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Rotating fluidized beds provide a unique opportunity to exploit fluidization under higher particle forces. The centripetal force in a rotating fluid bed is typically on the order of 10 times the force of gravity. Since the force keeping the particles in the unit is larger, the drag force can also be larger, allowing for higher gas and slip velocities. This operating regime provides intensified gas-solids contact through higher mass transfer, heat transfer, gas throughput, and bubble suppression. One application for using a rotating fluidized bed is in Chemical Looping Combustion (CLC). When solid fuels are used, oxygen carrier and ash are mixed in the process. In order to maintain high carbon capture efficiencies and recyclability of the oxygen carrier, the ash needs to be separated from the oxygen carrier. This separation can be done aerodynamically since the oxygen carrier is larger and heavier than the ash. It is theorized that rotating fluidized beds could improve both the gas-solid and solid-solid separation process efficiency and throughput as compared to conventional fluidized beds. A 43 cm diameter, 2.5 cm long vortex chamber has been designed and constructed to investigate the application to particle separation. A series of experiments have been performed to investigate the separation of different binary mixtures of solids. These experiments demonstrate the use of a rotating fluidized bed for high-G intensified particle separation that can be combined with high-G intensified gas-solids contact and gas-solids separation.

Coupled discrete particle method – computational fluid dynamics simulations are carried out to demonstrate the potential of combined high-G-intensified gas–solids contact, gas–solids separation and segregation in a rotating fluidized bed in a static vortex chamber. A case study with two distinct types of particles is focused on. When feeding solids using a standard solids inlet design, a dense and uniform rotating fluidized bed is formed, guaranteeing intense gas–solids contact. The presence of both types of particles near the chimney region reduces, however, the strength of the central vortex and is detrimental for separation and segregation. Optimization of the solids inlet design is required, as illustrated by stopping the solids feeding. High-G separation and segregation of the batch of particles is demonstrated, as the strength of the central vortex is restored. The flexibility with respect to the gas flow rate of the bed density and uniformity and of the gas–solids separation and segregation is demonstrated, a unique feature of vortex chamber generated rotating fluidized beds. With the particles considered in this case study, turbulent dispersion by large eddies in the gas phase is shown to have only a minor impact on the height of the inner bed of small/light particles.

High-G fluidization in vortex chambers allows intensifying the drying of granular materials. The modeling, simulation and scale-up of vortex chamber based biomass dryers are addressed. Non-stationary experiments, batch for the biomass, are carried out to complement the data on continuous woody biomass drying in vortex chambers available in the literature. The drying models differ in the way they do or do not account for interfacial mass and heat transfer limitations, a non-uniform distribution of the moisture in the biomass particles and intra-particle diffusion limitations. Discrimination between the different proposed drying models and estimation of the model parameter(s) follows from simulations of both the continuous and batch experiments and regression. The retained biomass drying model is then used to study scale-up of the technology, focusing on continuous operation. Two major issues are addressed: (i) the product uniformity and (ii) the air consumption and utilization. Different vortex chamber configurations are simulated and analyzed: a single chamber or different chambers operated in parallel or in series (compartmented), allowing introducing a CSTR-in-series type behavior for the particles, combined with air feeding in parallel or in series over the different chambers.

This review deals with gas–solid fluidized beds in vortex chambers. High-G fluidization can be achieved in a static geometry and allows significant process intensification. Thin, dense and more uniform particle beds can be obtained at high gas–solid slip velocities, intensifying interfacial transfer of mass, heat and momentum and reducing the gas–solid contact time. Existing fluidized bed processes can be carried out more efficiently and novel processing routes can be developed, e.g., involving cohesive particles or a dispersed liquid phase in relatively high concentrations. The first section of the review discusses the unique hydrodynamic characteristics of gas–solid fluidized beds in vortex chambers. The flow pattern, flexibility in the operating conditions and stability conditions are explained. The design of vortex chambers is dealt with in the second section and is critical for processing both larger and fine particles. The influence of the gas and solids in- and outlet design is focused on and insight is gained from recent theoretical, experimental and CFD studies. In the third section (potential) applications are discussed and process intensification and novel processing routes demonstrated. The fourth and last section presents extensions of the concept. Multi-zone operation and the integration of other technologies in vortex chambers are considered.

Vortex chambers allow high-G fluidization and are as such potentially interesting for processing cohesive particles. The first part of the paper deals with the formation of a rotating bed of cohesive particles in a vortex chamber. A careful vortex chamber design is required to generate a sufficiently strong high-G field and related sufficiently high particle residence time. Next, the low-temperature coating of the particles is addressed. A centrally positioned single-fluid pressure spray nozzle directed towards the bed is used. The influence of a dispersed coating solution on the bed stability and the segregation of uncoated and coated particles are studied. Agglomeration and the particle coating quality are analyzed by means of laser diffraction based particle size distribution measurements, SEM imaging and an active component release test. Because vortex chambers are extremely flexible with respect to the gas flow rate, the variation of the latter to control the agglomeration is focused on. The influence of the coating time and the coating solution injection pressure are also studied and the maximization of the coating efficiency discussed.

Two design aspects of vortex chambers for the generation of gas-solids rotating fluidized beds are experimentally studied for different types of particles: the solids outlet(s) and the gas inlets. Efficient solids retention and minimal solids losses via the chimney are aimed at so that the gas and solids residence times can be controlled independently. The importance of a strong vortex in the central particle bed freeboard region is demonstrated. It is shown that separate, well-dimensioned and -positioned solids outlets prevent a significant presence of particles in the freeboard region, increasing the vortex strength in this region. This is found to be particularly important when fluidizing small/light particles. The ratio centrifugal force-to-radial gas-solid drag force that is generated by the gas injection is shown to also have an important impact. Theoretically it is shown that this ratio strongly depends on the particle characteristics and to what extent it can be increased by increasing the gas injection velocity, preferentially by reducing the gas inlet slot size and otherwise the number of gas inlet slots. Experiments with different vortex chambers and particles qualitatively confirm the theoretical expectations, but show that limitations are encountered. A very high gas injection velocity prevents efficient penetration of especially fine/light particles in the gas inlet jets which is detrimental for the transfer of tangential momentum between the gas and the particle bed. Slots smaller than the particle size are also shown to be inefficient, as they generate rotational motion of the particles around their own center of gravity.

This chapter deals with rotating fluidized beds in static vortex chambers. High-G operation allows operation in a range of conditions very different from those in conventional fluidized beds, e.g. achieving extremely short gas–solid contact times. High-G operation also allows intensifying interfacial transfer of mass, heat and momentum. The latter allows generating high-density fluidized beds at high gas–solid slip velocities and reducing bubbling, opening perspectives for significantly increasing the efficiency of fluidized bed devices. Intensified interfacial momentum transfer also allows fluidizing particles that cannot be properly fluidized in conventional fluidized beds, such as large Geldart D- and fine/cohesive Geldart C-type particles, opening perspectives for a variety of novel applications in the energy, food and feed and pharma industries. After an introduction to high-G fluidization, the hydrodynamic characteristics and design aspects of vortex chambers for the generation of rotating fluidized beds are discussed. Next, illustrations of (potential) applications taking advantage of the intensified interfacial mass and heat transfer and of the intensified reactions are presented. The chapter ends with extensions of the concept and an outlook.

Computational Fluid Dynamics is used to evaluate the use of a rotating fluidized bed in a static geometry for the catalytic cracking of gas oil. A Eulerian–Eulerian flow model is used in combination with the Kinetic Theory of Granular Flow. The catalytic cracking reactions are described by a 10-lump model. Catalyst deactivation by coke formation is included. To operate at low catalyst coke content, the catalyst residence time is small and the catalyst makes on average only a limited number of rotations in the reactor. Therefore,the catalyst bed cannot be considered well-mixed and a local distribution of the catalyst coke content is to be accounted for. The catalyst coke content distribution function has no pre-described functional form and is discretized. A continuity equation is then solved for each of the classes of catalyst with a given coke content. The impact of the strongly endothermic cracking reactions on the particle bed temperature uniformity is also studied.

The concept and use of a rotating chimney for compressing rotating fluidized beds is theoretically and experimentally studied. A rotating chimney is shown to drastically increase the operating flexibility of rotating fluidized beds and to allow a significant improvement of the particle bed uniformity. In particular, the rate of solids losses via the chimney can be reduced and bubbling can be suppressed by compressing the rotating particle bed. (c) 2009 Elsevier B.V. All rights reserved.

Gas-solid heat transfer in rotating fluidized beds in a static geometry is theoretically and numerically investigated. Computational fluid dynamics (CFD) simulations of the particle bed temperature response to a step change in the fluidization gas temperature are presented to illustrate the gas-solid heat transfer characteristics. A comparison with conventional fluidized beds is made. Rotating fluidized beds in a static geometry can operate at centrifugal forces multiple times gravity, allowing increased gas-solid slip velocities and resulting gas-solid heat transfer coefficients. The high ratio of the cylindrically shaped particle bed "width" to "height" allows a further increase of the specific fluidization gas flow rates. The higher specific fluidization gas flow rates and increased gas-solid slip velocities drastically increase the rate of gas-solid heat transfer in rotating fluidized beds in a static geometry. Furthermore, both the centrifugal force and the counteracting radial gas-solid drag force being influenced by the fluidization gas flow rate in a similar way. rotating fluidized beds in a static geometry offer extreme flexibility with respect to the fluidization gas flow rate and the related cooling or heating. Finally, the uniformity of the particle bed temperature is improved by the tangential fluidization and resulting rotational motion of the particle bed. (c) 2008 Elsevier Ltd. All rights reserved.

Rotating fluidized beds in a static geometry are based on the new concept of injecting the fluidization gas tangentially in the fluidization chamber, via multiple gas inlet slots in its cylindrical outer wall. The tangential injection of the fluidization gas fluidizes the particles tangentially and induces a rotating motion, generating a centrifugal field. Radial fluidization of the particle bed is created by introducing a radially inwards motion of the fluidization gas, towards a centrally positioned chimney. Correctly balancing the centrifugal force and the radial gas-solid drag force requires an optimization of the fluidization chamber design for each given type of particles. Solids feeding and removal can be continuous, via one of the end plates of the fluidization chamber. The fluidization behavior of both large diameter, low density polymer particles and small diameter, higher density salt particles is investigated at different solids loadings in a 24 cm diameter, 13.5 cm long non-optimized fluidization chamber. Scale-up to a 36 cm diameter fluidization chamber is illustrated. Provided that the solids loading is sufficiently high, a stable rotating fluidized bed in a static geometry is obtained. This requires to minimize the solids losses via the chimney. With the polymer particles, a dense and uniform bed is observed, whereas with the salt particles a less dense and less uniform bubbling bed is observed. Solids losses via the chimney are much more pronounced with the salt than with the polymer particles. Slugging and channeling occur at too low solids loadings. The hydrostatic gas phase pressure profiles along the outer cylindrical wall of the fluidization chamber are a good indicator of the particle bed uniformity and of channeling and slugging. The fluidization gas flow rate has only a minor effect on the occurrence of channeling and slugging, the solids loading in the fluidization chamber being the determining factor for obtaining a stable and uniform rotating fluidized bed in a static geometry. (C) 2008 Elsevier B.V. All rights reserved.

The new concept of a rotating fluidized bed in a static geometry opens perspectives for fluidized bed nuclear reactor technology and is experimentally and numerically investigated. With conventional fluidized bed technology, the maximum attainable power is rather limited and maximum at a certain fluidization gas flow rate. Using a rotating fluidized bed in a static geometry, the fluidization gas drives both the centrifugal force and the counteracting radial gas-solid drag force in a similar way. This allows operating the reactor at any chosen sufficiently high solids loading over a much wider fluidization gas flow rate range and in particular at much higher fluidization gas flow rates than with conventional fluidized bed reactor technology, offering increased flexibility with respect to cooling via the fluidization gas. Furthermore, the centrifugal force can be a multiple of earth gravity, allowing radial gas-solid slip velocities much higher than in conventional fluidized beds. The latter result in gas-solid heat transfer coefficients one or multiple orders of magnitude higher than in conventional fluidized beds. The combination of dense operation and high fluidization gas flow rates allows process intensification and a more compact reactor design.

The new concept of a rotating fluidized bed in a static geometry (RFB-SG) is presented. The rotating motion of the particle bed and the tangential fluidization of the solids are obtained by the tangential injection of the fluidization gas via multiple gas inlet slots in the outer cylindrical wall of the fluidization chamber. The solids experience a radially outwards centrifugal force. The gas, on the other hand, is forced to move radially inwards towards a chimney with one or more outlet slots, creating a radially inwards gas-solid drag force and fluidizing the solids radially. The new fluidization concept is experimentally investigated and proven using one and the same non-optimized fluidization chamber design with either large diameter, low density polymer particles or small diameter, higher density Alumina particles. The fluidization chamber is operated in continuous mode, at different solids loadings and in the vertical and horizontal position. (c) 2007 American Institute of Chemical Engineers.

The influence of the inlet configuration on the flow pattern in dilute circulating fluidized beds is investigated. The solid flow model used is based on the kinetic theory of granular flow (KTGF). Interactions between the fluctuating motion of the gas and the solid phase are accounted for. A line-implicit simultaneous solution algorithm based on dual-time stepping is used for the numerical integration. The discretization of the inviscid fluxes is based on a low-Mach reformulation of the multi-phase preconditioned advection upstream splitting method (MP-AUSMP). Simulation results for a side solids inlet configuration are qualitatively verified using 3D LDA data of a cold-flow circulating fluidized bed pilot unit. The pilot riser has a diameter of 0.1 m and a height of 8.765 m. The side inlet used for solids feeding is positioned 0.58 m above the gas inlet and makes a 35° angle with the riser axis. The cold-flow pilot unit is operated in the dilute regime with a superficial gas velocity of 5.31 m s−1 and a solids flux of 3 kg m−2 s−1. Experimental and simulation results show that bypassing of solids by the gas occurs, but that the bypassing effects are quickly dissipated by the viscous terms. The gas–solid flow model is capable of describing the experimentally observed mixing behaviour. In simulations of dilute industrial scale risers, the gas is fed over the entire bottom section, whereas two kinds of solids inlet configurations are used: (1) the solids are fed through a central inlet tube at the bottom of the riser; (2) the solids are fed through a side inlet at a certain distance from the bottom of the riser. The outlet is of the abrupt T-type. With the first inlet configuration, the radial mixing of the solids is seen to be hindered, due to bypassing of the gas via the outer ring of the reactor tube. The bypassing effects are not quickly dissipated by the viscous terms. The impact of the latter is less important in large than in small diameter risers. Bypassing of the gas also plays an important role with the second inlet configuration. At the height of the solids inlet, the gas is seen to flow preferentially aside of the solids inlet and at the opposite site of the riser. This results in vortex formation, responsible for the primary mixing of gas and solids. More downstream, the maximum solids flux is calculated at the side of the solids inlet. Radial mixing is seen to be related to the granular temperature and the gas phase turbulence. The dilute industrial scale riser simulations show that inlet and outlet configuration effects are not independent, but interact. This has an important impact on radial mixing. Inlet and outlet effects can oppose each other or cooperate, resulting in complex riser behaviour.

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

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

The process intensification potential of rotating- and circulating rotating fluidized beds in a static fluidization chamber when used for the low-temperature pyrolysis and gasification of biomass is numerically evaluated. The species continuity equations and energy balance equations are based on complete mixing for the particles within given zones of the particle bed and plug flow for the gas. The reaction mechanism accounts for pyrolysis of biomass and tar, gas-phase combustion, the water gas shift reaction, and combustion and gasification of char. A comparison with current circulating fluidized bed riser technology is made. The circulation of inert solid with a high heat capacity and the separation of the flue gas from the production gas are also studied.

The new concept of a rotating fluidized bed in a static geometry was numerically and experimentally studied. The particle bed can be both tangentially and radially fluidized by injecting the fluidization gas tangentially in the static fluidization chamber via multiple gas inlet slots located in its outer cylindrical wall. The tangential fluidization of the particles induces a rotating motion of the particle bed. As a result of the particle bed rotational motion, the solids experience a radially outwards centrifugal force. A radially inwards gas-solid drag force and radial fluidization of the particle bed can be introduced by forcing the fluidization gas to leave the fluidization chamber via a chimney with one or multiple gas outlet slots, positioned at the axis of the fluidization chamber. The solids can be continuously fed and removed in and out of the fluidization chamber via solids inlet and outlet holes in the front or back ends of the fluidization chamber.The fluidization patterns of low-density polymer particles with a large diameter and of high-density salt particles with a small diameter were experimentally studied in a 24-cm diameter, 13.5-cm long non-optimized static fluidization chamber at different solids loadings. Scale-up to a 36-cm diameter fluidization chamber was also studied. With both types of particles, a rotating fluidized bed and an acceptable gas-solid separation was obtained provided that the solids loading was sufficiently high. Slugging and channeling and a non-uniform distribution of the gas over the gas inlet slots to the fluidization chamber may occur at low solids loadings and can be detected via well-chosen pressure measurements. The fluidization patterns observed in the same fluidization chamber were completely different with the polymer particles and with the salt particles. The polymer particles tend to form a dense and uniform bed, its behavior being mainly characterized by tangential fluidization. The salt particles tend to form a less dense, bubbling fluidized bed that is both tangentially and radially fluidized.Computational fluid dynamics simulations give an improved insight in the gas and solid phase flow pattern.