Search

A pilot-scale study of the Ohio State Carbonation Ash Reactivation (OSCAR) process was performed to demonstrate the reactivity of two novel calcium-based sorbents toward sulfur and trace heavy metal (arsenic, selenium, and mercury) capture in the furnace sorbent injection (FSI) mode on a 0.365 m3/s slipstream of a bituminous coal-fired stoker boiler. The sorbents were synthesized by bubbling CO2 to precipitate calcium carbonate (a) from the unreacted calcium present in the lime spray dryer ash and (b) from calcium hydroxide slurry that contained a negatively charged dispersant. The heterogeneous reaction between these sorbents and SO2 gas occurred under entrained flow conditions by injecting fine sorbent powders into the flue gas slipstream. The reacted sorbents were captured either in a hot cyclone (∼650 °C) or in the relatively cooler downstream baghouse (∼230 °C). The baghouse samples indicated ∼90% toward sulfation and captured arsenic, selenium and mercury to 800 ppmw, 175 ppmw and 3.6 ppmw, respecti...

The term “nanofluid” is used to describe a liquid that contains dispersed nanoparticles, which can have unique effects on the liquid, because of the enormous surface area of the nanoparticles and their interfacial force-induced microstructures. The enhanced heat-transfer properties of such nanofluids have been extensively reported in the literature; however, little is known regarding the effects of nanofluids on bubble behavior. Such effects are examined experimentally in this study using hydrophilic nanoparticles with bubble flows in bubble columns and microchannels. The data reveal a significant increase in the gas holdup in bubble columns and a decrease in bubble sizes, signifying an intriguing bubble−nanofluid interactive behavior.

A dynamic volume imaging based on the principle of electrical capacitance tomography (ECT), namely, electrical capacitance volume tomography (ECVT), has been developed in this study. The technique generates, from the measured capacitance, a whole volumetric image of the region enclosed by the geometrically three-dimensional capacitance sensor. This development enables a real-time, 3-D imaging of a moving object or a real-time volume imaging (4-D) to be realized. Moreover, it allows total interrogation of the whole volume within the domain (vessel or conduit) of an arbitrary shape or geometry. The development of the ECVT imaging technique primarily encloses the 3-D capacitance sensor design and the volume image reconstruction technique. The electrical field variation in three-dimensional space forms a basis for volume imaging through different shapes and configurations of ECT sensor electrodes. The image reconstruction scheme is established by implementing the neural-network multicriterion optimization image reconstruction (NN-MOIRT), developed earlier by the authors for the 2-D ECT. The image reconstruction technique is modified by introducing into the algorithm a 3-D sensitivity matrix to replace the 2-D sensitivity matrix in conventional 2-D ECT, and providing additional network constraints including 3-to-2-D image matching function. The additional constraints further enhance the accuracy of the image reconstruction algorithm. The technique has been successfully verified over actual objects in the experimental conditions

A new noninvasive system for multimodal electrical tomography based on electrical capacitance tomography (ECT) sensor hardware is proposed. Quasistatic electromagnetic fields are produced by ECT sensors and used for interrogating the sensing domain. The new system is noninvasive and based on capacitance measurements for permittivity and power balance measurements for conductivity (impedance) imaging. A dual sensitivity map of perturbations in permittivity and conductivity is constructed. The measured data along with the sensitivity matrix are used for the actual image reconstruction. The new multimodal tomography system has the advantage of using already established reconstruction techniques, and the potential for combination with new reconstruction techniques by taking advantage of combined conductivity/permittivity data. Moreover, it does not require direct contact between the sensor and the region of interest. The system performance has been tested on representative data, producing good results

Two novel sorbents (i.e. “regenerated sorbent” and “supersorbent”) for dry flue gas desulfurization were tested, and by-products characterized, using a pilot-scale version of the Ohio State Carbonation and Ash Reactivation (OSCAR) process. The main elements of the process consisted of sorbent production, a riser reactor, cyclone and baghouse. Trace elements, including As, Se and Hg, were found at higher levels in the OSCAR solid by-products (in both the cyclone and baghouse) compared to traditional lime spray dryer (LSD) ash. Polycyclic aromatic hydrocarbons (PAHs) detected on solid by-products were primarily small molecular weight compounds at low concentration (e.g., μg/kg). Small particulates (⩽3 μm) that escaped from the cyclone and were captured by the baghouse showed higher trace element concentrations, possibly due to the lower operating temperature and greater specific surface area of solids in the baghouse. Operating conditions including flue gas flow rate and sorbent injection rate influenced the levels of trace elements and PAHs in OSCAR by-product material. Capture of PAHs was observed to increase with Ca concentration in experiments using supersorbent injection. However, possible release of PAHs occurred with regenerated sorbent injection. The concentrations of trace elements in leachate for all OSCAR cyclone samples tested were below Resource Conservation and Recovery Act limits. The concentrations of most trace elements in OSCAR by-product were also below the limits regulated in the EPA 503 Rule except As and Se. The similarity in the physical and engineering properties of OSCAR cyclone samples to natural cohesive soils suggests that this material can be utilized in a variety of construction, reclamation, and agricultural applications.

A three-dimensional numerical model is developed to simulate the process of collision between an evaporative droplet and a high-temperature particle. This phenomenon is of direct relevance to many engineering process operations, such as fluid catalytic cracking (FCC), polyethylene synthesis, and electronic materials coating. In this study, the level-set method and the immersed-boundary method are combined to describe the droplet–particle contact dynamics in a fixed Eulerian grid. The droplet deformation is captured by one level-set function while the solid–fluid boundary condition is imposed on the particle surface through the immersed-boundary method involving another level-set function. A two-dimensional vapour-layer model is developed to simulate the vapour flow dynamics. Equations for the heat transfer characteristics are formulated for each of the solid, liquid and gas phases. The incompressible flow-governing equations are solved using the finite-volume method with the ALE (arbitrary Lagrangian Eulerian) technique. The simulation results are validated through comparisons with experimental data obtained from the new experimental set-up designed in this study. An important feature of the droplet impacting on a particle with film boiling is that the droplet undergoes a spreading, recoiling and rebounding process, which is reproduced by the numerical simulation based on the model. Details of the collision such as spread factor, contact time and temperature distribution are provided. Simulations are also conducted to examine the effects of the particle size and the collision velocity. Although the value for the maximum spread factor is larger for a higher impact velocity and for a smaller particle, the contact time is independent of the impact velocity and particle size. Both the normal collision and the oblique collision are considered in this study.

During the operation of multiphase systems such as fluidized beds, electrostatic charges are generated when the materials involved are dielectric in nature. The accumulation of electrostatic charges within the system can be operationally hazardous. Work on understanding and, hence, preventing the electrostatic charging phenomena has mostly focused on gas–solid media. Relatively little study has been performed on particulates and multiphase systems with non-conductive liquids as the medium. In this study, electrostatic charging in gas–liquid–solid fluidized beds with liquid as the continuum phase under different operating conditions was explored. Two different charge-reducing methods were also evaluated. Based on experimental studies, it was found that the superficial gas and liquid velocities have a significant effect on the rate of charge generation and transfer in a three-phase fluidized bed because of variation in the frequency and the intensity of the particle collisions. The local number density of the particles also affected the distribution of the electrostatic signal obtained. Two methods of reducing electrostatic charge accumulation were also investigated: adding fine powder and adding an anti-static agent such as Larostat 264A. When 15 wt% of fine glass powder was added to an air-Norpar15-HDPE (high density polyethylene) fluidized bed, the charge inside the fluidized bed was reduced by 72%. When, on the other hand, as little as 0.5 wt% of the anti-static agent, Larostat 264A in a liquid form, was added to the air-Norpar15-HDPE, the electrostatic level was quickly reduced by 83% and within 1 h the electrostatic charge was completely eliminated from the system.

Current worldwide commercial activities in converting natural gas to fuels and chemicals, or gas-to-liquids technology use slurry bubble column reactors with column sizes considerable larger than those currently in practice. Such commercial activities have prompted further fundamental research interest in fluid and bubble dynamics, transport phenomena and the scale up effects of three-phase fluidization systems. The fundamental behavior of particular relevance to these activities is associated with the elevated temperature and pressure conditions. This review attempts to summarize the salient characteristics of liquid, bubbles, and particles and their interactive behavior and dynamics in the process of bubble formation and bubble rising in gas–liquid–solid fluidization systems. Measurement techniques including both intrusive techniques such as the probes, and non-intrusive techniques such as tomography, that are used to study fluid and bubble properties in gas–liquid and gas–liquid–solid systems, are illustrated. Governing mechanisms of bubble–particle collision and bubble breakup are discussed. The state-of-the-art computational techniques, that consider both the discrete and the continuum approaches for movement of the particle and bubble phases along with the discrete simulation results, are presented. Of particular emphasis is the effect of pressure and temperature on the fluid and bubble dynamics in three-phase fluidization.

With the emerging challenge of climate change and the continued escalation of energy demands, innovative and flexible fuel conversion technologies are necessary and gaining recognition. Chemical looping technologies have the potential to not only reduce energy costs, but also to mitigate carbon emissions. Historically, the general concept of this reduction–oxidation mechanism has been suggested, but the process was never commercialized. Recent interests in carbon capture techniques have revitalized the adaptive chemical looping system. Chemical looping technologies can utilize both gaseous and solid fuels such as natural gas and coal, respectively, for power, hydrogen, or chemical generation. However, the success of technological adoption requires a thorough understanding of the types of chemical looping techniques, the design considerations, and the reactor modes of configurations. Current large-scale testing units are examined with the hope for near-term advancement and future commercial application. Keywords: chemical looping; chemical looping combustion; carbon capture; oxygen carrier; synthesis gas

This chapter discusses the applications of capacitance tomography in gas–solid fluidized bed systems. The chapter first introduces the basic principle of gas–solid fluidization and the industrial applications of fluidized bed reactors. The chapter then discusses the applications of capacitance tomography technique in fluidized beds, particularly the applications in pharmaceutical industry. The chapter also discusses the effective permittivities of gas–solid mixtures and their relation with phase distributions, which is essential for capacitance tomography technique.

Multiphase flow systems are a critical element of many industrial processes as they constitute the medium through which basic ingredients are processed to yield the final product(s). Electrical capacitance tomography (ECT) is an electric sensing modality that easily meets the high-speed demands of multiphase flow real-time imaging. Specific applications of ECT include fluidized beds, circulating fluidized beds, pneumatic conveying systems, bubbling beds, trickle beds, and combustion. Favorable features of ECT sensors for these applications are the low-profile and the noninvasive nature of the sensing apparatus, the fast imaging speed, safety, ease of use, sensor flexibility for fitting around virtually any vessel geometry, and relatively low complexity and low cost.

The influence of several process parameters on the calcination of a naturally occurring limestone and a precipitated mesoporous calcium carbonate (CaCO3) sorbent structure to calcium oxide (CaO) is detailed in this study. CaCO3 calcination is an integral part of a multicyclic carbonation−calcination reaction (CCR) process that separates carbon dioxide (CO2) from high-temperature gas mixtures into a pure CO2 stream. Maintenance of high sorbent reactivity over repeated CCR cycles reduces the capital and operating cost of the CCR process. A lower calcination temperature, required to maintain high sorbent reactivity, reduces the calcination rate of CaCO3. This study investigates various process conditions such as subatmospheric calcination, sorbent dispersion in a rotary calciner, use of a high thermal conductivity sweep gas, etc. in enhancing the calcination rate at lower calcination temperatures. The high-temperature gas−solid carbonation studies of the resulting CaO sorbent prove the necessity to maintain ...

The impact of a subcooled water and n-heptane droplet on a superheated flat surface is examined in this study based on a three-dimensional model and numerical simulation. The fluid dynamic behavior of the droplet is accounted for by a fixed-grid, finite-volume solution of the incompressible governing equations coupled with the 3-D level-set method. The heat transfer inside each phase and at the solid–vapor/liquid–vapor interface is considered in this model. The vapor flow dynamics and the heat flux across the vapor layer are solved with consideration of the kinetic discontinuity at the liquid–vapor and solid–vapor boundaries in the slip flow regime. The simulated droplet dynamics and the cooling effects of the solid surface are compared with the experimental findings reported in the literatures. The comparisons show a good agreement. Compared to the water droplet, it is found that the impact of the n-heptane droplet yields much less surface temperature drop, and the surface temperature drop mainly occurs during the droplet-spreading stage. The effects of the droplet’s initial temperature are also analyzed using the present model. It shows that the droplet subcooling degree is related closely to the thickness of the vapor layer and the heat flux at the solid surface.

A combined multilayer feed-forward neural network (MLFF-NN) and analogue Hopfield network is developed for nonlinear image reconstruction of electrical capacitance tomography (ECT). The (nonlinear) forward problem in ECT is solved using the MLFF-NN trained with a set of capacitance data from measurements based on a back-propagation training algorithm with regularization. The inverse problem is solved using an analogue Hopfield network based on a neural-network multi-criteria optimization image reconstruction technique (HN-MOIRT). The nonlinear image reconstruction based on this combined MLFF-NN + HN-MOIRT approach is tested on measured capacitance data not used in training to reconstruct the permittivity distribution. The performance of the technique is compared against commonly used linear Landweber and semi-linear image reconstruction techniques, showing superiority in terms of both stability and quality of reconstructed images.

A three-dimensional simulation study is performed for investigating the hydrodynamic behaviors of a cross-flow liquid nitrogen spray injected into an air-fluidized catalytic cracking (FCC) riser of rectangular cross-section. Rectangular nozzles with a fixed aspect ratio but different fan angles are used for the spray feeding. While our numerical simulation reveals a generic three-phase flow structure with strong three-phase interactions under rapid vaporization of sprays, this paper tends to focus on the study of the effect of nozzle fan angle on the spray coverage as well as vapor flux distribution by spray vaporization inside the riser flow. The gas-solid (air-FCC) flow is simulated using the multi-fluid method while the evaporating sprays (liquid nitrogen) are calculated using the Lagrangian trajectory method, with a strong two-way coupling between the Eulerian gas-solid flow and the Lagrangian trajectories of spray. Our simulation shows that the spray coverage is basically dominated by the spray fan angle. The spray fan angle has a very minor effect on spray penetration. The spray vaporization flux per unit area of spray coverage is highly non-linearly distributed along the spray penetration. The convection of gas-solid flow in a riser leads to a significant downward deviation of vapor generated by droplet vaporization, causing a strong recirculating wake region in the immediate downstream area of the spray.

Electrical capacitance tomography, based on the neural network multicriteria optimization image reconstruction technique, developed by this research group, is used to examine the column size effect on the real time, cross-sectional flow variation during the choking transition in a circulating fluidized bed. Two sizes of columns, 0.05 and 0.1 m i.d., are employed in this study for two types of particles, sand particles (group B) and fluid catalytic cracking catalysts (group A). For group B particles, the formation of the square-nosed slugs (0.05 m i.d. column) or the wall slugs (0.1 m i.d. column) is observed to occur in the regime transition when the gas velocity Ug is below the transport gas velocity Utr or when the solids circulation rate Gs is below the transport solids velocity Gs,tr. When Ug > Utr or Gs > Gs,tr, the formation of open slugs for both 0.05 and 0.1 m i.d. columns is observed in the regime transition. Clearly, for group B particles, these regime transitions accompanied by a distinct bed s...

The dense-phase transportation regime is noted as a flow regime in a gas-solid circulating fluidized bed with large solids throughputs, high bed density, and low gas and solids back mixing. The quasi-three-dimensional images obtained by the ECT with the NN-MOIRT reconstruction technique reveal a significantly different solids concentration distribution in the dense-phase transportation regime from that in the dense-phase fluidization regimes, i.e., the bubbling, the turbulent, and the slugging regimes. The transient and time-averaged flow behavior in the dense-phase transportation regime is compared to that in the dense-phase fluidization regimes based on the statistical properties including the standard deviation, power spectra, and intermittency index of the local and cross-sectional averaged solids concentration fluctuations. Examining the statistical properties indicates a less segregated solids concentration distribution over the bed cross section in the dense-phase transportation regime than in the fast fluidization regime. In the dense-phase transportation regime, at a given gas velocity below U tr , choking takes place upward along the CFB riser at a decreasing solids concentration as the solids circulation rate increases.

A new technique for solving the forward problem in electrical capacitance tomography sensor systems is introduced. The new technique is based on training a feed-forward neural network (NN) to predict capacitance data from permittivity distributions. The capacitance data used in training and testing the NN is obtained from preprocessed and filtered experimental measurements. The new technique has shown better results when compared to the commonly used linear forward projection (LFP) while maintaining fast prediction speed. The new technique has also been integrated into a modified iterative linear back projection (Landweber) reconstruction algorithm. Reconstruction results are found to be in favor of the NN forward solver when compared to the widely used Landweber reconstruction technique with LFP forward solver.

The electrical capacitance tomography (ECT) with neural network multi-criteria image reconstruction technique (NN-MOIRT) is developed for real time imaging of a gas-solid fluidized bed using FCC particles with evaporative liquid injection. Some aspects of the fundamental characteristics of the gas-solid flow with evaporative liquid injection, including real time and time averaged cross-sectional solids concentration distributions, the cross-sectional solids concentration fluctuations and the quasi-3D flow structures are studied. A two-region model and a direct image calculation are proposed to describe the dynamic behavior in both the bubble/void phase and the emulsion phase based on the tomographic images. Comparisons are made between the fundamental behaviors of the gas-solid flows with and without evaporative liquid injection for various gas velocities ranging from bubbling to turbulent fluidization regimes. Significant differences are observed in the behavior of the gas-solid flow with the evaporative liquid injection compared to the fluidized bed without liquid injection.

This document is the final report for the project titled “Chemical Looping Gasification for Hydrogen Enhanced Syngas Production with In-Situ CO2 Capture” under award number FE0012136 for the performance period 10/01/2013 to 12/31/2014.This project investigates the novel Ohio State chemical looping gasification technology for high efficiency, cost efficiency coal gasification for IGCC and methanol production application. The project developed an optimized oxygen carrier composition, demonstrated the feasibility of the concept and completed cold-flow model studies. WorleyParsons completed a techno-economic analysis which showed that for a coal only feed with carbon capture, the OSU CLG technology reduced the methanol required selling price by 21%, lowered the capital costs by 28%, increased coal consumption efficiency by 14%. Further, using the Ohio State Chemical Looping Gasification technology resulted in a methanol required selling price which was lower than the reference non-capture case.

The behavior of a 6 mm mesobubble in an acoustic standing wave field is examined both experimentally and numerically in this study. The acoustic standing waves at 16 and 20 kHz are generated using two Nickel magnetostrictive transducers located at the top and bottom of the column. Experimental studies of the rise velocity of a mesobubble in the acoustic field indicate an axial wavy rising pattern of the bubble synchronized with that of the standing wave. The bubble rise velocity is significantly lower than that in the absence of an acoustic field. The behavior of bubble volume contraction and expansion can be accounted for by a 3-D direct numerical simulation of the bubble dynamics and flow field based on the compressible N–S equations coupled with the level-set method. The experiments and simulation reveal a consistent value of the ratio of the Bjerknes force to the buoyancy force for a single mesobubble rising in the acoustic field to be at 20–25%.

The process of impact of an acetone droplet upon a hot flat surface is analyzed based on a 3D numerical simulation which considers the evaporation behavior. The 3D level‐set method is utilized to track the droplet surface variation during its deformation. The flow field within the droplet and the surrounding gas phase are solved using the finite volume method with the ALE (Arbitrary Lagrangian Eulerian) technique. The dynamic characteristics of the vapor flow are solved by a vapor flow model that accounts for the lubrication resistant effect of the vapor cushion formed by the film‐boiling evaporation. The heat flux across the vapor layer and the temperature fields in all phases are determined by using a full field heat transfer model. The effects of the impact velocity are illustrated in this study. The spreading and recoiling motions of the impacting droplets are compared at different impact velocities. As the impact velocity increases, the extent of the droplet spreading increases, but the resi...

The liquid entrainment in bubble columns is experimentally studied under high-pressure conditions. Water and Paratherm NF heat-transfer fluid are used as the liquid phase, with nitrogen and air as the gas phase. Operating pressures and superficial gas velocities vary by up to 3.13 MPa and 33 cm/s, respectively. Parameters include the droplet size and droplet velocity, and local and total entrainment rates are examined. The study indicates that the entrainment rate increases with system pressures and superficial gas velocities. The maximum droplet velocity is found to be located between the center and wall regions at low pressures and low superficial gas velocities; the specific location shifts toward the center as the pressure and superficial gas velocity increase. The distributions of the droplet velocity and droplet size are narrower at locations further away from the entrainment surface. The droplet velocity of water at a given location and operating condition is found to be higher than that of parathe...

The paper presents an experimental study on the drag forces of two interactive particles with unequal diameters. A circulating loop for the fluid flow is set up. The particles are arranged in a line parallel to the direction of the flow in the test section. Direct measurements of the drag force of the downstream trailing particle are performed by utilizing a micro-balance force measuring system. The tests are conducted under different conditions. The obtained results illustrate the effects of particle size ratio and Reynolds number on the drag force of the trailing particle. It is found that the drag force ratio of the trailing particle increases with the particle size ratio under both circumstances of the particle size ratio being larger than 1 and less than 1. The drag force ratio of the trailing particle tends to decreases with increasing particle Reynolds number for the present cases being studied.

The bed dynamic behavior in three gas−solid fluidized beds, 0.05, 0.1, and 0.3 m in diameters, is studied using the electrical capacitance tomography (ECT). The ECT employs the neural network multicriteria optimization image reconstruction technique. The time-averaged solids concentrations obtained by the ECT are generally in good agreement with those obtained by the optical fiber probe. The 0.1 m ID fluidized bed exhibits the spiral motion of rising bubbles in the bubbling regime. However, for the 0.3 m ID fluidized bed, more than one spiral motion of bubble swarms is observed in the bubbling regime. The small fluidized bed exhibits the round-nosed slug motion. The ECT studies reveal a radial symmetry of the time-averaged solids concentration distribution for the turbulent regime. Furthermore, the ECT provides the time-averaged and transient properties of the bubble/void phase and the emulsion phase. For a large fluidized bed, the standard deviations of the fluctuations of the cross-sectional averaged so...

To simulate the bubble, liquid and particle turbulence properties and their interactions in three-phase flows, a second-order moment three-phase turbulence model for gas–liquid–solid flows is proposed. The bubble, liquid and particle Reynolds stress equations, bubble–liquid and liquid–solid two-phase correlation equations are derived using the mass-weighed and time averaging and the closure models of diffusion, dissipation and pressure-strain terms similar to those used in single-phase flows. The two-phase correlation equations are closed with a two-time-scale dissipation term. The proposed model is applied to simulate gas–liquid flows and gas–liquid–solid flows in a channel. The prediction results for two-phase flows are in good agreement with the PIV measurement results. The prediction results for three-phase flows give the gas, liquid and solid velocities, volume fractions and Reynolds stresses, showing that in the case studied the turbulent fluctuation of 5 mm bubbles is stronger than that of liquid, while the turbulent fluctuation of 0.5 mm particles is weaker than that of liquid. Bubbles enhance liquid turbulence, while particles reduce liquid turbulence.

The effect of the physical activation on the dissolution of serpentine was investigated and a pH swing scheme was developed to improve the overall conversion of the CO2CO2 mineral sequestration process. Various methods of the surface agitation such as ultrasound, acoustic, and internal (in-situ) grinding were examined for their effectiveness in removing the diffusion limiting SiO2SiO2 layer in order to promote further dissolution of the inner MgO layer of serpentine. It was found that the fluidization of the serpentine slurry with 2 mm glass beads was most effective in refreshing the surface of the serpentine particles during the dissolution process. Unlike the external attrition grinding, this method could be much less energy intensive. It was also found that the mechanical agitation via the internal grinding alone did not enhance the dissolution of serpentine, while the combination of the internal grinding and Mg leaching solvent resulted in rapid serpentine dissolution. Using the proposed pH swing scheme, the overall conversion of the mineral carbonation radically improved. By controlling the pH of the system, three solid products were generated from the mineral carbonation process: SiO2SiO2-rich solids, iron oxide and MgCO3*3H2O. Since the iron oxide and MgCO3MgCO3 produced were highly pure, these value-added products could eventually reduce the overall cost of the carbon sequestration process.

The turbulent energy distributions in the gas−liquid bubble-column system and the effect of solids on the liquid-phase turbulence are investigated using laser Doppler and particle image velocimetries. The superficial gas velocity employed ranges from 0.025 to 7.5 cm/s, covering such bubble flow conditions as single-bubble chain, bubbly flow, and churn-turbulent flow. Turbulence induced by rising bubbles and liquid shear are examined. The energy containing ranges for the bubble- and shear-induced turbulence is determined from the liquid-phase power spectra. Experimental results indicate that the bubble-induced turbulence is the governing factor in the liquid-phase turbulence in bubbly flows. The analysis of power spectra indicates that the bubble-induced turbulence includes the turbulence from eddies in the bubble wake and that from the drift velocity change due to rising bubbles. The interaction between two turbulence fields is studied with a two-orifice gas distributor. The interaction can only be observ...

Micron-sized CaO, obtained by calcination of mesoporous CaCO3, attained 36 wt % CO2 sorption capacity after 100 cycles of carbonation and calcination reactions at 700 °C. The extent of simultaneous carbonation (XCO2) and sulfation (XSO2) of CaO at 700 °C was obtained under simulated flue gas conditions (10% CO2, 3000 ppm of SO2, 4% O2 in N2). CaO reacts with SO2 to form thermally stable CaSO4, which leads to a reduction in the CO2 capture capacity of CaO. Whereas XSO2 increases monotonically with the residence time, XCO2 goes through a maximum and eventually drops as a result of direct sulfation of CaCO3. The maximum value attained by XCO2 was 50% in 10 min in the first cycle. The highest XCO2/XSO2 ratio of 5 is attained at a residence time of 5 min. XSO2 is higher under simultaneous carbonation and sulfation conditions compared to sulfation of CaO or direct sulfation of CaCO3.

High-surface-area SiC has unique mechanical and thermal properties for use as a catalyst and sorbent support. A modified sol−gel route was chosen to synthesize SiC, where the precursor (phenyltrimethoxysilane) was hydrolyzed in the presence of a solvent (methanol) in order to enhance reaction rates and control the pore structure of the SiC formed on firing. High surface areas in the range of 450−620 m2/g and pore volumes in the range of 0.37−0.45 cm3/g were obtained. Use of NaOH instead of NH4OH in the final stage of gel formation resulted in a higher proportion of pores bigger than 50 A in the pore structure. Similar changes in pore structure were observed when a surfactant (sodium dodecyl sulfate) was added along with methanol to enhance the contact between the precursor and water.

The electrical capacitance tomography (ECT) based on the neural network multi-criteria optimization image reconstruction technique (NNMOIRT) developed by this research group is used to study the choking phenomenon for Geldart Group B particles in a circulating fluidized bed (CFB). The Group B particles employed are sand particles with a mean diameter of 240 μm and a particle density of 2200 kg/m 2 . The ECT examines the real-time, quasi-3D cross-sectional flow structure of a gas-solid circulating fluidized bed. The ECT with NNMOIRT reveals a double solids-ring flow structure at a low solids circulation rate and the presence of solids blobs at the center of the bed at a high solids circulation rate before choking in a CFB. This flow structure undergoes a distinct variation during the choking transition forming wall slugs/gas intervals when the gas velocity is below the transport velocity, U tr , or forming open slugs with blobs/ particles at the center when the gas velocity is above U tr . The standard deviation of the solids concentration fluctuation and the cross-sectional time-averaged solids concentration variation with increasing solids circulation rates exhibit a sharp change during the choking transition for a low gas velocity (

The turbulence energy distributions in the gas–liquid bubble column system and the effect of solids on the turbulence are investigated using the laser Doppler velocimetry and the particle image velocimetry. The superficial gas velocity employed ranges from 0.025 to 7.5 cm/s , covering such bubble-flow conditions as single-bubble chain, bubbly flow and churn-turbulent flow. Turbulence induced by rising bubbles through bubble wakes is also examined. Experimental results indicate that the bubble-induced turbulence dominates over the liquid shear-induced turbulence in turbulence generation under the operating conditions of this study. The development of the flow field and the turbulence energy of the liquid-phase in the nozzle region are probed. Furthermore, a self-similarity phenomenon is observed in a two-phase flow system. The analysis of the power spectra in gas, liquid and solid phases indicates that the Kolmogorov −5/3 law is obeyed in the inertial range. The presence of solids reduces the transition frequency from the energy-containing range to the inertial range. The effect of the solids on the liquid-phase turbulence is complex. It depends on solids properties and flow field around particles. A criterion based on the variation of a parameter defined by U g ( r )/ u mf is proposed to account for the effect of the solids on the liquid-phase turbulence. The prediction based on this criterion matches well with the experimental results.

Volumetric gas−liquid mass-transfer coefficients are investigated in bubble columns under high-pressure and moderate-temperature conditions by utilizing an oxygen desorption method. The oxygen concentration in the liquid phase, water or Paratherm NF heat-transfer fluid, is monitored with a high-pressure optical fiber oxygen probe. The study covers operating conditions up to pressures of 4.24 MPa and up to temperatures of 92 °C. The superficial gas and liquid velocities vary up to 40 and 0.89 cm/s, respectively. Experimental results show that system pressure, temperature, gas and liquid velocities, liquid properties, and column dimensions are major factors affecting mass transfer. The mass-transfer coefficient increases with both pressure and temperature. Both gas and liquid velocities improve mass transfer due to higher turbulence at high-velocity conditions. Liquid properties and column dimensions also have significant effects on mass transfer. The effect of liquid velocity on kla is mainly due to the ch...

A computational scheme for three-dimensional (3-D), discrete simulation of bubble dynamics in gas-liquid bubble columns and gas-liquid-solid fluidized beds is presented. This scheme describes the motion of the gas, liquid, and solid phases, respectively, based on the level-set interface tracking method, the locally averaged time-dependent Navier-Stokes equations coupled with the Smagorinsky Sub-Grid Scale stress model, and the Lagrangian particle motion equations. Various gas, liquid, and solid interactive forces are considered, which include those due to drag, added mass, interfacial tension, bubble-particle collision and particle-particle collision. The accuracy and validity of the simulation based on this scheme is examined through computational experiments on some well-known bubbling phenomena including the rise behavior of a single gas bubble in liquids and the bubble formation process from an orifice embedded in liquids. The computed bubble rise velocity, bubble shapes and their fluctuations, and bubble formation behavior in liquids show a good agreement with existing theories and experimental findings. The simulation is extended to investigate the effects of solids concentration on bubble formation and rise behavior. It is found that the bubbles are less coalesced in a fluidized bed with a higher solids concentration. A circulatory motion of particles with an upward flow in the center region and a downward flow near the wall, and a lateral solids concentration distribution in a gas-liquid-solid fluidized bed can also be predicted. The bubble formation and rise behavior in a multi-nozzle bubble column are simulated, and the limitation of the Smagorinsky Sub-Grid Scale stress model is discussed. © 2004 American Institute of Chemical Engineers AIChE J, 50: 288–301, 2004

Choking is commonly defined as a phenomenon where a sudden change in the solids holdup occurs in a gas–solid fluidization system. In this study, the electrical capacitance tomography (ECT) based on the neural network multicriteria optimization image reconstruction technique (NNMOIRT), developed by this research group, is used to probe the mechanism of choking formation by examining a real-time, quasi-3D cross-sectional flow structure of a circulating fluidized bed riser. The particles used are FCC catalysts. The ECT with NN-MOIRT reveals a double solids-ring flow structure and the presence of particle blobs at the center of the bed in the circulating fluidized bed (CFB) riser. This flow structure, when it is present at the entrance region of the riser, undergoes a distinct variation during the choking transition when the gas velocity is below the transport velocity Utr, but does not undergo a distinct variation when the gas velocity is above Utr. This flow structure, when it is present at the upper region of the riser, however, does not vary distinctly at any gas velocity. Such flow structure variations are not appreciably affected by the solids feeding patterns with or without a gas or solids distributor, or by the gas humidity. For the low gas velocities (

Axial dispersion coefficients of the liquid phase in bubble columns at high pressure are investigated using the thermal dispersion technique. Water and hydrocarbon liquids are used as the liquid phase. The system pressure varies up to 10.3 MPa and the superficial gas velocity varies up to 0.4 cm/s, which covers both the homogeneous bubbling and churn-turbulent flow regimes. Experimental results show that flow regime, system pressure, liquid properties, liquid-phase motion, and column size are the main factors affecting liquid mixing. The axial dispersion coefficient of the liquid phase increases with an increase in gas velocity and decreases with increasing pressure. The effects of gas velocity and pressure on liquid mixing can be explained based on the combined mechanism of global liquid internal circulation and local turbulent fluctuations. The axial liquid dispersion coefficient also increases with increasing liquid velocity due to enhanced liquid-phase turbulence. The scale-up effect on liquid mixing reduces as the pressure increases.

In this work, an analog neural network is utilized to develop a new image reconstruction technique for the linear as well as the non-linear process tomography. The ultrasonic computed tomography (CT) and the electrical capacitance tomography (ECT) are chosen to represent the linear and the non-linear tomography. The image reconstruction technique is based on a multi-criteria optimization, namely neural network multi-criteria optimization image reconstruction technique (NN-MOIRT). The optimization technique utilizes multi-objective functions: (a) the negative entropy function, (b) the function of the least weighted square error of projection (integral) values between the measured data and the estimated projection data from the reconstructed image, and (c) a smoothness function that gives a relatively small peakedness in the reconstructed image. The optimization image reconstruction problem is then solved using the Hopfield model with dynamic neural-network computing. The technique has been tested using simulated and measured data; this technique has shown significant improvement in accuracy and consistency compared with other available techniques for both linear and non-linear tomography.

A detailed parametric study quantifying the effect of various operating parameters on the reduction of nitric oxide (NO) in the presence of oxygen by inexpensive carbons was carried out. The selectivity of the carbon−NO reaction over the parasitic carbon−oxygen reaction was measured by a global selectivity parameter, defined as milligrams of NO reduced per gram of carbon consumed. An increase in the reaction temperature, bed height, and inlet NO concentration leads to a higher selectivity factor. However, there exists an optimum particle size of carbon that maximizes this selectivity. Whereas, in the absence of oxygen, the rate of the carbon−NO reaction was insignificant, the presence of oxygen in the inlet creates active sites that convert NO to nitrogen. An optimum inlet oxygen concentration provided the highest degree of NO reduction. The operating conditions can be selected to achieve >90% NO reduction at a selectivity of 60−100 mg of NO reduced/g of carbon.

Bed dynamic behavior in a gas-solid fluidization system is measured in real time using ECT based on the NNMOIRT recently developed. The ECT results reveal the time-averaged and transient characteristics of the bubble/void phase and the emulsion phase, which is of value to the verification of the 3-D computation codes with real physical systems. In the turbulent regime, the time-averaged solids holdup distribution exhibits radial symmetry, which is not the case for the bubbling regime. The standard deviations of the fluctuations of the cross-sectional, averaged bubble/void phase fraction, and the cross-sectional, averaged solids holdups in the bubble/void phase and in the emulsion phase, all peak at the transition velocity from the bubbling to the turbulent regimes Uc. The addition of 10% fine particles decreases the solids holdup in the emulsion phase due to the breakup of large bubbles. The ECT study indicates that optical fiber probe measurement of the bubble/void phase fraction may yield significantly different results depending on the threshold level selected for the measured solids holdup distribution. The bubble/void phase fraction measured by the optical fiber probe does not vary with bed temperature up to 400°C; the emulsion phase voidage is observed to increase as the bed temperature increases.

Bubble rise velocity is one of the important parameters characterizing bubble column systems. Mathematical models for predicting the velocity of an interactive spherical bubble rising in-line in liquids for intermediate Reynolds number range [Re ∼O(100)] are developed in the present study. The equation for the balance of forces on a bubble rising in-line is formulated. The models are derived based on this equation and different assumptions for the forces on the bubble. The ratios of the rise velocity of the trailing bubble to that of an isolated bubble, varying with the separation distance between the leading and trailing bubbles, are predicted by these models at Re of 35.4, 21.5 and 3.06. Comparisons between the predictions and the measurements show that the model incorporating both the wake effect and the bubble acceleration effect which includes the added mass and Basset forces can well predict the rise velocity of the trailing bubble in the far wake region of the leading bubble. The commonly used model which accounts for only the wake effect is found to lead to an overestimation of the rise velocity of the trailing bubble.

In this work, the electrical capacitance tomography (ECT) with neural network multi-criteria optimization image reconstruction technique (NN-MOIRT), early developed by the authors, is applied to imaging bubble column and three-phase fluidized bed systems in the real time manner. Air, norpar (paraffin) and glass-beads are used as the gas, liquid, and solid phases, respectively. A three-phase capacitance model coupled with a two-region model is proposed to attain the gas holdup and the solids fraction from the permittivity maps of the three-phase system. The two-region model assumes that the solids fraction in the emulsion phase in the no bubble region is the same as in the bubble region. The three-phase capacitance model combines series and parallel capacitance connections among gas, liquid and solid components to relate the three-phase permittivity to each phase holdup. A direct image calculation to obtain the gas holdup from the permittivity map of the three-phase system is also performed by determining the permittivity threshold for the gas bubbles. Comparisons of the gas holdup obtained by ECT with that obtained from liquid head measurement showed a good agreement, validating the applicability of the model and its associated image calculation.

Two promising clean coal processes, OSCAR and CARBONOX, which were developed in the authors' laboratory from initial fundamental research to the current stage of pilot demonstration, are highlighted.

A parametric model has been developed for the study of liquid jet evaporation in gas–solid suspension flows. The model takes into account the phase interactions with phase changes in the mass, momentum and energy conservation equations of all the gas, liquid, and solid phases. Parametric effects on the mixing characteristics such as evaporation length, temperature and velocity of each phase, trajectories, and the phase volume fraction distributions are illustrated. It is found that the evaporation length is shortened in the presence of particles in a liquid jet of any injection angle. The evaporation length decreases with the increase of solids loading as well as the increase of jetting angle from co-current to counter-current. Comparison of jet evaporation length between the previously reported experimental results and modeling predictions shows a good qualitative agreement.

Gas and solids mixing characteristics in the bubbling and turbulent regimes of a gas-solid fluidized bed are examined using helium and phosphor tracer techniques to obtain the gas and solids dispersion coefficients, respectively. The real time, quasi-3-D flow behavior is qualified and quantified by the electrical capacitance tomography (ECT) technique. The mixing behavior varies significantly with the flow regimes. As the gas velocity increases, axial and radial gas dispersion coefficients increase in the bubbling regime, reach a peak at U c , the transition velocity from the bubbling to turbulent regimes, and then decrease. In contrast, as the gas velocity increases, axial and radial solids dispersion coefficients increase in the bubbling regime and continuously increase through U c to the turbulent regime. Temperature and pressure have little effect on the gas and solids mixing behavior. A small quantity of fine particles is noted to drastically affect the gas and solids mixing behavior in the turbulent fluidized bed. The axial and radial dispersion coefficients of gas and solids reach their maximum when the fines content is about 15%. The ECT measurements illustrate the effect of adding fines on the flow behavior in the bed. A small quantity of fine particles disintegrate the bubble/void phase, significantly modifying bubble/void- and emulsion-phase mixing behavior.

The drag forces of particles aligned in a line parallel to the direction of relative motion between the fluid stream and the particles are investigated. The particle−particle interactions and the wake effect should be taken into account for quantitatively describing the drag force of the interactive particle. Under the circumstances of the Reynolds number (Re) being around 100, the drag force of the interactive trailing particle is analyzed based on the velocity distribution in the far wake region downstream of the leading particle. As a result, a semianalytical expression for the drag force of the trailing particle is formulated. It is utilized to calculate the drag force ratio of the trailing particle for Re of 54−154. Agreement between the calculation and the measured data is achieved.

Two versions of the second-order moment two-phase turbulence model are proposed in this study for simulating bubble–liquid two-phase turbulent velocity fluctuations and their interactions in bubble–liquid flows under the dispersed bubble regime. One of them is a full transport equation model; the other is an algebraic stresses model. The proposed model is used to simulate liquid and gas mean velocities, gas volume fraction, liquid and gas Reynolds stresses and turbulent kinetic energy in a 2-D bubble column. Furthermore, the bubble and liquid velocities, Reynolds stresses and gas volume fraction are measured using the PIV. The simulation results are in good agreement with the PIV results and experimental data in the literature. The studies reveal the liquid recirculation and bubble up-rising flow patterns, and anisotropic liquid and bubble normal Reynolds stresses. Bubble fluctuation is observed to be stronger than liquid fluctuation. Moreover, both the liquid velocity gradient and bubble–liquid interaction are important for the generation of liquid turbulence.

Experimental studies on the liquid weeping phenomenon at a submerged circular orifice have been conducted under a range of superficial orifice gas velocities (0.25 cm/s to 100 m/s), column and plate specifications, orifice sizes, fluid properties, and pressures up to 3.5 MPa. As the primary focus of this study, weeping rates and bubble formation at a single-orifice plate are investigated while operating within the bubbling regime at velocities of 0.25−100 cm/s. Upon monitoring of the pressure fluctuations within the plenum region, the bubbling frequency and nominal bubble size are determined to provide insight into the weeping phenomenon. Under similar scrutiny, weeping in the jetting regime, which is generally ignored or disregarded as trivial, is briefly considered for long-term consequences for industrial plants that typically operate over month or year periods.

A new and efficient direct numerical method with second-order convergence accuracy was developed for fully resolved simulations of incompressible viscous flows laden with rigid particles. The method combines the state-of-the-art immersed boundary method (IBM), the multi-direct forcing method, and the lattice Boltzmann method (LBM). First, the multi-direct forcing method is adopted in the improved IBM to better approximate the no-slip/no-penetration (ns/np) condition on the surface of particles. Second, a slight retraction of the Lagrangian grid from the surface towards the interior of particles with a fraction of the Eulerian grid spacing helps increase the convergence accuracy of the method. An over-relaxation technique in the procedure of multi-direct forcing method and the classical fourth order Runge-Kutta scheme in the coupled fluid-particle interaction were applied. The use of the classical fourth order Runge-Kutta scheme helps the overall IB-LBM achieve the second order accuracy and provides more accurate predictions of the translational and rotational motion of particles. The preexistent code with the first-order convergence rate is updated so that the updated new code can resolve the translational and rotational motion of particles with the second-order convergence rate. The updated code has been validated with several benchmark applications. The efficiency of IBM and thusmore » the efficiency of IB-LBM were improved by reducing the number of the Lagragian markers on particles by using a new formula for the number of Lagrangian markers on particle surfaces. The immersed boundary-lattice Boltzmann method (IBLBM) has been shown to predict correctly the angular velocity of a particle. Prior to examining drag force exerted on a cluster of particles, the updated IB-LBM code along with the new formula for the number of Lagrangian markers has been further validated by solving several theoretical problems. Moreover, the unsteadiness of the drag force is examined when a fluid is accelerated from rest by a constant average pressure gradient toward a steady Stokes flow. The simulation results agree well with the theories for the short- and long-time behavior of the drag force. Flows through non-rotational and rotational spheres in simple cubic arrays and random arrays are simulated over the entire range of packing fractions, and both low and moderate particle Reynolds numbers to compare the simulated results with the literature results and develop a new drag force formula, a new lift force formula, and a new torque formula. Random arrays of solid particles in fluids are generated with Monte Carlo procedure and Zinchenko's method to avoid crystallization of solid particles over high solid volume fractions. A new drag force formula was developed with extensive simulated results to be closely applicable to real processes over the entire range of packing fractions and both low and moderate particle Reynolds numbers. The simulation results indicate that the drag force is barely affected by rotational Reynolds numbers. Drag force is basically unchanged as the angle of the rotating axis varies.« less