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Direct numerical simulations with an immersed boundary-lattice Boltzmann method are used to investigate the effects of particle rotation on flows past random arrays of mono-disperse spheres at moderate particle Reynolds numbers. This study is an extension of a previous study of the authors [Q. Zhou and L.-S. Fan, "Direct numerical simulation of low-Reynolds-number flow past arrays of rotating spheres," J. Fluid Mech. 765, 396-423 (2015)] that explored the effects of particle rotation at low particle Reynolds numbers. The results of this study indicate that as the particle Reynolds number increases, the normalized Magnus lift force decreases rapidly when the particle Reynolds number is in the range lower than 50. For the particle Reynolds number greater than 50, the normalized Magnus lift force approaches a constant value that is invariant with solid volume fractions. The proportional dependence of the Magnus lift force on the rotational Reynolds number (based on the angular velocity and the diameter of the spheres) observed at low particle Reynolds numbers does not change in the present study, making the Magnus lift force another possible factor that can significantly affect the overall dynamics of fluid-particle flows other than the drag force. Moreover, it is found that both the normalized drag force and the normalized torque increase with the increase of the particle Reynolds number and the solid volume fraction. Finally, correlations for the drag force, the Magnus lift force, and the torque in random arrays of rotating spheres at arbitrary solids volume fractions, rotational Reynolds numbers, and particle Reynolds numbers are formulated. [ABSTRACT FROM AUTHOR]

The L-valve, as a solids flow control device, has been used extensively in fluidized beds and circulating fluidized beds for controlling the solids circulation rate. Knowledge on L-valves, however, is mostly limited to ambient flow conditions with Geldart A and B particles. Studies on the L-valve under high temperature conditions which are common in industrial applications are rare. This paper describes experimental studies that probe the characteristics of the L-valve operation under high temperature conditions using Geldart D particles. The relationships between the solids flow rate, aeration rate, and pressure drop are investigated and compared with those under ambient conditions using different groups of particles. The results indicate that the variation of the solids flow rate controlled by the L-valve aeration depends on the actual internal flow rate of the gas that flows through the L-valve rather than the external aeration flow rate of the gas that is introduced into the system. The actual aeration gas flow rate required for generating a given solids flow rate is the same so long as the location of the aeration tap is above the height-to-diameter ratio of 1.5 in the L-valve. Operating the L-valve with Geldart D particles needs more gas aeration compared to that with Geldart A and B particles for a given solids flow rate. However, under high temperature conditions, the solids flow for Geldart D particles in the L-valve behaves like those with much smaller particle sizes. For Geldart D particles, the aeration gas flow rate required under high temperature conditions is much less than that under ambient conditions. [ABSTRACT FROM AUTHOR]

In this study, the high-pressure carbonation kinetics of calcium oxide (CaO) derived from three calcium-based sorbents, namely, limestone (CaCO3), calcium hydroxide [Ca(OH)2], and precipitated calcium carbonate (PCC), used in the calcium looping process (CLP) system were studied using a magnetic suspension balance (MSB) analyzer. Different total pressures (1000–15000 torr) and concentrations of CO2(10–30%) were tested to determine their effects on the carbonation reaction rate at a specific operating temperature of the CLP system, namely, 700 °C. The carbonation reaction rate was found to increase with increasing concentration of CO2(10–30%) at a constant total pressure of 5000 torr and to exhibit first-order kinetics. However, the total pressure has an effect on the carbonation reaction rate only at lower total pressures. With a 20% CO2stream, the reaction rate was observed to increase until the total pressure reached 4000 torr, beyond which a further increase in total pressure had a negative effect on the rate of the carbonation reaction of CaO derived from all three precursors. Further, the carbonation reaction had a different reaction order with respect to the partial pressure of CO2. It was found that the reaction was first-order at lower total pressures but changed to zeroth-order when the total pressure exceeded 4000 torr. The different reaction order under elevated pressures can be explained by the Langmuir mechanism. In addition, the reaction rate of carbonation conducted at high total pressure was greater than that at atmospheric pressure, under cyclic testing. The results also showed that there was no significant difference in the behavior of the carbonation reaction of CaO at elevated pressures, regardless of the different precursors used to generate the CaO. [ABSTRACT FROM AUTHOR]

Much of the fundamental research reported in the literature on gas−solid fluidization properties has been performed with large gas−solid fluidized beds. However, little is known regarding gas−solid fluidization in the mini- and microscale channel sizes ranging from 10−3to 10−2m and 10−5to 10−4m, respectively. The wall effects in the mini- and microchannels significantly affect the hydrodynamics of gas−solid fluidization. Such effects are examined experimentally in this study using FCC particles in six mini- and microchannels with sizes ranging from 700 μm to 5 mm. The data reveal a significant increase in the minimum fluidization and bubbling velocities as well as the wall friction in the mini- and microchannels compared to those in large fluidized beds. Additionally, the maximum stable bubble size increases with the superficial gas velocity and channel size. The round-nosed slug and the wall slug are observed in the channels. Correlations for predicting the fluidization regime transition in large fluidized beds are not adequate for predicting that in the mini- and microchannels. Also, differing from fluidization in a large bed, there is regime transition instability in that particulate fluidization is observed to form in the 700 μm and 1 mm channels through the bubbling/slugging transition as the gas velocity increases beyond that for the fixed bed. [ABSTRACT FROM AUTHOR]

Clean-coal technologies that include carbon dioxide and sulfur capture during the production of electric power, liquid fuels, and hydrogen represent a major thrust area. The calcium looping process (CLP) is one such technology that is being developed to convert syngas obtained from coal gasification to hydrogen using a regenerable calcium oxide sorbent. It integrates the water−gas shift reaction with in situ carbon dioxide, sulfur, and halide removal at high temperatures while eliminating the need for a water−gas shift catalyst and reducing the overall footprint of the hydrogen production process. The CLP comprises three reactors: the carbonation reactor, where the thermodynamic constraint of the water−gas shift reaction is overcome by the constant removal of the carbon dioxide product and high-purity hydrogen is produced with contaminant removal; the calciner, where the calcium sorbent is regenerated and a sequestration-ready carbon dioxide stream is produced; and the hydrator, where the calcined sorbent is reactivated to improve its recyclability. In this article, the reaction chemistry occurring in the three calcium looping reactors and the performance of the reactors at various process conditions are presented through thermodynamic and experimental analyses. High-purity H2with less than 1 ppm of H2S is obtained in the carbonation stage at a stoichiometric steam-to-carbon ratio at high pressures. Although calcination of the sorbent under realistic conditions causes severe sintering and a loss in reactivity, sorbent reactivation by hydration is effective in restoring sorbent reactivity. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The hydrodynamics and heat transfer phenomena during the collision process of a liquid droplet and a hot particle, both in motion, are illustrated by direct numerical simulation in this study. The three-dimensional level-set method is used to portray the surface deformation of the droplet. The immersed boundary method is employed by means of the particle level-set function so that the particle-fluid boundary conditions are satisfied. The governing equations for the droplet and the surrounding gas phase are solved using the finite-volume method. To account for the multiscale effect due to lubrication resistance induced by the vapor layer between the droplet and solid surface or solid particle formed by the film-boiling evaporation, a vapor flow model is developed, which quantifies the pressure and velocity distributions along the vapor layer. The temperature fields in all phases and the local evaporation rate on the droplet surface are illustrated using a full-field heat transfer model. The convergence of the simulation model is analyzed and verified by using different grid sizes in the computation. The normal and oblique collisions between the droplet and the particle are simulated. It is found that the particle sizes have a significant effect on the collision dynamics in a normal collision. When the droplet size is larger than the particle size, the contact time is shorter than the droplet vibration period and is controlled by the dynamics of the particle. In an oblique collision, the increasing obliquity causes a decrease in contact area and contact time, and hence, a reduction in the heat loss of the particle during the collision process. [ABSTRACT FROM AUTHOR]

Examines the kinetics and mechanism behind the capture of gas-phase arsenic oxide by lime. Interaction between arsenic oxide and lime; Influence of temperature on the capture of gas-phase arsenic oxide by lime; Role of surface area of the sorbent particle in gas-solid chemical reactions.

Redox reactions between fine solid fuels, such as pulverized coal powder, and coarse oxygen carrier particles can be carried out in a fixed/moving bed reactor chemical looping system. The migration pattern of the solid fuel powder and its contact time with coarse particles can significantly affect the reaction rate and the product yield. A number of challenges exist in transporting/mixing of fuel powder and in removing noncombustible waste (e.g., coal ash) from the reactor vessel in the chemical looping operation. Thus, it is important to understand the hydrodynamic behaviors of fine particles in such situations. This study describes an experimental approach that examines migration characteristics of fine particles (Geldart A/B), in both spatial and temporal aspects, in a packed bed of coarse particles (Geldart D). The experimental variables include the particle size distribution of the fine powder, the fine to coarse mass ratio, and flow conditions. At a given upward aeration flow within the range that is higher than the terminal velocity of the fine particles but lower than the minimum fluidization velocity of coarse particles (Ut < Us < Umf,c), the fine particles may travel both upward and downward depending on the gas flow rate and the physical properties of particles and gas. The spatial transport pattern in terms of the upward and static transport partition (wt %) of Geldart A particles can be characterized as an exponential function of a group of dimensionless numbers (e.g., Stk*, Rep* and Us/Ut). The time-dependent upward transport rate of fine particles is measured to determine the temporal migration characteristics. Cluster response time (τc) is introduced to describe how fast a cluster of fine particles in a packed bed respond to the ambient flow. This parameter is normalized by the response time of fine particle (τp) and further correlated with the pseudo-particle Reynolds number (Rep*) via an inverse power function with two coefficients. [ABSTRACT FROM AUTHOR]

This article reports recent advances and progress in the field of electrical capacitance volume tomography (ECVT). ECVT, developed from the two-dimensional electrical capacitance tomography (ECT), is a promising non-intrusive imaging technology that can provide real-time three-dimensional images of the sensing domain. Images are reconstructed from capacitance measurements acquired by electrodes placed on the outside boundary of the testing vessel. In this article, a review of progress on capacitance sensor design and applications to multi-phase flows is presented. The sensor shape, electrode configuration, and the number of electrodes that comprise three key elements of threedimensional capacitance sensors are illustrated. The article also highlights applications of ECVT sensors on vessels of various sizes from 1 to 60 inches with complex geometries. Case studies are used to show the capability and validity of ECVT. The studies provide qualitative and quantitative real-time three-dimensional information of the measuring domain under study. Advantages of ECVT render it a favorable tool to be utilized for industrial applications and fundamental multi-phase flow research. [ABSTRACT FROM AUTHOR]

Passive cyclonic gas-liquid separators (PCGLSs) are commonly used in microgravity conditions where gravity settling separation is difficult or impossible. In this study, displacement-current phase tomography (DCPT) is used to measure various features of the gasliquid flow inside of a PCGLS. The liquid holdup, liquid angular velocity, and gas core size are investigated. The liquid holdup is also measured in a gas-liquid flow that simulates the injection flow for a PCGLS. It is found that the gas core contracts and expands in a periodic motion as air is injected with water. This motion becomes more noticeable as the air flow rate is increased. It is also found that the liquid layer angular velocity has a positive linear trend with the air flow rate under constant water flow rates. A basic linear relation is derived to relate the liquid angular velocity to the air and water flow rates. All DCPT and electrical capacitance phase tomography (ECVT) results closely match the visual confirmation methods used for each flow feature. [ABSTRACT FROM AUTHOR]

A three-dimensional ECVT sensing technique is applied to imaging complex slugging phenomena of a gas-solid fluidized bed under ambient and elevated temperature conditions. The study indicates that the time interval between rising slugs decreases with an increase in the gas velocity, reaching a nearly steady time interval value of about 1 s between two slugs when the gas velocity is ~1.7 m/s above the minimum fluidization velocity. The fluidized bed behaves as a bubbling fluidized bed at low gas velocities. In slugging regime, the slug rise velocity increases with the gas velocity. A mechanistic analysis of forces around the dense phase solid particles suggests that the relationship between the slug rise velocity and the gas velocity for the square-nosed slugging bed is not strictly linear and is highly related to the interparticle forces, internal friction of particles, and gas velocity in addition to the wall stress. [ABSTRACT FROM AUTHOR]

A novel design of a coal gasifier using the chemical looping concept is introduced in the present study for high purity, H2-rich syngas generation using coal and methane as cofeeds. In this work, an iron-titanium composite metal oxide (ITCMO), capable of cracking the heavy hydrocarbons produced in coal pyrolysis as well as regulating the product syngas purity, is used as the oxygen carrier. The cocurrent moving bed avoids back-mixing of solid and gas reactants, allowing both phases to interact, reaching thermodynamic equilibrium conditions at the reactor gas outlet. This paper focuses on demonstrating the cocurrent moving bed reducer with the ITCMO oxygen carrier. A sensitivity analysis is performed to determine the optimal operating conditions for converting Powder River Basin coal using ASPEN Plus modeling. The tar-cracking capability is ascertained by the gas chromatography-mass spectrometry analysis. The bench scale moving bed reducer substantiated its capability of achieving near-full conversion of the carbon species. The cofeeding of methane can yield a high purity syngas with H2/CO ratio of 2 or higher, which is suitable for downstream chemical synthesis. The gas and solid compositions obtained at reducer outlets match the predictions from the ASPEN Plus model. The results indicate that the extent of char gasification at the top moving bed is a critical factor for achieving a high coal conversion. The results further indicate that the sulfur in the coal is mostly converted into the gas phase emitted with the syngas product in the reducer, while the remainder is retained in the ash. [ABSTRACT FROM AUTHOR]

Directly upgrading natural gas is limited by the stability of its primary component, methane, and process economics. Since the 1980s, oxidative coupling of methane (OCM) has shown potential to produce ethylene and ethane (C2s). The typical OCM approach catalytically converts methane to C2 products using molecular oxygen, reducing process efficiency. To overcome this, chemical looping OCM converts methane to hydrocarbons via intermediate oxygen carriers rather than gaseous cofed oxidants. The chemical looping approach for OCM has been studied mechanistically for the first time with a Mn-Mg-based catalytic oxygen carrier (COC). The COC delivered stable performance in a fixed bed for 100 cycles for more than 50 h with a 63.2% C2 selectivity and 23.2% yield. These experimental results and original process simulations of an OCM chemical looping system for C2 or liquid fuel production with electricity cogeneration present a direct method for methane utilization. [ABSTRACT FROM AUTHOR]

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 CO2to 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 SO2gas 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, respectively. [ABSTRACT FROM AUTHOR]

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. CaCO3calcination 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 CO2stream. 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 a high porosity structure during limestone calcination. [ABSTRACT FROM AUTHOR]