 cm

b)



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Figure 5


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Figure 6



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Figure 7

Static 0° Static inclined 15° 0.2 Hz (Period = 5 s ) 0.1 Hz (Period = 10 s) 0.05 Hz (Period = 20 s)


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Figure 8



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Figure 9


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Figure 10



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Figure 11


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Figure 12



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Figure 13


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Figure 14



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Figure 15


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Figure 16



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Figure 18



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Figure 19


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Figure 20



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Figure 21


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Figure 22



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Figure 23

b)

a)

c)

d)


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Figure 24



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Figure 25


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Figure 26



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Figure 27


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Figure 28



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TOC graphic


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