Gotowa bibliografia na temat „Gas-liquid distribution three phase monolith reactors”

This paper presents a unified model that inter-relates gas flow rate, liquid flow rate, and hold-ups of each of the liquid, gas, and solid phases in three-phase, fluidized-bed biofilm (TPFBB) process. It describes how carrier properties, biofilm properties, and gas and liquid flow velocities control the system dynamics, which ultimately will affect the density, thickness, and distribution of the biofilm. The paper describes the development of the mathematical model to correlate the effects of gas flow rate, liquid flow rate, solid concentration, and biofilm thickness and density. This knowledge is critically needed in light of the use of TPFBB processes in treating industrial wastewater, which often has high substrate concentration. For example, the proper design of the TPFBB process requires mathematical description of the cause-effect relationship between biofilm growth and fluidization.

Scientists require methods to monitor the distribution of gas bubbles in gas-liquid bubble column reactors. One non-destructive method that can potential satisfy this requirement in industrial situations is ultrasonic transmission tomography (UTT). In this paper, an ultrasonic transmission tomography sensor is designed for measuring bubble distribution in a reactor. Factors that influence the transducer design include transmission energy loss, the resonance characteristics and vibration modes of the transducer, and diffusion angles of the transducers, which are discussed. For practical application, it was found that an excitation frequency of 300 kHz could identify the location and size of gas bubbles. The vibration mode and diffusion also directly affect the quality of the imaging. The geometric parameters of the transducer (a cylinder transducer with a 10 mm diameter and 6.7 mm thickness) are designed to achieve the performance requirements. A UTT system, based on these parameters, was built in order to verify the effectiveness of the designed ultrasonic transducer array. A Sector-diffusion-matrix based Linear Back Projection (SLBP) was used to reconstruct the gas/liquid two-phase flow from the obtained measurements. Two other image processing methods, based on SLBP algorithm named SLBP-HR (SLBP-Hybrid Reconstruction) and SLBP-ATF (SLBP-Adaptive Threshold Filtering), were introduced, and the imaging results are presented. The imaging results indicate that a gas bubble with a 3 mm radius can be identified from reconstructed images, and that three different flow patterns, namely, single gas bubble, double gas bubble with different diameters, and eccentric flow, can be identified from reconstructed images. This demonstrates that the designed UTT sensor can effectively measure bubble distribution in gas-liquid bubble column reactors.

Increasing volumes of wastewater combined with limited space availability and progressively tightening European standards promote the development of new intensive biotechnologies for water treatment. Fixed biomass processes offer several advantages compared with conventional biological treatments: higher volumetric load, increased process stability and compactness of the reactors. The purpose of this paper is to present a new concept of gas-lift mobile bed, the circulating floating bed reactor (CFBR). The reactor design is simple and does not require any complex technical devices (easier effluent and air-flow distribution, no primary settling, no back-washing). This new process is studied and developed in an industrial-scale prototype. The optimum hydrodynamic characteristics of the CFBR (liquid circulation velocity 0.3-0.4 m s−1, kLa 50-300 h−1, average mixing time 85 s) were not deteriorated by the high solid hold-ups (up to 40% v/v) of the floating media. On the contrary, three-phase operating improves the local gas hold-up in the downcomer. Improved hydrodynamics in the CFBR guarantee high nitrification rates and operation stability either in tertiary (up to 2 kgN m−3 d−1) or secondary (up to 0.6 kgN m−3 d−1) nitrification. The results show that nitrification is the limiting step in simultaneous C+N treatment. The negative effect of the increasing C/N ratio is more pronounced than stepwise decreasing of the temperature. The study of the biofilm composition and activity shows an effective control of the attached biomass growth by the high liquid circulation velocity. It is concluded that this new three-phase bioreactor ensures not only an enhanced process stability and biological reaction rate through an effective biofilm control but also guarantees an excellent synergy between hydrodynamic and biological performances. These advantages are highlighted by the simplicity of the reactor design. Thus, this innovative technology will be an attractive solution for intensive wastewater treatment for nitrogen and carbon removal.

Two-phase flow characteristics in vertical capillary downflow were investigated in order to obtain understanding of the behaviour of three-phase monolith reactors. Experiments were conducted using air and dyed water in round and square capillary tubes of 2 mm and 3 mm diameter. The flow regimes and transitions observed were recorded using high speed videography and this data was used to produce flow maps for each tube. The gas and liquid superficial velocities used ranged from 0.001 to 10 m/s and 0.0001 to 1 m/s respectively. The flow regimes and their transitions were found to be a strong function of tube geometry and surface tension effects, and some differences were observed between capillaries of round and square section. This has significant implications for the design of microchannel reactors. Annular, slug-annular, slug, bubbly and churn flow regimes were observed in the round tubes; channelling/irregular flow was observed in the square tubes in place of annular and slug-annular flow.

The objective of this work was to investigate the relative contribution of the convective and dispersive mixing mechanisms to the overall solid phase mixing mechanism for three-phase fluidized bed reactors. Noninvasive Radioactive Particle Tracking (RPT) data were obtained at various operating conditions, reactor diameters and particle systems. The structural wake model was updated and consists of three sub-phases: the particle wake and downflow-emulsion phase following the convective mixing mechanism and the vortex-emulsion phase following the dispersive mixing mechanism.The particle velocity mean and STD increased with the superficial liquid and gas velocity as well as the reactor diameter for each particle phase. Therefore, the extent of mixing increased under these operating parameters. The particle phase's holdup and a new Mixing Mechanism Indicator (MMI), however, exhibited a much more complex trend. For the larger reactor (Dc = 0.292 m), the convective mixing mechanism dominated and at low superficial liquid velocity the contribution of the convective mixing mechanism increased with superficial gas velocity. This trend, however, was reversed when the superficial liquid velocity increased. For the smaller reactor (Dc = 0.10 m), the random movement of the solid dominated. Therefore, the extent of mixing and the mixing mechanism did not follow the same trend. The CFD and the mixing model have to follow both those hydrodynamic properties.Relations to estimate mean and STD particle velocity distribution as well as particle phase holdup were developed. Solid in the established region mainly followed the convective mixing mechanism. Random movement of the solid was mostly observed at the top of the bed, but it was also present in the established region and at the bed bottom. The volume of each region depended on the operating conditions, reactor diameter and particle system. Furthermore, the particle wake expulsion frequency range was similar to the wake shedding frequency found in literature. It is, thus, possible to assume that wake shedding was mainly responsible for the solid exchange between particle phases.

Chemical engineering aims, on the one hand, at simulating and predicting phenomena with respect to chemical reactions, such as intrinsic reaction kinetics, mass transport, sorption effects, thermodynamic and hydrodynamic phenomena and, on the other hand, at the design, construction, and optimization of the corresponding reactors in which these reactions are performed. The present chapter starts with explaining how intrinsic reaction rates of chemical transformations occurring on a heterogeneous catalyst surface may be disguised by mass and heat transfer phenomena and how the occurrence of such limitations can be diagnosed. Subsequently, adsorption phenomena are described and it is explained how to account for them in a kinetic model. The third section of this chapter comprises a strategy to extrapolate gas phase kinetics towards liquid or three-phase reactions envisaging the up-scaling from ideal laboratory scale conditions to realistic commercial applications. Next, the focus moves from reaction towards reactor engineering. First, the traditional reactor types, i.e., batch, semi-batch, plug flow, and continuous stirred tank reactors, are discussed. Subsequently, microreactors, which are characterized by a much larger surface-to-volume ratio and, hence, exhibit an enhanced mass and heat transfer, are discussed. Finally, various methods of energy input are reported. Some specific reactor types such as monolith and membrane reactors, which are able to dramatically decrease the pressure drop, are discussed in more detail in the fifth section. The final section of this chapter aims at reactor and process design. It starts with a discussion on the hierarchical design strategy of chemical processes. Subsequently, reactor selection based on the specific boundaries of the indented application is addressed. The chapter wraps up with a discussion on the phenomena that should be accounted for while designing the selected reactor, i.e., capillary condensation, the catalyst wetting efficiency, the flow regime, and axial and radial dispersion.

Abstract Liquid holdup and pressure drop were measured during the co-current down flow of air and water through a monolith in the Taylor flow regime. The model presented accounts for the significant, up to three fold, increase in frictional pressure drop that is caused by the presence of gas bubbles. It is accurate to within 20%. In addition, the model presented is used to predict hydrodynamic stability, which is defined as the situation where all channels transport gas and liquid in the direction of mass flow. Essential for stability is a sufficiently good initial liquid distribution, which was achieved with a shower-type distributor. Furthermore, distribution was significantly enhanced by the natural occurrence of a well-mixed foam (aerated liquid) layer on top of the monolith at liquid holdup values above 0.5. The quality of the liquid distribution across the monolith follows directly from on-line, integral liquid holdup measurements.

SKYTHIA is a computer code for computational simulation of transient multi-phase flows based on three multi-component velocity fields in a porous structure that may change its geometry in time. The foundation of the computer code SKYTHIA allows applications for mathematical simulation of a variety of processes. From • two-phase gas-plasma multi-component hydrogen detonation in pipe-network with dissociation of the gases, • through condensation water-steam shock waves in complex pipe networks, • gas solution and dissolution in liquids, dissolved gas release from water in pipe network and gas-slug formation and transport, • pressure wave propagation, piping force computation and risk analysis in conventional island of 1700 MWe power plant including detailed models of the high pressure turbine, • diesel injection problems, • particles sedimentation in water, • turbulent mixing and transport in a nuclear power plant sump, • termite injection by high pressure steam-hydrogen mixture into air environment, melt-water interaction in postulated SWR 1000 severe accidents, alumina melt jet dropped into a subcooled water, Urania melt jet dropped in water, • void formation in existing-, • or future boiling water reactors, • void fraction and velocity distribution in nuclear reactors with different thermal powers, • modern steam generator simulation, thermal coupling of multi-phase non-equilibrium three fluid non-homogeneous non-equilibrium flow inside the primary piping systems to complete 3D multi-phase non-equilibrium three fluid non-homogeneous non-equilibrium flow inside secondary systems with cyclones and dryers, • volume fraction of steam in family of steam generators with different power, • water velocities and void fraction in flooding reservoir for primary emergency condenser being operating on the secondary site as boiler; thermal coupling of multi-phase non-equilibrium three fluid non-homogeneous flow inside the primary piping systems to complete 3D multi-phase non-equilibrium three fluid non-homogeneous flow inside secondary systems, • complete system for moisture separation of typical PWR, dynamic performance: multi-phase non-equilibrium three fluid non-homogeneous flow inside the secondary moisture separation system, • local volume fractions of oxide and sodium liquid as a function of (r, z) in the vertical plane for a fast breeder reactor during melt water interaction; energetic interaction of molten reactor material with liquid sodium in argon environment, • modern pre-heater (condenser) simulation, thermal coupling of single phase flow inside the primary piping systems to complete 3D multi-phase non-equilibrium three fluid non-homogeneous non-equilibrium condensing flow inside secondary systems, etc. All this applications demonstrate the capability of single model architecture to handle different material systems, different intensities of interactions, and large variety of the spatial and temporal scales of the simulated processes. This paper gives brief information about the basic principles used to build SKYTHIA, part of the validation procedure and illustrations of some very complex process simulations.

Helically coiled tube are widely used as the basic heat transfer elements in steam generators of the next generation reactors, such as HTR-PM (High Temperature Gas-cooled Reactor), IRIS (International Reactor Innovative and Secure) and SMART (System-integrated Modular Advanced Reactor), because of the advantages in reducing space, enhancing heat transfer, accommodating thermal stress and preventing two-phase flow instabilities. Owing to the presence of gravity and centrifugal force that being perpendicular to the main flow, two-phase flow in helically coiled tubes has different features with either vertical flow or horizontal flow. To ensure safety and reliability of the plant, it is necessary to carry out detail investigation on the two-phase flow phenomena and mechanisms in helically coiled tubes. However, less research has been carried out on this subject than on straight tubes. In this work, the upward air-water slug and plug flows in helically coiled tubes have been numerically analyzed based on the computational fluid dynamics (CFD) techniques. Three dimension models of helically coiled tubes with inner diameter of 16 mm, coil diameter of 0.1 and 0.4m, pitch of 0.08 and 0.16m are constructed, for which the structural meshes are generated by software ANSYS ICEM. The gas-liquid interface is captured by the volume of fluid (VOF) approach adopting geo-reconstruction scheme for interface interpolation, which is solved by a pressure-based transient solver in the commercial CFD software ANSYS FLUENT 14.5. Bubble chord length, slug/plug frequency, bubble velocity and void fraction under different superficial velocities have been investigated. The numerical results meet well with the pictures recorded by a high speed camera. It is revealed that in slug regime, the bubbles mainly migrate towards the top and inner wall of the tube due to the combined action of gravity and centrifugal force, leading to a highly asymmetrical internal phase distributions. Meanwhile, the secondary flow in the cross section introduced by the centrifugal force enhances the turbulence and prevents small bubbles to coalescent into enlarged bubbles. Accordingly the intermittent flow regime in helically coiled tubes is narrower than that in straight horizontal tubes. Furthermore, the influences of geometrical parameters on phase distribution characteristics are predicted. The results show that the bubble length will increase along with the increase of the coil diameter or the pitch of the helically coiled tube. And the bubble frequency will increase with the decreasing of the tube coil diameter.